US20020008711A1 - Apparatus and method for displaying zoomed version of stored image by displaying and shifting absed on pixel overlap - Google Patents

Abstract

A method of displaying a zoomed version of stored image on a display, where the stored image is defined by a set of data entries mapped to respective pixels of the display. The stored image is first scaled relative to the display in accordance with the desired zooming ratio. The scaled image is then located at an initial position relative to the display and the extent to which each display pixel is overlapped by features of the scaled image is determined. A colour tone is assigned to each display pixel in accordance with the extent of the overlap. The scaled image is then shifted relative to said initial position one or more times and, for the or each shift, the overlap of each display pixel is recalculated and a new colour tone assigned. The sets of assigned colour tones are then displayed cyclically on the display to produce a displayed image.

Description

FIELD OF THE INVENTION
• The present invention relates to an apparatus and method for displaying an image and in particular for displaying a zoomed version of a stored image.[0001]
BACKGROUND OF THE INVENTION
• Electronic displays commonly provide for zooming in and out of a stored image in order to enable a user to see more clearly details of the image or to obtain an overview of the image. An image for display on an electronic display is commonly stored in an electronic memory by way of a matrix of data entries which are mapped on a 1:1 basis with pixels of the display. In order to zoom in on the image, i.e. to make the image or portions of the image larger on the display, each data entry is ‘expanded’ to cover two or more pixels. However, in order to avoid distortion of the image, each data entry must be expanded to cover a square block of pixels. It is therefore only possible to zoom in on the image by a factor of 2, 3, 4 etc. This is inconvenient, for example, where it is desired to expand text so as to allow it to be more easily read but where expansion by a factor of two or more will result in the edges of the text extending beyond the edges of the display. The user must ‘roam’ around the image, displaying only bits of it at a time, in order to read the entire text. A problem also arises where an image is too large to be displayed on a display and stored data entries have to be mapped to ‘partial’ pixels. Solutions proposed to overcome these problems include creating new type fonts in the case of zooming in, and merely dropping pixels in the case of zooming out.[0002]
• One application where these problems arise is in mobile communication devices which have only a small display and the capability to receive facsimile transmissions.[0003]
SUMMARY OF THE INVENTION
• It is an object of the present invention to overcome or at least mitigate the disadvantages of conventional zooming methods. In particular, it is an object of the present invention to provide an apparatus and method capable of substantially stepless zooming.[0004]
• According to first aspect of the present invention there is provided a method of displaying a zoomed version of stored image on a display, where the stored image is defined by a set of data entries mapped to respective pixels of the display, the method comprising the steps of:[0005]
• (1) scaling the stored image relative to the display in accordance with a desired zooming ratio;[0006]
• (2) locating the scaled image at an initial position relative to the display;[0007]
• (3) determining the extent to which each display pixel is overlapped by features of the scaled image, and assigning to each display pixel a corresponding colour tone;[0008]
• (4) shifting the scaled image relative to said initial position one or more times and, for the or each shift, repeating step (3); and[0009]
• (5) cyclically displaying each of the sets of assigned colour tones in turn for as long as the zoomed version is to be displayed.[0010]
• It will be understood that the terms ‘zoomed’ and ‘zooming’ used in relation to the present invention relate both to the enlargement and reduction of images.[0011]
• Preferably, step (5) comprises shifting the scaled image in two orthogonal directions (x,y), where the maximum shift from said initial position in the x and the y direction is less than the width of one display pixel (L). Preferably, where a zooming factor of {fraction (p/s)} is applied to scale the image in step (1), and p and s are both integers and s is the lowest common denominator, each shift produced by step (5) translates the scaled image by a multiple of {fraction (L/s)} in one or both of the x and y directions. More preferably, the maximum shift is L −{fraction (L/s)} which results in each edge feature of the scaled image being sharp in at least one of the initial position and the shifted positions. In this way, it is possible to achieve stepless zooming in which only integers and fixed point calculations are used. The method may be implemented directly in machine code language to achieve sufficient speed for real time zooming.[0012]
• Preferably, the step of assigning a colour tone to a display pixel comprises mapping the fractional coverage of the display pixel, by features of the scaled image, to a linear range of colour tones. For a monochrome display, said linear range comprises grey-level tones. For a colour display, where the stored image comprises a set of data entries for each of a plurality of colours (e.g. red, green and blue), the method of the above first aspect may be carried out separately for each set of image pixels.[0013]
• Where the data entries of the stored image correspond themselves to colour tones, step (3) may additionally comprise for each display pixel determining a function of both the fractional overlap and the tone(s) of the overlap, said assignment being made on the basis of the determined function.[0014]
• Preferably, the time interval between the display of successive sets of assigned colour tones is between {fraction (1/20)} th of a second and 1 second.[0015]
• According to second aspect of the present invention there is provided apparatus for displaying a zoomed version of a stored image, the apparatus comprising a display having a matrix of display pixels, a memory for storing an image as a set of data entries mapped to said display pixels, and processing means arranged to:[0016]
• scale the stored image relative to the display in accordance with a desired zooming ratio;[0017]
• locate the scaled image at a first position relative to the display;[0018]
• determine the extent to which each display pixel is overlapped by the scaled image and to assign to each display pixel a corresponding colour tone;[0019]
• shift the scaled image relative to the display one or more times and repeat the steps of determining and displaying for each shift; and[0020]
• cyclically display each of the sets of assigned colour tones in turn for as long as the zoomed version is to be displayed.[0021]
• In one embodiment of the present invention, the apparatus is a combined mobile telephone and personal digital assistant. The display may be a liquid crystal display.[0022]
BRIEF DESCRIPTION OF THE DRAWINGS
• For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which:[0023]
• FIG. 1 shows a combined personal data assistant/mobile telephone device;[0024]
• FIG. 2 shows a simplified schematic functional diagram of the device of FIG. 1;[0025]
• FIG. 3 shows schematically a portion of a display of the device of FIG. 1 on which is displayed an image;[0026]
