Development Pages



Colour Brightness Graph
For a colour, 256 brightnesses in chart form
The down-pointing arrow at the top of the gradations chart shows the brightness of the picked colour. The up-pointing arrow at the foot of the chart shows the selected brightness; a brightness can be selected by clicking on the chart and that then shows in the rightmost sample rectangle.
Brightnesses are calculated upwards and downwards from the picked colour, to give 256 brightnesses in total. At the boundaries, i.e. if a value of any one of the red, green or blue values goes out of bounds as a new brightness is being calculated, the excess is redistributed among the remaining values that are within bounds. This produces a perceptually-smooth spread.
This method of calculating brightness uses all three channels, the red, the green and the blue; it is therefore different from calculating brightness by in effect dragging the rgb sliders up and down in unison, which can only go as dark as the lowest non-zero red, green, or blue value moved to zero, or the highest moved to 255. The unison method is used when simulating filters: see Simulated Colour Filters.
Selected from Graph:
Brightness: RGB:
Brightness calculation formula:
all of the brightness options, including gamma in this context, produce a straight-line graph; each formula has a different brightness distribution

Dave Collier 2020 . . . email me . . .