Remove brightness limitation

[maandree]

I cannot see any reason why the upper limit for brightness is set at 1,0, and I think it should be removed because it is (I beleave) an artifical limitation without reason, other than perhaps that colours start to look wrong above 1,0. Sure you would probably not combine decreasing the colour temperature with extra brightness. However, (1) redshift supports making the screen bluer rather than reder and in that case you might prefer that and (2) you may want to use redshift instead of xrandr (or wantever) to configure gamma and brightness as you would also be able to configure temperature.

[jonls]

No, it is actually not an artificial limitation. The kind of "brightness" adjustment that Redshift does is a fake brightness using the gamma ramps (which are also used for the redness effect). Redshift does not actually adjust the screen or the backlight, but just the pixel values that are sent from the graphics card. Since the pixel values have a max of 1.0, the brightness has a max of 1.0.

The brightness setting of Redshift was requested in the past but I'm actually considering maybe removing it in the future or maybe putting a big warning on it since it seems to be widely misunderstood. The tool xbacklight (or similar) is the best way to adjust the brightness because it actually adjusts the light source in the screen directly. The brightness setting in Redshift can be useful (maybe) in a few cases where the screen adjustment is too coarse grained or does not work for some reason, I can't really think of other use cases. Maybe some day Redshift will be able to adjust brightness through the same mechanism as xbacklight, but there are issues with that too and it will be tricky to implement correctly.

[maandree]

xbacklight be used with CRT:s and a graphics device needs to suppot backlight. So the next best thing might be xrandr --brightness and when that is used, the effects of redshift are reset. Is truncating the value to 1,0 difficult?

[jonls]

From the xrandr man page

Multiply the gamma values on the crtc currently attached to the
output to specified floating value. Useful for overly bright or
overly dim outputs. However, this is a software only modifica‐
tion, if your hardware has support to actually change the
brightness, you will probably prefer to use xbacklight.

This seems like the same thing as Redshift implements. As I understand it you'd like to set brightness above 1.0 because that is possible using xrandr? I guess that could be done, but I'm not sure I understand how that would be useful. It would introduce unexpected visual effects because we can't go above a pixel value of 1.0. I'm afraid that people already confuse brightness and backlight, but for values in [0;1] that is not a huge problem because at least it works more or less as expected. Allowing values above 1.0 changes that so that suddenly the result is unexpected. I'm willing to consider the change but it would have to come with a big warning I think.

[maandree]

xrandr has no upper limit (or lower, you can actually have it set to a negative value).
I do not see it as important to be able to do this but I do not see why it should not be possible.
It could be useful if you want to use redshift (perhaps for making the screen blue) but also a bit brighter than it usually is.

I agree that it the unexpected effects deserves a warning, but haps it should not be possible to use values above 1,5 or below 0,1 if a special options is not used. This values could make it impossible to read what is on the screen.