Re: Lab working space vs. LCH
Re: Lab working space vs. LCH
- Subject: Re: Lab working space vs. LCH
- From: Don Hutcheson <email@hidden>
- Date: Sat, 26 May 2001 13:58:15 -0400
I completely agree with Chris Cox. In fact It's a relief to hear him putting
Lab in it's place.
For computational reasons, CIELab is a convenient and relatively
well-proportioned color space, at least for certain functions. But the a*
and b* units are 100% non-intuitive and have no parallels in art or
photography. You can learn to manipulate a* and b* (with difficulty) but I
can't think of one good reason to bother.
Attempting to work in Lab to do photographic changes just takes more effort
than RGB. Over the years I've found that if you can't correct a photographic
problem in RGB, you're looking at it wrong. Sure, there are some cool tricks
you can do in Lab, but switching in and out of Lab just to do something
weird should be avoided except in creative situations.
Lab appears to make some people feel more powerful (or important) but to my
mind, it just slows things down. I've always applauded anything that
simultaneously simplified and improved the process of scanning and color
correction. Lab does neither.
The one useful thing about Lab, as Chris points out, is L*, but the best way
to access L* is in LCH (Lightness, Chroma and Hue.) CIELCH(ab) is a really
useful, portable and standardized color space that also happens to be
visually INTUITIVE. As a test I taught my son when he was 6 to understand
colors in terms of LCH (I used the word Saturation instead of Chroma). He
had no trouble grasping it and teaching it to his class. Imagine trying to
teach a 6 year old Lab or CMYK!
LCH was the default control system for most of the editing tools in
Colorblind Edit (CBE), even tools that worked on the RGB curves. It was a
delight to be able to change the lightness alone, or the hue alone, or the
saturation (Chroma) alone, of a point on a set of RGB curves, or a selected
color. In this respect CBE walked all over Photoshop for quick, intuitive,
photographically natural moves.
You can sort of use LCH in Photoshop via the Hue/Saturation control, which
lets you alter colors in terms of Hue, Saturation and Lightness, the Edit -
Fade function, which lets you modify a change in various ways including
Luminosity, Hue and Saturation, and the Mode condition for Layers, which
also includes Luminosity, Hue and Saturation options. Unfortunately some of
these don't seem to work in true CIELab-based LCH, but rather in a fast but
crude RGB approximation. For example, when you completely desaturate an RGB
image, light and dark colors end up at the same lightness, indicating the
math did a simple averaging of RGB, not a true calculation of relative
lightness. Nevertheless, these are some of the most powerful and
under-utilized features in Photoshop.
One of the most common suggested reasons for using Lab in Photoshop is to
sharpen the L* layer. You can do the same thing much more efficiently by
sharpening the RGB or CMYK image and then fading the USM as Luminosity. In
fact a nice feature would be an "L*" switch or Mode condition in the USM
dialog.
With gentle and polite persuasion from enough users, I bet we can get Chris
and Adobe to look at expanding the range of true CIELCH controls in
Photoshop. This would improve Photohsop's usefulness in a truly
device-independent ICC workflow, add a nice professional touch and make a
fun project, don't you think Chris?
Don
*************************************
Don Hutcheson
Hutcheson Consulting
(Color Management Solutions)
www.hutchcolor.com
11 Turnburry Rd
Washington, NJ 07882
Phone: (908) 689 7403
Fax: (908) 689 5305
Mobile: (908) 500 0341
email@hidden
*************************************