CN106504200B - Image illumination compensation method and system based on hue offset estimation and point-by-point hue mapping - Google Patents
Image illumination compensation method and system based on hue offset estimation and point-by-point hue mapping Download PDFInfo
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Abstract
An image illumination compensation method based on hue shift estimation and point-by-point hue mapping extracts hue shift and hue mapping functions respectively corresponding to three primary color channels from a calibration graph containing matrix arrangement in an off-line stage, and maps an image to be detected point-by-point according to the obtained hue mapping functions in an on-line stage, thereby realizing image illumination compensation. Compared with the existing gamma correction method, the gamma correction method is simpler and more efficient, and can quickly obtain and process the calibration result.
Description
Technical Field
The invention relates to a technology in the field of image processing, in particular to an image illumination compensation method and system based on hue shift estimation and point-by-point hue mapping.
Background
The image illumination compensation technique is an indispensable part in image processing. Because the position of the light source, the surrounding environment and the like in the process of acquiring the picture can cause certain uneven illumination and can generate larger influence on the picture quality, the picture needs to be optimized by means of image processing to perform illumination compensation. The existing techniques such as a color sense consistency method, a target region color similarity method under motion estimation, a color space conversion method, a histogram equalization method, and a gamma correction extremely improved method.
A LEARNING-BASED technique FOR improving the subjective quality of IMAGEs is proposed in the text "LEARNING-BASED IMAGE quality IMPROVEMENT FOR VIDEO recording", by Zicheng Liu et al at ICME2007 conference. The method eliminates the influence of illumination on the subjective quality of the picture to a certain extent, but firstly, a large number of pictures which look high in quality to human eyes need to be selected for training, so that the method is complex and has certain difficulty in realization.
In addition, the color space conversion method cannot solve the problem of correlation among color channels; the histogram equalization method tends to form discontinuous patches in the image.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides an image illumination compensation method and system based on hue shift estimation and point-by-point hue mapping, the hue shift estimation is obtained according to calibration, and then a hue mapping function is established for each pixel point to perform illumination compensation on the image.
The invention is realized by the following technical scheme:
the invention relates to an image illumination compensation method based on hue shift estimation and point-by-point hue mapping, which extracts and obtains hue shift and hue mapping functions respectively corresponding to three primary color channels from a calibration graph containing matrix arrangement in an off-line stage, and maps the image to be detected point-by-point according to the obtained hue mapping functions in an on-line stage, thereby realizing the image illumination compensation.
The calibration plot is preferably a white background and contains (2N + 1) solid color filled squares, with N being a natural constant.
The extraction comprises the steps of detecting square areas from a shot image after shooting a calibration graph, calculating the average value of colors in each square area, and constructing a curved surface to obtain a deviation color distribution graph; and establishing a corresponding tone mapping function of the three primary color channel for each pixel in the shot image by taking the square in the middle position in the horizontal and vertical directions of the calibration graph as a reference.
The edge detection is carried out on the detected square area through a Prewitt operator, then morphological operation expansion and corrosion treatment are carried out, and (2N + 1) ((2N + 1)) maximum connected areas are obtained, and each connected area is the square area.
The deviation color distribution diagram is as follows: and performing linear interpolation according to the respective average values of RGB (red, green and blue) channels of each square area and the average value of Z = R channel, the average value of Z = G channel and the average value of Z = B channel, wherein X-Y is the two-dimensional coordinate of the pixel point, so as to obtain the curved surfaces of the three channels under a Z-X-Y three-dimensional orthogonal coordinate system, namely three deviation color distribution diagrams.
The tone mapping function is that: for any pixel point in the image, obtaining the intensity value of the pixel point corresponding to the channel according to the deviation color distribution diagram, and performing linear fitting on a target line segment; in the fitting process, when Y corresponding to X = m (m < 255) reaches 255, it is set that Y corresponding to X is 255 when X is greater than m and smaller than 255.
The starting point of the target line segment is the origin (0, 0), the abscissa of the end point is the intensity value of the channel of the color shift distribution diagram, and the ordinate is the average value of the intensity of the channel corresponding to all pixels in the square area located in the middle of the calibration diagram.
The point-by-point mapping of the image to be measured refers to: and mapping each pixel of the image to be detected by using the tone mapping function to obtain a tone compensation result for eliminating the illumination influence.
The invention relates to a system for realizing the method, which comprises the following steps: calibration module, fitting module and processing module, wherein: the calibration module receives a shot image aiming at the calibration graph, is connected with the fitting module and outputs pixel information extracted from the calibration graph, the fitting module is connected with the processing module and outputs a tone mapping function calculated according to the pixel information, and the processing module performs real-time illumination compensation on an online input image to be detected according to the tone mapping function and outputs a compensated image.
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FIG. 1 is a calibration chart of the present invention;
FIG. 2 is a schematic diagram illustrating the effects of the embodiment.
