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I have tried the coding. But i don't understand what does mean idx = Igray == 0? Can someone explain it to me.

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syafini alias
syafini alias 2018-5-12
评论： syafini alias 2018-5-12
if true
% code
endSeparate to RGB channel
Ir = imgcrop(:,:,1);
Ig = imgcrop(:,:,2);
Ib = imgcrop(:,:,3);
% Extract the background (black) region
Igray = rgb2gray(imgcrop);
idx = Igray == 0;
% Calculate average RGB of the region
Rave = uint8(mean(Ir(~idx)));
Gave = uint8(mean(Ig(~idx)));
Bave = uint8(mean(Ib(~idx)));

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采纳的回答

Ameer Hamza
Ameer Hamza 2018-5-12
This code is calculating the average of RGB channels while excluding the pixels where the intensity level is zero.
The line
idx = Igray == 0;
find all the pixels in grayscale image Igray, where the intensity is 0. It will return a logical matrix idx. Since only those pixels are required where intensity level is not 0, therefore we invert the logical matrix using ~idx,
Ir(~idx)
will return all the required pixels and then using mean() find the average. See Logical Indexing here.
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Ameer Hamza
Ameer Hamza 2018-5-12
编辑：Ameer Hamza 2018-5-12
As @Walter mentioned, mean() will do average along first nonscalar dimensions. In case of 2D matrix, it will average all the columns. Either use mean2() or convert to a single column before taking average like this
Rave = uint8(mean(Ir(:)));
Gave = uint8(mean(Ig(:)));
Bave = uint8(mean(Ib(:)));
disp([Rave,Gave,Bave]);
or take mean() twice
Rave = uint8(mean(mean(Ir)));
Gave = uint8(mean(mean(Ig)));
Bave = uint8(mean(mean(Ib)));
disp([Rave,Gave,Bave]);
all will produce same output.

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KSSV
KSSV 2018-5-12
编辑：KSSV 2018-5-12
You need to read about logical indexing in MATLAB.
idx = Igray == 0;
The above line gives the indices of pixel zero's in the matrix data Igray.

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