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The I2TU BT.709 standard calculates relative - apparent - luminance. The HSV space, in turn, provides the ability to change the absolute value of the brightness. The question arose of how to relate these values. Let's say in HSV space the brightness of a color x is 90%, while the formula for relative brightness is 70%. How do I calculate the amount of change in brightness in HSV space so that the relative brightness is, say, reduced to 60%?

I could only get to the trivial option - too much, but I want to find a more effective solution.

Marionette
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  • Complex topic, and many different interpretations. Note: HSV is often calculates as simple formula from sRGB (and forcing ranges, and forcing integers). E.g. pure/primary sRGB blue is often described as 100% brightness (correct from electric point on screen), but we perceive blue as a darked colour compared to 100% green) (and BT.709 has also own problem with luminance). How? Just do the double conversion. With constant hue then you can adapt with a factor. Possibly Wikipedia has direct formula (but check the assumption and limitation of that shortcut) – Giacomo Catenazzi Jul 09 '21 at 07:13
  • I'm not very good at mathematics, so can you please explain in more detail what transformations and how exactly should be performed? – Marionette Jul 09 '21 at 07:56

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