If you need non-standard channel configuration, you'd better use OpenEXR. From the wiki: It is notable for supporting multiple channels of potentially differen

If you need non-standard channel configuration, you'd better use OpenEXR. From the wiki: It is notable for supporting multiple channels of potentially different pixel sizes, including 64-, 32- and 16-bit floating point values, as well as various compression techniques which include lossless and lossy compression algorithms.