CN102135827A

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Info

Publication number: CN102135827A
Application number: CN2010105297232A
Authority: CN
Inventors: W·M·维塔
Original assignee: Apple Computer Inc
Current assignee: Apple Inc
Priority date: 2010-01-21
Filing date: 2010-10-28
Publication date: 2011-07-27
Anticipated expiration: 2030-10-28
Also published as: CN102135827B

Abstract

The invention relates to a negative pixel compensation method and a device, a touh sensor device and a terminal device, in particular to the negative pixel compensation in a touch sensor panel. A method can compensate for a negative pixel effect in touch signal outputs due to poor grounding of an object touching the panel. To do so, the method can include determining at least one bound for a negative pixel compensation factor based on touch signal values, estimating the compensation factor within the determined bound based on the touch signal values that are negative, where the negative values indicate the presence of the negative pixel effect, and applying the estimated compensation factor to the touch signal outputs to compensate the touch signal values for the negative pixel effect.

Description

Method and device for compensating negative pixel effect, touch sensitive device and terminal device

Technical Field

The present disclosure relates generally to touch sensitive devices and, more particularly, to compensating for negative pixel effects on touch sensitive devices.

Background

Many types of input devices are currently available for performing operations in computing systems, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, and touch screens. Touch sensitive devices, and touch screens in particular, are becoming increasingly popular due to their ease and versatility of operation as well as their declining price. Touch sensitive devices can include a touch sensor panel, which can be a transparent panel having a touch sensitive surface, and a display device, such as a Liquid Crystal Display (LCD), which can be placed partially or fully behind the panel so that the touch sensitive surface can cover at least a portion of the viewable area of the display device. Touch sensitive devices can enable a user to perform various functions by touching the touch sensor panel using a finger, stylus, or other object at a location generally indicated by a User Interface (UI) being displayed by the display device. In general, a touch sensitive device can recognize a touch event and the location of the touch event on a touch sensor panel, and a computing system can then interpret the touch event in accordance with a display that appears when the touch event occurs, after which one or more actions can be performed based on the touch event.

When an object touching the touch sensor panel is poorly grounded, the touch output value representing the touch event may be erroneous or distorted. The probability of such erroneous or distorted values may further increase when two or more simultaneous touch events occur on the touch sensor panel.

Disclosure of Invention

The present disclosure relates to compensating touch signals representing a touch at a touch sensor panel for errors caused by poor grounding of a user or other object touching the panel. One such error may be a negative pixel effect, where a significant negative amount of touch and/or a reduced positive amount of touch may be sensed by the panel during multiple simultaneous touches. A method for compensating for this effect may include: determining at least one limit for a compensation factor based on the touch signal value; estimating a compensation factor within the determined bounds based on the touch signal value being a negative value, wherein a negative touch signal may be indicative of the effect; and applying the estimated compensation factor to the touch signal to compensate the touch signal.

Drawings

FIG. 1 illustrates an exemplary touch operation of a touch sensor panel according to various embodiments.

FIG. 2 illustrates an exemplary negative pixel effect in a touch sensor panel receiving multiple simultaneous touches by a poorly grounded finger, in accordance with various embodiments.

FIG. 3 illustrates an exemplary method for compensating for negative pixel effects in a touch sensor panel in accordance with various embodiments.

FIG. 4 illustrates an exemplary bias noise (bias noise) calculation that can be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments.

FIG. 5 illustrates an exemplary compensation factor bound determination that can be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments.

FIG. 6 illustrates another exemplary compensation factor bound determination that may be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments.

FIG. 7 illustrates an example compensation factor estimation that can be included in an example method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments.

FIG. 8 illustrates an exemplary compensation factor application that can be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments.

FIG. 9 illustrates exemplary compensation selections that can be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments.

FIG. 10 illustrates another exemplary compensation option that can be included in exemplary methods for compensating for negative pixel effects in a touch sensor panel according to various embodiments.

FIG. 11 illustrates an exemplary computing system that can compensate for negative pixel effects in accordance with various embodiments.

FIG. 12 illustrates an exemplary mobile phone that can compensate for negative pixel effects in accordance with various embodiments.

FIG. 13 illustrates an exemplary digital media player that can compensate for negative pixel effects in accordance with various embodiments.

FIG. 14 illustrates an exemplary personal computer that can compensate for negative pixel effects in accordance with various embodiments.

Detailed Description

In the following description of the various embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the various embodiments.

The present disclosure relates to compensating for negative pixel effects in a touch sensor panel due to poor grounding of a user or other object touching the panel. The compensation method may include: determining at least one limit for a negative pixel compensation factor based on the touch signal value; estimating a compensation factor within the determined bounds based on the touch signal value being a negative value, wherein a negative signal value represents the negative pixel effect; and applying the estimated compensation factor to the touch signal to compensate the touch signal value for negative pixel effects.

The ability to measure negative pixel effects in a touch sensor panel can advantageously provide more accurate and faster touch detection, as well as power savings, since the measurements do not have to be repeated subject to poor grounding conditions. In addition, the panel may be more robustly adapted to various grounding conditions of a user or other subject.

The terms "poorly grounded," "ungrounded," "not grounded," "not well grounded," "not properly grounded," "isolated," and "floating" may be used interchangeably to indicate a poorly grounded condition that may exist when an object is not low impedance electrically coupled to the ground of the touch sensor panel.

The terms "grounded," "properly grounded," and "well grounded" may be used interchangeably to indicate a good grounding condition that may exist when an object is low impedance electrically coupled to the ground of the touch sensor panel.

The touch sensor panels described and illustrated herein can include configurations in which conductive drive and sense lines (to be described below) can be formed on opposite sides of a substrate, on the same side of a substrate, on the same layer on the same side of a substrate, or on different substrates, and so forth. Although the touch sensor panels described and illustrated herein have drive and sense lines formed in rows and columns that are orthogonal to one another, it should be understood that other geometric configurations are possible, such as concentric circles and radial lines in a polar configuration, diagonal lines in a diagonal configuration (oblique configuration), non-orthogonal lines, and so forth.

FIG. 1 illustrates an exemplary touch operation of a touch sensor panel according to various embodiments. In the example of FIG. 1, touch sensor panel 100 can include an array ofpixels 106, whichpixels 106 can be formed at the intersections ofrow lines 102 andcolumn lines 104, although it will be understood that other pixel configurations can be used, such as drive and sense regions adjacent to each other on a single layer of the panel. Eachpixel 106 may have an associatedmutual capacitance Csig 114 formed between crossing row and

column lines

102, 104. As shown in FIG. 1,row lines 102 can function as drive lines andcolumn lines 104 can function as sense lines, where the drive lines can be stimulated by stimulation signals 110 provided by drive circuitry (not shown), the stimulation signals 110 can include an Alternating Current (AC) waveform, and the sense lines can transmit touch or sense signals 103, which are indicative of a touch at the panel 100, to sensing circuitry (not shown), which can include a sense amplifier for each sense line.

To sense a touch at the panel 100, in some embodiments,multiple drive lines 102 can be stimulated substantially simultaneously bystimulation signals 101 to capacitively couple with crossingsense lines 104, forming capacitive paths for coupling charge from the drive lines to the sense lines. Thecrossing sense lines 104 can output an output signal representative of the coupled charge or current. While some of thedrive lines 102 are being stimulated, other drive lines can be coupled to ground or other DC levels. In other embodiments, eachdrive line 102 can be sequentially stimulated by thestimulation signals 101 to capacitively couple with thecrossing sense line 104, which crossingsense line 104 can output an output signal representative of the coupled charge or current, while the other drive lines can be coupled to ground or other DC levels. In still other embodiments, there may be a combination ofmultiple drive lines 102 being stimulated substantially simultaneously and a single drive line being stimulated sequentially.

When a well-grounded user's finger (or other object) touches the panel 100, the finger can cause thecapacitance Csig 114 to decrease by an amount Δ Csig at the touch location. This change in capacitance Δ Csig can result from charge or current from the stimulateddrive line 102 being shunted to ground by the touching finger rather than being coupled to thecrossing sense line 104 at the touch location. The touch signal 103 representing the capacitance change Δ Csig can be sent by thesense lines 104 to the sensing circuitry for processing. The touch signal 103 can indicate a pixel where the touch occurred and an amount of touch that occurred at that pixel location.

When a poorly grounded user's finger (or other object) touches the panel 100, the finger capacitance Cfd to the stimulateddrive line 102, the finger capacitance Cfs to thecrossing sense line 104 at the touch location, and the finger capacitance Cgnd to user ground can form a secondary capacitive path coupling charge from the drive line to the sense line. Some of the charge generated by the stimulateddrive line 102 and sent through the finger is coupled back to thecrossing sense line 104 via an auxiliary capacitive path, rather than ground. Thus, instead of thecapacitance Csig 114 of the pixel at the touch location being reduced by Δ Csig, Csig can only be reduced by (Δ Csig Cneg), where Cneg can represent a so-called "negative capacitance" caused by charge coupled into the crossing sense line due to poor grounding of the finger. The touch signal 103 may also generally indicate the pixels where the touch occurred, but with an indication of a lesser amount of touch than actually occurred.

When multiple poorly grounded user fingers (or other objects) simultaneously touch the panel 100 at different locations, first finger capacitances Cfd and Cfs can be formed at the touch locations of the first finger as described above, i.e., at the intersections of the stimulateddrive lines 102 andsense lines 104. Some of the charge from the first finger may also be coupled back into the panel 100 by the second finger, so that second finger capacitances Cfd and Cfs may form at the touch location of the second finger, i.e., at the intersection of theunstimulated drive line 102 andsense line 104. The capacitance to user ground Cgnd may also be formed as described above. Thus, the touch signal 103 may indicate the pixels where the first finger touched, but with an indication of a lesser amount of touch than actually occurred, as previously described. The touch signal 103 can also indicate a false touch at a pixel formed by the crossing of a stimulateddrive line 102 and asense line 104 of a second finger and/or at a pixel formed by the crossing of an unstimulated drive line of a second finger and a sense line of a first finger. The touch signal 103 may indicate an apparent negative amount of touch at these pixels due to the charge being coupled back into the panel by the second finger. This may be the so-called "negative pixel effect".

sense lines

102 and 104. The capacitance to user ground Cgnd may also be formed. Thus, the touch signal 103 may indicate the pixel where the second finger touched, but with an indication of a lesser amount of touch than actually occurred, as previously described. The touch signal 103 can also indicate a false touch at pixels formed by the crossing of a stimulateddrive line 102 and asense line 104 of a first finger and/or at pixels formed by the crossing of an unstimulated drive line of a first finger and a sense line of a second finger and a significant amount of negative touch at these pixels due to charge coupling back into the panel 100 through the first finger, producing a negative pixel effect.

FIG. 2 illustrates an exemplary negative pixel effect in a touch sensor panel receiving multiple simultaneous touches by a poorly grounded finger, in accordance with various embodiments. As shown in FIG. 2, the row lines 202 can function as drive lines and the column lines 204 can function as sense lines. In the example of FIG. 2, a first poorly grounded finger (represented by a circle symbol and identified as "finger 1") can touch atpixel 206a of touch sensor panel 200, while a second poorly grounded finger (represented by a circle symbol and identified as "finger 2") can touch atpixel 206b of the panel. When a drive line (or row line) 202a of panel 200 is stimulated, the capacitance along a first path between thedrive line 202a and a sense line (or column line) 204a can be (Csig- Δ Csig). Because these fingers are poorly grounded, a second capacitive path may be formed between thedrive line 202a and thesense line 204a, with capacitances Cfd (between thedrive line 202a and the first finger) and Cfs (between thesense line 204a and the first finger), and a third capacitive path may be formed between thedrive line 202c and thesense line 204b via the second finger, with capacitances Cfd (between thedrive line 202c and the second finger) and Cfs (between thesense line 204b and the second finger). Capacitance Cgnd may also be formed between the finger and user ground. The capacitance may result from charge or current drawn by the first finger from the stimulateddrive line 202a being coupled back to the panel 200 at the

pixels

206a and 206b rather than being shunted to ground. Similar capacitances may be formed at the first finger and the second finger when thedrive line 202c is stimulated. Thus,pixels 206c and 206d, which are proximate to the touched

pixels

206a and 206b but did not receive a touch, may indicate a negative amount of touch ("negative pixels").

Thus, detecting the negative pixel effect and compensating the touch signal for the effect can improve touch sensing of the touch sensor panel under poor grounding conditions.

Some methods of compensating for the negative pixel effect iteratively process the touch signal until the effect is compensated. However, this approach is computationally expensive and time consuming. A faster and less computationally expensive approach is desirable in some cases. According to various embodiments, this may be accomplished by determining a factor (or parameter) representing a negative pixel effect and using the factor to compensate for the effect in the touch signal, as described above.

