Participant

Question

changing LAB values

Forum|Forum|4 years ago
June 13, 2021
3 replies
4398 views

In Photoshop, I create a color fill layer with the LAB color 80,120, 80 (RGB is 255,0,60). Then I go back with the eyedropper on that fill layer and the LAB color has changed to 55,81,45 while the RGB color values are the same at 255,0,60. Why does the LAB values change (although the actual color does not)?

Problem or error

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D Fosse

Community Expert

Not at my workstation to test right now - but are you all sure that Lab color is within sRGB gamut? It's at least right at the gamut boundary if it produces R 255 and G 0 right off.

D Fosse

Community Expert

Just checked that Lab color, and it's way way out of sRGB gamut. It's also slightly out of Adobe RGB gamut (which you can just see on a wide gamut monitor).

In other words, all bets are off here. Small inaccuracies can be expected at the gamut clipping point.

TheDigitalDog

Inspiring

I don't see gamut the issue; the reported numbers are the problem. It should be consistent in both locations and isn't. PS “knows” the color space when entering the numbers in the first place and presents them incorrectly.

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

Chuck Uebele

Community Expert

I believe L*A*B* values only go up to 100, not 255, like RGB, so I'm not sure how you got 120, but if you managed to input that, PS most likely adjusted the values.

TheDigitalDog

Inspiring

Lab value should go to -128/127.

Again, all I did was make a new document in sRGB.

Foreground color set in Lab to 80/120/80. PS totally allows that.

RGB values are what the OP reported.

Fill with foreground color.

RGB values are OK, Lab values are way off.

Can someone else try this and let me know what they see? The lab values reported in the Info Palette should of course show 80/120/80. I get Lab values of 55/81/45. Boom, head exploding.

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

Chuck Uebele

Community Expert

I was going to try, but my Adobe apps are all screwed up, due to some issue trying to verify my subscription status. Dead in the water right now.

TheDigitalDog

Inspiring

Need to see a screen capture but keep in mind, a Lab value is a fixed value, but the RGB values may not be (for example, if you converted from Adobe RGB (1998) to sRGB).

Is it possible you've got a layer with some Blending Mode on?

What is the RGB Working Space?

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

TheDigitalDog

Inspiring

Hold on, I just tried this in sRGB. Looks like a bug! Indeed, the info paleete showing Lab is wrong no matter the sampling size. I made an entire new document in sRGB with Lab 80,120, 80 and the foreground picker shows 255/0/60 yet the info palette shows RGB is 255,0,60. That's messed up.

I'll fill a bug report.

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

J

jaramdAuthor

Participant

Wow!

Nice catch, thanks for checking it out... thanks...

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