Relationship: RGB, Tone values & Brightness

Here’re my questions:

1. Are RGB values and Tone values being used interchangeably?

2. How is Brightness related to RGB values? For that matter, is RGB (130,130,130) brighter than RGB (127,127,127)?

Thanks.
Jc1

Hi jc1,

Here is my try

AFAIK they are linked up to each other but not interchangeable. Tone value just indicates the luminance (light/dark), whereas RGB contains both color information and luminance information.

Yes, RGB (130,130,130) is a bit brighter than RGB (127,127,127). On a 8 bit image, you have 255 tone steps for each channel (R= Red, G=Green, B=Blue channel) from 0 = black to 255 = white.

In your example RGB (130,130,130) indicates a lighter grey colour than RGB (127,127,127). So you see, if all color tone value are equal, you will get a grey color.
To express in another way, the color details are containing in the relation of these 3 RGB values. For example pure red will have (255,0,0) as RGB value. In theory all red tones are ranging from (1-255, 0,0), green tones (0, 1-255, 0) and blue tones (0,0, 1-255)...

Hope I could help a bit.

Hoang-Tran

hi

The parameter called B or "Brightness" in particular means something quite different in HSB space to absolute brightness, and will be referred to here as relative brightness. B measures the brightness of a colour compared to the maximum possible for a colour of the same hue and saturation, which means having the same ratio of R/G/B. The numerical value of B is given by the brightness of the brightest RGB component as a percentage of 255. Thus all colours having at least one RGB component equal to 255 are said to have a brightness of 100.

Thanks