Is there a built-in Demosaicing option in Matlab which doesn't use interpolation and instead just reduces the image size?

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Shida
Shida 2017-8-17
评论： MatlabUser 2018-10-19
I am aware of demosaic(I,sensorAlignment) function in matlab. But if one would want to reduce noise and just reduce the resolution instead (e.g, to a quarter), does matlab already have a built-in function for that?

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Neil Guertin
Neil Guertin 2017-8-22
There is not currently a built in way to do this. However, it is pretty simple to write:
I = imread('mandi.tif');
I = I(1:end-mod(end,2),1:end-mod(end,2)); %In case image dimensions are odd
I2 = zeros([size(I)/2 3],class(I));
I2(:,:,1) = I(2:2:end,2:2:end);
I2(:,:,2) = I(1:2:end,2:2:end)/2 + I(2:2:end,1:2:end)/2;
I2(:,:,3) = I(1:2:end,1:2:end);
imshow(I2)
However, there will be some artifacts that interpolation would have smoothed out: look at Mandi's chin for example. Also note that you are actually losing resolution in the green channel by averaging the two green pixels when you do it this way.
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Shida
Shida 2017-8-23
Thanks Neil. You are right, interpolation does help against artifacts. I am using a Canon EOS with .cr2 format so I have an 'rggb' bayer pattern. But indeed I don't get much difference if I skip interpolation (and instead just reduce the image size to a quarter). I am using dcraw for conversion which seems to already do a reasonable job and I wasn't able to get anything better this way. Thanks again for your response.

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