CN101159878B - Color matching method, and image capturing apparatus and electronic device using the same - Google Patents

Abstract

A color matching method includes: capturing a plurality of main color signals in a digital image; a conversion step of obtaining a 3×3 color matrix from the plurality of main color signals, and converting the plurality of main color signals into 3×1 illumination, hue, and saturation (LAB) coordinate matrices respectively; and a color difference calculation step of recursively iterating and calculating the output and color difference of the plurality of colors according to a color correction formula composed of the color matrix, a preset weight matrix, and a correction matrix until the color difference is less than a critical value.

Description

Color matching method and image capturing device and electronic equipment using same

【Technical field】

The present invention relates to a color matching method, an image capturing device using the same or an electronic device equipped with an image capturing device, especially a color matching method for processing electronic digital images, and an image capturing device using the same or an electronic device equipped with an image capturing device Electronic equipment.

【Background technique】

In recent years, electronic devices with color image capture devices such as digital cameras, electronic video cameras, and mobile phones have become popular. Generally speaking, semiconductor image sensors are installed in these electronic devices to convert captured images into electrical signals. Due to the inherent limitation of the color sensing performance of the image sensor, the color of the output image based on the image sensor usually needs to be corrected. In addition, the color of the image will also vary depending on the lighting conditions. For example, the visual perception of color is quite different under moonlight and outdoor sunlight. Therefore, it is very important for the color processing of the obtained electronic images to conform to the perception of human visual senses.

In these electronic devices, the image signal output by the image sensor will undergo a series of signal processing, wherein the color matching process will correct the color of the obtained image so that the output image has an undistorted color expression.

With regard to color correction processing, many prior art techniques using correction matrices to correct the color of images are known. For example, U.S. Patent No. 7,053,935 published on May 30, 2006, has disclosed the matching result between the human visual system and a unique set of spectral response curves and only uses a preset correction matrix in the color correction process. However, due to A predetermined correction matrix is used, so the result of the correction process cannot be dynamically adjusted, so it is difficult to obtain fast and accurate color correction results, and cannot provide high-quality images. Since the prior art uses a fixed correction matrix to calibrate the color, the chromatic aberration is large and cannot quickly converge to a predetermined value.

Therefore, a color matching method capable of dynamically adjusting the color difference and quickly converging to a predetermined value is required to obtain highly accurate color display.

【Content of invention】

Considering the above, the present invention uses a dynamically adjustable correction matrix to achieve color difference convergence with high accuracy and speed to display high-fidelity color images.

An object of the present invention is to provide a color matching method capable of performing color correction on digital images, which performs color correction processing on acquired images according to a plurality of main colors in the acquired images.

According to an aspect of the present invention, a color matching method is provided, including: extracting a plurality of main color signals in a digital image; a conversion step, obtaining a 3×3 color matrix from the plurality of main color signals, and taking the plurality of main color signals The color signals are respectively converted into a 3×1 illuminance, hue, saturation (LAB) coordinate matrix; and, in the color difference calculation step, according to the color correction formula formed by the color matrix, the preset weight matrix and the correction matrix, iteratively The outputs and color differences of the plurality of colors are iteratively calculated until the color difference is smaller than a critical value.

In addition, the value of each element in the correction matrix can be dynamically changed according to the current color difference and the previous color difference to quickly obtain the color difference smaller than the critical value. Moreover, unlimited number of recursive calculations can be performed on multi-dimensional colors to obtain highly realistic color image display with very small color difference.

According to another aspect of the present invention, an image capture device and an electronic device are provided, which can perform fast and highly accurate color correction on the captured image, so as to provide a highly realistic color image display with small color difference.

[Simple description of the diagram]

Fig. 1 is a flowchart illustrating the digital image processing flow;

Fig. 2 is a flowchart illustrating a color matching method according to an embodiment of the present invention;

Fig. 3 is a color diagram for illustrating a color matching method according to an embodiment of the present invention;

Figure 4 shows the number of iterations and the maximum excess for different PID coefficients; and

FIG. 5 shows a color diagram and a color coordinate diagram before and after the color matching process according to the present invention.

