Question

I need a logic to re-size an image so that its always 320X240 or smaller and should maintain aspect ratio.

Answer 1

1) determine which side of the image is the larger one
2) if its width, calc: faktor = 320/width, else faktor = 240/height;
3) downscale the image by size.x *faktor, size.y *faktor.

example:

Given: image has 1024×640

1) its wider than high.
2) faktor = 320 / 1024 -> 0.3125
3) 1024 * 0.3125 = 320 (huh!)     
   640 * 0.3125 = 200.