I have been having a heck of a time with photoshop trying to export some layers which have transparent edges but need to line up (top, repeating-middle and bottom images for a faux rounded corner situation). They keep on ending up one pixel off... I tried setting up slices, I tried using the same selection marquee and just repositioning it downward. I tried selecting based on guides.. and every time the selection did not line up. I can fix this with CSS, but I would much rather have the images be starting at the same point, and wondering what the best way to achieve this is!
I'm pretty sure the problem must be with subpixels and how they are selected, or it could be related to the border of the image being transparent and photoshop dropping the transparent pixels when the selection is copied.
I just need to know how photo-shop handles these situations and what options I have to make a reliable workflow for getting properly sized and positioned images saved out.