【Implementation】

Embodiments according to the present invention will be described with reference to the drawings.

Figure 1 is a flow chart illustrating the general digital image processing process.

As shown in FIG. 1 , the original image signal output obtained by the image sensor in the image capture device will be digitally clamped in step 101 . In step 101, optical black is used as the black reference standard in the color sensor, and the obtained values of color channels such as red, green, blue (hereinafter referred to as RGB) are subtracted from the optical black level to make each color channel The base value does not vary greatly or cause significant errors due to the physical performance of the sensor for different colors.

Then, proceed to step 102 to perform channel shift processing. In step 102, channel offset processing is performed on the clamped color channels such as RGB, so that the values of these color channels have equal or very similar levels. The color channels (RGB) after these processes will have the same color base value and their numerical resolution can be maximized.

Then, proceed to step 103 . In step 103, a color white balance process is performed so that the color performance is the same as the grayscale.

Afterwards, proceed to step 104 to perform image interpolation, and combine the three primary color images of the obtained image to form an image frame to be displayed.

After the image interpolation, the color of the obtained image may not be accurate, so color matching processing is required to adjust the image to an accurate color, so step 105 is performed to perform color matching processing.

Finally, the image signal processed above will undergo gamma correction in step 106, so that the captured image can be displayed harmoniously depending on different output devices, and then the image signal is output (step 107).

General digital image processing needs to be completed through the above processing steps. Regarding color matching processing, the prior art uses a predetermined fixed correction matrix to perform color matching processing, so it is difficult to quickly and accurately obtain high-quality images with accurate colors. The color matching process in the image processing according to the present invention will be described in detail below.

FIG. 2 is a flowchart illustrating a color matching method according to an embodiment of the present invention.

As shown in Figure 2, at first in step 201, the signals of the three main spectral colors blue, green and red are obtained, that is, the blue in the first row of the third column as shown in Figure 3, the green in the second row of the same column, and the green in the second row of the same column as shown in Figure 3 Three rows of red. Figure 3 is a color map captured by an image capture device for image processing.

Then, proceed to step 202, according to the famous CIE (Commission Internationale De L'Eclairage) conversion, obtain a 3×3 matrix (1) for color correction from the red, green and blue (RGB) three-color signal, and simultaneously convert the three-color RGB into a corresponding 3x1 matrix (2). The matrices (1) and (2) are as follows:

$\left[\begin{array}{ccc}{a}_{11}& a_{12}& a_{13}\\ a_{\mathrm{twenty\; one}}& a_{\mathrm{twenty\; two}}& a_{\mathrm{twenty\; three}}\\ a_{31}& a_{32}& a_{33}\end{array}\right]$ matrix(1)

$\left[\begin{array}{c}{L}_{\mathrm{in}}\\ a_{\mathrm{in}}\\ b_{\mathrm{in}}\end{array}\right]$ matrix(2)

Among them, the matrix (1) is calculated based on CIE and the color image signal obtained. In the matrix (2), _Lin represents the illuminance of the color signal, a _in represents the hue, and _bin represents the saturation, which is generally called Lab coordinate.

In this embodiment, the matrices (1) and (2) obtained according to red, blue and green are as follows:

$\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; 0.94</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.08</span>}& \mathrm{<span\; class="notranslate">\; 0.14</span>}\\ \mathrm{<span\; class="notranslate">\; 0.13</span>}& \mathrm{<span\; class="notranslate">\; 0.81</span>}& \mathrm{<span\; class="notranslate">\; 0.08</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.27</span>}& \mathrm{<span\; class="notranslate">\; 0.32</span>}& \mathrm{<span\; class="notranslate">\; 0.60</span>}\end{array}\right]$