Compensation for the negative pixel effect is approximately expressed as follows from the relationship between the measured touch image Im (the image captured by the touch sensor panel and subject to the negative pixel effect) and the raw touch image I (which should be but not the image of the negative pixel effect):

I＝I_m+R×f(I_m) (1)

where R is a negative pixel compensation factor, which may be a function of Cfd, Cfs, Cgnd, and the panel design constant, thereby indicating a ground condition; and f (I)_m) From the measured image I_mThe touch signals follow the corrected image represented along the drive lines (row lines) and sense lines (column lines) as follows:

f(I_m)＝∑I_m，row×∑I_m，col (2)

wherein, sigma I_m，rowTouch signal measured along a drive line (row line); and Σ I_m，colTouch measured along a sense line (column line)The sum of the signals. Measured touch signal I_mCan be a measure of the change in capacitance Δ Csig, as described above.

For each pixel, equation (1) can be expressed as follows:

where (i, j) — the location of a pixel formed by the intersection of a drive line (row line) i and a sense line (column line) j in the touch sensor panel;

while

Equation (1) shows that the original image I can be obtained by using the compensation term R × f (I)_m) Compensating the measured image I_mThereby reducing or eliminating the negative pixel effect. Thus, by estimating an appropriate negative pixel compensation factor R and applying that factor to the measured touch signal, negative pixel effects in the measured image can be compensated for according to various embodiments. Despite the equation(1) Linear compensation is shown, it being understood that non-linear compensation is also possible.

FIG. 3 illustrates an exemplary method for compensating for negative pixel effects in a touch sensor panel in accordance with various embodiments. In the example of FIG. 3, touch signals from pixels of a touch sensor panel can be measured to provide a touch image I_m(305). In some embodiments, the capacitance Csig1 at each pixel when there is no touch can be compared to the capacitance Csig2 determined at that pixel when there is a touch, so that the capacitance change Δ Csig1-Csig2 can constitute the touch signal measurement. The capacitance Csig1 may be indicative of a background capacitance, which may be determined prior to operation or periodically during operation of the panel. Based on measured touch signals I_mAnd the characteristics of the touch sensor panel, the bounds at which the negative pixel compensation factor R is expected can be determined to ensure that the factor R to be subsequently estimated is a reasonable estimate (310). The negative pixel compensation factor R within the determined bounds may then be estimated (315). The estimated negative pixel compensation factor R may be applied to the measured touch image I_mE.g. by using equation (1) in order to restore the original image I without negative pixel effect (320). This method will be described in more detail below.

Some touch sensor panels, especially larger panels, can introduce considerable noise into the measured touch image, which can adversely affect negative pixel compensation. Thus, the measured touch image may be pre-processed to reduce noise before negative pixel compensation is performed, for example, as shown in FIG. 4.

FIG. 4 illustrates an exemplary bias noise (bias noise) calculation that can be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments. In the example of FIG. 4, touch image I has been measured_m(305) The bias noise may then be subtracted from the measured image. To this end, it can be determined whether a touch signal from a pixel along a sense line (column line) of the touch sensor panel is less than a predetermined noise threshold (405)). The noise threshold may be predetermined as follows. The touch signal is measured when there is no touch at the touch sensor panel. In a touch image without noise, the touch signal value should be approximately 0, indicating no touch. However, in a noisy touch signal, when there is no touch, the touch signal value may be non-0, which indicates a noisy bias in the panel. An average of the touch signals may be calculated, and a noise threshold may be set to the average. Since the noise bias is typically a function of the touch sensor panel design and is somewhat static, the noise threshold can be calculated prior to operation of the panel and, if desired, can be updated occasionally during panel operation. If the touch signal is less than the threshold, the touch signal is deemed to be non-touch and is indicative of noise in the panel (410).

It may be determined whether there are enough non-touch signals to calculate a reasonable noise bias (415). In some embodiments, the number of non-touch signals may be compared to a minimum amount, and if greater than the minimum amount, it is sufficient to calculate the noise bias. For example, the minimum amount may be determined empirically based on panel operation, design, and the like. A noise bias voltage may be calculated from the non-touch signal (420). In some embodiments, the noise bias can be calculated as an average of the non-touch signals. In some embodiments, the noise bias may be calculated as the median (mean) of the non-touch signals. Other techniques can also be used to calculate the noise bias from the non-touch signal. The calculated noise bias voltage can be subtracted 425 from all touch signals in the sense line (or column line).

The method can be repeated for each sense line to subtract the noise bias from all touch signals in that sense line (430).

Measured image I after subtracting noise bias from touch signal_mWhich may then be used to determine a negative pixel compensation factor R limit and the method of fig. 3 may proceed as described above (310).

FIG. 5 illustrates a block diagram that can includeExemplary compensation factor limits are determined in an exemplary method for compensating for negative pixel effects in a touch sensor panel. In the example of FIG. 5, touch image I has been measured_m(305) Thereafter, a limit for the negative pixel compensation factor R may be determined (310). Depending on the touch sensor panel design, negative pixel compensation according to equation (1) may or may not be well applied. The degree of goodness may depend on panel size, wiring (wiring), pixel layout, pixel proximity, and the like. Thus, for a panel design (labeled "A" in FIG. 5) where equation (1) does not apply well, the method may determine the bounds in one way. For a panel design (labeled "B" in FIG. 5) that applies equation (1) well, the method may determine the limits in another way. Larger panels are typically, but not always, in the "a" design category; in contrast, smaller panels are typically, but not always, in the "B" design category.

A touch sensor panel design whose boundaries are to be determined can be determined (505). If the panel design belongs to the "A" category, an upper limit negative pixel compensation factor R1 can be generated based on the maximum touch signal that can be sensed or reached by the touch sensor panel Smax (510). This can be done by selecting the measured touch image I_mAnd using equation (1) to determine a maximum compensation factor R that will give the corrected touch signal value in the original touch image I of the selected maximum touch signal value Smax. The maximum compensation factor R may be set to an upper limit factor R1. This assumes that the maximum touch signal value is in the measured touch image I_mIs approximately the same as the location of the maximum touch signal value in the original touch image I, which may or may not apply in some cases. This also assumes that the touch image I is being measured_mHas a value Smax in the original image, which may or may not be applicable in some cases. Where this assumption can be applied, the negative pixel compensation factor R may be equal to the upper limit factor R1. However, in case that this assumption cannot be applied, the original touchThe value of the maximum touch signal in the touch image I may be less than Smax so that the negative pixel compensation factor R may be less than the upper limit factor R1.

