Hi Pekka, 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). -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
