he block on the left below shows monitor RGB red, green and blue in brightnesses 255, 192, 128 and 64 (e.g. RGB 255,0,0 192,0,0, 128,0,0 and 64,0,0 for red). The block on the right shows these converted to greyscale by the formula that is selected from the options panel: this page is interactive, you can click in the radio buttons and checkboxes.
The numbers in the monocrome squares show the brightness level 0-255 by the:
SELECTED BRIGHTNESS CALCULATION FORMULA
N
ote that some formulas are more convincing than others when looked at this way. The linear formulas (which includes Lightness and Average under every condition) are especially weak.
omit brightness values
And there are the print colours: Yellow, Cyan, Magenta, also in brightnesses 255,255 192,192 128,128 64,64 (e.g. yellow 255 is made up of 255 red and 255 green).
And then there are twelve hues separated on the color circles by 30°, i.e on the HSV or HSB colour space they are hues 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300 and 330°. At any given brightness level each of these should look about equally bright. Some brightness calculation formulas work better than others with this. See too my page Equivalent Colour Brightnesses.