A three dimensional (3D) graphics applications programming interface (API) extension provides support for specifying images in a packed float format. In the packed float format, floating point values of three color components are represented as N bits, where N is less than the total number of bits required for a standard half-precision or full precision format. For example, the blue, green, and red components may each be encoded to have a 5-bit exponent and a 5- or 6-bit mantissa with an implied leading 1. The packed float format is used to represent high dynamic range textures in a compact encoding to reduce the memory footprint needed to store the image data compared with other high dynamic range formats.