Setting curves/levels in Lab mode
cocasana
Registered Users Posts: 150 Major grins
Hi there! I was looking for some suggestions on how one should set the white and black point in curves/levels in Lab mode!
I mean..., when you upload one of those two functions, and you double click on the black and white eyedroppers you can set them (in RGB i've set them 13,13,13;242,242,242), but how should one set them correctly in Lab mode? Thank you so much, Carlo
I mean..., when you upload one of those two functions, and you double click on the black and white eyedroppers you can set them (in RGB i've set them 13,13,13;242,242,242), but how should one set them correctly in Lab mode? Thank you so much, Carlo
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Comments
That translates into Lightness values of 2 for blacks and 96 for whites. More or less. Converting from RGB to LAB and back again doesn't involve a color drift (unless you spec some impossible colors in LAB, but even then you wouldn't notice since Photoshop kindly displays the RGB approximation for you onscreen). But neutrals will remain neutral, so you might as well set your black/white points in RGB before converting to LAB.
—Korzybski
Those translations are totally dependent on the monitor profile!
For example, a Lab Lightness value of 5 is 13,13,13 on one PC of mine, while it is 9,9,9 on my laptop in the Adobe RGB working space. RGB is a device dependent color sapce.
The safe values for photo editing according to Dan Margulis (who is a LAB master) is 5L for blacks and 97L for whites.
Katrin Eismann recommends 5B for blacks and 97B on the HSB scale.
Note that HSB gives you different LAB values depending on your monitor profile as well.
Yes, profiles always affect conversions. But, the larger point holds: whatever the profile, and whether or not one starts and ends up in sRGB or Adobe RGB or some exotic space, going from RGB to LAB and back entails no effective shift of hue, and neutrals remain neutral.
Also, while there remains room for discussion on the importance of this point, RGB allows for 256 gradations of value while LAB lightness only permits 100. What this means is that a shadow of 6, 6, 6 in RGB might translate into a lightness value of 2 in LAB, but so will 7, 7, 7, and 8, 8, 8, and 9, 9, 9, as Photoshop, unlike Illustrator, only allows integer values to be used for color specs.
I use LAB for many tasks that are not possible in RGB or CMYK; balancing highlights and shadows is not one of them.
—Korzybski