RGB values and color space

[Doc_Pit]

I'm just trying to check my understanding of color space.  Given that sRGB is a subset of Adobe RGB, I would expect that any color that falls within that common, overlapping area would have the same RGB numeric values; i.e., changing from Adobe RGB to sRGB would not alter the numeric values  of any color that is common to  both gamuts. Is that correct?  (I ask because sometimes things that seem straightforward are not.)

[D Fosse · Accepted solution]

No, it's the opposite. In any color space, you have the values 0 - 255 in each color channel. You have the same number of steps in the ladder, but some ladders are longer than others.

That's why all numbers have to be remapped when going from one color space to another. That's what the profile conversion is. All the numbers are recalculated.

[Doc_Pit]

I should have seen that.  Yes and thank you.

[NB, colourmanagement net]

No

The same RGB values have different meanings in different colourspaces

the colourspace profile provides the meaning relative to human colour perception

How:

An ICC profile provides a table between RGB and Lab or XYZ (amongst other things) - Lab or XYZ refers to visual appearance.

Lab or XYZ values for a particular RGB 'triplet' in Adobe RGB has quite a different meaning to the same RGB triplet in sRGB.

I hope this helps

neil barstow, colourmanagement.net :: adobe forum volunteer

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