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What does the Lab color values in Photoshop mean?

Forum|Forum|9 years ago
March 30, 2017
4 Antworten
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I am using Adobe Photoshop CS6 in a Windows 7 environment. I am familiar with the L*a*b* color system and color values as, for example, described here Understanding Photoshop color modes

I just opened a photo in RAW format in Photoshop and chose Image > Mode > Lab Color. I looked at the Histogram for each color channel and it does not show the values I expected. For example:

Lightness has a mean value of 109.61 > not between 0 and 100

a has a mean value of 130.67 > not between -128 and 128

b has a mean value of 140.98 > not between -128 and 128.

So my questions: What does these values mean and why are they not within the expected range? How are the values calculated? Is there any way to convert the values to the expected range?

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Beste Antwort von c.pfaffenbichler

I expect all three are given as »0-to-255« and not as percentages or -128 to 128 (which would seem (edited) incorrect in an 8bit file as it would necessitate 257 values).

sharons73627271Autor

Participant

Thanks everyone who replied! This was very helpful, and I know what to do now!

Until next time!

D Fosse

Community Expert

The histogram shows the standard 8 bit 256 values, even in Lab mode where the traditional 8-bit scale is 0-100 (as it also is in CMYK).

The same for a and b channels, the middle point in the readout is 128, not 0.

Don't ask me why it's done this way. But it should be easy to convert if you need it.

c.pfaffenbichler

Antwort

Community Expert

I expect all three are given as »0-to-255« and not as percentages or -128 to 128 (which would seem (edited) incorrect in an 8bit file as it would necessitate 257 values).

sharons73627271Autor

Participant

Thank you so much for your reply, that is very helpful. But is there any way I can convert between the Photoshop values and -128 to 128? I need to compare my values to values that are displayed as -128 to 128.

c.pfaffenbichler

Community Expert

One could create a Script that translates the values or even a custom Panel (I could not, but I assume it is possible in principle), but you have to decide whether the effort is justified.

B

bzareenk

Inspiring

Read this article. Its very informative.

What is Lab Color? – Photoshop Colour Mode – photoshopbuzz.com

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