The 7 ICC Profile Types
by Steve Upton
Color Times 7 - a summary of the seven ICC profile types
Though we tend to use three different profile types - those for scanners, monitors and printers, the ICC has actually created a total of 7 different profile types. Each has its own capabilities and situations for best use. Here's a quick summary of the 7 profile types and how they may be useful in your workflow:
First there's the device profiles. These are the profiles we typically think about when we think of ICC profiles. This includes:
- Input Profiles: eg RGB -> Lab
- Monitor Profiles: eg RGB <-> Lab
- Print Profiles: eg Lab <-> CMYK
Device profiles perform 1/2 of the conversion when converting from one device to another. For instance, a scanner Input profile converts from RGB->Lab and then a press Print profile converts the rest of the way from Lab->CMYK. Used together they convert your scanner RGB file to press CMYK.
Monitor and Print profiles can convert color in each direction. So if you have a Lab color value you want to output on a printer, the Lab->CMYK portion of the profile gets used. If you have a CMYK value that you want to convert into a color (eg proofing CMYK values) then the CMYK->Lab portion of the profile is used.
You may have noticed that the Input profile is the only profile listed with a single-direction arrow ->. Input profiles have the distinction of containing only device->Lab capabilities. When you think about it this make sense as you'll want to convert from a scanner's RGB values to Lab values but you won't have a need to convert from Lab colors to the scanner's RGB - there's no ability to output anything on a scanner after all.
If you are confused about the difference between device values (like RGB and CMYK) and colors (like Lab) please see my Color of Toast article.
There are several other profile types that don't get used as often but can be quite powerful. They are:
- Device Link profiles (eg CMYK -> CMYK)
- Abstract profiles (eg Lab -> Lab)
- Space profiles (eg Lab -> LCH)
- Named Color Profiles (eg Pantone 256 = Lab(x,x,x))
Device link profiles are a unique and power type of profile with their ability to convert directly from device colors to device colors. This means a direct conversion from CMYK to CMYK can be performed by one link profile and so they are not applied in pairs like normal device profiles. Typical link profiles are created by permanently combining the two device profiles from a transformation into a single hard-coded link file. This link performs the same transformation in the same way as the original two-profile combination and it also contains the CMM's (hopefully) correct math that was used to create it. This additional component can make link profiles effective in RIPs that do not convert color reliably due to some flaw or limitation in their internal CMM.
Device link profiles left in this basic condition are quite useful but if additional processing is applied to them they become essential to certain conversions and effects. One common effect is to tune the portion of the profile responsible for K-only conversions so they produce K-only results. This black-preservation ability is coveted by those who have the need to convert from one CMYK space to another but do not want to have K-only colors converted into 4-color grays. ColorThink Pro is able to create device link profiles with clean K conversions.
Other device-link effects take advantage of the device to device capability of a link profile. This capability means a "null" profile can be created that does absolutely nothing to the CMYK data that flows through it. Then, certain device-space edits such as individual channel curve bumps or ink-reduction effects can be added to the link. One ink-reduction effect we built into a client's profile converts any colors that have total ink levels over a certain amount to K=100, C=30. Any files sent through this profile have no conversion applied if their inking is OK but as soon as pixels are discovered with high ink levels they are corrected. It's fast, simple and it's effect can be created in no other way with no other kind of profile.
A few other points about device links:
- only one rendering intent is available, that which was selected at the time the link was created.
- links cannot be embedded into images
- the rendering intent encapsulated in the link is selected in the 'default intent' field in the profile's header.
- a profile sequence tag in link profiles documents the profiles used to create the profile.
If device links convert from device to device then abstract profiles are the opposite; they convert from Lab to Lab. Where the device link's domain is device-space edits, abstracts are all about Lab-space (color) edits. Contrast bumps, increasing saturation, and gray or sepia effects are just a few examples of simple color edits than can be captured within an abstract profile.
But, like link profiles, a little ingenuity and number crunching and the real power behind abstract profiles can be released. The complex effect of a photographic process such as cross-processing can be captured in an abstract and applied to any image. Color differences between two systems can be also be captured and used to either correct one of the systems or recreate the effect somewhere else (such as the feel of a certain photographic film type).
We are just beginning to scratch the surface of the powerful capabilities of these profiles.
Unfortunately Photoshop does not support the use of either abstract or device link profiles. Luckily, in the case of abstracts, we have a solution in ColorThink Pro's new ColorCast technology. ColorCast allows an abstract profile's effect to be embedded into another profile such as the Adobe RGB working space. The result is a "normal" RGB device profile that Photoshop can apply to any image, performing the function of the original abstract profile. sneaky!
Abstract profiles are also not allowed to be embedded into images.
- Editor's note:
- As of Photoshop version CS4, Photoshop now supports the use of abstract and device link profiles, as well as converting to multi-channel profiles. Accurate soft-proofing is not yet implemented.
Sometimes there's a need to convert between a non-device color space and Lab. An example of this would be the converting of Lab colors to an alternate color space that warped colors for some effect or other purpose. These profiles are quite rare, you are not likely to come across them in normal workflows.
Named Color Profiles
If all other profiles are like math formulas, Named Color Profiles (NCPs) are like lists or palettes. The NCP profile stores a list of colors where each color contains a name, Lab color value and (optionally) device values. NCP profiles are supported in some color utilities and also in Mac OS X as palettes in the color picker. Unfortunately they are not supported in the major publishing applications from Adobe, Quark etc. Perhaps some day NCP profiles will gain wider support and we will finally have a standard method of storing and using color palette lists.
OK, you caught me. ColorCast profiles are not part of the ICC standard. In fact, ColorCast profiles are 'normal' device profiles (typically printer) which have been altered with a special color effect such as proofing a 6-color press.
ColorThink Pro uses our patent-pending ColorCast technology to build profiles that allow many profiles to be used in places where they are not typically supported such as 6-channel profiles in Photoshop. ColorThink calculates the effect of proofing with a complex profile and then embeds this effect into either a working space or print profile. The profile appears to the system as a normal RGB or CMYK profile so it can be applied for soft and hard proofing in Photoshop without the need for any additional software plug-ins.
Though the three types of device profiles are the most commonly created and used in photographic and graphic arts workflows, it is worth learning more about the extra profile types, as they have capabilities that can solve some sticky color problems easily and with high quality results.
Thanks for reading,