技术领域technical field
本发明涉及图像处理领域，更具体地涉及一种背光补偿方法和装置。The present invention relates to the field of image processing, and more particularly to a backlight compensation method and device.
背景技术Background technique
在视频监控系统中，对各种监控对象的信息识别受到光照、天气条件等的影响。对于其中存在背光区域的监控图像(这里称为背光图像)，背光补偿成为一个需要关注的问题。这是因为，背光区域的灰度级过低会导致背光区域的画面太黑，从而使得背光区域的画面的细节模糊甚至无法识别。In a video surveillance system, information recognition of various surveillance objects is affected by light, weather conditions, etc. For surveillance images in which there are backlit areas (herein referred to as backlit images), backlight compensation becomes a concern. This is because the too low gray level of the backlight area will cause the picture in the backlight area to be too dark, so that the details of the picture in the backlight area will be blurred or even unrecognizable.
背光补偿也称作逆光补偿或逆光补正，它可以有效补偿摄像机在逆光环境下拍摄时主体画面黑暗的缺陷。当引入背光补偿功能时，可以使监视器上的主体画面明朗。在背光图像处理中，处于背光区域中的像素的亮度被改善，并且像素之间的对比度增加。但是，在大多数背光补偿方案中，在背光区域中的像素的亮度被改善的同时，亮光区域中的像素的亮度也被改善，这使得整个图像亮度整体增高，尤其亮光区域容易过渡曝光。虽然在一些其他背光补偿方案中，只有背光区域中的像素的亮度被改善，但是这些方案中提取出背光区域的处理也具有非常高的复杂性。Backlight compensation, also known as backlight compensation or backlight correction, can effectively compensate for the dark defects of the main picture when the camera is shooting in a backlight environment. When the backlight compensation function is introduced, the subject screen on the monitor can be made clear. In backlit image processing, the luminance of pixels in a backlit area is improved, and the contrast between pixels is increased. However, in most backlight compensation schemes, while the brightness of pixels in the backlight area is improved, the brightness of pixels in the bright area is also improved, which makes the brightness of the entire image increase overall, especially the bright area is prone to overexposure. Although in some other backlight compensation schemes, only the brightness of pixels in the backlight area is improved, the processing of extracting the backlight area in these schemes is also very complicated.
发明内容Contents of the invention
鉴于以上所述的一个或多个问题，本发明提供了一种新颖的背光补偿方法和装置。In view of one or more problems mentioned above, the present invention provides a novel backlight compensation method and device.
根据本发明实施例的背光补偿方法包括：将背光图像的灰度级范围划分为背光区间AB、过渡区间BC、以及亮光区间CD三个区间；分别利用不同的补偿函数对灰度级处于不同区间的像素的灰度级进行背光补偿，其中用于所述三个区间的补偿函数均为一次补偿函数。The backlight compensation method according to the embodiment of the present invention includes: dividing the gray scale range of the backlight image into three intervals: the backlight interval AB, the transition interval BC, and the bright light interval CD; Backlight compensation is performed on the gray levels of the pixels, and the compensation functions used in the three intervals are all linear compensation functions.
根据本发明实施例的背光补偿装置包括：区间划分单元，用于将背光图像的灰度级范围划分为背光区间AB、过渡区间BC、以及亮光区间CD三个区间；以及背光补偿单元，用于分别利用不同的补偿函数对灰度级处于不同区间的像素的灰度级进行背光补偿，其中用于所述三个区间的补偿函数均为一次补偿函数。The backlight compensation device according to the embodiment of the present invention includes: an interval division unit, configured to divide the gray scale range of the backlight image into three intervals: the backlight interval AB, the transition interval BC, and the bright light interval CD; and a backlight compensation unit for Different compensation functions are used to perform backlight compensation on gray levels of pixels whose gray levels are in different intervals, wherein the compensation functions used in the three intervals are all linear compensation functions.
