2011

Table Of Contents
NOTE When using the Premultiply tool, make sure the output image is never
processed by a tool that produces incorrect results while operating on an
image with premultiplied data. Tracking of whether images are stored in
premultiplied format or not, does not occur.
Unpremultiply Tool
The Unpremultiply tool lets you recover an alpha-unpremultiplied foreground
image from an alpha-premultiplied image whose foreground may have been
composited on a solid color other than black.
The Unpremultiplied tool takes an alpha-premultiplied image as its input and
outputs a corresponding alpha-unpremultiplied image. It assumes the input
image consists of a foreground composited over a solid color background; if
the background is a color other than black, you can explicitly specify this
background color so that the tool can correctly separate the foreground layer
from this background and output the foreground layer alone. Optionally, your
can ask the tool to guess the background color.
The Unpremultiplied tool has a single parameter:
To:Use:
Specify the background color so that the tool can
correctly separate the foreground layer from the
background and output the foreground layer alone.
Background
Have the tool analyze the input image and guess
the background color and set the color widget to
that color.
Guess
To unpremultiply an image:
Drag the Unpremultiply tool from the Tools tab to the dependency graph
in the Schematic view.
414 | Chapter 17 Image Processing Tools