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HSL is a Gamut predicated upon three axes:

• Hue is the predominant wavelength of a particular color, such as Persimmon, Valiant Violet, or Rally Green…or whatever a particular paint manufacturer wants to name them. Hue is what most folks think of as “color.” I don’t know how to explain the concept of color without using the word “color” or going deep into the wavelengths and chemistry. Sorry.
• Saturation is the purity of a Hue, ranging from gray (equal amounts of Primaries) of the same luminance to the maximum amount of one or two Primary Color constituents of the subject Hue. As a Hue is saturated, one or two of the Primary Colors (R, G, or B) will be increased and a third will be decreased. When the extreme values of Primary Colors have been achieved, you have an ultimately saturated Hue. Fully saturated Hues lie on the “skin” of any particular Gamut-it’s important to know that.
• Lightness is the intensity of…well…radiated or reflected electromagnetic energy, if you wish to be accurate. Black isn’t reflecting or radiating any energy-it enjoys a Lightness value of zero. White is the diametric of black, and every intermediate Hue has a distinguishable Lightness.

There are other Gamuts predicated upon three axes, such as Lab and HSV, but they employ different metrics for those various axes (you’ve already become familiar with Lab here). The variety of Gamuts using a three-axis architecture should not be confused with the Tristimulus RGB model, which does suspend itself within three axes but uses three different extremities (R, G, and B, oddly enough) to define its girth/footprint in a single planar quadrant, and is not positioned upon the Origin or any of its cardinal axes.

Although Lab is heroic and ubiquitous (it’s the foundational Working Space in Photoshop), I’ve featured HSL because of its peculiar virtues including a discreet Luminance and Saturation axes and its ability to serve as an easily digestible illustrative tool for exploring Color Management. You are unable to work in HSL within Photoshop even using Curvemeister-”HSB, ” also known as “HSV,” is distinguished from “HSL” in spite of all those “H’s” and “S’s” floating about. Norman Koren explains it all here…and frankly, I’m thankful he does (the L and V in HSL and HSV are distinguished, and even the S is varied with Luminance).

Perhaps you’ll humor me and purchase this program: Gamutvision-it’s well under $100 and a stellar learning tool. In terms of our series on the Gamut, I’m changing horses in midstream, but I just “discovered” Gamutvision and disappointed with myself in having not done so earlier.

The following graphic series demonstrates a remapping assignment for my primary workstation’s CMS.

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Mapping of the constituent colors in the subject image, in Gamutvision. The wireframe represents the entire aRGB Working Space, while the various plots represent the points within the Gamut occupied by the image color elements.

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In this image the wireframe represents the Output Profile of my Canon i9900 using Canon’s dedicated inks and Ilford Classic Gloss Media. Note that while all of the image’s color plots were encapsulated by the aRGB Working Space, some of them exceed the Output Profile!

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The vectors show the displacement (both in direction and magnitude) of the various color clusters as they are remapped to the Output Profile.

There are many choices to be made in determining each vector, and it is the “mindset” of the algorithm used to effect the displacement that is termed the “Rendering Intent.” If we could concurrently graph the vectors of two separate Rendering Intents in Gamutvision, the divergent vectors would be obvious, I think, particularly in extremely high and low luminance areas.

You might have noticed that the Gamut renderings are placed along the Y axis in the display box in Gamutvision and not confined to a Quadrant I (+, +) Yxy graph as we’re so used to seeing with the Tristimulus RGB model. It’s so because we’re actually looking at Lab renderings of the aRGB Gamut and Output Profile, which aren’t confined to a single display schema. The axial distribution of Yellow, Blue, Green and Magenta is a dead giveaway if you’ve been looking at Gamuts for a while…God forbid I’d actually read the labels (indices).

Nonetheless, you’ll notice too that the vertical axes in the examples are Luminance axes. Hopefully you’re grinning as you reconsider that Photoshop keeps Curves manipulations in Lab quite pure (as opposed to its treatment of Curves in RGB), that Curvemeister allows manipulations in HSB-and that like me you are developing a deep appreciation for independent Luminance and Saturation.

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