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
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