The upper limit factor R1 may be iterated to make fine adjustments to provide an improved or tight upper limit factor R2 (515). This may be achieved because the factor R1 may not be as accurate as preferred since equation (1) may not be fully applicable to the panel design. To calculate the upper limiting factor R2, the measured image I_mCorrected image f (I)_m) And the upper limit factor R1 may be applied to equation (1) to calculate the image Ir1 generated using the factor R1. The position Pr1 of the maximum touch signal value in the image Ir1 may be selected. Using equation (1), the maximum compensation factor R may be based on the measured image I_mThe touch signal value at position Pr1, the maximum panel touch signal value Smax, and the corresponding corrected image f (I)_m) The maximum compensation factor R can be determined. The maximum compensation factor R may be set to an upper limit factor R2. Further iterations may be done to further refine or tighten the ceiling factor. Preferably, the number of iterations may be smaller to improve efficiency. The upper limit of the negative pixel compensation factor may be set to a factor R2 (520).

If the panel design belongs to the "B" category, an upper limit negative pixel compensation factor R1 may be generated based on the maximum touch signal that can be sensed by the touch sensor panel (525). This can be done by selecting the measured touch image I_mAnd using equation (1) to determine a maximum compensation factor R that will give the measured image I_mIs in the original touch image I, and the corrected touch signal value in the original touch image I. The maximum compensation factor R may be set to an upper limit factor R1.

Another upper-bound negative pixel compensation factor R2 may be generated based on the sum of the pixel values in the original touch image I (530). This can be achieved by estimating the upper limit factor R2 as follows:

wherein,

is ground capacitance scaled with a constant b; g ═ Σ I is the sum of the corrected touch image values in the original touch image I; and a, b ═ touch sensor panel design constants, which can be obtained through simulation and/or empirical measurements for a given panel sensing pattern design. The constants a, b may be determined prior to panel operation.

To calculate the upper-bound negative pixel compensation factor R2 using equation (4), for example, "worst case" C may be selected_gnd，sclA value representing a worst ground condition. This value may be determined experimentally or estimated based on observations of panel operation. Since the original image I has not been calculated at this time, the value G can be estimated as the measured touch signal image I_mOr the measured image I or the sum of the absolute values of the touch signals in_mOf the touch signals having a positive value. Selected C_gnd，sclThe value and the estimated G value may be applied to equation (4) to calculate the compensation factor. The calculated compensation factor may be set as the upper limit factor R2. The upper limit of the negative pixel compensation factor may be set to the minimum of two upper limit factors R1 and R2 (535).

The lower limit of the negative pixel compensation factor may be set to 0 or some value substantially close to 0 (540). The negative pixel compensation factor R within the determined upper and lower limits may then be estimated, and the method of fig. 3 may be performed as described above (315).

FIG. 6 illustrates another exemplary compensation factor bound determination that may be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments. In the example of FIG. 6, touch image I has been measured_m(305) Thereafter, a limit for the negative pixel compensation factor R may be determined (310). Characteristics of a touch on the touch sensor panel, such as touch intensity, can affect negative pixel compensation. Full touch at the touch sensor panel (full touch) may generate a measured touch image I_mShould be close to the touch value of the maximum touch signal that the panel can sense. Thus, the maximum touch signal can be a suitable metric for determining a compensation factor for a full touch; conversely, a light touch (light touch) at the touch sensor panel can generate a much lower touch value, which can falsely indicate a large negative pixel effect requiring large compensation compared to a maximum touch signal. Thus, the sum of pixel values may be a more appropriate metric for determining a compensation factor for a light touch.

A determination can be made as to whether the touch at the touch sensor panel is a full touch or a light touch (605). For a full touch, an upper limit negative pixel compensation factor R1 may be generated based on the maximum touch signal that the touch sensor panel may sense (610). This may be achieved as described above. For light touches, an upper negative pixel compensation factor R1 may be generated based on the sum of the pixel values calculated in the original touch image I (615). This may be achieved as described above.

The upper limit of the negative pixel compensation factor may be set to a factor R1 (620). The lower limit of the negative pixel compensation factor may be set to 0 or a value substantially close to 0 (625). The negative pixel compensation factor R within the determined upper and lower limits may then be estimated, and the method of fig. 3 may be performed as described above (315).

FIG. 7 illustrates negative pixel effects that can be included in compensating for touch sensor panels according to various embodimentsExemplary compensation factor estimation in an exemplary method of (1). Measured touch image I_mIs adjusted to 0 or substantially close to 0 to compensate for the negative pixel effect. Measured touch image I_mThe positive pixels in (b) may be adjusted, e.g., boosted to a more positive value, to compensate for the negative pixel effect. A negative pixel compensation factor R can be estimated that can successfully make this adjustment. Since the negative pixels generally provide most of the information needed to estimate the factor R, the measured image I_mThe negative pixel in (1) can be selected for estimation while 0 and positive pixels can be ignored.

In the example of FIG. 7, after the bounds of the negative pixel compensation factor R have been generated (310), they may be based on the measured image I_mEstimates a negative pixel compensation factor R (315) within these bounds. For this purpose, the measured image I can be determined_mIs less than a defined threshold value (705) indicating a likelihood that the pixel is a negative pixel. In general, the more negative the measured image value of the pixel (i, j), the greater the likelihood that the pixel is a negative pixel. If the measured image value is less than the threshold, then pixel (i, j) may be selected as the negative pixel for estimating the negative pixel compensation factor R. May be in the measured image I_mDetermines a corrected image f (I) of the pixel_m). Each corrected image pixel (i, j) can be determined (710) by summing the measured touch signals along drive line (row line) i, summing the measured touch signals along sense line (column line) j, and multiplying the two sums as in equation (2). The factor R (I, j) of the pixel can be estimated within the determined bounds using equation (3) such that the original image pixel I (I, j) is equal to 0 (715). If the estimated factor R (i, j) is out of bounds, then the factor R (i, j) may be set to either the upper or lower limit that is closer. Additionally, or alternatively, the factor R (i, j) associated with the outlier pixel may be discarded. If the measured image value exceeds the threshold (710), then pixel (i, j) is unlikely to be a negative pixel and therefore may be ignored. For measuringTo touch image I_mMay repeat the negative pixel selections (705) - (715) for all pixels (720), (725).

