From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 78DB02356AD for ; Mon, 31 Mar 2025 14:55:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743432924; cv=none; b=ciyNVARugCJBRUtUsoqbxzNrOz67JNkUYAaVllGQLB8NxcDTjMH5U1vm0KS9XvJ7K0P29ln8jh4Ka/wnYrE7iS9IW9bId+Q+wZvqvCIg32UL4KWnFo+sGpKkRnzkyXEc5S+2F8kP/rbuxmDbTBHWeLq2rBl8aqTJUHE82Lj3mo8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743432924; c=relaxed/simple; bh=Q9O8UjLPceVEDCDVbzGN5rZyqSeVA1cCqDcPa6gtF7w=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XEUuxiGokV39CW61+sI5S9lFk1g2pECaTjNkYbDpTYXxMeL8eB+/jg2ZiJjQ3QdwzU9ipyi4hxtLNUJsgvQPDWL3p94VcnuX2J6W87iPONq9ZI/0KKGYqe/7UoAsgNHsHqC3ABb0kJWgleUaIlVK8grJui9tdlePKLUD4Y6ohGo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=wej7R7w+; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="wej7R7w+" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 82399725; Mon, 31 Mar 2025 16:53:28 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1743432808; bh=Q9O8UjLPceVEDCDVbzGN5rZyqSeVA1cCqDcPa6gtF7w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=wej7R7w+Pso2p0b4aeIXBL2u8ndNKcj+OZ6IYfyKD53IJoflnrCT7g29kYHpSG04c KrEhXY1ajSpi8jPbE551RKqC/EWPdscU05czKxVEHwz+bNTiAElp9/96FHOnJxKTwT o5LQszvm6ZJTqSKouOeFuzvpUdWcAZXddc24GGzk= Date: Mon, 31 Mar 2025 17:54:56 +0300 From: Laurent Pinchart To: Pekka Paalanen Cc: Geert Uytterhoeven , Tomi Valkeinen , Vishal Sagar , Anatoliy Klymenko , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Michal Simek , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Dmitry Baryshkov Subject: Re: [PATCH v4 03/11] drm/fourcc: Add DRM_FORMAT_Y8 Message-ID: <20250331145456.GB27882@pendragon.ideasonboard.com> References: <20250326-xilinx-formats-v4-3-322a300c6d72@ideasonboard.com> <20250327112009.6b4dc430@eldfell> <20250327175842.130c0386@eldfell> <20250331105446.098f0fbe@eldfell> <20250331082135.GB13690@pendragon.ideasonboard.com> <20250331135337.61934003@eldfell> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250331135337.61934003@eldfell> On Mon, Mar 31, 2025 at 01:53:37PM +0300, Pekka Paalanen wrote: > On Mon, 31 Mar 2025 11:21:35 +0300 Laurent Pinchart wrote: > > On Mon, Mar 31, 2025 at 10:54:46AM +0300, Pekka Paalanen wrote: > > > On Thu, 27 Mar 2025 17:35:39 +0100 Geert Uytterhoeven wrote: > > > > On Thu, 27 Mar 2025 at 16:59, Pekka Paalanen wrote: > > > > > On Thu, 27 Mar 2025 16:21:16 +0200 Tomi Valkeinen wrote: > > > > > > On 27/03/2025 11:20, Pekka Paalanen wrote: > > > > > > > On Wed, 26 Mar 2025 15:55:18 +0200 Tomi Valkeinen wrote: > > > > > > >> On 26/03/2025 15:52, Geert Uytterhoeven wrote: > > > > > > >>> On Wed, 26 Mar 2025 at 14:23, Tomi Valkeinen wrote: > > > > > > >>>> Add greyscale Y8 format. > > > > > > >>>> > > > > > > >>>> Acked-by: Dmitry Baryshkov > > > > > > >>>> Signed-off-by: Tomi Valkeinen > > > > > > >>> > > > > > > >>> Thanks for your patch! > > > > > > >>> > > > > > > >>>> --- a/include/uapi/drm/drm_fourcc.h > > > > > > >>>> +++ b/include/uapi/drm/drm_fourcc.h > > > > > > >>>> @@ -405,6 +405,9 @@ extern "C" { > > > > > > >>>> #define DRM_FORMAT_YUV444 fourcc_code('Y', 'U', '2', '4') /* non-subsampled Cb (1) and Cr (2) planes */ > > > > > > >>>> #define DRM_FORMAT_YVU444 fourcc_code('Y', 'V', '2', '4') /* non-subsampled Cr (1) and Cb (2) planes */ > > > > > > >>>> > > > > > > >>>> +/* Greyscale formats */ > > > > > > >>>> + > > > > > > >>>> +#define DRM_FORMAT_Y8 fourcc_code('G', 'R', 'E', 'Y') /* 8-bit Y-only */ > > > > > > >>> > > > > > > >>> This format differs from e.g. DRM_FORMAT_R8, which encodes > > > > > > >>> the number of bits in the FOURCC format. What do you envision > > > > > > >>> for e.g. DRM_FORMAT_Y16? fourcc_code('G', 'R', '1', '6')? > > > > > > >> > > > > > > >> I wanted to use the same fourcc as on V4L2 side. Strictly speaking it's > > > > > > >> not required, but different fourccs for the same formats do confuse. > > > > > > >> > > > > > > >> So, generally speaking, I'd pick an existing fourcc from v4l2 side if > > > > > > >> possible, and