本发明能够提高处于背光区域中的像素的灰度级，同时扩大背光图像中处于不同灰度级的像素的灰度级之间的差值，从而使得整个视场的可视性增强。The invention can improve the gray level of the pixels in the backlight area, and at the same time expand the difference between the gray levels of the pixels in different gray levels in the backlight image, thereby enhancing the visibility of the entire field of view.
附图说明Description of drawings
从下面结合附图对本发明的具体实施方式的描述中可以更好地理解本发明，其中：The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:
图1示出了根据本发明实施例的背光补偿装置的框图；FIG. 1 shows a block diagram of a backlight compensation device according to an embodiment of the present invention;
图2示出了根据本发明实施例的背光补偿方法的流程图；FIG. 2 shows a flowchart of a backlight compensation method according to an embodiment of the present invention;
图3是示出示例性的背光图像中的像素灰度级的分布状况的直方图；3 is a histogram showing the distribution of pixel gray levels in an exemplary backlight image;
图4是示出图3所示的背光图像的灰度级范围的区间划分情况的示意图；Fig. 4 is a schematic diagram showing the interval division of the gray scale range of the backlight image shown in Fig. 3;
图5是示出用于图4所示的各个区间中的像素的灰度级的补偿函数的示意图；FIG. 5 is a schematic diagram showing a compensation function for gray levels of pixels in the respective intervals shown in FIG. 4;
图6是示出用于确定图4中所示的过渡区域BC的方法的示意图；FIG. 6 is a schematic diagram showing a method for determining the transition region BC shown in FIG. 4;
图7a和7b分别是示出背光补偿之前的背光图像和背光补偿之后的修正图像的示意图。7a and 7b are schematic diagrams showing a backlight image before backlight compensation and a corrected image after backlight compensation, respectively.
具体实施方式detailed description
下面将详细描述本发明各个方面的特征和示例性实施例。下面的描述涵盖了许多具体细节，以便提供对本发明的全面理解。但是，对于本领域技术人员来说显而易见的是，本发明可以在不需要这些具体细节中的一些细节的情况下实施。下面对实施例的描述仅仅是为了通过示出本发明的示例来提供对本发明更清楚的理解。本发明绝不限于下面所提出的任何具体配置和算法，而是在不脱离本发明的精神的前提下覆盖了相关元素、部件和算法的任何修改、替换和改进。Features and exemplary embodiments of various aspects of the invention will be described in detail below. The following description covers numerous specific details in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is only to provide a clearer understanding of the present invention by showing examples of the present invention. The present invention is by no means limited to any specific configuration and algorithm presented below, but covers any modification, replacement and improvement of related elements, components and algorithms without departing from the spirit of the present invention.
图1示出了根据本发明实施例的背光补偿装置的框图。图2示出了根据本发明实施例的背光补偿方法的流程图。下面结合图1和图2详细说明根据本发明实施例的背光补偿装置和方法。FIG. 1 shows a block diagram of a backlight compensation device according to an embodiment of the present invention. Fig. 2 shows a flowchart of a backlight compensation method according to an embodiment of the present invention. The backlight compensation device and method according to the embodiments of the present invention will be described in detail below with reference to FIG. 1 and FIG. 2 .
如图1所示，根据本发明实施例的背光补偿装置包括区间划分单元102和背光补偿单元104。区间划分单元102将背光图像的灰度级范围划分为背光区间AB、过渡区间BC、以及亮光区间CD三个区间(即，执行步骤S202)。背光补偿单元104利用不同的补偿函数分别对灰度级处于不同区间的像素的灰度级进行背光补偿(即，执行步骤S204)。其中，用于背光区间AB、过渡区间BC、以及亮光区间CD三个区间的补偿函数均为一次补偿函数。As shown in FIG. 1 , the backlight compensation device according to the embodiment of the present invention includes an interval division unit 102 and a backlight compensation unit 104 . The interval division unit 102 divides the grayscale range of the backlight image into three intervals: the backlight interval AB, the transition interval BC, and the bright light interval CD (ie, step S202 is performed). The backlight compensation unit 104 uses different compensation functions to respectively perform backlight compensation on gray levels of pixels whose gray levels are in different intervals (ie, execute step S204 ). Wherein, the compensation functions used in the three intervals of the backlight interval AB, the transition interval BC, and the bright light interval CD are all linear compensation functions.
