AOA!
how can i upsample an image. downsample is easy just not read the next pixel value. i tried read an image to m. and then tried m(1:0.5:end, 1:0.5:end) for upsampling but that didn't work, a warning "Warning: Integer operands are required for colon operator when used as index" is generated, so plz help me if any body knows something.
I did not realy understand what u mean.If u want to unsample an already sampled signal,then i think this book can be of help.Otherwise explain your question again.
From 256x256, you can do pixel replication OR biliinear interpolation OR cubic interpolation to upsample your image. Here is a link I found which gives implementation code to upsample image using sinc function: **broken link removed**
Hope this helps.