ChannelPacking

Channel packing means using different grayscale images in each of a texture's image channels... Red, Green, Blue, and optionally Alpha.

These channels are usually used to represent traditional RGB color data, plus Alpha transparency. However each channel is really just a grayscale image, so different types of image data can be stored in them.

Individual channels can be extracted by a shader to use them for particular effects, for example the red channel for glow, green channel for specular, blue channel for sound types, alpha channel for physics info, etc. Each channel can have a totally different layout, and thus use different UVs.

Games use this technique to avoid loading separate grayscale images, which saves Memory. The tradeoff is in increased shader complexity.

See also Texture atlas and MultiTexture.

Compression Artifacts

If you save a channel-packed texture using DXT compression, it may introduce blocky artifacts to your channels. See also Normal_Map_Compression.

Tools

• Photoshop alpha channels
• Gimp alpha channels
• Channel Shuffle

Examples

Two channel-packed textures, which store a total of six unique textures, see An exercise in modular textures - Scifi lab UDK on the Polycount Forum. Image by Tor 'Snefer' Frick.

A channel-packed texture used to texture an entire scene, see [UDK Oil Rig Observation Outpost] on the Polycount Forum. Image by Wiktor 'Disting' Öhman.

A channel-packed texture used in Mass Effect 3, see Mass Effect 3 art - Marc-Antoine Hamelin on the Polycount Forum. Image by Marc-Antoine 'Marcan' Hamelin.

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