Resizing an image that is half as large in both height and width without imresize

Hi there, I am trying to write a function that provided an image matrix returns an image that is half as large in both height and width. Each pixel in the returned image should be the average of 4 pixels from the input image without the use of matlab's imresize

Answer 1

[Image Analyst]

Try this:

kernel = ones(2)/4;
out = conv(double(grayImage), kernel, 'same');
out = out(1:2:end, 1:2:end);

[Image Analyst]

It replaces (blurs) each pixel with the average of pixels in the surrounding 2-by-2 neighborhood, just like you asked. By the way, usually the mask is an odd number so that the neighbors are centered on the pixel. Why are you not using an odd number like most everyone else?