A support question that arose recently made me realize that some 3ds Max and VIZ users are unclear what the alpha channel in image files is or why it's important. I'll attempt and overview here that will shed some light on the topic to help you decide whether Alpha channel images are important in your workflow.

First, a little history:

In the early days of computing the number of colors visible on the screen or in images was limited, at first to 8 colors, then to 16, and then enormous jump to 256 colors; and the rest is history.  Computers and images are now capable of utilizing or displaying many more colors than the human brain can perceive, but you need to know a little about antialiasing and color depth to make sense of Alpha channel.

In the 1970s, when computers primarily displayed 256 colors, a diagonal line drawn across the computer display was extremely jagged because the low resolution monitors could only show small rectangles (pixels) of color.  To overcome this jagged appearance engineers invented antialiasing methods that gave the illusion that the diagonal line was smoother by blending the line color with the background color along the edges of the diagonal line, thereby reducing the stair-stepping effect.

However, if you had a red diagonal line on a white background and you lifted the red line to composite onto a yellow background, the result was terrible because the edges of the red line had varying degrees of white pixels from the previous antialiasing. We'll look at more on antialiasing later, but first a bit of a discussion of color depth.

Color displays and images are often defined in terms of bit depth; an 8-bit (2 to the power of 8) can have a total of 256 colors, a 16-bit image can have over 65,000 colors, and a 24-bit image can have a total of 16.7 million colors.  The human brain can only perceive about 65,000 colors, but the 24-bit images allow enough color choices to give smooth gradients in complex shaded scenes.  8-bit and 16-bit images always show a significant amount of banding due to limited color choices, so the 24-bit image became the de facto standard. Yes, there are more colors to choose from with 24-bit images, but the problem of antialiasing in composited images still remains.

Enter the 32-bit image.  You might imagine that this type of image would have contained many more colors than the 24-bit image, but that's not true; it still has 16.7 million colors. A 32-bit image is made of 24 bits of color information and an extra 8-bits of transparency information; the Alpha channel.

32-bit images use this transparency information to gradually lighten the colors of our red line against the background.  Now when the red line is lifted from the white background and composited onto the yellow background, the result is a smooth transition with antialiased edges.

So what...?

When you create materials in 3ds Max and VIZ there are many situations where images are composited within the Material Editor; in the Composite map type, in Opacity mapping, and in Bump mapping to name a few examples and the edges of these effects will be much cleaner and more dependable if you use images with alpha channel.

The more commonly used filetypes that can store Alpha channel information are; TGA, TIF, and PNG.  The TGA and TIF files are both 32-bit, 24-bits of color and 8-bits of transparency, while the PNG file can go as high as 48-bits of color with 8-bits of transparency.

When images are rendered from 3ds Max 8 or VIZ and one of the above filetypes is specified, the black background pixels will become transparent information and objects will render with varying degrees of grayscale at their edges to form the Alpha channel.