RetouchPRO

Go Back   RetouchPRO > Technique > Photo Retouching
Register Blogs FAQ Site Nav Search Today's Posts Mark Forums Read


Photo Retouching "Improving" photos, post-production, correction, etc.

RGB CMYK LAB and Dan Margulis !

Reply
 
Thread Tools
  #1  
Old 10-03-2007, 01:22 PM
Hello_taipan's Avatar
Hello_taipan Hello_taipan is offline
Member
 
Join Date: Jul 2007
Location: Belgium
Posts: 68
RGB CMYK LAB and Dan Margulis !

Been reading Dan Margulis these days (thnx adamz!) and a whole new world opened to me: (2 actually) CMYK and LAB.

what brings me to wonder about the importance and avantages of each mode.

Why, when, n how do you guys choose to work in which mode ?
i guess it's not about one being used to work in rgb or cmyk or lab, but rather exploiting the properties of each one.
Reply With Quote top
  #2  
Old 10-03-2007, 02:12 PM
edgework edgework is offline
Senior Member
 
Join Date: Jul 2004
Location: Brooklyn
Posts: 494
Re: RGB CMYK LAB and Dan Margulis !

Quote:
Originally Posted by Hello_taipan View Post
Been reading Dan Margulis these days (thnx adamz!) and a whole new world opened to me: (2 actually) CMYK and LAB.

what brings me to wonder about the importance and avantages of each mode.

Why, when, n how do you guys choose to work in which mode ?
i guess it's not about one being used to work in rgb or cmyk or lab, but rather exploiting the properties of each one.
As Dan likes to say, every file has 10 channels. Even if you don't need CMYK for output purposes its four channels are a great source of targeted masks. Borrowing a black plate for use as a layer mask in RGB and LAB gives you a shot at much more refined shadow work than either space is capable of simply using master RGB curves in luminosity mode (like taking a sledge hammer to open a jewelry box) or the lightness channel in LAB (still too much punch and no subtlety).

The C, M, and Y channels tend to contain more pure color information than corresponding RGB channels simply because the shadow detail has been removed and sent to the black plate. Subtraction operations with Calculations are a good way to isolate specific colors for masking purposes (for example subtracting magenta from Cyan leaves you with a fairly decent green selection).

In LAB, you can achieve similar results using the Blend-if sliders, much more effectively than RGB or CMYK. Each color channel in those spaces affects two different colors at once (Magenta will cover everything from orange to purple, Yellow everything from Green to Orange and cyan shows up in green through purple), whereas in lab, you can focus on red, blue, green or yellow separately, to much better effect.

If your colors are looking dull, nothing brightens them up like LAB. Increasing saturation in RGB is not the same, since by definition, increasing saturation in a color removes what Margulis calls the contaminating hues, which are what provides detail (pull all the magenta out of green leaves and you're left with a bunch of bright green blobs). And there is nothing to compare with his Man-From-Mars technique in LAB for bringing out colors that you think aren't there. A great move (in moderation).

Even if I'm not outputting in CMYK, a move into that space for skin tweaking is always called for. RGB can be a bit of a bludgeon with skin. CMYK curves are far more subtle. And a contrast curve in the magenta channel with the adjustment layer in Luminosity mode works wonders on a face that has more or less correct numbers but looks flat and dead.

And LAB is the space of choice for killing color casts, as far as I'm concerned; one, because you can easily attack color and not mess up the detail, and two, it's easy, with Blend-If sliders, to deal with multiple casts (highlights too red, shadows too green, for example) in a way that RGB and CMYK can have a real problem with.

The a and b channels have some really bizzare applications as well, again because they are targeting discrete colors rather than each channel being a component of an additive or subtractive result. It's possible to use them for color masks that are fairly precise. Dan shows some nifty used by blending them into themselves in overlay mode to enhance tone.

If you don't need CMYK output, it's sometimes a risk to actually convert the file into CMYK, but if you can get away with it, you can bring out much better shadow detail. And sometimes you can copy the file back into your RGB master and just use the enhanced shadow areas, leaving the.

Lots of stuff you can do.
Reply With Quote top
  #3  
Old 10-03-2007, 02:36 PM
lurch's Avatar
lurch lurch is offline
Senior Member
Patron
 
Join Date: Jul 2006
Location: SoCal
Posts: 574
Re: RGB CMYK LAB and Dan Margulis !

Great exposition, edgework. You've given us a good, comprehensive, color space tutorial.

<C>
Reply With Quote top
  #4  
Old 10-03-2007, 02:43 PM
Markzebra's Avatar
Markzebra Markzebra is offline
Senior Member
 
Join Date: Aug 2001
Location: London, UK
Posts: 718
Re: RGB CMYK LAB and Dan Margulis !

Yeah you have to be very careful with LAB, its very destructive if you use it on 8 bit images and convert those straight back and forth. This process compresses the color information into a very small area of the A and B channels. One way to minimise this damage is to convert your image to 16 bit then convert to LAB, do your edits and convert back. Another point that Margulis for some reason took many years acknowledge, is that a lot of the edits achievable in LAB can be done on the original RGB or CMYK document using Blend modes and luminosity/colour calculations. Its not always necessary to damage your file by converting to a different mode.

Margulis is a great teacher, but he has never been great a technician and the folks at Abode have had a few problems over the years with this

Last edited by Markzebra; 10-03-2007 at 03:16 PM.
Reply With Quote top
  #5  
Old 10-03-2007, 02:59 PM
Hello_taipan's Avatar
Hello_taipan Hello_taipan is offline
Member
 
Join Date: Jul 2007
Location: Belgium
Posts: 68
Re: RGB CMYK LAB and Dan Margulis !

Edgework: u're awsome. i now have folders in my head where i can put ideas in order . thanks so much.

