Mean of CIE L*a*b values in a masked image

Hello,

I am trying to get the mean of LAB values on a masked image, but i suspect that my code is computing the black and not only the colors masked. I'm a new matlab user and I apologize if my code is a mess.

Thank you very much for your attention.

Felipe Castro

% CIE L*a*b transformation
I = rgb2lab(Image);
    
% L max and min for the segmantation
LMin = 0.0;
LMax = 30.0;
    
sliderBW = (I(:,:,1) >= LMin) & (I(:,:,1) <= LMax);
BW = sliderBW;
maskedRGBImage = Icropped;
maskedRGBImage(repmat(~BW,[1 1 3])) = 0;

maskedLAB = rgb2lab(maskedRGBImage);
    
% mean per pixel
mean_Lab = mean(maskedLAB, 4); 

% mean overall 
mean_L = mean2(mean_Lab(:,:,1));
mean_a = mean2(mean_Lab(:,:,2));
mean_b = mean2(mean_Lab(:,:,3));

Answer 1

[Image Analyst]

Yes, it was a mess but that's OK, I fixed it:

% Read in demo image.
rgbImage = imread('peppers.png');
subplot(1, 2, 1);
imshow(rgbImage);
title('Original RGB Image')
% CIE L*a*b transformation
labImage = rgb2lab(rgbImage);

% L max and min for the segmantation
LMin = 0.0;
LMax = 30.0;

mask = (labImage(:,:,1) >= LMin) & (labImage(:,:,1) <= LMax);
subplot(1, 2, 2);
imshow(mask);
title('Mask Image')

% Get individual LAB images
[lImage, aImage, bImage] = imsplit(labImage);
% Get the mean ONLY within the mask region.
mean_L = mean(lImage(mask))

mean_L = 20.0609

mean_a = mean(aImage(mask))

mean_a = 20.3502

mean_b = mean(bImage(mask))

mean_b = -7.0802

[Felipe]

Thank you very much! it worked beautifully.

Image Analyst, you are the best :)

[Image Analyst]

You're welcome. Just be aware that those LAB are just arbitrary values gotten from book formulas. They are not the real LAB values you'd get from the objects in your scene if you had used a colorimeter or spectrophotometer on them. For example if you cut the exposure by half the L value would be about half even though the object in your scene didn't change its intrinsic color at all. The "true" LAB values of the object are intrinsic to the object and illuminant, though you can get almost whatever LAB you want just by changing the lighting and exposure on your scene.