PRMG RGB gamut warning profile - sRGB based (beta)The PRMG_RGB-sRGB_based.icc profile is intended to be used as a destination profile for checking to see if source image content extends significantly beyond the ICC v4 Perceptual Reference Medium Gamut.
This profile is identified as being sRGB based because it contains the perceptual transforms from the sRGB_v4_ICC_preference.icc profile in all rendering intents. The profile assigns to RGB image data the PCS colorimetry produced by color re-rendering sRGB values to the ICC v4 Perceptual Reference Medium (PRM). Consequently, the color gamut represented in the PCS will not exactly match the PRMG, although it should be close enough for most purposes. (Most gamut warning software allows colors to go somewhat outside the destination profile gamut before identifying them as out-of-gamut.)
It is also possible to convert to the PRMG_RGB-sRGB_based.icc profile. When this is done the result will be RGB data describing image colorimetry on the PRM (as opposed to on the sRGB reference display). Such data can be useful when it is desired to exchange PRM colorimetry in an RGB file where all possible RGB values represent valid PRM colors. However, it should be noted that the transforms in this profile use interpolation of three-dimensional look-up tables, and are therefore not completely invertible. Multiple conversions into and out of PRMG RGB will cause image degradation.
A better choice for a RGB working space and exchange color encoding for PRM colorimetry is the ROMM RGB color encoding specified in ISO 22028-2, and implemented in the ISO22028-2_ROMM-RGB.icc profile. This profile contains analytical transforms that do not involve interpolation and therefore round-trip much better than the PRMG_RGB-sRGB_based.icc profile. The only disadvantage to using ROMM RGB as a working space is that a significant percentage of the possible RGB values represent colors that are outside the PRMG, and in some cases outside the spectral locus. When editing, care must be taken to avoid using these RGB values. In workflows where this is a concern the PRMG_RGB-sRGB_based.icc profile offers an alternative, so long as care is taken to keep the number of conversions to and from the working space at an absolute minimum.
The ICC recommends the use of the ISO22028-2_ROMM-RGB.icc profile as the PRM working space and exchange encoding, and the PRMG_RGB-sRGB_based.icc profile as a gamut warning profile to check for the use of ROMM RGB colors outside the PRMG.
To use the PRMG_RGB-sRGB_based.icc profile for gamut warning purposes in Adobe Photoshop:
Download ISO22028-2_ROMM-RGB.icc profile.