image_borderscan

declaration:

::lua
function image_borderscan(vid) => x1,y1,x2,y2

Special case used mostly for images with a hollowed section in the middle (e.g. bezels) and an outer border. Works by scanning alpha- values from the center of the image and outwards.

caveats:
Doesn't work in memory- conservative mode (assumes the buffer is directly accessible).