Is L (Lightness) 0–255? Or 0–100?
Searching online says the range is 0–100, but when I look at Photoshop, isn’t it usually 0–255?
For A, is it green and red, or magenta? Why do different sources or regions describe it differently, with some people saying it represents red?
What do positive and negative values mean?
Why does a negative value represent green, while a positive value represents magenta?
In CIELab the colour is split into three components:
L is Lightness and ranges from 0 to 100 (You can check this in the colour picker which works in integers)
a is green - red with negative values towards green and positive values towards red. In Photoshop it is clamped between -128 and +127
b is blue to yellow with negative values towards blue and positive values towards yellow. Again, in Photoshop, it is clamped -128 and +127
As for the descriptions in different regions it probably comes from the vague nature of a description such as ‘Red’. Red as in RGB 255,0,0 when converted to Lab has a positive a (red) component and also a positive b (yellow) component. Without that b component it tends toward magenta.
You can experiment with the colour picker by clicking on the circle next to L and altering the Lab components to see the resulting colour.
Dave
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