Hi!
Export the type of the brightness curve via the new sysfs attribute
'scale'. The value of the attribute may be a simple string like
'linear' or 'non-linear', or a composite string similar to
'compatible' strings of the device tree. A composite string consists
of different elements separated by commas, starting with the
most-detailed description and ending with the least-detailed one. An
example for a composite string is "cie-1931,perceptual,non-linear"
This brightness curve was generated with the CIE 1931 algorithm, it
is perceptually linear, but not actually linear in terms of the
emitted light. If userspace doesn't know about 'cie-1931' or
'perceptual' it should at least be able to interpret the 'non-linear'
part.
I'm not sure the comma-separated thing is a good idea. If it is, it should
go to the Documentation, not to changelog.
quoted hunk ↗ jump to hunk
+What: /sys/class/backlight/<backlight>/scale
+Date: June 2019
+KernelVersion: 5.4
+Contact: Daniel Thompson <daniel.thompson@linaro.org>
+Description:
+ Description of the scale of the brightness curve. The
+ description consists of one or more elements separated by
+ commas, from the most detailed to the least detailed
+ description.
+
+ Possible values are:
+
+ unknown
+ The scale of the brightness curve is unknown.
+
+ linear
+ The brightness changes linearly in terms of the emitted
+ light, changes are perceived as non-linear by the human eye.
+
+ non-linear
+ The brightness changes non-linearly in terms of the emitted
+ light, changes might be perceived as linear by the human eye.
non-linear is not too useful as described.
quoted hunk ↗ jump to hunk
+ perceptual,non-linear
+ The brightness changes non-linearly in terms of the emitted
+ light, changes should be perceived as linear by the human eye.
+
+ cie-1931,perceptual,non-linear
+ The brightness curve was calculated with the CIE 1931
+ algorithm. Brightness changes non-linearly in terms of the
+ emitted light, changes should be perceived as linear by the
+ human eye.
Is it useful to know difference between perceptual, and cie-1931?
Would it be useful to export absolute values in some well-known units?
If I'm in dark room, I may want 100mW/m^2 of backlight... And it would
be nice if I could set same backlight intensity on all my devices easily.
Pavel