for blue $\left[\begin{array}{c}{L}_{\mathrm{in}}\\ a_{\mathrm{in}}\\ b_{\mathrm{in}}\end{array}\right]=\left[\begin{array}{c}25.408\\ -17.46\\ -52.8\end{array}\right]$

for green $\left[\begin{array}{c}{L}_{\mathrm{in}}\\ a_{\mathrm{in}}\\ b_{\mathrm{in}}\end{array}\right]=\left[\begin{array}{c}57.993\\ -43.63\\ 42.28\end{array}\right]$

for red $\left[\begin{array}{c}{L}_{\mathrm{in}}\\ a_{\mathrm{in}}\\ b_{\mathrm{in}}\end{array}\right]=\left[\begin{array}{c}53.75\\ 95.18\\ 9.35\end{array}\right]$

As mentioned above, according to the CIE standard, the basic linear color matrix generated after RGB conversion is used for color correction described later.

Then, proceed to step 203 , apply the obtained matrix to the following equation (1) to perform an iterative operation of color correction.

$\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}\end{array}\right]<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]<span\; class="notranslate">\; +</span>\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; x</span>}\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\end{array}\right]$

Equation (1)

in, $\left[\begin{array}{ccc}{w}_{11}& w_{12}& w_{13}\\ w_{\mathrm{twenty\; one}}& w_{\mathrm{twenty\; two}}& w_{\mathrm{twenty\; three}}\\ w_{31}& w_{32}& w_{33}\end{array}\right]$ called the weight matrix

$\left[\begin{array}{ccc}{k}_{11}& k_{12}& k_{13}\\ k_{\mathrm{twenty\; one}}& k_{\mathrm{twenty\; two}}& k_{\mathrm{twenty\; three}}\\ k_{31}& k_{32}& k_{33}\end{array}\right]$ called the correction matrix

The value of each element in the weight matrix is a preset value, in this embodiment is

$\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; 0.98</span>}& \mathrm{<span\; class="notranslate">\; 0.01</span>}& \mathrm{<span\; class="notranslate">\; 0.01</span>}\\ \mathrm{<span\; class="notranslate">\; 0.01</span>}& \mathrm{<span\; class="notranslate">\; 0.98</span>}& \mathrm{<span\; class="notranslate">\; 0.01</span>}\\ \mathrm{<span\; class="notranslate">\; 0.01</span>}& \mathrm{<span\; class="notranslate">\; 0.01</span>}& \mathrm{<span\; class="notranslate">\; 0.98</span>}\end{array}\right]$

According to the present invention, each element in the correction matrix is defined as follows:

k _ij ＝P _ij +D _ij +I _ij , P _ij , D _ij , and I _ij will be described in detail later

The above ΔE system is a color difference function, according to CIEI 976, ΔE system is defined as

$\mathrm{<span\; class="notranslate">\; \&Delta;E</span>}<span\; class="notranslate">\; =</span>\sqrt{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; Ref</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; Ref</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; Ref</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Among them, L _out , a _out , b _out are the calculated Lab coordinates of the output color signal, and L _Ref , a _Ref , b _Ref are the Lab coordinate reference values of the obtained color signal. In other words, the color difference refers to the difference between the output color and the captured real color, and the color ΔE can be represented by the distance between Lab coordinates.

In step 203, according to Equation 1, an iterative operation is performed on each color and the operation result of each color is compared with a reference value to obtain a color difference value. According to this embodiment, calculations are performed on the above-mentioned three colors of red, green and blue. However, according to the present invention, calculations can also be performed on more different colors, that is, multi-dimensional color calculations can be performed.

Then, proceed to step 204, compare the color difference value obtained in step 203 with the preset critical value, if the color difference value is smaller than the critical value, it means that the color correction has reached the requirement, and then end the color matching process, if it is greater than the critical value, Then proceed to step 205 to calculate new P _ij , D _ij , and I _ij according to the following equation,

Pij=Ep= _Kp xΔE(t)

D _ij = Ed = K _d x (ΔE(t)-ΔE(t-1))

I _ij ＝Ei＝K _i ∫ _{_∞} ΔE(t)dt

Among them, K _p , K _d , and K _i are proportional control coefficients, differential control coefficients, and integral control coefficients respectively, ΔE(t) represents the current color difference value, and ΔE(t-1) represents the previously stored color difference value .

