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A Gamut (or “Color Space”) is simply a three-dimensional volume of colors that represent the entire set of colors that is either used as a reference volume or describes the capability of a piece of hardware (e.g. a monitor or printer).

This post and its predecessor are dedicated to my friends Josh and Marc, who are considering conversion to a color-managed workflow at their office. It would be best if any reader were familiar with the basics of Gamuts outlined in that earlier post before getting involved in this post. The value of this post is heavily dependent upon separate study of the various resources linked in either post: I’m simply trying to help construct a broad understanding of the concepts. Again, I’ll strongly recommend that you pick up ColorThink and/or Gamutvision software.

Of course, we’re essentially trying to make our images look good. At a basic level we’re simply adjusting Contrast and certain spatial features such as rotation and perspective, then blindly depending on the virtues of the Working Space, conversion intent, and printer Gamut to output an acceptable product. Many of us purchase high grade printers under the mistaken presumption that doing so will maximize the quality of our output. Fortunately-for those who want to take the next step or thirty-there is a great deal of potential beyond those basics.

A more advanced strategy in image preparation is to recognize the nature of an image’s color signature (that is, how it maps out relative to its assigned Gamut), then prepare that image for a particular output purpose by maximizing particular virtues (such as color accuracy, or perhaps saturation). To effectively manipulate an image for a specific purpose, it would be best to understand the character of particular Working Spaces/Gamuts (sRGB, aRGB, etc.), the nature of the Output Profiles to be employed (the Profile of your printer/ink/media combination), and the way that your Color Management System (”CMS”) converts an image to an Output (printer) Profile.

Fortunately, Photoshop is dripping with the capability to police your CMS policies (how PS effects Color Management), and of course, they far exceed the scope of a single post…but now you know why they’re there and why they’re important!

Preparing an image without considering the nature of its assigned Gamut and the method of conversion to the Output Profile is much like catching butterflies with a scattergun-it’s rather indiscriminate, relies upon chance, and tends to compromise the product.

You should understand the difference between Assigning a Profile and Converting To a Profile. You should also become proficient at “Softproofing” your images: Allowing Photoshop to identify the colors within an image that exceed, and thus need to be “remapped” to the Output Profile. The problem is defined well here, and Softproofing is explained well within Photoshop Help (press F1 and search on “Proof Setup,” “Proof Colors,” and “Gamut Warning”). Andrew Rodney authored an excellent article on Working Spaces which Adobe has made available here.

The “secret” to all of this CMS rigamarole is that simply knowing what a Gamut is, that Working Space Gamuts are generally larger than Output Profiles, and that there are different ways to convert the large Working Gamuts to the smaller Output Profiles isn’t really enough. We need to intelligently select our image preparation and the method we’re using to convert between Gamuts within our production process.

At this point you’re probably thinking that I’m going to link a very technical white paper on the math. Absolutely! Here it is, here’s another, and here’s a corroborating document with some Color Theory fundamentals as well. I believe that recognizing the depth of the technical underpinnings produces a healthy respect for the process-particularly concerning the .jpg DCT and .jp2 wavelet math. If you’re already an advanced practitioner, you might find this .js conversion visualization interesting (Bonus! It’s from RIT!).

Within our typical photography/Photoshop context there are 4 Gamut Conversions we should be familiar with: Perceptual, Saturation, Relative Colorimetric, and Absolute Colorimetric. newsandtech.com has a superb explanation by John Nate with very digestible graphics (accurate graphics on this matter would be extremely difficult to comprehend, particularly in two dimensions) on those four Gamut Conversions here.

For the purposes of visible-spectrum handheld aerial photography I recommend that you narrow your focus to the Perceptual Intent. If you are interested in developing a truly functional understanding of Gamut remapping, Undercolor, Linearity, Delta E, Black Point Compensation, etc., please make the investment in either ColorThink Pro and/or Gamutvision.

L