下面结合图3和图4所示的示例，来说明区间划分单元102的处理过程。具体地，图3是示出示例性的背光图像中的像素灰度级的分布状况的直方图。图4是示出图3所示的背光图像的灰度级范围的划分情况的示意图。其中，在图3和图4中，横坐标表示灰度级，纵坐标表示处于相应灰度级的像素的数目。The processing procedure of the interval division unit 102 will be described below with reference to the examples shown in FIG. 3 and FIG. 4 . Specifically, FIG. 3 is a histogram showing the distribution of pixel gray levels in an exemplary backlight image. FIG. 4 is a schematic diagram showing the division of the gray scale range of the backlight image shown in FIG. 3 . Wherein, in FIG. 3 and FIG. 4 , the abscissa represents the gray level, and the ordinate represents the number of pixels at the corresponding gray level.
如图4所示，可以将图3所示灰度级范围划分为三个区间：AB区间(背光区间)、BC区间(过渡区间)、以及CD区域(亮光区间)。在这里假设，灰度级处于AB区间的像素处于背光图像的背光区域中，灰度级处于BC区间的像素处于背光图像的过渡区域中，并且灰度级处于CD区间的像素处于背光图像的亮光区域中。另外，从图3和图4可以看出，在背光区域中灰度级为G1的像素的数目最大，为峰值A；在亮光区域中灰度级为G2的像素的数目最大，为峰值B。As shown in FIG. 4 , the grayscale range shown in FIG. 3 can be divided into three intervals: AB interval (backlight interval), BC interval (transition interval), and CD area (bright light interval). It is assumed here that the pixels whose gray level is in the AB interval are in the backlight area of the backlight image, the pixels whose gray level is in the BC interval are in the transition area of the backlight image, and the pixels whose gray level is in the CD interval are in the bright light of the backlight image in the area. In addition, it can be seen from Figure 3 and Figure 4 that the number of pixels with gray level G1 is the largest in the backlight area, which is peak A; the number of pixels with gray level G2 is the largest in the bright light area, which is peak B.
在背光补偿处理中，需要提高处于背光区域中的像素的灰度级，同时扩大背光图像中处于不同灰度级的像素的灰度级之间的差值。基于以上假设，根据本发明的实施例给出了三个分别适用于背光区域、过渡区域、和亮光区域的一次补偿函数f1(x)、f2(x)、和f3(x)。下面结合图5来说明背光补偿单元104的处理过程。In the backlight compensation process, it is necessary to increase the gray level of the pixels in the backlight area, and at the same time expand the difference between the gray levels of the pixels in different gray levels in the backlight image. Based on the above assumptions, the embodiment of the present invention provides three first-order compensation functions f1(x), f2(x), and f3(x) respectively applicable to the backlight area, the transition area, and the bright light area. The processing procedure of the backlight compensation unit 104 will be described below with reference to FIG. 5 .
