ColorChecker function does not work?

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Roger Breton 2024-1-30

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2075976-colorchecker-function-does-not-work

评论： Roger Breton 2024-1-30

在 MATLAB Online 中打开

I am trying to follow the example here:

Comparison of Auto White Balance Algorithms - MATLAB & Simulink (mathworks.com)

I use this code:

cfa = rawread("DSC_0136.NEF"); 
J = demosaic(cfa,"rggb");
A_sRGB = lin2rgb(J);
montage({J,A_sRGB})
title("Original Image Before and After Gamma Correction")
chart_sRGB = colorChecker(A_sRGB);
% chart_sRGB = colorChecker(rgb, sensitivity=0);
DisplayChart(chart_sRGB)

But I keep running into this error:

Error using colorChecker

Color patches were not detected. Try adjusting the Sensitivity parameter or turning off the Downsample parameter.

This is my test NEF:

Why is the functioon failing?

I tried varying the sensitivity from 0 to 1 and turning downsampling off to no avail.

Is the function not designed to operate on a picture of the chart that's full-frame?

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Roger Breton 2024-1-30

From the ColorChecker documentation, I discovered that it was possible to manually detect the chart by supplying the corner points? So I used the MathWorks ColorChecker chart that "works", giving this output:

chart =

colorChecker with properties:

Image: [876×1312×3 uint8]

RegistrationPoints: [4×2 double]

ColorROIs: [24×1 struct]

... to try to "reverse-engineer" the chart object?

I imported the image into Adobe Illustrator and looked up the "RegistrationPoints" array onto the image. Using these coordinates, I tried to create the chart object using this code:

cornerPoints = [1113,632;638,636;632,323;1110,320];

chart = colorChecker(rgbImage,"RegistrationPoints",cornerPoints);

This method may not be elegant but if it allows me to experiment with the more advanced functions I want to get at like "measure WhiteBalance", it's worth the effort! So here is my result: