Dual ISO preview (WIP)
Finally managed to clean up this experiment. Now you can check the focus on dual ISO images, in QuickReview, with a non-destructive method (very similar to drawing zebras).
To try it, you may want to change this:
static int preview_gains[4] = {4, 0, 0, 4};
to match the ISO pattern (which rows are bright and which are dark) and the gain value (4 is for ISO 1600). Things are not yet autodetected.