An image is made up of one or more channels. For each pixel in the image, there are channel values for all of the image's channels. ImageGear supports the following channel types:

• Color channel - channel value describes a pixel's color. The number of color channels in an image is determined by the image's color space. For example, an RGB image has three color channels, one for each color component: red, green, and blue. CMYK has four color channels, and grayscale has only one.
• Alpha channel - channel value describes how much a pixel should be blended with another pixel during an alpha blending operation. In ImageGear, an image can have only one alpha channel, which can contain either non-premultiplied (as in PNG) or premultiplied (as in TIFF) alpha values. Also, only images with RGB or grayscale color channels can have alpha channels.
• Extra channel - extra data associated with the image on a per-pixel basis. For example, if an image being loaded contains multiple alpha channels, the first alpha channel will be loaded as the image's alpha channel, and the others will be loaded as extra channels. Extra channels are maintained in the image but do not contribute to display or alpha blending operations.

Each channel has a bit depth associated with it. This is the number of bits used to represent a value for the channel. This bit depth can be up to 32 bits on 32-bit platforms and up to 64 bits on 64-bit platforms. It is possible to have an image with multiple channels that differ in bit depth. For example, you could have an RGB image with 8 bits per color channel and a 1-bit alpha channel. Or you could have a 5-6-5 RGB image with 5 bits for red and blue channels and 6 bits for the green channel.