In the touch image I that has been measured_mAfter calculating the negative pixel compensation factor R (I, j) for the selected negative pixel in (a), a weighting factor may be calculated for each factor R (I, j) to determine the entire measured image I_mThe global negative pixel compensation factor R (730). In this way, pixels that experience a negative pixel effect may make the greatest contribution to the global factor R. In some embodiments, the weighting factor may be calculated based on the difference between the selected negative pixel value and the value 0. In some embodiments, the weighting factor may be calculated as the probability that the estimated factor R (i, j) adjusts the selected negative pixel value to 0. In some embodiments, the weighting factor may be calculated based on a selected pattern of negative pixel values. Other parameters for calculating the weighting factors are also possible. The calculated weighting factor may be applied to its corresponding negative pixel compensation factor R (i, j) to produce a global negative pixel compensation factor R (735). In some embodiments, the global factor R may be calculated as a weighted average of the factors R (i, j). In some embodiments, the global factor R may be calculated as the median of the factors R (i, j). In some embodiments, the global factor R may be calculated as a pattern of factors R (i, j). In some embodiments, the global factor R may be calculated as a combination of a weighted mean and a pattern of the factor R (i, j). Other techniques for calculating the global factor R are also possible. The global factor R may then be applied to the measured touch image I_mTo recover the original image I that has been compensated for the negative pixel effect as in equation (1) and the method of fig. 3 may proceed as described above (320).

In some embodiments, additionally or alternatively, it may be determined whether pixel (i, j) is likely a negative pixel based on the corrected image pixel rather than the measured image pixel (705). For example, each corrected image pixel (i, j) may be compared to a noise threshold. In some embodiments, the noise threshold may be set based on the noise variance of each pixel in the corrected image, where, for example, a corrected image pixel may be calculated as the sum of measured image pixels in the row in which the pixel is located multiplied by the sum of measured image pixels in the column in which the pixel is located, as in equation (2), and the noise variance may be calculated based on the noise variance of each of the row and column pixels. If the corrected image pixel (i, j) value is equal to or below the noise threshold, pixel (i, j) is ignored as not providing sufficient information for estimating the negative pixel compensation factor.

FIG. 8 illustrates an exemplary compensation factor application that can be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments. In the example of FIG. 8, after estimating the negative pixel compensation factor R (315), the factor R may be applied to the measured touch image I_mTo recover the original touch image I (320) with the negative pixel effect compensated. Negative pixel compensation factor R and corrected image f (I)_m) May be multiplied (805) (determined according to equation (3)) and the resulting product added to the measured touch image I_mAs in equation (1) to recover the original image I (810) that had no negative pixel effect. The original image I may then be used for further processing.

Negative pixel compensation can be applied when the touch sensor panel is subjected to a negative pixel effect, and can be omitted when the panel is not subjected to a negative pixel effect. However, in some cases, there may be a fairly rapid change between having a negative pixel effect and not having a negative pixel effect. For example, a panel user may fluctuate between a grounded state (in which there is no negative pixel effect) and an ungrounded state (in which there is a negative pixel effect). Additionally or alternatively, the panel may alternate between detecting a negative pixel effect and not being able to detect a negative pixel effect, for example, due to the location of a touch at the panel. In this way, negative pixel compensation can be turned on or off, which results in undesirable image flicker between displaying the measured touch image or displaying the compensated touch image. Thus, logic may be included in the negative pixel compensation to selectively apply compensation to prevent or reduce image flicker and/or any other condition that may cause spurious variations between successive images.

FIG. 9 illustrates exemplary compensation selections that can be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel, in accordance with various embodiments. In the example of FIG. 9, after the original touch image I (320) that has compensated for the negative pixel effect has been restored, the measured touch image I can be maintained between successive images_mTo prevent or reduce image flicker as follows. The maximum value of the original touch image I that has compensated for the negative pixel effect may be selected (905), and the measured touch image I_mMay be selected (910). The scaling factor β may be selected to be applied to the selected original image I value to scale it to the selected measured image I_mA value (915). In some embodiments, β may take about 80% to 90% of its original calculated value, such that the maximum value of the original touch image I may be reduced to the measured touch image I_mAbout 80% to 90% of the maximum value of (c). The selected scaling factor β can then be applied to the entire original image I to create a scaled original touch image Ic, where the maximum value is approximately the same as the maximum value in the measured image. In some embodiments, the scaling factor β may be a composite of multiple scaling factors selected to appropriately scale the original image I.

In the original image I and thus the scaled original image Ic, the negative pixels have been compensated so that their value will be 0 or close to 0; otherwise, the measured image I_mA negative pixel in (a) will have a negative value. The positive pixels have been compensated so that their values will be adjusted positively. Thus, it is determined which pixels have been compensated by comparing the scaled original image values and the measured image values for each pixel (920). If the scaled original image values are greater than the measured image values, then the pixels have been compensated for the negative pixel effect and the scaled original image values should be used in the final compensated image (930). Otherwise, the pixel has not been compensated, or is only slightly compensated, andand the measured image values should be used in the final compensated image (925).

As a result, only the energies of these significantly compensated pixels may change between successive images, while the energies of these pixels that are not compensated or are only slightly compensated are maintained at the measured touch image values between successive images. Thus, the total energy of the final compensated image is substantially unchanged from the previously displayed image, thereby reducing or eliminating image flicker.

FIG. 10 illustrates another exemplary compensation option that can be included in an exemplary method for compensating for negative pixel effects in a touch sensor panel in accordance with various embodiments. In the example of FIG. 10, after the original touch image I (320) that has compensated for the negative pixel effect has been restored, the measured touch image I is taken between successive images_mTo the intensity of the original touch image I to prevent or reduce image flicker as follows. The maximum value of the original touch image I that has compensated for the negative pixel effect may be selected (1005), and the measured touch image I_mMay be selected (1010). A scaling factor beta larger than 1 may be selected to be applied to the selected measured image I_mThe value to scale it to the selected original image I value (1015). β may be 1.0 or more. The selected scaling factor beta may then be applied to the entire measured image I_mTo create a scaled measured touch image I_mcWherein the maximum value is substantially the same as the maximum value in the original image.

In the original image I, the negative pixels have been compensated so that their value will be 0 or close to 0; otherwise, the measured image I_mAnd thus scaled measured image I_mcA negative pixel in (a) will have a negative value. The positive pixels have been compensated so that their values will be adjusted positively. Thus, by comparing the scaled measured image values with the original image values for each pixel, it is determined which pixels have been compensated (1020). If the scaled measured image value is smaller than the original image value, then the pixel has already beenThe negative pixel effect is compensated for and the original image values should be used in the final compensated image (1030). Otherwise, the pixel has not been compensated, or is only slightly compensated, and the scaled measured image values should be used in the final compensated image (1025).

