I frequently have to process batches of video frames that often have non sq. pixels ; I'd be frustated to have a lossy PNG loader in GIL.
I don't think that silently rescaling an image with nonsquare pixels is good practice. A nonsquare pixel is still a pixel. Imagine that you want to apply a filter to a non sq. pix. PNG file, if GIL silently changes the image size, there's no way for you to get back the original image size and pixels. Not to mention that depending on the image type you may want to use different filter kernels to do the resize.
IMHO the best solution would be to simply provide a way to know the pixel aspect ratio, and let users of the lib handle it the way they want, i.e. rescale or not or whatever.
I can only agree here. Gil makes it very easy to create a new image type based on a pixel type. When reading non-sq pixels I would suggest to create a new pixel type containing the pixel's aspect ratio. Perhaps, we can even have such information in a image_view type. As for the io extension I would try to refrain from any post processing as much as possible, especially when using read_image( ... ). Regards, Christian