The definition of the alpha channel refers to transparency on a per-pixel basis. It controls the transparency of an image. Some pixel data in each image is always intended for transparency information. The alpha channel specifies how the pixel’s colors should be merged with another pixel when the two are overlaid, one on top of the other. A value of 100% in the alpha channel gives a fully solid pixel and 0% provides full transparency. By selecting values between 0% and 100%, pixels can be shown through the background (similar to glass), and therefore retain their anti-aliasing regardless of the background. The alpha channel is supported by PNG and TIFF image formats. Image formats that do not support the alpha channel, lack transparency. GIF format supports transparency, it is a basic transparency type that does not use the alpha channel and should be avoided when attempting to save images containing alpha-based transparency. The TGA file format also supports alpha transparency but is not as common as PNG.