Colour Brightness Experiment

There are two colour panels, one left, one right, titled Base Colour and Adjusted.

To the left of the colour panels there are four sliders.

The leftmost slider adjusts the BRIGHTNESS of the base colour that is in the left panel and shows the result in the right panel.

The three RGB sliders that are to the left of the colour panels adjust the colour (hue) in the leftmost panel, when you move them they simultaneously set the rightmost colour panel to match the leftmost, which they have to do, if you think about it.

The three sliders to the right of the colour panels are not for sliding by hand, they show the brightness RGB values of the rightmost colour panel. They are there as sliders solely to show the RGB values in a graphic format that is relative to the sliders on the left.

to the right of the colour panels, where it says ‘Colour Brightness Value’ there are nine options, each one showing the brightness value of both the base colour (the leftmost colour panel) and the adjusted colour (the rightmost colour panel).

Each of the Colour Brightness Values is expressed according to a different formula.

There are different ways to calculate greyscale from a colour. They all work well for different jobs.

Key:

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	0.212655R + 0.715158G + 0.072187*B, also known as the Luminosity formula, see Puzzling Greys.
YIQ	0.299R + 0.587G + 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.

† The Steps Type boxes and buttons specify different ways to calculate brightness levels, as follows. Note that some of these difference are marginal with some colour triads, it varies.

† Steps Type Key:

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.