As a result, only those pixels that are significantly compensated may have their intensities varied between successive images, while those pixels that are not compensated or only slightly compensated may have little or no variation in their intensities between successive images. In case there is a small change in the intensity of pixels that are not compensated or only slightly compensated, some measures may be taken to smooth the change in order to avoid a small amount of image flicker.

It should be appreciated that the method of compensating for negative pixel effects is not limited to those illustrated in fig. 3-10, but may include other and/or additional actions capable of negative pixel compensation in accordance with various embodiments.

FIG. 11 illustrates an exemplary computing system 1100 that can compensate for negative pixel effects in a touch sensor panel according to various embodiments described herein. In the example of FIG. 11, computing system 1100 can include touch controller 1106. Touch controller 1106 can be a single Application Specific Integrated Circuit (ASIC) that can include one or more processor subsystems 1102, which can include one or more main processors, such as ARM968 processors, or other processors with similar functionality and capabilities. However, in other embodiments, the processor functions may be implemented instead by dedicated logic, such as a state machine. The processor subsystems 1102 can also include peripheral devices (not shown), such as Random Access Memory (RAM) or other types of memory or storage, watchdog timers and the like. Touch controller 1106 can also include a receiving portion 1107 for receiving signals, such as touch signals 1103 of one or more sensing channels, other signals from other sensors, such as sensor 1111, and the like. Touch controller 1106 can also include a demodulation portion 1109, such as a multi-stage vector demodulation engine, panel scan logic 1110, and a transmit portion 1114 for transmitting stimulation signals 1116 to touch sensor panel 1124 to drive the panel. The panel scan logic 1110 can access the RAM 1112, automatically read data from the sense channels, and provide control for the sense channels. In addition, the panel scan logic 1110 can control the transmit section 1114 to generate stimulation signals 1116 at various frequencies and phases that can be selectively applied to rows of the touch sensor panel 1124.

Touch controller 1106 can also include a charge pump 1115 that can be used to generate a supply voltage for transmit portion 1114. The stimulus signal 1116 may have a magnitude greater than the maximum voltage by cascading two charge storage devices, such as capacitors, to form the charge pump 1115. Thus, the actuation voltage (e.g., 6 volts) may be higher than the voltage level that a single capacitor can handle (e.g., 3.6 volts). Although fig. 11 shows the charge pump 1115 separate from the transmit part 1114, the charge pump may be part of the transmit part.

Computing system 1100 can also include a touch sensor panel 1124, which can be, for example, the panel illustrated in FIG. 1 above.

Computing system 1100 can include a main processor 1128 for receiving output from processor subsystem 1102 and performing actions based on the output, including, but not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device coupled to the main device, answering a telephone call, placing a telephone call, terminating a telephone call, changing volume or audio settings, storing information related to telephone communications, such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or computer network, allowing authorized individuals to access restricted areas of the computer or computer network, loading a user profile associated with user preferred settings of a computer desktop, allowing access to web content, initiate a specific procedure, and/or encrypt or decode a message, etc. Main processor 1128 may also perform other functions that may not be related to panel processing and may be coupled to program storage 1132 and display device 1130, such as an LCD display for providing a UI to a user of the device. In some embodiments, host processor 1128 may be a separate component from touch controller 1106, as shown. In other embodiments, host processor 1128 may be included as part of touch controller 1106. In still other embodiments, the functionality of main processor 1128 may be performed by processor subsystem 1102 and/or distributed among other components of touch controller 1106. Display device 1130 together with touch sensor panel 1124, when located partially or fully below the touch sensor panel or when integrated with the touch sensor panel, can form a touch sensitive device, such as a touch screen.

Note that negative pixel compensation, as well as one or more of the functions described above, may be performed, for example, by firmware stored in memory (e.g., one of the peripherals), by processor subsystem 1102, or stored in program storage 1132 and executed by main processor 1128. The firmware can also be stored and/or transmitted in any computer-readable storage medium for execution by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a "computer-readable storage medium" can be any medium that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a Random Access Memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disk such as a CD, CD-R, CD-RW, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, and memory sticks, and the like.

The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In this context, a "transmission medium" may be any medium that can communicate, propagate, or transport the program for use by or in connection with the execution system, apparatus, or device. The transmission medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, or infrared wired or wireless propagation medium.

It should be understood that the touch sensor panel is not limited to being touch-type as described in fig. 11, but may be a proximity panel or any other panel according to various embodiments. Further, the touch sensor panel described herein may be a multi-touch sensor panel.

It should also be understood that the computing system is not limited to the components and configuration of fig. 11, but may include other and/or additional components in various configurations capable of compensating for negative pixel effects in accordance with various embodiments.

FIG. 12 illustrates an exemplarymobile phone 1200 that can perform negative pixel compensation, which can include a touch sensor panel 1224, adisplay 1236, and other computing system modules, according to various embodiments.

FIG. 13 illustrates an exemplary digital media player 1300 that can perform negative pixel compensation, which can include a touch sensor panel 1324, a display 1336, and other computing system modules, in accordance with various embodiments.

FIG. 14 illustrates an exemplarypersonal computer 1400 that can perform negative pixel compensation according to various embodiments, which can include a touch sensor panel (track pad) 1424, a display 1436, and other computing system modules.

By compensating for negative pixel effects according to various embodiments, the mobile phones, media players, and personal computers of FIGS. 12-14 may achieve power savings, improved accuracy, improved speed, and improved robustness.

According to an embodiment of the present disclosure, there is provided a method for compensating for a negative pixel effect, the method including: determining at least one limit for a compensation factor based on the touch image values; estimating a compensation factor within the determined bounds based on the touch image value being a negative value; and applying the estimated compensation factor to the touch image value to compensate the touch image value.

According to a first aspect of this embodiment, determining at least one limit for the compensation factor comprises: determining an upper limit of the compensation factor based on at least one of the sum of the maximum achievable touch image value and the desired touch image value; and determining that a lower limit of the compensation factor is about 0.

According to a first aspect of this embodiment, estimating the compensation factor within the determined bounds comprises: estimating a compensation factor for each negative touch image value; calculating a weighting factor for each estimated compensation factor; and applying the calculated weighting factor to the corresponding estimated compensation factor to produce a compensation factor within the determined bounds.

