Colour Brightness Experiment
Colour Brightness Values

Colour Brightness Levels : Greyscale
STW*
0 0 gXYZ
0 0 sXYZ
0 0 XYZ
0 0 gYIQ
0 0 sYIQ
0 0 YIQ
0 0 Lightness
0 0 Average
0 0 
STW*  The SEEMS TO WORK formula devised by me and described on Readable Text in Colour – STW*. 
gXYZ  Inverse gamma using the XYZ coefficients of R: 0.212655, G: 0.715158 and B: 0.072187, inverse gamma as described on StackOverflow. 
sYIQ  Inverse gamma using the YIQ coefficients of R: 0.299, G: 0.587, B: 0.114, YIQ coefficients also known as Digital CCIR601. 
sXYZ  Square root using the XYZ coefficients: sqrt((0.212655*(R^2)) + (0.715158*(G^2)) + 0.072187*(B^2)). 
sYIQ  Square root using the YIQ coefficients: sqrt((0.299*(R^2)) + (0.587*(G^2)) + (0.114*(B^2)). 
XYX  0.212655*R + 0.715158*G + 0.072187*B, also known as the Luminosity formula, see Puzzling Greys. 
YIQ  0.299*R + 0.587*G + 0.114*B, as in the Web Accessibility Guidelines from the W3C, see Holes in the W3C Colour Readability Guidelines. 
Lgt  Lightness: ½ × (max(R,G,B) + min(R,G,B)), see Puzzling Greys. 
Avg  Average:(R + G + B) ÷ 3, see Puzzling Greys. 
STW* Exponent  The exponent for the SEEMS TO WORK formula devised by me and described on Readable Text in Colour – STW*. This field enables the exponent for the formula to be varied. 
Fractions  To calculate the next brightness level the code goes up in one hundreds of a brightness level for each of the red, green and blue elements. This therefore gives an accurate value for each of the 255 levels. 
+1  To calculate the next brightness level the code goes up by 1 for each brightness level for each of the red, green and blue elements. Sometimes it might need to increment by two. This therefore gives a rough value for each of the 255 levels, most of the time it should be right, but not guaranteed. 
Redistribute Excess  When, in calculating the next brightness level by adding to the previous brightness level, one of the triad is greater than 255, its excess over 255 is redistributed to the other two elements of the triad, see StackOverflow for the formula for how to do this. 
Clamp  When, in calculating the next brightness level by adding to the previous brightness level, one of the triad is greater than 255, it is clamped at 255 see StackOverflow for the formula for how to do this. For certain hues this changes the hue slightly in the upper brightness ranges. 
This page is now to be found at landofinterruptions.co.uk/colourbrightness