if not, invent a new one. > > > > > > > > > > > > > > what's the actual difference between DRM_FORMAT_R8 and DRM_FORMAT_Y8? > > > > > > > > > > > > > > Is the difference that when R8 gets expanded to RGB, it becomes (R, 0, > > > > > > > 0), but Y8 gets expanded to (c1 * Y, c2 * Y, c3 * Y) where c1..c3 are > > > > > > > defined by MatrixCoefficients (H.273 terminology)? > > > > > > > > > > > > > > That would be my intuitive assumption following how YCbCr is handled. > > > > > > > Is it obvious enough, or should there be a comment to that effect? > > > > > > > > > > > > You raise an interesting point. Is it defined how a display driver, that > > > > > > supports R8 as a format, shows R8 on screen? I came into this in the > > > > > > context of grayscale formats, so I thought R8 would be handled as (R, R, > > > > > > R) in RGB. But you say (R, 0, 0), which... also makes sense. > > > > > > > > > > That is a good question too. I based my assumption on OpenGL behavior > > > > > of R8. > > > > > > > > > > Single channel displays do exist I believe, but being single-channel, > > > > > expansion on the other channels is likely meaningless. Hm, but for the > > > > > KMS color pipeline, it would be meaningful, like with a CTM. > > > > > Interesting. > > > > > > > > > > I don't know. Maybe Geert does? > > > > > > > > I did some digging, and was a bit surprised that it was you who told > > > > me to use R8 instead of Y8? > > > > https://lore.kernel.org/all/20220202111954.6ee9a10c@eldfell > > > > > > Hi Geert, > > > > > > indeed I did. I never thought of the question of expansion to R,G,B > > > before. Maybe that expansion is what spells R8 and Y8 apart? > > > > > > I do think that expansion needs to be specified, so that the KMS color > > > pipeline computations are defined. There is a big difference between > > > multiplying these with an arbitrary 3x3 matrix (e.g. CTM): > > > > > > - (R, 0, 0) > > > - (R, R, R) > > > - (c1 * Y, c2 * Y, c3 * Y) > > > > I'd be very surprised by an YUV to RGB conversion matrix where the first > > column would contain different values. What we need to take into account > > though is quantization (full vs. limited range). > > A good point, are the Y coefficients always 1.0 after quantization > range has been accounted for? As far as I understand, they should be. RGB is full range, so the Y range should map to [0.0, 1.0] in RGB space. I'm also not aware of any colorspace where a grey colour would have different R, G and B values. There's a related but separate question: if Y is a luma (in Y'CbCr terms), it will not be linear, compared to the Y luminance (YCbCr). We have a DEGAMMA_LUT to linearize data, but that's in the CRTC output path, not in the plane path, and I don't see any API element to specify the transfer function of data input to a CRTC. > That makes Y8 produce (Y, Y, Y), and we have our answer: R8 should be > (R, 0, 0), so we have both variants. Or do we need Y-formats at all? > > Can we specify Y, R, G and B be nominal values in the range 0.0 - 1.0 > in the KMS color processing? > > > > I forgot to consider that in the discussion of single-channel displays, > > > because the displays obviously do not consider any other channel than > > > the one. > > > > > > Using DRM_FORMAT_Y8 FB with a single-channel display might even be > > > surprising, because the proposed Y8 definition would result in c1 * Y, > > > and not Y. The default c1 comes from the BT.601 matrix IIRC? > > > > > > Therefore I think the difference between R8 and Y8 has been found. Now > > > we just need to determine whether R8 means (R, 0, 0) or (R, R, R) to > > > nail down the color operations as well. There are questions like what > > > is the outcome at the video signal level when we have one KMS plane > > > with an R8 FB and another KMS plane with an RGBA8888 FB on the same > > > CRTC? What about Y8 or NV12 in the mix? What if the video signal is > > > single-channel, RGB, or YCbCr? -- Regards, Laurent Pinchart