According to a third aspect of this embodiment, calculating a weighting factor for each estimated compensation factor comprises: calculating a difference between the corresponding negative touch image value and 0; and associating the weighting factor with the calculated difference.

According to a third aspect of this embodiment, calculating a weighting factor for each estimated compensation factor comprises: calculating the probability that the corresponding compensation factor adjusts the corresponding negative touch image value to 0; and associating the weighting factor with the calculated probability.

According to a first aspect of this embodiment, applying the estimated compensation factor to the touch image values comprises: calculating a correction image value representing a correction to be made to the touch image value; and adding the product of the estimated compensation factor and the calculated correction image value to the touch image value.

According to a first aspect of this embodiment, the method further comprises: subtracting a noise bias from the touch image value.

According to a first aspect of this embodiment, the method further comprises: applying a scaling factor to at least one of the touch image values and compensated touch image values to obtain image consistency.

According to the first aspect of this embodiment, the touch image value indicates a grounding condition.

According to another embodiment of the present disclosure, there is provided a method for compensating for a negative pixel effect, the method including: analyzing negative pixel values of the touch image to determine a compensation factor; applying the determined compensation factor to the touch image to produce a compensated image substantially entirely free of the negative pixel values; and selectively scaling the compensated image or the touch image to provide image display uniformity.

According to a first aspect of this embodiment, selectively scaling the compensated image or the touch image comprises: scaling the compensated image such that an overall energy of the compensated image is substantially the same as an overall energy of the touch image.

According to a second aspect of this embodiment, scaling the compensated image comprises: selecting a scaling factor for scaling high pixel values of the compensated image to high pixel values of the touch image; and applying the scaling factor to all pixel values of the compensated image.

According to a first aspect of this embodiment, selectively scaling the compensated image or the touch image comprises: scaling the touch image so that an overall intensity of the touch image is substantially the same as an overall intensity of the compensated image.

According to a fourth aspect of this embodiment, scaling the touch image comprises: selecting a scaling factor for scaling high pixel values of the touch image to high pixel values of the compensated image; and applying the scaling factor to all pixel values of the touch image.

According to still another embodiment of the present disclosure, there is provided a touch sensitive device including: a touch sensor panel comprising a plurality of touch locations for sensing touches on the touch sensor panel; and a processor in communication with the touch sensor panel, the processor configured to capture an image of the sensed touch, identify negative values in the captured image, determine a limit for a compensation factor for adjusting the captured image based on the identified negative values, estimate the compensation factor within the determined limit, and adjust the identified negative values to about 0 using the estimated compensation factor.

According to a first aspect of this embodiment, adjusting the identified negative value to about 0 is based on a non-linear relationship between the captured image and the compensation factor.

According to a first aspect of this embodiment, adjusting the identified negative value to about 0 is based on a linear relationship between the captured image and the compensation factor.

According to a first aspect of this embodiment, the device is incorporated into at least one of a mobile phone, a digital media player, and a personal computer.

According to still another embodiment of the present disclosure, there is provided a method of performing negative pixel compensation, the method including: determining at least one characteristic associated with the touch sensor panel; and selectively applying negative pixel compensation to an image captured by the touch sensor panel based on compatibility of the negative pixel compensation with the determined feature.

According to a first aspect of this embodiment, selectively applying the negative pixel compensation to an image captured by the touch sensor panel comprises: selecting at least one of a negative pixel compensation based on a maximum touch signal sensed by the touch sensor panel and a negative pixel compensation based on a sum of touch signals expected in an image without negative pixels; and applying the selected negative pixel compensation to pixels in the captured image.

According to a first aspect of this embodiment, the feature is a panel design.

According to a first aspect of this embodiment, the characteristic is a touch type.

According to still another embodiment of the present disclosure, there is provided a terminal device including: a touch sensor panel comprising a plurality of touch locations for sensing touches on the touch sensor panel; a processor in communication with the touch sensor panel and the display, the processor configured to capture an image of the sensed touch, identify negative values in the captured image, determine a limit for a compensation factor for adjusting the captured image based on the identified negative values, estimate the compensation factor within the determined limit, and adjust the identified negative values to about 0 using the estimated compensation factor; and a display for displaying the compensated image.

According to still another embodiment of the present disclosure, there is provided an apparatus for compensating for a negative pixel effect, the apparatus including: means for determining at least one limit for a compensation factor based on the touch image values; means for estimating a compensation factor within the determined bounds based on the touch image value being a negative value; and means for applying the estimated compensation factor to the touch image values to compensate for the touch image values.

According to the first aspect of this embodiment, the apparatus further comprises: means for applying the estimated compensation factor to the negative touch image value to set the negative touch image value to approximately 0.

According to the first aspect of this embodiment, the apparatus further comprises: means for applying the estimated compensation factor to a positive touch image value to boost the positive touch image value in a positive direction.

According to a first aspect of this embodiment, the means for determining at least one limit for the compensation factor comprises: means for determining an upper limit of the compensation factor based on at least one of the sum of the maximum achievable touch image value and the desired touch image value; and means for determining that a lower limit of the compensation factor is about 0.

According to still another embodiment of the present disclosure, there is provided an apparatus for compensating for a negative pixel effect, the apparatus including: means for analyzing negative pixel values of the touch image to determine a compensation factor; means for applying the determined compensation factor to the touch image to produce a compensated image substantially entirely free of the negative pixel values; and means for selectively scaling the compensated image or the touch image to provide image display uniformity.

According to still another embodiment of the present disclosure, there is provided an apparatus for negative pixel compensation, the apparatus including: means for determining at least one characteristic associated with the touch sensor panel; and means for selectively applying negative pixel compensation to an image captured by the touch sensor panel based on compatibility of the negative pixel compensation with the determined feature.

According to yet another embodiment of the disclosure, there is provided a computer readable storage medium having stored thereon a set of instructions for compensating for negative pixel effects in a touch sensor panel, which when executed by a processor, causes the processor to: determining a limit for a compensation factor based on a value of a touch image captured by the touch sensor panel; estimating a compensation factor within the determined bounds based on a negative touch image value representing the negative pixel effect; and applying the estimated compensation factor to the touch image value to compensate for the negative pixel effect.

According to a first aspect of this embodiment, the processor applies the estimated compensation factor to the negative touch image value to set the negative touch image value to approximately 0.

According to a first aspect of this embodiment, the processor applies the estimated compensation factor to touch image values that are positive values to increase the positive touch image values in a positive direction.

