Hi Uwe, On Fri, Aug 16, 2019 at 06:51:48PM +0200, Uwe Kleine-König wrote: > On Tue, Jul 09, 2019 at 12:00:05PM -0700, Matthias Kaehlcke wrote: > > Backlight brightness curves can have different shapes. The two main > > types are linear and non-linear curves. The human eye doesn't > > perceive linearly increasing/decreasing brightness as linear (see > > also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED > > linearly to human eye"), hence many backlights use non-linear (often > > logarithmic) brightness curves. The type of curve currently is opaque > > to userspace, so userspace often uses more or less reliable heuristics > > (like the number of brightness levels) to decide whether to treat a > > backlight device as linear or non-linear. > > > > Export the type of the brightness curve via the new sysfs attribute > > 'scale'. The value of the attribute can be 'linear', 'non-linear' or > > 'unknown'. For devices that don't provide information about the scale > > of their brightness curve the value of the 'scale' attribute is 'unknown'. > > > > Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > > I wonder what kind of problem you are solving here. Can you describe > that in a few words? The human eye perceives brightness in a logarithmic manner. For backlights with a linear brightness curve brightness controls like sliders need to use a mapping to achieve a behavior that is perceived as linear-ish (more details: http://www.pathwaylighting.com/products/downloads/brochure/technical_materials_1466797044_Linear+vs+Logarithmic+Dimming+White+Paper.pdf) As of now userspace doesn't have information about the type of the brightness curve, and often uses heuristics to make a guess, which may be right most of the time, but not always. The new attribute eliminates the need to guess. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