图5是示出用于图4所示的各个区间中的像素的灰度级的补偿函数的示意图。为了扩大灰度级范围，在根据本发明的实施例中使用了从0到255的所有灰度级(即，使得经背光补偿的背光区间的最小灰度级为0，并使经背光补偿的亮光区间的最大灰度级为255)。为了降低过渡区域中的像素的对比度，对灰度级处于过渡区间的像素的灰度级进行背光补偿后得到的经背光补偿的过渡区间[B1，C1)需要满足以下条件：FIG. 5 is a diagram showing a compensation function for gray levels of pixels in the respective sections shown in FIG. 4 . In order to expand the gray scale range, all gray scales from 0 to 255 are used in the embodiment according to the present invention (that is, make the minimum gray scale of the backlight interval after backlight compensation be 0, and make the backlight compensated The maximum gray level in the light range is 255). In order to reduce the contrast of pixels in the transition region, the backlight-compensated transition interval [B1, C1) obtained after performing backlight compensation on the gray levels of pixels in the transition region needs to meet the following conditions:
其中，Nt表示灰度级处于过渡区间BC的像素的数目，Nb表示灰度级处于背光区间CD的像素的数目，Nl表示灰度级处于亮光区间AB的像素的数目，Nt+Nb+Nl表示背光图像中的像素的总数目。Among them, Nt represents the number of pixels whose gray level is in the transition interval BC, Nb represents the number of pixels whose gray level is in the backlight interval CD, Nl represents the number of pixels whose gray level is in the bright light interval AB, Nt +Nb +Nl represents the total number of pixels in the backlit image.
在确定出B1和C1后，即可确定函数f1(x)、f2(x)、和f3(x)。具体地，可以通过将图5中所示的(A，0)和(B，B1)两个点作为用于背光区间AB的一次补偿函数f1(x)的函数曲线上的两个点来求解该一次补偿函数f1(x)；可以通过将图5中所示的(B，B1)和(C，C1)两个点作为用于过度区间BC的一次补偿函数f2(x)的函数曲线上的两个点来求解该一次补偿函数f2(x)；并且可以通过将图5中所示的(C，C1)和(D，255)两个点作为用于亮光区间CD的一次补偿函数f3(x)的函数曲线上的两个点来求解该一次补偿函数f3(x)。After B1 and C1 are determined, the functions f1(x), f2(x), and f3(x) can be determined. Specifically, it can be solved by taking the two points (A, 0) and (B, B1) shown in Fig. 5 as two points on the function curve of the first-order compensation function f1(x) for the backlight interval AB This primary compensation function f1 (x); can be by (B, B1) and (C, C1) two points shown in Fig. Two points to solve the first-order compensation function f2(x); and the two points (C, C1) and (D, 255) shown in Figure 5 can be used as the first-order compensation function f3 for the bright light interval CD (x) on the two points on the function curve to solve the compensation function f3 (x).
然后，利用一次补偿函数f1(x)对灰度级处于背光区间AB的像素的像素级进行背光补偿(即，通过将f1(x)与像素级相乘得到经背光补偿的像素级)，利用一次补偿函数f2(x)对灰度级处于过渡区间BC的像素的像素级进行背光补偿(即，通过将f2(x)与像素级相乘得到经背光补偿的像素级)，并且利用一次补偿函数f3(x)对灰度级处于亮光区间CD的像素的像素级进行背光补偿(即，通过将f3(x)与像素级相乘得到经背光补偿的像素级)。Then, use the primary compensation function f1(x) to perform backlight compensation on the pixel level of the pixel whose gray level is in the backlight interval AB (that is, obtain the backlight-compensated pixel level by multiplying f1(x) with the pixel level), and use The first-order compensation function f2(x) performs backlight compensation on the pixel level of the pixel whose gray level is in the transition interval BC (that is, the backlight-compensated pixel level is obtained by multiplying f2(x) by the pixel level), and uses the first-order compensation The function f3(x) performs backlight compensation on the pixel level of the pixel whose gray level is in the bright light interval CD (that is, the backlight-compensated pixel level is obtained by multiplying f3(x) with the pixel level).
另外，BC区间的决定方法参考图6。图6中，x轴表示像素的灰度级。HIST表示超过某灰度级的像素个数与像素总个数的比率。SW(Slide Window，滑动窗)表示HIST的积分值小于0.2的窗口。当这个窗口取得最大时，即SWmax区间的位置就是过渡区间BC的位置。In addition, refer to FIG. 6 for the determination method of the BC section. In FIG. 6, the x-axis represents the gray level of the pixel. HIST represents the ratio of the number of pixels exceeding a certain gray level to the total number of pixels. SW (Slide Window, sliding window) indicates a window whose integral value of HIST is less than 0.2. When the window is at its maximum, that is, the position of the SWmax interval is the position of the transition interval BC.
