The two types of Transparency

Just a reminder of the difference between the two types of transparency and why alpha channel transparency is the preferred choice for module designers.

In GIF Style transparency (also known as bitmap or mask transparency), one of the available colors is designated to represent transparent areas of the image. A particular pixel can only be complete opaque or completely transparent, there is no partial transparency.

It is very difficult to get images using GIF style transparency to blend into the background they are displayed on. The edge of the image goes from completely opaque to completely transparent in one pixel. The image edge tends to look ‘hard’ and the images have a ‘pasted on’, ‘fake’ look.

In Alpha channel transparency, an additional 8 bits (the Alpha Channel) is allocated for each pixel and these 8 bits specify how transparent the pixel is. Any particular pixel can have up to 256 levels of transparency.

With an alpha channel and a good image editor, you have far more flexibility and control over the transparency of the image. The edges of an image can be made to become increasingly transparent as you approach the edge of the image. The result is that the image blends smoothly into the background with no sign of an edge, even on a background with a contrasting color. You can also generate partially transparent images, or parts of images that allow the background to show partially through. This is impossible with GIF style transparency.

GIF Style transparency is not bad, it is just far more limited in application than Alpha channel transparency.