I'm going to have to ping Bruce and see if he did this purely as an interesting exercise or he feels that its useful, because just about every color geek I respect in the US thinks this L* stuff is a bunch of baloney. There was a rash of long but interesting discussions last month on all this, some good posts by both Karl Lang and Chris Murphy which basically points out, this is a solution in search of a problem. [{POST_SNAPBACK}][/a]
Actually Karl Lang created this space back in 2005 (with permission of Bruce L.) after I bothered him long enough. It happens that this is just a local call for me. Perhaps you remember the initial discussion in the robgalbraith forum.
Its a big deal in Europe, but the bottom line is, no one there from the list had anything useful to prove that this is of use.
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No problem. It’s after midnight here, so you may allow me just to quote from an earlier discussion (with Gernot Hoffmann):
>> Further, for introduction: Tonal settings in Photoshop can be calculated on a pure RGB basis, completely ignoring the underlying gamma. I won’t say that Photoshop operates this way, but it’s possible to do this on a descriptive basis.
For example, moving the Levels’-blackpoint slider to the right, subtracts a respective value from all RGB data in the deep shadows. The more general equation should be:
RGBout = a x (RGBin - BP)
a = 255 / (255 - BP)
wherein BP refers to a Levels’-blackpoint setting from 0 to a value BP
Now let’s take a brief, 3-step grayscale in Adobe RGB with dark grays of RGB 9, 16 and 21. In a copy file (!) and converted to sRGB (!), this makes 4, 7 and 13. Understandable, due to the lower local gamma of sRGB. Nonetheless, both grayscales should look right the same on screen.
The next step is mentioned ‘image editing practice’ to move the Levels’-blackpoint slider towards a value where the first patch reaches zero. In case of Adobe RGB, the value for BP setting is 9. In case of sRGB, the value for BP setting is just 4 (see above numbers).
Now what is the result. The grayscale in Adobe RGB turns to RGB 0, 7 and 12. Whereas with the copy file ‘in’ sRGB the new grayscale is 0, 4 and 9. Big difference!
Zero to 12 in Adobe RGB corresponds to below / equal L* 1. A critical range and the grayscale tends to disappear on screen. Zero to 9 in sRGB goes up to L* 3. The steps should stay clearly visible on screen or print.
Just give it a try.<<
Another aspect is that a numerically lower BP setting is less damaging for [a href=\"http://www.c-f-systems.com/Phototips.html#RAW]Color integrity[/url] a la David Dunthorn.
Andrew, - we really don’t have to argue here. At the end of the day, I find the implementation with LR/ACR (acting on linear data while showing a gamma encoded histogram) better than to combine the two contradictive requirements in one working space. Just in Photoshop, I would not use a straight 2.2 gamma space, even though I notice that many liked Adobe RGB.
Please note, I’m not at all talking about this “L* monitor calibration & profiling” thing here.
Peter
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