图7a和7b分别是示出背光补偿之前的背光图像和背光补偿之后的修正图像的示意图。从图7a和图7b可以看出，通过本发明可以提高处于背光区域中的像素的亮度，同时可以扩大背光图像中处于不同灰度级的像素的灰度级之间的差值，从而使得整个视场的可视性增强。7a and 7b are schematic diagrams showing a backlight image before backlight compensation and a corrected image after backlight compensation, respectively. It can be seen from Fig. 7a and Fig. 7b that the brightness of the pixels in the backlight area can be improved through the present invention, and at the same time, the difference between the gray levels of the pixels in different gray levels in the backlight image can be enlarged, so that the entire Visibility enhancements in the field of view.
以上已经参考本发明的具体实施例来描述了本发明，但是本领域技术人员均了解，可以对这些具体实施例进行各种修改、组合和变更，而不会脱离由所附权利要求或其等同物限定的本发明的精神和范围。The present invention has been described above with reference to the specific embodiments of the present invention, but those skilled in the art will understand that various modifications, combinations and changes can be made to these specific embodiments without departing from the requirements set by the appended claims or their equivalents. The spirit and scope of the present invention defined by the material.
根据需要可以用硬件或软件来执行步骤。注意，在不脱离本发明范围的前提下，可向本说明书中给出的流程图添加步骤、从中去除步骤或修改其中的步骤。一般来说，流程图只是用来指示用于实现功能的基本操作的一种可能的序列。The steps can be performed by hardware or software as desired. Note that steps may be added to, removed from, or modified in the flowcharts presented in this specification without departing from the scope of the present invention. In general, a flowchart is only used to indicate one possible sequence of basic operations for implementing a function.
本发明的实施例可利用编程的通用数字计算机、利用专用集成电路、可编程逻辑器件、现场可编程门阵列、光的、化学的、生物的、量子的或纳米工程的系统、组件和机构来实现。一般来说，本发明的功能可由本领域已知的任何手段来实现。可以使用分布式或联网系统、组件和电路。数据的通信或传送可以是有线的、无线的或者通过任何其他手段。Embodiments of the present invention may utilize programmed general purpose digital computers, utilize application specific integrated circuits, programmable logic devices, field programmable gate arrays, optical, chemical, biological, quantum or nanoengineered systems, components and mechanisms accomplish. Generally speaking, the functions of the present invention can be realized by any means known in the art. Distributed or networked systems, components and circuits can be used. Communication or transfer of data may be wired, wireless or by any other means.
还将意识到，根据特定应用的需要，附图中示出的要素中的一个或多个可以按更分离或更集成的方式来实现，或者甚至在某些情况下被去除或被停用。实现可存储在机器可读介质中的程序或代码以允许计算机执行上述任何方法，也在本发明的精神和范围之内。It will also be appreciated that one or more of the elements shown in the figures may be implemented in a more separate or integrated manner, or even removed or disabled in some cases, depending on the needs of a particular application. It is also within the spirit and scope of the present invention to implement a program or code storable in a machine-readable medium to allow a computer to perform any of the methods described above.
此外，附图中的任何信号箭头应当被认为仅是示例性的，而不是限制性的，除非另有具体指示。当术语被预见为使分离或组合的能力不清楚时，组件或者步骤的组合也将被认为是已经记载了。Furthermore, any signal arrows in the figures should be considered as illustrative only, and not restrictive, unless specifically indicated otherwise. Combinations of components or steps are also considered to have been recited when terms are foreseen to obscure the ability to separate or combine.
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| CN201210337130.5ACN103685867B (en) | 2012-09-12 | 2012-09-12 | Backlight compensation method and device |
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