A pre-multiplied image is one where the RGB channels have been multiplied by the alpha channel. This means it is a fourchannel image in which the red, green and blue channels have already been multiplied by the integrated matte (alpha) channel.
A pre-multiplied image is one where the RGB channels have been multiplied by the alpha channel. This means it is a fourchannel image in which the red, green and blue channels have already been multiplied by the integrated matte (alpha) channel.