• FIG. 4 shows an enlarged view of the display portion of FIG. 3 with a scaled version of the image displayed thereon;[0027]
• FIG. 5 shows the enlarged display portion of FIG. 4 with the scaled image displayed at three different positions;[0028]
• FIGS. 6[0029]ato6eare flow diagrams describing a method of displaying a scaled version of a stored image on a display of the device of FIG. 1.
DETAILED DESCRIPTION
• Combined personal data assistant/mobile telephone devices are expected to become commonplace over the next few years as the demand for mobile data communication services increases. One[0030]such device1 is illustrated in FIG. 1 and has a “clam-shell” type construction with akeyboard2 and adisplay3 located on opposed inner surfaces. The functional structure of thisdevice1 is illustrated in FIG. 2 where a central processing unit (CPU)4 carries out the main processing operations of thedevice1 in response to user input via thekeyboard2. Amemory5 stores data, including data corresponding to images to be displayed on the display. Such display data can be extracted from thememory5, processed, and transferred to thedisplay3 by theCPU4.
• Assume for example that the device has received a facsimile transmission from a remote station. The facsimile is stored in a block of the[0031]memory5 as a set of data entries, each of which can be thought of as an ‘image pixel’ and which is either black or white. The width of the image in image pixels corresponds to the width of thedisplay3 in display pixels although the length of the image is generally considerable greater than the length of the display. The user may select to display the image in unzoomed form in which case the image pixels of an upper portion of the image are mapped on a one to one basis with the display pixels to display that upper portion on the display. The user can then scroll down the image as appropriate. FIG. 3 illustrates aportion6 of thedisplay3, where the image displayed is the letter ‘N’. As can be seen, there is a one to one mapping between the display pixels7 (having a length L in both the x and y directions) and theimage pixels8.
• The user may request to zoom the stored image on the display[0032]3 (centred on the centre of the display3) using one of an expand and acompress key9,10. Typically the length of time for which a key9,10 is pressed will determine the zooming ratio. For the purpose of illustration, assume that the user selects to display the stored image, compressed by a factor of ⅔. An imaginary enlargement of theentire display3 by a factor of 3 is carried out (illustrated in FIG. 4 for the display portion6). The stored image is then enlarged by a factor of 2 to give the required relative zooming ratio of ⅔. This can be generalised such that the zooming ratio is {fraction (p/s)} where p and s are both integers and s is the lowest common denominator.
• Due to the differences in the scaling operations performed on the image and on the[0033]display3, thepixels8 making up the image are now smaller than thepixels7 of thedisplay3. The next step in the zooming process is to compute the area of each notionallyenlarged display pixel7 which is overlapped by features (i.e. black areas) of the notionally enlarged image. For example, from FIG. 4, it can be seen that the topleft display pixel7ahas {fraction (7/9)}ths of its area covered by features of the image. Now assume that thedisplay3 is capable of displaying ten different grey levels (or tones) ranging from white to black (0 to 9). A grey level is then assigned to eachdisplay pixel7 by mapping the determined fractional coverage to the linear grey scale. For example, the upperleft pixel7ais assigned a grey level of 8 whilst the upper pixel, second from the left,7bis assigned a grey level of 2.
• From FIG. 4, it will be appreciated that the left hand edge of the image “N” will consist of a line of pixels displayed with a grey level of 8 and will therefore appear relatively sharp on the[0034]display3. However, the right hand edge of the image is displayed as a line of pixels having a grey level of only 4 and will therefore appear somewhat blurred on thedisplay3. It will also be appreciated however that if the image is shifted to the right by ⅔ of a display pixel length L, the right hand edge of the image will become sharp whilst the left hand edge will become blurred. Similarly, other edge features of the image will become blurred or sharp at intermediate positions of the image relative to thedisplay3.
• By cyclically moving the image relative to the[0035]display3, with a maximum shift in the x and y directions of ⅔ L, it is possible to ensure that all edge features are sharp at least one position during the cycle. For the image ‘N’ shown in FIG. 4, this range of movement is illustrated by the lightly shadedarea11. It is not necessary to consider the infinite range of positions within which the image can be shifted. Rather, it is only necessary to consider discrete shifts of d in the x and y directions, where d={fraction (1/3)} L (or more generically {fraction (1/s)} L). The three positions which the image takes relative to the display in the x direction are illustrated in FIG. 5(a) to5(c). Similarly, the image can take three positions relative to the display in the y direction giving a total of nine positions.
• The fractional coverage of each[0036]display pixel7 by image features is determined at each of these nine positions and grey levels assigned to the pixels accordingly. The result is a set of display pixel/grey level assignments for each relative position. These are stored in thememory5 of thedevice1. It is noted that it is possible to compute these data sets using only integers and fixed point calculations, i.e. floating point calculations are not required.
• The method may be implemented directly in machine code language to achieve sufficient speed for real time zooming.[0037]
• The[0038]CPU4 then causes each of the grey scale sets, or ‘fuzzy’ images, to be displayed in turn, for example at intervals of 500 ms, continuously repeating this cycle for as long as the zoomed image is to be displayed. It is noted that the time interval between the display of successive sets of grey scales should be long enough to allow each displayed set to be perceived by the viewer. Moreover, the time interval may be determined to some extent by the speed of the display.
• This process is equally applicable to zooming in on a stored image, i.e. where the image is enlarged relative to the[0039]display3. It may also be applied to colour images where the image is stored, for example, by way of three independent data sets corresponding to the colours red, green, and blue. In this case, the process is carried out separately for each data set, where the fractional overlap of eachdisplay pixel7 is mapped to a linear tonal scale for the appropriate colour. At each relative shift, a composite image is displayed by combining the corresponding three colour tone set.
• FIGS. 6[0040]ato6eare flow charts illustrating in detail an implementation of the dynamic zooming process described above.
• It will be appreciated that modifications may be made to the above described embodiment without departing from the scope of the present invention. For example, where the stored image comprises a grey level assigned to each pixel, the zooming process may compute, at each shift and for each display pixel, a function which is a combination of the fractional coverage and the grey level(s) of the overlapping image feature(s). For example, this function may be the product of the fractional coverage and of the grey level. The function value may then be mapped to a linear grey level scale to assign a grey level to the display pixel.[0041]

