Hi, I noticed that the y-index for images input with the PNG reader is reversed, i.e. y=0 refers to the bottom row of an image (as viewed in xv). Apparently the PNG writer reverses it again so the output is not flipped.But, if I set rows 0 to 100 to all black pixels, in the output it is the bottom 100 rows not the top 100 that are black. Is there a reason for this? Tolga