# In RGB, what is each step from 0 to 255 called?

From the Wikipedia page on the RGB color model -> Numeric representations:

A color in the RGB color model is described by indicating how much of each of the red, green, and blue is included. The color is expressed as an RGB triplet (r,g,b), each component of which can vary from zero to a defined maximum value. If all the components are at zero the result is black; if all are at maximum, the result is the brightest representable white.

What exactly is each step in one channel/color? What does it increase? Luma? Intensity? Saturation? Chroma? Chrominance?

• Intensity, terms luma, chroma, saturation are names of channels in other color systems. There is also no definition for one step the stepping by no means has to be 0 to 255 Commented Oct 12, 2014 at 15:41

## 2 Answers

Interesting question!

I honestly don't understand Luma, Chroma and Chrominance well enough to explain why it is or isn't increased by adding to one or more of the channels. It might increase them, or it might not. I wouldn't know.

It definetly does NOT increase saturation. If we start at (0, 0, 0) and add the same ammount to all channels, the saturation stays zero.

However, adding to a channel increases Brightness. This is intuitively true, given that the color component on a screen shines brighter for higher values.

It is also well defined, that is,

brightness = (R+G+B)/3

Source: Wikipedia

• Historically, it increased the voltage to the red, green, or blue CRT element. A curse for graphic designers and programmers, because this is not a linear function, and each CRT element also had a "response curve" of its own. One may assume modern hardware tries to emulate this original behavior; if not, "old" digital images would look off-tone. Commented Oct 12, 2014 at 13:28
• @Jongware actually its nonliear because our eye is nonlinear. Commented Oct 12, 2014 at 21:05

I don't think the increase necessarily refers to a change in color that is the same for each increment. Mac, windows, Photoshop etc each have their own 256 palette and resulting indices. Each individual color, RGB, will have a 0-255 number indicating the relative amount of that color in the "blend"