Frame memory (SRAM) size for an image
If you store an image in an SRAM, generally you want to be able to split the address bus into an x and a y component.  To do this, at least one of them must be a power of 2.  For 320 x 240, you have to round 320 up to 512 to get a power of 2.  512 x 240 is 122880.  If you shrink it down to 128x96, it's more efficient because 128 is already a power of 2 so you can fit it in a 128 x 96 = 12288 byte SRAM.  There's your factor of 10.