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Masking certain RGB values for an image

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Oliver
Oliver 2011-9-26
Hello. I was wondering if there is a way to mask/delete certain pixels in an image if you know the range of RGB values you want to remove. Thanks for any help, Olly

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Jan
Jan 2011-9-26
Yes.
RGB = rand(400, 200, 3);
R = RGB(:, :, 1);
G = RGB(:, :, 2);
B = RGB(:, :, 3);
mask2D = (0.2 < R & R < 0.3) & ... % [EDITED]: && -> &
(0.1 < G & G < 0.4) & ...
(0.6 < B & B < 0.65);
mask = cat(3, mask2D, mask2D, mask2D);
RGB(mask) = 0;
I do not know how a pixel could be deleted without destroying the shape of the image.
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Image Analyst
Image Analyst 2011-10-8
An alternate way if you want to use mask2D and not create the 3D mask:
% Mask the image.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask2D, class(rgbImage)));
In the end, it doesn't make any difference though - this is just the style that Sean prefers.
Walter Roberson
Walter Roberson 2011-10-8
Hmmm, which is faster, cat(3,X,X,X) or repmat(X,1,1,3) ?
Logically cat(3) should be, but I can't test at the moment.

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Image Analyst
Image Analyst 2011-9-26

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