When resizing a portrait to a card image one is left with an image that shows the same properties, apart from the dimensions, as the portrait.

However, some other step must be necessary in order to switch off the background (cards have a black background if you look in the fiiles, which is transparent in-game). Can anyone tell me what needs to be done to the portrait (something to do with the alpha layer I suspect) other than a resize in order to make it the same as vanilla cards?

I have PSP, but any instructions would be useful and most appreciated.

Thx.