On Thu, 10 Sep 2020 15:39:07 -0400 Vitaly Prosyak <vitaly.pros...@amd.com> wrote:
> On 2020-09-10 2:07 p.m., Vitaly Prosyak wrote: > > > > > > On 2020-09-10 1:51 p.m., Laurent Pinchart wrote: > >> Hi Vitaly, > >> > >> On Thu, Sep 10, 2020 at 01:09:03PM -0400, Vitaly Prosyak wrote: > >>> On 2020-09-10 6:56 a.m., Laurent Pinchart wrote: > >>>> On Thu, Sep 10, 2020 at 01:28:03PM +0300, Pekka Paalanen wrote: > >>>>> On Thu, 10 Sep 2020 12:30:09 +0300 Laurentiu Palcu wrote: > >>>>>> On Thu, Sep 10, 2020 at 11:50:26AM +0300, Pekka Paalanen wrote: > >>>>>>> On Thu, 10 Sep 2020 09:52:26 +0200 Daniel Vetter wrote: > >>>>>>>> On Thu, Sep 10, 2020 at 10:25:43AM +0300, Pekka Paalanen wrote: > >>>>>>>>> On Wed, 9 Sep 2020 13:57:28 +0300 Laurentiu Palcu wrote: > >>>>>>>>> > >>>>>>>>>> Hi all, > >>>>>>>>>> > >>>>>>>>>> I was wondering whether you could give me an advise on how to > >>>>>>>>>> proceed further > >>>>>>>>>> with the following issue as I'm preparing to upstream the next set > >>>>>>>>>> of patches > >>>>>>>>>> for the iMX8MQ display controller(DCSS). The display controller > >>>>>>>>>> has 3 planes, > >>>>>>>>>> each with 2 CSCs and one degamma LUT. The CSCs are in front and > >>>>>>>>>> after the LUT > >>>>>>>>>> respectively. Then the output from those 3 pipes is blended > >>>>>>>>>> together and then > >>>>>>>>>> gamma correction is applied using a linear-to-nonlinear LUT and > >>>>>>>>>> another CSC, if > >>>>>>>>>> needed. > >>>>>>> Hi, > >>>>>>> > >>>>>>> hmm, so FB -> CSC -> LUT -> CSC -> blending? > >>>>>>> > >>>>>>> Is it then > >>>>>>> blending -> LUT -> CSC -> encoder > >>>>>>> or > >>>>>>> blending -> CSC -> LUT -> encoder? > >>>>>> The DCSS pipeline topology is this: > >>>>>> > >>>>>> FB1->CSC_A->LUT->CSC_B-\ > >>>>>> FB2->CSC_A->LUT->CSC_B-|-blender->LUT->CSC_O->encoder > >>>>>> FB3->CSC_A->LUT->CSC_B-/ > >>>>>> > >>>>>> Basically, CSC_A is used to convert to a common colorspace if needed > >>>>>> (YUV->RGB) as well as to perform pixel range conversions: > >>>>>> limited->full. > >>>>>> CSC_B is for gamut conversions(like 709->2020). The CSC_O is used to > >>>>>> convert to the colorspace used by the output (like RGB->YUV). > >>>>> I didn't realize that it would be correct to do RGB-YUV conversion in > >>>>> non-linear space, but yeah, that's what most software do too I guess. > >>>>> > >>>>>>> Are all these LUTs per-channel 1D LUTs or something else? > >>>>>> LUTs are 3D, per pixel component. > >>>>> Sorry, which one? > >>>>> > >>>>> An example of a 3D LUT is 32x32x32 entries with each entry being a > >>>>> triplet, while a 1D LUT could be 1024 entries with each entry being a > >>>>> scalar. 1D LUTs are used per-channel so you need three of them, 3D LUTs > >>>>> you need just one for the color value triplet mapping. > >>>>> > >>>>> A 3D LUT can express much more than a 4x4 CTM. A 1D LUT cannot do the > >>>>> channel mixing that a CTM can. > >>>>> > >>>>> So if you truly have 3D LUTs everywhere, I wonder why the CSC matrix > >>>>> blocks exist... > >>>> Possibly because the 3D LUT uses interpolation (it's a 17x17x17 LUT in > >>>> R-Car), having a separate CSC can give more precision (as well as > >>>> allowing the two problems to be decoupled, at a relatively low hardware > >>>> cost). > >>> If you put nonlinear signal to 3DLUT then your > >>> precision would be improved. > >>> How many bits each color value has in 3DLUT ? > >> The whole display pipeline uses 8 bits per component. > > It is pretty low , please, use always nonlinear signal in the pipe and it > > allows you to compress and 'win' about 2 bits. The DRM driver is not in control of that, though. Userspace controls it through what values it happens to upload to the LUTs and matrices. This raises a good point: userspace must be aware of both LUT size and precision to decide if and how to use it. > Do you have alpha and de-alpha blocks in your pipeline? > You can do CSC and blending in nonlinear mode, it is less accurate than in > linear, but it is viable way. It may be viable in some cases and not others. That too is a userspace decision. > Also alpha should be removed (if it is applied) before CSC. Right. Thanks, pq
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