How to overlay a mask on an image with zero transperancy?

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Tawsif Mostafiz
Tawsif Mostafiz on 6 Mar 2022
Edited: DGM on 6 Mar 2022
I am trying to overly this mask:
Onto this bw image:
Using this code:
maskedRgbImage1 = bsxfun(@times, bw, cast(mask, 'like', bw));
The output is like this:
But I want the red mask to completely overlap the black part, like this:
How can I do that?
  1 Comment
Simon Chan
Simon Chan on 6 Mar 2022
You may use function imoverlay.
Notice that the size of the attached images are not the same.

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Accepted Answer

DGM on 6 Mar 2022
Edited: DGM on 6 Mar 2022
You can still use basic masking methods. Note that in this case, the images as supplied are both uint8. If your working images are logical class, you might need to deal with making sure they're compatible with arithmetic operations with images of integer numeric class. They're also mismatched in size by a few pixels. I'm assuming that's just an issue with the way the images were saved; otherwise, you'll have to figure out how to fix the size mismatch. I just elected to crop off the difference.
RB = imread('redblob.png');
BB = imread('blackblob.png');
RB = RB(6:end,:,:); % they aren't the same size
% use logical masking
mask = repmat(any(RB<255,3),[1 1 3]); % create a mask where the red blob is
outpict1 = BB;
outpict1(mask) = RB(mask); % compose
% use multiplicative composition
mask = repmat(uint8(any(RB<255,3)),[1 1 3]); % create a mask where the red blob is
outpict2 = RB.*mask + BB.*(1-mask); % compose

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