Then, returning to step 203, the obtained P _ij , D _ij , and I _ij are substituted into the correction matrix in equation (1) for iterative calculation.

In this way, the iterative operation is performed until the color difference is smaller than the critical value.

According to this example, the values of K _p , K _d , and K _i are different in the case of i=j and i≠J, that is, the correction matrix according to this embodiment is as follows:

$\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; 1.21</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2.13</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.53</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}& \mathrm{<span\; class="notranslate">\; 1.1</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}& \mathrm{<span\; class="notranslate">\; 1.1</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}\\ \mathrm{<span\; class="notranslate">\; 1.1</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}& \mathrm{<span\; class="notranslate">\; 1.21</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2.13</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.53</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}& \mathrm{<span\; class="notranslate">\; 1.1</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}\\ \mathrm{<span\; class="notranslate">\; 1.1</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}& \mathrm{<span\; class="notranslate">\; 1.1</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}& \mathrm{<span\; class="notranslate">\; 1.21</span>}\mathrm{<span\; class="notranslate">\; Ep</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2.13</span>}\mathrm{<span\; class="notranslate">\; Ed</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.53</span>}\mathrm{<span\; class="notranslate">\; Ei</span>}\end{array}\right]$

According to the above, the color matching process is performed with different K _p , K _d , and K _i coefficients, and the obtained results are shown in FIG. 4 . FIG. 4 shows the number of calculations and the maximum excess value to achieve the desired color difference under different values of K _p , K _d , and K _i according to the color matching process of this embodiment. According to the results of this embodiment, it can be seen that when the error is larger, a larger K _p value means a faster response, which also means that the feedback to be compensated is larger. A larger K _d reduces the overshoot of the adjusted compensation and can distinguish the direction of chromatic aberration. Larger K _i means that the error is eliminated in the steady state, but at the cost of causing a larger excess in compensation and slowing down the approach to the target value.

Through the above-mentioned operation steps, the correction matrix required for the color matching of the image processing can be obtained by using the three main colors RGB in the standard color map as a reference. When dealing with the color matching of any captured image, the value of each element in this correction matrix can be changed according to the color difference of each iterative operation, so it can be changed dynamically, so that the color difference can be quickly reduced to achieve a high degree of fidelity color image. Here, although three colors of RGB are used to illustrate this embodiment, the present invention can use more than three colors to perform color matching processing, and the number of iterative operations performed is not limited.

Table 1 below shows the effect produced when each control coefficient is modulated in the embodiment of the color matching method according to the present invention.

Table 1

After processing as described above, the final color correction result obtained is shown in FIG. 5 . Figure 5a is the image before correction and its CIE LAB coordinate diagram, and Figure 5b is the image after correction and its CIE LAB coordinate diagram. From Figure 5b, it is obvious that the chromatic aberration after correction has largely converged.

According to the present invention, since the color difference matching process can be performed on multi-dimensional colors, and the number of iterations to achieve the best error value (that is, the minimum color difference) is not limited, that is, according to the present invention, since multi-dimensional color iterations can be used, the iterations can Execute and update the content values in the 3×3 matrix until the error (chromatic aberration) is below a preset threshold.

According to the present invention, according to the currently measured color difference information and the previous color difference information, the value of each element of the correction matrix is dynamically adjusted for the next iterative calculation and further calculation, so that the color difference can be quickly converged to best value.

The color matching method according to the present invention can be implemented in software or firmware.

The color matching method according to the present invention can be used in electronic devices such as digital cameras, digital video recorders, mobile phones, etc. that are provided with color image capture devices or displays, to process the captured color images, or in computer systems, To perform color matching processing on color images.

