ProPhoto RGB is a color space for use with photographic output in mind. It is an output referred RGB color space that offers an especially large gamut. ProPhoto RGB was developed by Kodak. The ProPhoto RGB color space encompasses over 90% of possible surface colors in the CIE L*a*b* color space, and 100% of likely occurring real-world surface colors documented by Pointer in 1980, making ProPhoto even larger than the Wide-gamut RGB color space. The ProPhoto RGB primaries were also chosen in order to minimize hue rotations associated with non-linear tone scale operations. One of the downsides to this color space is that approximately 13% of the representable colors are imaginary colors that do not exist and are not visible colors.
When working in color spaces with such a large gamut, it is recommended to work in 16-bit color depth to avoid posterization effects. This will occur more frequently in 8-bit modes as the gradient steps are much larger.
There are two corresponding scene space color encodings known as RIMM RGB intended to encode standard dynamic range scene space images, and ERIMM RGB intended to encode extended dynamic range scene space images.