Just as you can vary the amount of paint when working with pigments and a brush, VizPaint2D lets you control the transparency of whatever you apply to the canvas, including paint, grades, text, pasted pictures, and even erasing.
Transparency and opacity are opposites. The higher the transparency value, the more the pattern, color, or design of any underlying picture is visible through it. Lower transparency values create more opaque effects, revealing less of the underlying picture.
VizPaint2D stores each component of the color on a separate channel-there is one channel for each color component and one channel for the transparency component. The channel that contains transparency information is called the alpha channel. (In other systems, the alpha channel may be referred to as the matte channel.)
VizPaint2D allows you to paint on the alpha channel, which is especially important when you will be layering (or compositing) two or more pictures. For more information, see "Compositing pictures" on page 375.