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Author Topic: Dan Margulis' LAB mode book  (Read 7013 times)
PeterLange
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« Reply #20 on: September 23, 2005, 02:27:11 PM »
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PeterLange, I'm a good way into the book and I haven't come accross any mention yet of blue turning purple - but perhaps it may surface later on in the context of something more important - I'll see by the time I'm finished.

.... You sound like a very bright fellow, but there really is no substitute to reading the book before raising issues about whether or not it addresses, confirms or debunks your own particular insights.
Mark,

1+1= 2, 2+2=4, and changing color saturation on Lab basis is prone to change the perceived hue (see Real World Color Management p.71, or Bruce Lindbloom’s concept for a Uniform Perceptual Lab).  Just try said chapter 1 technique to boost both a & b channels simultaneously, and compare HSB hue before / after (in particular relevant for blue to magenta hues).

If the principles of Lab edits are once understood on a 3D basis, it’s hard to call Lab the most powerful color space (anymore).  Otherwise, we would have to ask why all other known color gurus did not recognize this, yet.

If Dan’s book only provides a cheerleading perspective on Lab, I’d downgrade it to about point 42 on my reading list.  If it also provides a critical review on Lab including strength & weakness analysis, I’d place it among the top ten.  Awareness of a problem is the first step to overcome it … imo.

Aren’t we all here to gain (& share) some knowledge and to save some time on this way.

Cheers! Peter

--
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Mark D Segal
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« Reply #21 on: September 23, 2005, 03:20:46 PM »
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Peter - yes I've seen page 71 of Real World Color Management and it simply confirms the obvious fact that nothing in this world is perfect - including LAB - but as they also say in the "Real World" in this case it hardly matters. That's why I discounted the importance of the blue/purple issue in my previous post.

And I agree with you - we engage in these discussions to be helpful to eachother - that is why I recommended that you read the book. One of its serious qualities is that it very carefully distinguishes the kinds of situations where Lab is preferable for doing certain things and those where RGB or CMYK would be preferable (much of which sails clear over the heads of many people - on other websites of course, it wouldn't happen here, heavens forbid - who have been blabbering alot of stuff they haven't properly digested). So by your criterion, I think the book goes from 42 to 8 (or somewhere else between 1 and 10 - I don't know what else is vying for high priority on your list - I've lost track of mine there is so much - a very bad thing indeed ).  Cheesy  Cheers.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
Tim Gray
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« Reply #22 on: September 25, 2005, 12:24:06 PM »
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Just spent this am playing the the basic technique in Chapter 1.  Even with just this one chapter (actually only the first half) I consider the $ well spent.  I re-processed some of my shots from Dead Horse Point and Canyonlands (ideal candidates) and while the end results were not necessarily any better than my previous processing efforts, they were significanly faster and less painful.  I also processed a city skyline night shot and the subtle pop of color was something I would not have likely achieved in my normal workflow.  Margulis makes it clear that not all shots benefit from a LAB treatment, but a number do.
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Graham Welland
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« Reply #23 on: September 25, 2005, 03:09:58 PM »
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One thing I found after using LAB for image optimization was that I'm missing a feature in PS to allow me to keep layers reflecting the application of curves in LAB mode and my other manipulations using RGB.

I like to keep my PSD files with all adjustments as adjustment layers so that I can always go back and tweek images as I become aware of new/better techniques, my PS skills get better or just to revisit and try something new. With RGB/LAB mode conversions I have to flatten the image when I change modes so to keep a full history I have to save a LAB mode file & adjustments and then copy the RGB result back into a new layer in my RGB master.

Not a big deal but something that might be a nice feature for Photoshop 11/12 etc.

I've found that some of the LAB techniques combined with blending modes & masks have eliminated in one step some RGB adjustments that took multiple adjustment layers to achieve a similar result.

Ultimately Dan's book (and his previous adjustment by numbers book) provide additional tools to add to your Photoshop arsenal. Use them when you need them, or don't.
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Graham
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