Detailed Description
The embodiment comprises the following steps:
an off-line preparation stage:
in a first step, a calibration graph containing 5 × 5=25 yellow filled squares as shown in fig. 1 is made.
And secondly, shooting the calibration graph, detecting a square area in the shot graph by using a Prewitt operator, namely edge detection, and then performing morphological expansion operation and corrosion operation on the image to obtain 25 maximum communication areas, namely boundaries of 25 squares.
The morphological filtering is to perform dilation and erosion operations on the image.
And thirdly, respectively calculating the average value of the intensity of each channel of RGB of each square area as the intensity value of all pixel points in the square. And performing linear interpolation according to the discrete points in the squares to obtain three curved surfaces, and obtaining the intensity value of the RGB channel of each pixel point.
The curved surface is as follows: the Z axis is the intensity value of the R, G or B channel, and X and Y are the coordinates of the pixel points.
And fourthly, respectively establishing a corresponding tone mapping function of each channel of RGB for each pixel point in the calibration graph by taking the average value of the three channels of RGB in the middle square area as a target value.
The tone mapping function is that: performing linear fitting on the target line segment in a two-dimensional orthogonal coordinate system; in the fitting process, when Y corresponding to X = m (m < 255) reaches 255, it is set that Y corresponding to X is 255 when X is larger than m and smaller than 255.
The starting point of the target line segment is the origin (0, 0), the abscissa of the end point is the intensity value of the channel of the color shift distribution diagram, and the ordinate is the average value of the intensity of the channel corresponding to all pixels in the square area located in the middle of the calibration diagram. When the intensity value of the pixel in any channel of R, G or B is 100 and the target value of the channel is 200, the obtained tone mapping function is as shown in fig. 2.
And (3) an online detection stage:
and fifthly, taking the intensity value of each channel of each pixel of the image to be detected as X, using the tone mapping function obtained in the fourth step, and taking the function value Y corresponding to X as the intensity value of the channel of the pixel point of the processed image, and finally obtaining the tone compensation result for eliminating the illumination influence.
The illumination condition of the image to be detected when the image to be detected is shot is completely the same as the shooting condition of the calibration graph.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (6)
1. An image illumination compensation method based on hue shift estimation and point-by-point hue mapping is characterized in that hue shift and hue mapping functions respectively corresponding to three primary color channels are extracted and obtained from a calibration graph containing matrix arrangement in an off-line stage, and the point-by-point mapping is carried out on an image to be detected according to the obtained hue mapping functions in an on-line stage, so that image illumination compensation is realized;
the extraction comprises the steps of detecting square areas from a shot image after shooting a calibration graph, calculating the average value of colors in each square area, and constructing a curved surface to obtain a deviation color distribution graph; establishing a corresponding tone mapping function of a three-primary-color channel for each pixel in the shot image by taking a square in the middle position in the horizontal and vertical directions of the calibration graph as a reference;
the deviation color distribution diagram is as follows: performing linear interpolation according to the respective average values of the RGB channels of each square area and the average value of the Z = R channel, the average value of the Z = G channel and the average value of the Z = B channel, wherein X-Y is the two-dimensional coordinate of the pixel point, so as to obtain the curved surfaces of the three channels under a Z-X-Y three-dimensional orthogonal coordinate system, namely three deviation color distribution diagrams;
the tone mapping function is that: for any pixel point in the image, obtaining the intensity value of the pixel point corresponding to the channel according to the deviation color distribution diagram, and performing linear fitting on a target line segment to obtain a tone mapping function;
the starting point of the target line segment is the origin (0, 0), the abscissa of the end point is the intensity value of the channel of the color shift distribution diagram, and the ordinate is the average value of the intensity of the channel corresponding to all pixels in the square area located in the middle of the calibration diagram.
2. The method of claim 1, wherein the calibration chart is a white background and comprises (2n + 1) squares filled with pure colors, and N is a natural constant.
3. The image illumination compensation method of claim 1, wherein the square region is detected by using a Prewitt operator to perform edge detection, and then performing morphological operation expansion and corrosion processing to obtain (2n + 1) maximum connected regions, and each connected region is the square region.
4. The method of claim 1, wherein in the fitting process, when X = m and Y reaches 255 at m <255, Y is set to be 255 when X is larger than m and smaller than 255.
5. The image illumination compensation method of claim 1, wherein the point-by-point mapping of the image to be measured is: and mapping each pixel of the image to be detected by using the tone mapping function to obtain a tone compensation result for eliminating the illumination influence.
6. A system for implementing the method of any of claims 1-5, comprising: calibration module, fitting module and processing module, wherein: the calibration module receives a shot image aiming at the calibration graph, is connected with the fitting module and outputs pixel information extracted from the calibration graph, the fitting module is connected with the processing module and outputs a tone mapping function calculated according to the pixel information, and the processing module performs real-time illumination compensation on an online input image to be detected according to the tone mapping function and outputs a compensated image.
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