[Intel-gfx] [PATCH] drm/i915/icl: Handle YCbCr to RGB conversion for BT2020 case

[Shankar, Uma]

>-----Original Message-----
>From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com]
>Sent: Tuesday, May 7, 2019 9:08 PM
>To: Shankar, Uma <uma.shankar at intel.com>
>Cc: Sharma, Shashank <shashank.sharma at intel.com>; intel-
>gfx at lists.freedesktop.org
>Subject: Re: [Intel-gfx] [PATCH] drm/i915/icl: Handle YCbCr to RGB conversion for
>BT2020 case
>
>On Tue, May 07, 2019 at 02:35:15PM +0000, Shankar, Uma wrote:
>>
>>
>> >-----Original Message-----
>> >From: Intel-gfx [mailto:intel-gfx-bounces at lists.freedesktop.org] On
>> >Behalf Of Ville Syrjälä
>> >Sent: Tuesday, May 7, 2019 7:37 PM
>> >To: Sharma, Shashank <shashank.sharma at intel.com>
>> >Cc: intel-gfx at lists.freedesktop.org
>> >Subject: Re: [Intel-gfx] [PATCH] drm/i915/icl: Handle YCbCr to RGB
>> >conversion for
>> >BT2020 case
>> >
>> >On Tue, May 07, 2019 at 06:32:57PM +0530, Shashank Sharma wrote:
>> >> From: Uma Shankar <uma.shankar at intel.com>
>> >>
>> >> Currently input csc for YCbCR to RGB conversion handles only
>> >> BT601 and Bt709. Extending it to support BT2020 as well.
>> >>
>> >> Signed-off-by: Uma Shankar <uma.shankar at intel.com>
>> >> Signed-off-by: Shashank Sharma <shashank.sharma at intel.com>
>> >> ---
>> >>  drivers/gpu/drm/i915/intel_sprite.c | 24 ++++++++++++++++++++++++
>> >>  1 file changed, 24 insertions(+)
>> >>
>> >> diff --git a/drivers/gpu/drm/i915/intel_sprite.c
>> >> b/drivers/gpu/drm/i915/intel_sprite.c
>> >> index 44aaeac1b2ed..2536e757bec2 100644
>> >> --- a/drivers/gpu/drm/i915/intel_sprite.c
>> >> +++ b/drivers/gpu/drm/i915/intel_sprite.c
>> >> @@ -433,6 +433,18 @@ icl_program_input_csc(struct intel_plane *plane,
>> >>  			0x9EF8, 0x7800, 0xABF8,
>> >>  			0x0, 0x7800,  0x7ED8,
>> >>  		},
>> >> +		/*
>> >> +		 * BT.2020 full range YCbCr -> full range RGB
>> >> +		 * The matrix required is :
>> >> +		 * [1.000, 0.000, 1.474,
>> >> +		 *  1.000, -0.1645, -0.5713,
>> >> +		 *  1.000, 1.8814, 0.0000]
>> >> +		 */
>> >> +		[DRM_COLOR_YCBCR_BT2020] = {
>> >> +			0x7BC8, 0x7800, 0x0,
>> >> +			0x8928, 0x7800, 0xAA88,
>> >> +			0x0, 0x7800, 0x7F10,
>> >> +		},
>> >>  	};
>> >>
>> >>  	/* Matrix for Limited Range to Full Range Conversion */ @@ -461,6
>> >> +473,18 @@ icl_program_input_csc(struct intel_plane *plane,
>> >>  			0x8888, 0x7918, 0xADA8,
>> >>  			0x0, 0x7918,  0x6870,
>> >>  		},
>> >> +		/*
>> >> +		 * BT.2020 Limited range YCbCr -> full range RGB
>> >> +		 * The matrix required is :
>> >> +		 * [1.164, 0.000, 1.717,
>> >> +		 *  1.138, -0.1873, -0.6504,
>> >> +		 *  1.1380, 2.1417, 0.0000]
>> >
>> >Where are those 1.138 coming from?
>>
>> Hi Ville,
>> This is the original YCBCR to RGB BT2020 matrix:
>> {
>>         1.00000000000,  0.00000000000,  1.47460000000,
>>         1.00000000000,  -0.16455312684, -0.57135312684,
>>         1.00000000000,  1.88140000000,  0.00000000000 };
>>
>> We have to convert Limited Range YCbCr to Full Range RGB. Hence we need to
>apply a scale factor:
>>  yscalefactor = 219.0 * normalizingfactor;  cbcrscalefactor = 224.0 *
>> normalizingfactor;
>>
>>  /* Scale factors are inverted for LR to FR conversion */
>> yscalefactor = 1.0 / yscalefactor;  cbcrscalefactor = 1.0 /
>> cbcrscalefactor;
>>
>> This yields the above results.
>
>Those are the coefficients for Y, so they should still be the same for all three output
>channels.
>
>igt_color_encoding gives me:
>|1.1644, 0.0000, 1.6787,|
>|1.1644,-0.1873,-0.6504,|
>|1.1644, 2.1418, 0.0000,|

Ok, I used the igt_color_encoding method and able to get values what you got.
Will update the matrix. Thanks Ville.

>Looks like we're also misprogramming the Y pre-offset for the full range YCbCr case.
For full range, I am getting same values as programmed above. Looks ok, can you double check.

Regards,
Uma Shankar

>--
>Ville Syrjälä
>Intel