I'm starting to feel more comfortable now Wayne.
At least, I was not misunderstanding anything from scratch ......... :-)
Your points on Lab promise to be very useful for me, and feel better
after your understanding of wrong procedure or lack of complete info in
that thread. It sort of scared me - because I didn't find any color
shift either !! _ ;-) - but failed to understand why.
Took me about two weeks to think about this point, and the other related
points I mentioned - in an effort to find something in common to the
three techniques.
I apologize for the length of the topic, but once I identified a
question it brought to my mind another one which seemed related.
This quickly resulted in a mess which took me about an hour to put down
in English words ...
So, there's no urgency to have Margulis' book ... could you point to
some other direction, Wayne ?
Thanks a lot.
Fernando.
WayneS wrote:
> At 12:17 AM 12/13/2008, Fernando wrote:
>
>> <snip>
>>
>> Found this very clever
>> <http://www.luminous-landscape.com/tutorials/instant_photoshop.shtml>:
>> "Go to *Image / Mode / Lab Color* and then *Window / Show Channels*. In
>> the *Channels *palette select the *Lightness channel*. Now choose
>> *Filter / Sharpen / Unsharp Mask*."
>>
>> _ and I felt happy for a couple of days, until found this thread:
>> <http://www.luminous-landscape.com/forum/lofiversion/index.php/t28753.html>
>>
>> Wow - if there's trouble when going to sRGB from Adobe RGB '98 (
>> "conversion *intents*" ) - it should be worse when going from RGB to
>> Lab, and coming back to RGB !!!.
>>
>
> I'm not sure the person was operating correctly. It was not clear if
> he was using 8-bit depth, but even more, is implied that if the wrong
> color engine is used, Microsoft ICM versus Adobe ACE Engine, it will
> create the color shifts. I have converted files back and forth, using
> 16 bit depth, and have not see any such effect on color.
>
> There is discussion in Dan's book that when converting out of
> gamut colors between spaces will produce different colors.
>
> But if you start out in sRGB or Adobe RGB 98 and convert to Lab
> and back, you should not see any problems. If you do, then there
> is something wrong in the workflow. Only out of gamut colors should
> see shifts. But all in-gamut color should be OK.
>
>
>> OK, despite it looks right for me, the rationale of a round trip to Lab
>> is confusing. I don't completely understand Lab, and feel too lazy to
>> read Dan Margulis books (http://en.wikipedia.org/wiki/Dan_Margulis).
>>
>
> I work in Lab regularly and to me it is now easier to understand than
> RGB. Lightness is obvious. The AB color is confusing because
> 50% grey is neutral. Reminds me of when I argued with my grade
> school teacher that you *can to* subtract 5 from 3 and get -2. But she
> said you cannot take away more apples than you have. I guess
> that was before credit was invented :-) The gov'ment does it all
> the time now.
>
> It is unfortunate the way Dan Margulis wrote his book requires
> such mental gymnastics from the reader. In my opinion, his writing
> style greatly contributes to the confusion about Lab for most people.
>
> If only someone like Katrin Eismann would write a book on Lab color.
>
> WayneS
>
>
>
>
--
Dr. Fernando González Gentile M.D.
Av.L.P.Ponce 1526B - 11600 Montevideo, Uruguay.
Phone: +598 2 7084858
Fax: +598 2 7087396
<fgnzalez@xxxxxxxxxxxxx>
--
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