The profile name is for the convenience of the artist or user of the image; in practice, it will probably be similar to the profile description tag, which is embedded in the profile itself. The compression method byte currently must be zero, indicating a compressed stream in zlib format, using the deflate compression method. As with zTXt and the actual image data, a future major revision of the PNG spec may define other compression methods, in which case this byte will be allowed to take on other values.

Aside from uncompressing it, ordinary decoders will not be expected to know anything about the ICC profile other than the fact that they can be large (i.e., more than 64 KB); instead, they will simply hand it off to the local color management system for appropriate processing. Encoders should ensure two things: that the profile is a valid ICC profile and that it refers either to an RGB color space (for color images, including colormapped ones) or to a grayscale color space. CMYK color spaces, for example, are disallowed. Likewise, multiple copies of iCCP are disallowed; if the iCCP chunk is present, it must come before any PLTE or IDAT chunks.

By mid-1998, there were indications that something of a ``TIFF effect'' applied to the ICC profile format; that is, profiles from different vendors were not necessarily interoperable with each other or with different color management systems.[84] Presumably this will be worked out by the time the ICC specification becomes an official standard, but in the meantime, it is something of which PNG implementors should be aware.

[84] This is hardly surprising for a format that attempts to deal with such a thorny problem.