INPUT PROFILES IN THE WORKFLOW

The Importance of Input Profiles

When using ICC color workflows, an accurate device profile of your printer, inks, and paper is essential, but it is only half the battle. Color is also controlled by your choice of ICC input profile, which determines what color device will be 'simulated' by your prints. This is more than just a matter of "fine tuning". Choosing the wrong input profile can cause your color to be wrong by many delta E. If you don't control your input profiles, it simply doesn't matter how well you've profiled your output devices.

Adobe RGB and sRGB Comparison

Consider the above illustration, which uses the Profile View feature of Wasatch SoftRIP to compare the 3D color gamut of an Adobe RGB color profile to an sRGB color profile (which is nearly identical to the gamut of an Apple RGB profile). We're illustrating with these two profiles because they are both offered within the Nikon D100 digital SLR, a state-of-the-art digital camera. There is no one definition of "correct" RGB, even within this one camera.

In the illustration, the Adobe profile's color gamut has been rendered as a multi-colored transparent shape, while the sRGB profile has been rendered as a multi-colored solid shape. This is done to illustrate that the colors available in the Adobe RGB color gamut extend far beyond those available in the sRGB gamut (the difference in green, for example, is over 20 delta E).

If a photograph taken in the Adobe RGB color space is printed with an sRGB (or Apple RGB) input profile, colors will be substantially reduced in saturation, or "muted". Likewise, a photograph taken in an sRGB space and printed with an Adobe RGB input profile will be oversaturated, and the print will contain color errors of over 20 delta E. These errors will exist even if your output profile is "perfect".

The profiles used for the above illustration are selectable standard working spaces in Adobe Photoshop and can also be downloaded from Adobe and sRGB web sites. Any user of Wasatch SoftRIP can download these profiles and use Profile View to study the issue further.

Another common problem is the fundamental conflict between accurately modeling ANSI SWOP CMYK color and printing beautifully high contrast pictures.

ANSI TR001 SWOP CMYK

Approximation with stretched L

The gamut hull on top is from an industry standard accurate profile of SWOP printing, a profile that is often used for ICC managed color proofing. When combined with an accurate output profile (and repeatable ink and paper), it turns your inkjet printer into a highly standardized color proofing system.

Note, however, that the gamut hull never touches bottom in this illustration - it never reaches the black point. Any accurate profile of SWOP printing won't visit any point darker than an L value of about 7.8%. Because no black darker than 7.8% can ever be specified through the input profile, prints made this way often exhibit "dusty blacks", and never show the full brilliance possible with inkjet printing. When beautiful prints are preferred to accurate proofs, a profile such as the "Approximation with stretched L" will produce better results (both these ICC profiles are included with Wasatch SoftRIP).

There are dozens of different input color spaces in common use as ICC profiles, and the input profiles included with Wasatch SoftRIP include a rich set of industry-standard options. Whether or not you get good out-of-box color depends on how well these "generic"' profiles match your needs. If they don't, Wasatch SoftRIP makes it easy for you to set up whatever you need, and Wasatch Profile View is a powerful tool for analysis of what's happening.