Although the embodiments have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such variations and modifications are to be understood as being included within the scope of the various embodiments as defined by the appended claims.

Claims

1. A method for compensating for negative pixel effects, the method comprising:

determining at least one limit for a compensation factor based on the touch image values;

estimating a compensation factor within the determined bounds based on the touch image value being a negative value; and

applying the estimated compensation factor to the touch image value to compensate for the touch image value.

2. The method of claim 1, wherein determining at least one bound for a compensation factor comprises:

determining an upper limit of the compensation factor based on at least one of the sum of the maximum achievable touch image value and the desired touch image value; and

the lower limit of the compensation factor is determined to be about 0.

3. The method of claim 1, wherein estimating a compensation factor within the determined bounds comprises:

estimating a compensation factor for each negative touch image value;

calculating a weighting factor for each estimated compensation factor; and

the calculated weighting factor is applied to the corresponding estimated compensation factor to produce a compensation factor within the determined bounds.

4. The method of claim 3, wherein calculating a weighting factor for each estimated compensation factor comprises:

calculating a difference between the corresponding negative touch image value and 0; and

the weighting factor is associated with the calculated difference.

5. The method of claim 3, wherein calculating a weighting factor for each estimated compensation factor comprises:

calculating the probability that the corresponding compensation factor adjusts the corresponding negative touch image value to 0; and

associating the weighting factor with the calculated probability.

6. The method of claim 1, wherein applying the estimated compensation factor to the touch image values comprises:

calculating a correction image value representing a correction to be made to the touch image value; and

adding the product of the estimated compensation factor and the calculated correction image value to the touch image value.

7. The method of claim 1, further comprising:

subtracting a noise bias from the touch image value.

8. The method of claim 1, further comprising:

applying a scaling factor to at least one of the touch image values and compensated touch image values to obtain image consistency.

9. The method of claim 1, wherein the touch image value indicates a grounding condition.

10. A method for compensating for negative pixel effects, the method comprising:

analyzing negative pixel values of the touch image to determine a compensation factor;

applying the determined compensation factor to the touch image to produce a compensated image substantially entirely free of the negative pixel values; and

selectively scaling the compensated image or the touch image to provide image display uniformity.

11. The method of claim 10, wherein selectively scaling the compensated image or the touch image comprises:

scaling the compensated image such that an overall energy of the compensated image is substantially the same as an overall energy of the touch image.

12. The method of claim 11, wherein scaling the compensated image comprises:

selecting a scaling factor for scaling high pixel values of the compensated image to high pixel values of the touch image; and

applying the scaling factor to all pixel values of the compensated image.

13. The method of claim 10, wherein selectively scaling the compensated image or the touch image comprises:

scaling the touch image so that an overall intensity of the touch image is substantially the same as an overall intensity of the compensated image.

14. The method of claim 13, wherein scaling the touch image comprises:

selecting a scaling factor for scaling high pixel values of the touch image to high pixel values of the compensated image; and

applying the scaling factor to all pixel values of the touch image.

15. A touch sensitive device, comprising:

a touch sensor panel comprising a plurality of touch locations for sensing touches on the touch sensor panel; and

a processor in communication with the touch sensor panel, the processor configured to capture an image of the sensed touch, identify negative values in the captured image, determine a limit for a compensation factor for adjusting the captured image based on the identified negative values, estimate the compensation factor within the determined limit, and adjust the identified negative values to about 0 using the estimated compensation factor.

16. The touch sensitive device of claim 15, wherein adjusting the identified negative value to approximately 0 is based on a non-linear relationship between the captured image and the compensation factor.

17. The touch sensitive device of claim 15, wherein adjusting the identified negative value to approximately 0 is based on a linear relationship between the captured image and the compensation factor.

18. The touch sensitive device of claim 15, wherein the device is incorporated into at least one of a mobile phone, a digital media player, and a personal computer.

19. A method of negative pixel compensation, the method comprising:

determining at least one characteristic associated with the touch sensor panel; and

selectively applying negative pixel compensation to an image captured by the touch sensor panel based on compatibility of the negative pixel compensation with the determined feature.

20. The method of claim 19, wherein selectively applying the negative pixel compensation to images captured by the touch sensor panel comprises:

selecting at least one of a negative pixel compensation based on a maximum touch signal sensed by the touch sensor panel and a negative pixel compensation based on a sum of touch signals expected in an image without negative pixels; and

the selected negative pixel compensation is applied to pixels in the captured image.

21. The method of claim 19, wherein the feature is a panel design.

22. The method of claim 19, wherein the characteristic is a touch type.

23. A terminal device, comprising:

a touch sensor panel comprising a plurality of touch locations for sensing touches on the touch sensor panel;

a processor in communication with the touch sensor panel and the display, the processor configured to capture an image of the sensed touch, identify negative values in the captured image, determine a limit for a compensation factor for adjusting the captured image based on the identified negative values, estimate the compensation factor within the determined limit, and adjust the identified negative values to about 0 using the estimated compensation factor; and

and the display is used for displaying the compensated image.

24. An apparatus for compensating for negative pixel effects, the apparatus comprising:

means for determining at least one limit for a compensation factor based on the touch image values;

means for estimating a compensation factor within the determined bounds based on the touch image value being a negative value; and

means for applying the estimated compensation factor to the touch image value to compensate for the touch image value.

25. The apparatus of claim 24, further comprising:

means for applying the estimated compensation factor to the negative touch image value to set the negative touch image value to approximately 0.

26. The apparatus of claim 24, further comprising:

means for applying the estimated compensation factor to a positive touch image value to boost the positive touch image value in a positive direction.

27. The apparatus of claim 24, wherein the means for determining at least one bound for a compensation factor comprises:

means for determining an upper limit of the compensation factor based on at least one of the sum of the maximum achievable touch image value and the desired touch image value; and

means for determining that a lower limit of the compensation factor is about 0.

28. An apparatus for compensating for negative pixel effects, the apparatus comprising:

means for analyzing negative pixel values of the touch image to determine a compensation factor;

means for applying the determined compensation factor to the touch image to produce a compensated image substantially entirely free of the negative pixel values; and

means for selectively scaling the compensated image or the touch image to provide image display consistency.

29. An apparatus for negative pixel compensation, the apparatus comprising:

means for determining at least one characteristic associated with the touch sensor panel; and

means for selectively applying negative pixel compensation to an image captured by the touch sensor panel based on compatibility of the negative pixel compensation with the determined feature.