Claims (10)

1. A method of displaying a zoomed version of stored image on a display, where the stored image is defined by a set of data entries mapped to respective pixels of the display, the method comprising the steps of:

(1) scaling the stored image relative to the display in accordance with a desired zooming ratio;

(2) locating the scaled image at an initial position relative to the display;

(3) determining the extent to which each display pixel is overlapped by features of the scaled image, and assigning to each display pixel a corresponding colour tone;

(4) shifting the scaled image relative to said initial position one or more times and, for the or each shift, repeating step; and

(5) cyclically displaying each of the sets of assigned colour tones in turn for as long as the zoomed version is to be displayed.

2. A method according toclaim 1, wherein step comprises shifting the scaled image in one of two orthogonal directions (x,y), where the maximum shift from said initial position in the x and the y direction is less than the width of one display pixel (L).

3. A method according toclaim 1 or2, wherein a zooming factor of {fraction (p/s)} is applied to scale the image in step, and p and s are both integers and s is the lowest common denominator, each shift produced by step translating the scaled image by a multiple of {fraction (L/s)} in one or both of the x and y directions.

4. A method according toclaim 3, wherein the maximum shift is L−{fraction (L/s)} which results in each edge feature of the scaled image being sharp in at least one of the initial position and the shifted positions.

5. A method according to any one of the preceding claims, wherein the step of assigning a colour tone to a display pixel comprises mapping the fractional coverage of the display pixel, by features of the scaled image, to a linear range of colour tones.

6. A method according to any one of the preceding claims, wherein the data entries of the stored image correspond themselves to colour tones, and step additionally comprises, for each display pixel, determining a function of both the fractional overlap and the tone(s) of the overlap, said assignment being made on the basis of the determined function.

7. A method according toclaim 5 or toclaim 6 when appended toclaim 5, wherein the display is a monochrome display and said linear range comprises grey-level tones.

8. A method of displaying a stored colour image on a colour display, where the stored image comprises a set of data entries for each of a plurality of colours, the method comprising carrying out the method of any one ofclaims 1 to6 for each of said colours.

9. A method according to any one of the preceding claims, wherein the time interval between the display of successive sets of assigned colour tones is between {fraction (1/20)}0 th of a second and 1 second.

10. Apparatus for displaying a zoomed version of a stored image, the apparatus comprising a display having a matrix of display pixels, a memory for storing an image as a set of data entries mapped to said display pixels, and processing means arranged to:

scale the stored image relative to the display in accordance with a desired zooming ratio;

locate the scaled image at a first position relative to the display;

determine the extent to which each display pixel is overlapped by the scaled image and to assign to each display pixel a corresponding colour tone;

shift the scaled image relative to the display one or more times and repeat the steps of determining and displaying for each shift; and

cyclically display each of the sets of assigned colour tones in turn for as long as the zoomed version is to be displayed.

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