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CM Theory and Practice Profiles, color spaces, perception, science.

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Old May 8th, 2008, 05:41 AM
Doug Kerr Doug Kerr is offline
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Default HSV/HSL color models and the "hexcone" and "bi-hexcone" - new tutorial article

In a recent thread here, I discussed the "hexcone" and "bi-hexcone" figures often cited in connection with the HSV and HSL color models, respectively. These are said to "represent" the two color spaces, or perhaps their gamuts, but it is not at all clear what that might mean. For one thing, these geometric figures are not three-dimensional "plots" of the gamuts of the color spaces in their own native coordinate systems, nor in any other recognizable coordinate system (or color space).

While the tapering of the "bi-hexcone" figure (for HSL) at its top and bottom is said to reflect that some property of the color space is available over a range that declines as the luminance either increases to its maximum (at "white") or decreases to "black", we cannot discern just what that property is - and in any case, the vertical axis of the figure cannot represent luminance (the shape of the figure does not comport with that).

I have just posted to my technical information site, The Pumpkin, a new tutorial article, "The HSV and HSL Color Models and the Infamous Hexcones", available here:

http://Doug.Kerr.home.att.net/pumpkin/index.htm#HSV-HSL

This article investigates the mystery surrounding the geometric figures in depth, with extensive illustrations. The "hexcone" metaphor is traced back to the work of Alvy Ray Smith, who developed the HSV color model.

The conclusion of the article is that the hexcone and bi-hexcone figures do not have any real meaning, do not in any way "represent" the two color spaces or their gamuts, and do not help us visualize any of their properties.

This article is published in celebration of my 72nd birthday, today.
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Old May 9th, 2008, 07:26 AM
Doug Kerr Doug Kerr is offline
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Default Tutorial article - erratum

I discovered late yesterday that in the released version of my new tutorial article, "The HSV and HSL Color Models and the Infamous Hexcones", three figures (now figures 1-3) had inadvertently been omitted.

A corrected version of the article(Issue 2) has now been posted to The Pumpkin. It can be accessed via the same link as previously, which I will give again here for convenience:

http://Doug.Kerr.home.att.net/pumpkin/index.htm#HSV-HSL

My apologies for any inconvenience this error might have caused.

Best regards,

Doug
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Old May 12th, 2008, 08:18 AM
Doug Kerr Doug Kerr is offline
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Join Date: May 2006
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Default The cones, the cones! - tutrial article expanded

I have just posted to my technical information site, The Pumpkin, a revised and enlarged version of my recent tutorial article, "The HSV and HSL Color Models and the Infamous Hexcones".

The article has had a number of editorial "improvements". It also includes a discussion of a rationale sometimes given for the "bi-cone" as a "representation of the HSL color model".

Also included is an appendix discussing in detail a different HSL color model used by Canon in its Picture Style Editor software package.

The updated article can be accessed via the same link as previously, which I will give again here for convenience:

http://Doug.Kerr.home.att.net/pumpkin/index.htm#HSV-HSL

Today is Carla and my "8:11" wedding anniversary (8 years, 11 months). As one of my anniversary gifts to her, I didn't ask her to copy edit this latest incarnation of the article, so my apologies for any editorial anomalies in it.

Best regards,

Doug
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