RGB/Lab coding

[mikemeister_admin]

Hi,

I'm puzzled by the numbers attached to a colour in different colour models/profiles.
When I pick up a colour in Photoshop, say red as (255,0,0) then Photoshop gives Lab representation  (63,90,78)
And this will change depending upon which colour profile used.
I've not been able to reproduce the Lab numbers from the course material  (51,81,70).

How may this be explained?

sikarlse.

[-default]

The Lab numbers represent an absolute color and brightness, while RGB numbers depend on the working space.  So, for example, in Adobe RGB, RGB(0,0,255) is a more intense blue color than the same color values in sRGB.

In general, the course material assumes you are working in sRGB, though this is not really required, and you can work in whatever color space you like for a particular image.  Be careful with screenshots - they are usually only approximations of the original RGB values.