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Tue, 08 Mar 2022 01:06:47 -0800 (PST) Received: from eldfell ([194.136.85.206]) by smtp.gmail.com with ESMTPSA id f21-20020ac251b5000000b004478fa4a744sm2871298lfk.56.2022.03.08.01.06.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Mar 2022 01:06:46 -0800 (PST) Date: Tue, 8 Mar 2022 11:06:43 +0200 From: Pekka Paalanen To: Geert Uytterhoeven Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , Javier Martinez Canillas , Sam Ravnborg , Helge Deller , linux-fbdev@vger.kernel.org, linux-m68k@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 RFC 08/10] drm/fourcc: Document that single-channel "red" can be any color Message-ID: <20220308110643.5220f8ae@eldfell> In-Reply-To: <585dc03acb4016bba910e7d15fec3ef4f0aec5b0.1646683502.git.geert@linux-m68k.org> References: <585dc03acb4016bba910e7d15fec3ef4f0aec5b0.1646683502.git.geert@linux-m68k.org> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: multipart/signed; boundary="Sig_/hJXpHsxaCnYZ11VUzvhv1th"; protocol="application/pgp-signature"; micalg=pgp-sha256 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Sig_/hJXpHsxaCnYZ11VUzvhv1th Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Mon, 7 Mar 2022 21:52:43 +0100 Geert Uytterhoeven wrote: > Traditionally, the first channel has been called the "red" channel, but > the fourcc values for single-channel "red" formats can also be used for > other light-on-dark displays, like grayscale. >=20 > Signed-off-by: Geert Uytterhoeven > --- > RFC, as I have no immediate need for these formats. >=20 > v2: > - New. > --- > include/uapi/drm/drm_fourcc.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) >=20 > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h > index 457ed39cc48f08e1..f0187cf20e4619d2 100644 > --- a/include/uapi/drm/drm_fourcc.h > +++ b/include/uapi/drm/drm_fourcc.h > @@ -104,16 +104,16 @@ extern "C" { > #define DRM_FORMAT_C4 fourcc_code('C', '4', ' ', ' ') /* [7:0] C0:C1 4:= 4 two pixels/byte */ > #define DRM_FORMAT_C8 fourcc_code('C', '8', ' ', ' ') /* [7:0] C 8 one = pixel/byte */ > =20 > -/* 8 bpp Red */ > +/* 8 bpp Red (or generic light-on-dark) */ > #define DRM_FORMAT_R8 fourcc_code('R', '8', ' ', ' ') /* [7:0] R */ > =20 > -/* 10 bpp Red */ > +/* 10 bpp Red (or generic light-on-dark) */ > #define DRM_FORMAT_R10 fourcc_code('R', '1', '0', ' ') /* [15:0] x:R 6:= 10 little endian */ > =20 > -/* 12 bpp Red */ > +/* 12 bpp Red (or generic light-on-dark) */ > #define DRM_FORMAT_R12 fourcc_code('R', '1', '2', ' ') /* [15:0] x:R 4:= 12 little endian */ > =20 > -/* 16 bpp Red */ > +/* 16 bpp Red (or generic light-on-dark) */ > #define DRM_FORMAT_R16 fourcc_code('R', '1', '6', ' ') /* [15:0] R litt= le endian */ > =20 > /* 16 bpp RG */ Hi Geert, this is a good idea. I just wonder whether light-on-dark is an accurate description. To me, light-on-dark means things like bright characters on a dark background, but that is a property of the image as a whole and not a property of the pixel format. What I think you are after here is that increasing channel value mean increasing brightness. How to word that concisely... Direct relationship to brightness (vs. inverse relationship to brightness)? This does not imply a linear relationship, and I'd also use "brightness" to denote that it is a qualitative factor relating to human observation. 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