Markzebra: thx for the precisions. i had a feeling about these damages when playing around in LAB. now u mention that ill be more careful. i'll investigate the can & cannot do under each mode.

cheers!

Last edited by Hello_taipan; 10-03-2007 at 03:11 PM.
Reply With Quote top
  #6  
Old 11-12-2007, 02:04 AM
jenniferfrances's Avatar
jenniferfrances jenniferfrances is offline
Member
 
Join Date: Jan 2007
Location: New York
Posts: 40
Re: RGB CMYK LAB and Dan Margulis !

Being an owner of about 20 photoshop books, I am fearful of buying 20 more!
Are Dan's books the most comprehensive?
Should I go for "The Classic Guide to Color Correction" or "Photoshop Lab color.."

I am interested in learning more about working with channels & color modes (in hopes that all the material doesn't fly completely over my head)

Which is my best bet?
or does anyone prefer a different author?
Reply With Quote top
  #7  
Old 11-12-2007, 02:41 AM
Michel B Michel B is offline
Senior Member
 
Join Date: Apr 2007
Location: France, Paris
Posts: 153
Re: RGB CMYK LAB and Dan Margulis !

Excellent explanation! I'll keep it with this other great thread:
http://www.retouchpro.com/forums/rp-...power-ten.html
Reply With Quote top
  #8  
Old 11-12-2007, 07:19 AM
edgework edgework is offline
Senior Member
 
Join Date: Jul 2004
Location: Brooklyn
Posts: 494
Re: RGB CMYK LAB and Dan Margulis !

Quote:
Originally Posted by jenniferfrances View Post
Being an owner of about 20 photoshop books, I am fearful of buying 20 more!
Are Dan's books the most comprehensive?
Should I go for "The Classic Guide to Color Correction" or "Photoshop Lab color.."

I am interested in learning more about working with channels & color modes (in hopes that all the material doesn't fly completely over my head)

Which is my best bet?
or does anyone prefer a different author?
If you haven't read Dan's book on Lab, you should, regardless of whatever other sources you might consult. Understanding the inner workings of that space has altered my own workflow considerably. There are moves in Lab that cannot be replicated elsewhere.

His "Professional Photoshop" (latest edition) is also a fundamental source, and repeats virtually nothing from his Lab book. I'm not a disciple, I don't slavishly follow all his advice, and there are many who absolutely disagree with his approaches, particularly if they spend a lot of their time in color labs working with calibration and profiles. Dan's just not "scientific" enough for them, and they're probably right. Thing is, in the real world, where you need to get real results and satisfy pain-in-the-ass clients, Dan's techniques just work; they enable you to immediately improve your thinking about color and to produce results. So for the working stiff, it's hard to find things to complain about.
Reply With Quote top
  #9  
Old 11-12-2007, 06:25 PM
Markzebra's Avatar
Markzebra Markzebra is offline
Senior Member
 
Join Date: Aug 2001
Location: London, UK
Posts: 718
Re: RGB CMYK LAB and Dan Margulis !

Yes - if your a beginner you may find the LAB book quite frightening. Being comfortable in a color space means taking the time to work in there. If you are used to RGB color correction there is nothing wrong with it, there are powerful Saturation moves and many of the things achievable in LAB are actually achievable within the confines of RGB. Photoshop uses LAB anyway behind the scenes to calculate things like Color range and blending. CMYK also has its uses, as an abstract space. Margulis argued for years that Professionals should always color correct in CMYK and his Professional Photoshop, is still a CMYK based book. Probably the best written but a little flawed. If you want to learn CMYK, and you should if you want a full grasp of the subject, its great

One new way to work with other modes Ive never heard mentioned yet by Margulis or anyone else - is the fact that you can use Smart Objects to do a lot less damage. Ill try and give you an example - duplicate your Background layer, convert the duplicate to a smart object. Open the duplicate and then convert the Smart Object LAB. Attach a LAB curve or any other adjustment to the Smart object and save it. Now use blend modes, blend if, to make the converted LAB version of your file interact with RGB base pixels. Now back in the master document you potentially have the full power of the 10 channels at your disposal, with no converting the base pixels back and forth. You could have both a LAB and a CMYK version of your file residing in the original, with all the power that entails - channels can be copied back and forth.

Last edited by Markzebra; 11-12-2007 at 06:32 PM.
Reply With Quote top
  #10  
Old 11-12-2007, 07:04 PM
Tom K's Avatar
Tom K Tom K is offline
Member
 
Join Date: Feb 2006
Location: In the middle of Connecticut
Posts: 50
Re: RGB CMYK LAB and Dan Margulis !

Hi JeniferFrances,

Dans book, "The Classic Guide to Color Correction" is a real head-banger.
Every time I try to read and understand more than a few pages at a time
I bang my head on the keyboard as I doze off to sleep..
The book is excellent but for me a very slow read.

I would highly recommend it...... Tom
Reply With Quote top
Reply

  RetouchPRO > Technique > Photo Retouching


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Photoshop Channel concepts: The Power of Ten Graphics23 RP Tutorials 102 07-27-2011 11:57 AM
LAB Book mdavis Non-RetouchPRO Resources 14 08-08-2006 08:24 PM
Reconsidering 16 bit Ed_L Input/Output/Workflow 14 11-01-2005 10:41 AM
Dan Margulis Lab color DannyRaphael Non-RetouchPRO Resources 0 10-28-2005 12:44 PM
PC/Win filter for Lab mode: Minor ab Manip Stroker Software 15 09-25-2005 08:16 PM


All times are GMT -6. The time now is 11:12 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
SEO by vBSEO ©2011, Crawlability, Inc.
Copyright © 2016 Doug Nelson. All Rights Reserved