Creating arbitrary sized blank pngs/jpegs

Question

I want to create arbitrary sized pngs and jpeg images of a single block colour at a specified x,y size, however I do not want to do this by generating a raw image in memory and encoding/compressing it due to potential memory requirements.

How would this be done?

Answer 1

You could make your own generator. Pseudo-code for a PNG generator is:

write_png_header(width,height);
gzip_scanline(width,colour);
for(y=1; y<height; y++) { // scanline 0 already written
  write_type_copy_previous();
  gzip_zero_delta(width);
}

Answer 2

It's unclear what language you're using, or what your use case is, but I use the convert program from the imagemagick suite to do this:

convert -size 300x300 xc:transparent missing_normal.png

If you're creating images for a browser you could just create a single 1x1 image, then use the width and height attributes to let the browser scale it for you.