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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 88ba95bedb "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@chromium.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
27 lines
902 B
Plaintext
27 lines
902 B
Plaintext
What: /sys/class/backlight/<backlight>/scale
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Date: July 2019
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KernelVersion: 5.4
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Contact: Daniel Thompson <daniel.thompson@linaro.org>
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Description:
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Description of the scale of the brightness curve.
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The human eye senses brightness approximately logarithmically,
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hence linear changes in brightness are perceived as being
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non-linear. To achieve a linear perception of brightness changes
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controls like sliders need to apply a logarithmic mapping for
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backlights with a linear brightness curve.
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Possible values of the attribute are:
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unknown
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The scale of the brightness curve is unknown.
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linear
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The brightness changes linearly with each step. Brightness
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controls should apply a logarithmic mapping for a linear
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perception.
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non-linear
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The brightness changes non-linearly with each step. Brightness
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controls should use a linear mapping for a linear perception.
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