The following two guidelines in the standard specific Ranking Criteria don't really do a great job at recommending/advising against what they're intended to do.
Reason being that the in game "luminosity" (the L in HSL), which can be seen when selecting a custom colour, is not actually perceived brightness, but rather the lightness of the colour. This means regardless of hue, a colour with the same lightness will end up having the same "luminosity" (see HSL/HSV in the below picture).
The human eye is naturally more sensitive to green/red than blue, leading to colours like yellow being apparently brighter than blue, something which HSL does not account for.
Because of this, blue colours at the minimum accepted luminosity will be much darker than yellow colours at the same threshold, leading to inconsistencies in the perceived brightness recommended. This does not make sense considering that the intention of both guidelines is to prevent combo colours from being too visually bright or dark in gameplay.
I would propose using the HSP Colour Format instead of the in game one for measuring this. The thresholds specified here are the equivalent to what the old guidelines had. Adding the formula as part of the glossary prevents issues rooting from relying on third party sources.
Following these changes, colours such as these would no longer be recommended (the brighter ones only in kiai), but are fine according to the current guidelines:
Whereas these would be fine even after the changes:
These are not recommended according to current guidelines (again brighter ones only in kiai):
Whereas those same colours would be fine after the changes, until made like this, at which point they would no longer be recommended:
Only problem with this is that it's much less convenient to find whether some colour is potentially too dark/bright, since you can no longer simply look at the "lum" value in the custom combo colour window, but it is a lot more accurate in determining the brightness, and has neither any false-negatives nor false-positives unlike the current method.
These are guidelines and don't necessarily need to be applied very strictly, so favouring accuracy over convenience would make sense. It is also easier to judge the brightness of combo colours like this using common sense, since they are now literally how bright or dark you perceive them to be, rather than based on some "lum" variable behind the scenes.
osu! Ranking Criteria wrote:
Avoid using combo colours, slider borders or hitcircleoverlays with ~50 luminosity or lower. Dark colours like these impact readability of approach circles with low background dim and the other elements partially give up their functions as borders.
osu! Ranking Criteria wrote:
Avoid using combo colours with ~220 luminosity or higher during kiai times. They create bright pulses which can be unpleasant to the eyes.
Reason being that the in game "luminosity" (the L in HSL), which can be seen when selecting a custom colour, is not actually perceived brightness, but rather the lightness of the colour. This means regardless of hue, a colour with the same lightness will end up having the same "luminosity" (see HSL/HSV in the below picture).
The human eye is naturally more sensitive to green/red than blue, leading to colours like yellow being apparently brighter than blue, something which HSL does not account for.
Because of this, blue colours at the minimum accepted luminosity will be much darker than yellow colours at the same threshold, leading to inconsistencies in the perceived brightness recommended. This does not make sense considering that the intention of both guidelines is to prevent combo colours from being too visually bright or dark in gameplay.
I would propose using the HSP Colour Format instead of the in game one for measuring this. The thresholds specified here are the equivalent to what the old guidelines had. Adding the formula as part of the glossary prevents issues rooting from relying on third party sources.
Proposal wrote:
Perceived brightness: The brightness of the HSP Colour Format is calculated using the following formula:
sqrt(0.299 * R ^ 2 + 0.587 * G ^ 2 + 0.114 * B ^ 2 )
Proposal wrote:
Avoid using combo colours, slider borders or hitcircleoverlays with ~53 perceived brightness or lower. Dark colours like these impact readability of approach circles with low background dim and the other elements partially give up their functions as borders.
Proposal wrote:
Avoid using combo colours with ~233 perceived brightness or higher during kiai times. They create bright pulses which can be unpleasant to the eyes.
Following these changes, colours such as these would no longer be recommended (the brighter ones only in kiai), but are fine according to the current guidelines:
Whereas these would be fine even after the changes:
These are not recommended according to current guidelines (again brighter ones only in kiai):
Whereas those same colours would be fine after the changes, until made like this, at which point they would no longer be recommended:
Only problem with this is that it's much less convenient to find whether some colour is potentially too dark/bright, since you can no longer simply look at the "lum" value in the custom combo colour window, but it is a lot more accurate in determining the brightness, and has neither any false-negatives nor false-positives unlike the current method.
These are guidelines and don't necessarily need to be applied very strictly, so favouring accuracy over convenience would make sense. It is also easier to judge the brightness of combo colours like this using common sense, since they are now literally how bright or dark you perceive them to be, rather than based on some "lum" variable behind the scenes.