How can I downsample an image?

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 ?

Answer 1

[Walter Roberson]

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;

[bkshn]

Hello walter Roberson, thanks for your answer.

I have a question Does this formula contains all pixels in an Image?

Could you help me How it works?

[Walter Roberson]

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]

Hello Walter Roberson

I think it's ok for grayscale image. Could you help me about rgbImage?

thanks