How can I downsample an image?

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bkshn
bkshn 2015-7-2
评论： bkshn 2015-7-8
Hello
I want to downsample an image and I want to replace one pixel in new Image with average of four pixel in first image.
Could you help me ?

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Walter Roberson
Walter Roberson 2015-7-2
Letting the image be IM and assuming it is double(),
NewImage = (IM(1:2:end, 1:2:end) + IM(2:2:end, 1:2:end) + IM(1:2:end, 2:2:end) + IM(2:2:end, 2:2:end)) / 4;
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Walter Roberson
Walter Roberson 2015-7-5
This formula processes all pixels in the image at the same time. I just noticed that it will fail if the height or width are odd.
It works by taking the average of the pixels at (I,J), (I+1,J), (I,J+1), (I+1,J+1), doing so for every second row and ever second column.
bkshn
bkshn 2015-7-8
Hello Walter Roberson
I think it's ok for grayscale image. Could you help me about rgbImage?
thanks

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