While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalents included within the spirit and scope of the appended claims. The scope of the following claims is to be construed in the broadest sense to encompass all such modifications and equivalent structures and functions.

Claims (7)

1. A color matching method for digital images, comprising the following steps: Capture a plurality of main color signals in digital images as input signals; The conversion step is to obtain a 3×3 color matrix from the plurality of main color signals, and convert the plurality of input color signals into a 3×1 illuminance, hue, saturation (LAB) coordinate matrix, the color matrix and the input LAB coordinate matrix are expressed as follows: Color matrix: $\left[\begin{array}{ccc}{a}_{11}& a_{12}& a_{13}\\ a_{\mathrm{twenty\; one}}& a_{\mathrm{twenty\; two}}& a_{\mathrm{twenty\; three}}\\ a_{31}& a_{32}& a_{33}\end{array}\right]---\left(1\right)$ Input matrix: $\left[\begin{array}{c}{L}_{\mathrm{in}}\\ a_{\mathrm{in}}\\ b_{\mathrm{in}}\end{array}\right]---\left(2\right)$ Each element a ₁₁ to a ₃₃ of the color matrix is a real number, and Lin, a _in , and _bin represent the LAB coordinates of each color after _conversion ; and The color difference calculation step is to recursively iteratively calculate the output and color difference of the plurality of colors according to the color correction formula formed by the color matrix, the weight matrix and the correction matrix, until the color difference is less than a critical value, and the color difference is defined as

Among them, L _out , a _out , and b _out are the LAB coordinates of the color output, L _Ref , a _Ref , and b _Ref are the LAB reference coordinates of the color, and the color correction formula (1) is $\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}\end{array}\right]<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]<span\; class="notranslate">\; +</span>\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; x</span>}\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ in, $\left[\begin{array}{c}{L}_{\mathrm{out}}\\ a_{\mathrm{out}}\\ b_{\mathrm{out}}\end{array}\right]$ is the LAB coordinate matrix of the color output, $\left[\begin{array}{ccc}{w}_{11}& w_{12}& w_{13}\\ w_{\mathrm{twenty\; one}}& w_{\mathrm{twenty\; two}}& w_{\mathrm{twenty\; three}}\\ w_{31}& w_{32}& w_{33}\end{array}\right]$ is the weight matrix, $\left[\begin{array}{ccc}{k}_{11}& k_{12}& k_{13}\\ k_{\mathrm{twenty\; one}}& k_{\mathrm{twenty\; two}}& k_{\mathrm{twenty\; three}}\\ k_{31}& k_{32}& k_{33}\end{array}\right]$ For the correction matrix, each element in the correction matrix is defined as follows: k _ij =P _ij +D _ij +I _ij Among them, P _ij =Ep=K _p xΔE(t) D _ij = Ed = K _d x (ΔE(t)-ΔE(t-1)) ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Ei</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{<span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&infin;</span>}\mathrm{<span\; class="notranslate">\; \&Delta;E</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}$ Wherein, K _p , K _d , and K _i are proportional control coefficients, differential control coefficients, and integral control coefficients, respectively. 2. The method as claimed in item 1 of the scope of the patent application, wherein the converting step is performed according to the standards of the International Council of Illumination (CIE). 3. The method as claimed in claim 1, wherein the relationship between the elements in the correction matrix is that each element of i=j is not equal to each element of i≠j, but each element of i=j is equal to each other, And the elements of i≠j are also equal to each other. 4. A color image capture device, using the method according to any one of items 1 to 3 of the scope of the patent application to perform color matching processing on the captured color image. 5. A digital camera with a color image capture and a display, wherein the color image capture uses the method in any one of items 1 to 3 of the scope of the patent application to perform color matching processing on the captured color images. 6. A mobile phone with a color image capturer and a display, wherein the color image capturer uses the method according to any one of items 1 to 3 in the scope of the patent application to perform color matching processing on the captured color image. 7. A computer system that performs color matching processing on color images by using the method of any one of items 1 to 3 in the scope of the patent application.

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