How to apply same 2D logical mask to each 3D layer effctively?

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JAI PRAKASH
JAI PRAKASH 2018-7-13
评论： Walter Roberson 2018-7-14
RGB = imread('onion.png');
mask = RGB(:,:,1)>100;
%%How can I do something like below
RGB(mask,1:3) = 0; % I want to apply same 2D 'mask' for all the 3 layers
I got this intuition from this post "logical operation on a column within a matrix" .

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回答（1 个）

Image Analyst
Image Analyst 2018-7-13
Try this:
% Mask the image using bsxfun() function to multiply the mask by each channel individually.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, 'like', rgbImage));
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Image Analyst
Image Analyst 2018-7-13
It might be slightly faster but it's not general. It's depending on there being at least some red in every pixel of Im2 that you want to use as a mask. So it won't work for a general color where the shape in Im2 could be anything but would work in your specific computer graphics case.
Walter Roberson
Walter Roberson 2018-7-14
Using the multiply version can be faster sometimes because the multiply version on sufficiently large matrices can be sent to LAPACK for multithreaded execution.

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