From: Enric Balletbo Serra <eballetbo-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> To: Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org> Cc: Daniel Thompson <daniel.thompson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Doug Anderson <dianders-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Enric Balletbo i Serra <enric.balletbo-ZGY8ohtN/8qB+jHODAdFcQ@public.gmane.org>, Jingoo Han <jingoohan1-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Richard Purdie <rpurdie-Fm38FmjxZ/leoWH0uzbU5w@public.gmane.org>, Jacek Anaszewski <jacek.anaszewski-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Brian Norris <briannorris-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Guenter Roeck <groeck-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Lee Jones <lee.jones-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Alexandru Stan <amstan-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, linux-leds-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org> Subject: Re: [RFC v2 2/2] backlight: pwm_bl: compute brightness of LED linearly to human eye. Date: Mon, 18 Dec 2017 11:40:59 +0100 [thread overview] Message-ID: <CAFqH_52z9O+0ZVB-rMTCNzw+55m26fDGKeaj-Fz-ccO74+j_MA@mail.gmail.com> (raw) In-Reply-To: <20171215205735.GB19442@amd> Hi Pavel, 2017-12-15 21:57 GMT+01:00 Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org>: > Hi! > >> Yes, I think that how you describe luminance and lightness is right, >> and sounds good improve the doc. >> >> To be clear the correction table for PWM values can be calculated with >> this code. >> >> OUTPUT_SIZE = 65535 # Output integer size >> INPUT_SIZE = 2047 >> >> def cie1931(L): >> L = L*100.0 >> if L <= 8: >> return (L/902.3) >> else: >> return ((L+16.0)/116.0)**3 >> >> x = range(0,int(INPUT_SIZE+1)) >> y = [int(round(cie1931(float(L)/INPUT_SIZE)*(OUTPUT_SIZE))) for L in x] > > Can we just generate the table on the fly? Should not be hard to do in > fixed point, right? This was discussed a bit in previous RFC which had the code to generate the table on the fly, see [1]. The use of a fixed table or an on the fly table is something that I'll let the maintainers to decide. I've no strong opinion on use the on the fly table if someone takes care to review deeply the fixed point maths :) [1] https://lkml.org/lkml/2017/9/4/335 Regards, Enric > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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From: Enric Balletbo Serra <eballetbo@gmail.com> To: Pavel Machek <pavel@ucw.cz> Cc: Daniel Thompson <daniel.thompson@linaro.org>, Doug Anderson <dianders@google.com>, Enric Balletbo i Serra <enric.balletbo@collabora.com>, Jingoo Han <jingoohan1@gmail.com>, Richard Purdie <rpurdie@rpsys.net>, Jacek Anaszewski <jacek.anaszewski@gmail.com>, Rob Herring <robh+dt@kernel.org>, Brian Norris <briannorris@google.com>, Guenter Roeck <groeck@google.com>, Lee Jones <lee.jones@linaro.org>, Alexandru Stan <amstan@google.com>, linux-leds@vger.kernel.org, "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [RFC v2 2/2] backlight: pwm_bl: compute brightness of LED linearly to human eye. Date: Mon, 18 Dec 2017 11:40:59 +0100 [thread overview] Message-ID: <CAFqH_52z9O+0ZVB-rMTCNzw+55m26fDGKeaj-Fz-ccO74+j_MA@mail.gmail.com> (raw) In-Reply-To: <20171215205735.GB19442@amd> Hi Pavel, 2017-12-15 21:57 GMT+01:00 Pavel Machek <pavel@ucw.cz>: > Hi! > >> Yes, I think that how you describe luminance and lightness is right, >> and sounds good improve the doc. >> >> To be clear the correction table for PWM values can be calculated with >> this code. >> >> OUTPUT_SIZE = 65535 # Output integer size >> INPUT_SIZE = 2047 >> >> def cie1931(L): >> L = L*100.0 >> if L <= 8: >> return (L/902.3) >> else: >> return ((L+16.0)/116.0)**3 >> >> x = range(0,int(INPUT_SIZE+1)) >> y = [int(round(cie1931(float(L)/INPUT_SIZE)*(OUTPUT_SIZE))) for L in x] > > Can we just generate the table on the fly? Should not be hard to do in > fixed point, right? This was discussed a bit in previous RFC which had the code to generate the table on the fly, see [1]. The use of a fixed table or an on the fly table is something that I'll let the maintainers to decide. I've no strong opinion on use the on the fly table if someone takes care to review deeply the fixed point maths :) [1] https://lkml.org/lkml/2017/9/4/335 Regards, Enric > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
next prev parent reply other threads:[~2017-12-18 10:40 UTC|newest] Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-16 14:11 [RFC v2 0/2] backlight: pwm_bl: support linear brightness to human eye Enric Balletbo i Serra 2017-11-16 14:11 ` [RFC v2 1/2] backlight: pwm_bl: linear interpolation between values of brightness-levels Enric Balletbo i Serra 2017-11-20 18:58 ` Rob Herring 2017-11-27 11:21 ` Enric Balletbo Serra [not found] ` <CAFqH_50VqFJ-p=gRp9md4eHDHM5NpD6zPFfjwPY4LKTh2x6sHQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2017-11-27 23:55 ` Doug Anderson 2017-11-27 23:55 ` Doug Anderson 2017-11-27 23:52 ` Doug Anderson 2017-12-15 14:40 ` Daniel Thompson 2017-12-18 9:47 ` Enric Balletbo Serra 2017-12-18 13:15 ` Daniel Thompson [not found] ` <20171116141151.21171-1-enric.balletbo-ZGY8ohtN/8qB+jHODAdFcQ@public.gmane.org> 2017-11-16 14:11 ` [RFC v2 2/2] backlight: pwm_bl: compute brightness of LED linearly to human eye Enric Balletbo i Serra 2017-11-16 14:11 ` Enric Balletbo i Serra 2017-11-30 0:44 ` Doug Anderson [not found] ` <CAD=FV=WY-2MmjRxGGaJrQjyeWt+k4_k7j12M4LxAnnZxJF7sXw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2017-11-30 11:27 ` Daniel Thompson 2017-11-30 11:27 ` Daniel Thompson [not found] ` <c6450f50-5c12-dc52-4340-b068c0b38c54-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> 2017-11-30 16:57 ` Doug Anderson 2017-11-30 16:57 ` Doug Anderson 2017-11-30 18:34 ` Enric Balletbo Serra 2017-11-30 18:34 ` Enric Balletbo Serra 2017-11-30 19:06 ` Doug Anderson 2017-12-15 20:57 ` Pavel Machek 2017-12-18 10:40 ` Enric Balletbo Serra [this message] 2017-12-18 10:40 ` Enric Balletbo Serra 2017-12-18 12:33 ` Pavel Machek 2017-12-18 13:53 ` Daniel Thompson 2017-12-15 14:51 ` Daniel Thompson 2017-12-18 10:27 ` Enric Balletbo Serra [not found] ` <CAFqH_50Jqs5_5n7D019_ZxvQD1FPCZAYhaLunNm6qzj_cH3tiw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2017-12-18 13:31 ` Daniel Thompson 2017-12-18 13:31 ` Daniel Thompson 2017-12-18 16:46 ` Doug Anderson [not found] ` <CAD=FV=VEakDGqfEkOZbuiq=FvUw46=6u9rTOgTk5FyJ9_2Rh4A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2017-12-18 20:21 ` Daniel Thompson 2017-12-18 20:21 ` Daniel Thompson
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