From: Sven Schwermer <sven@svenschwermer.de>
To: "Marek Behún" <marek.behun@nic.cz>,
"Jacek Anaszewski" <jacek.anaszewski@gmail.com>,
pavel@ucw.cz, linux-leds@vger.kernel.org,
thierry.reding@gmail.com, u.kleine-koenig@pengutronix.de,
lee.jones@linaro.org, post@lespocky.de
Subject: Re: [PATCH v3 1/2] dt-bindings: leds: Add multicolor PWM LED bindings
Date: Mon, 31 Jan 2022 09:55:58 +0100 [thread overview]
Message-ID: <16e48f33-2a69-ad59-3fd5-f1e25f46e413@svenschwermer.de> (raw)
In-Reply-To: <YfeLTxVAmwjU6PFr@ada-deb-carambola.ifak-system.com>
Hi,
On 1/31/22 08:10, Alexander Dahl wrote:
>> I know that color curves were being discussed at the time multicolor
>> was being introduced, and AFAIK Pavel didn't like it, but I don't
>> remember the reasons anymore.
>>
>> As far as I understand it though, for PWM LEDs there is an equation for
>> gamma correction.
>
> That's right, and it gets a little more complicated if you have RGB
> instead of a single LED. A start for reading might be this:
>
> https://hackaday.com/2016/08/23/rgb-leds-how-to-master-gamma-and-hue-for-perfect-brightness/
>
> (I had bookmarked that back when I was hacking on firmware for an 8bit
> microcontroller controlling an RGB LED through soft PWM few years
> ago. A very simple solution is a precalculated static lookup table.)
This is a very interesting topic which I was gonna ask about on this
list anyways. IMHO, the Linux leds subsystem needs a uniform way to deal
with lightness/gamma correction. There is some previous work in pwm_bl
and led_bl with their `brightness-levels` device tree property and
cie1931 correction function (drivers/video/backlight/pwm_bl.c). It would
be very nice to have this functionality in the led class. Having
something similar for multi-color as well would be fantastic.
Sven
next prev parent reply other threads:[~2022-01-31 8:56 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-26 10:48 [PATCH v3 0/2] Multicolor PWM LED support sven
2022-01-26 10:48 ` [PATCH v3 1/2] dt-bindings: leds: Add multicolor PWM LED bindings sven
2022-01-27 21:24 ` Jacek Anaszewski
2022-01-28 20:36 ` Marek Behún
2022-01-28 23:04 ` Jacek Anaszewski
2022-01-28 23:26 ` Marek Behún
2022-01-31 7:10 ` Alexander Dahl
2022-01-31 8:55 ` Sven Schwermer [this message]
2022-02-12 11:54 ` Pavel Machek
2022-01-26 10:48 ` [PATCH v3 2/2] leds: Add PWM multicolor driver sven
2022-02-02 12:33 ` Andy Shevchenko
2022-02-06 9:17 ` Sven Schwermer
[not found] ` <CAHp75VeSD5bYERp=s9Dzd0xScVc+sYSdc8W4XBfCVXJgyWMPyA@mail.gmail.com>
2022-02-06 11:04 ` Sven Schwermer
2022-02-06 12:25 ` Andy Shevchenko
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