Some observation about RGB duck vs LAB duck

[mikemeister_admin]

Hi,
The first screen is after setting S/H/N using wizard in LAB, and the second after doing the same thing in RGB. As you can see, I was able to make both aluminum band and the duck's chest close to neutral in LAB, but failed to achieve the same in RGB: no matter how I moved neutral point around the band, I couldn't make white chest feathers neutral. Hmm...
As for end results, the version I like the best is the one that I've done using both photoshop tools and CM: Auto Levels followed by using CM wizard in LAB, and then Saturation boost (the last screen).

[ggroess]

Leonid,
Part of the reason for the neutral trouble in RGB is the brightness difference.  The Band is darker than the feathers and you actually can adjust for both to be neutral.  One of the assignments later in the course is a "Color By The Numbers" correction using RGB. 

Try to make the same correction in LAB without the wizard and using only CM.  Try it without the auto levels. 
Please read the following articels:

http://www.curvemeister.com/wiki/index.php?title=Highlight_and_Shadow_Thresholding

and

http://www.curvemeister.com/wiki/index.php?title=Thresholding_Using_Highlight_and_Shadow_Points

In CM you can set the levels at the same time as you adjust the color. 
Greg

[mikemeister_admin]

Even if it is possible to make both band and feathers neutral in RGB, it seems that its just easier to do it in LAB. I don't have much experience with LAB, so one of the reasons I did the duck both in RGB and LAB was to see what LAB has to offer. So far, I like it: LAB definitely makes some corrections easier and faster (and there also is wgCMYK, can't wait to learn what it has to offer!).
About doing "Auto Levels" before correcting in CM. My reasoning was following: because of LAB nature, it is not possible to achieve in LAB what "Auto Levels" does. And I do like "Auto Levels": in many cases it makes image better. In case of the duck, "Auto Levels" removed some of the color cast and made duck look more natural to me. This is why I used it, to remove the color cast, not because I didn't know how to do thresholding in CM. And it took only few mouse clicks. So, here is a question: is there some keyboard shortcut in CM for "Auto Levels"-like correction?

[ggroess]

One of the problems with auto levels is you are letting the program choose for you what is the highlight and shadow threshold.  The easiest way to get this out of LAB is to remember that color is separate from brightness in LAB.  You can use the channels in CM to see the L channel.

Click on the lightness channel in both places shown in shot1 your image will look like shot2.
Make adjustments to the L channel as needed like shot 3.

See next posting


Greg

[ggroess]

Shot 6 is the after and before of the image and shot 7 is the auto levels.

Note the color shift from Auto levels....

[j2e4a8n]

Hi,

It seems to me that if the file is in RGB there will be a color shift.

If the file is in LAB there wont be a color shift.

Jean

[ggroess]

that is true because in LAB the color is separate from the brightness