On 10/21/2015 06:13 PM, Lionel Landwerlin wrote:
On 21/10/15 01:57, Zhao Yakui wrote:
On 10/21/2015 12:48 AM, Lionel Landwerlin wrote:
In the following formula for the conversion :
R = Clamp ( 1.164(Y-16/255) + 1.596(Cr-128/255))
G = Clamp ( 1.164(Y-16/255) - 0.813(Cr-128/255) - 0.392(Cb-128/255))
B = Clamp ( 1.164(Y-16/255) + 2.017(Cb-128/255))
we must substract 16 (or 16/255 if dealing with [0.0, 1.0] floats) to
Y before applying the multiplier coefficent. The shader was missing
the substraction.
Hi,
Thanks for your patch.
The issue comes from the confusing formula between YUV and RGB.
As you see from the below link, it has several different formulas
about YUV to RGB.
>http://www.equasys.de/colorconversion.html
And ITU has three standards for the conversion between YUV and RGB.
(BT601, 709, 2020).
Even for BT601, it will also have the different conversion if the
footroom/headroom is considered.
If you hope to fix the conversion issue, I prefer that the shader is
based on the generic conversion matrix and the conversion matrix is
passed. In such case we can pass the different conversion matrix for
the different standard.
Yeah, I was wondering because the driver's code base includes more
generic shaders that work with a matrix passed from userspace :
http://cgit.freedesktop.org/vaapi/intel-driver/tree/src/shaders/render
Why isn't the driver using those shaders?
The shaders in src/shaders/render is mainly used for the vaPutSurface,
which is based on 3D pipeline.
And the YUV ->RGB conversion in VPP is based on media pipeline, which
will have the sampling quality, especially when the scaling is involved.
Indeed having a matrix would be best. What the current conversion being
used right now?
Reading your link it seems it's neither BT601 nor BT709.
What Genwole said is right. It is for the YPbPr and full-range.
Of course it is also mentioned for JPEG conversion.
> https://en.wikipedia.org/wiki/YCbCr
I think that the better solution is to implement the conversion based on
the conversion matrix. (In such case the full-range/limited range can be
considered. And the different standards can also be supported).
Thanks
Yakui
Thanks
Yakui
---
src/shaders/post_processing/gen7/YUV_to_RGB.g4a | 16 ++++++++++++++++
src/shaders/post_processing/gen7/pl2_to_rgbx.g75b | 16 ++++++++++++++++
src/shaders/post_processing/gen7/pl2_to_rgbx.g7b | 16 ++++++++++++++++
src/shaders/post_processing/gen8/YUV_to_RGB.g8a | 16 ++++++++++++++++
src/shaders/post_processing/gen8/pl2_to_rgbx.g8b | 16 ++++++++++++++++
src/shaders/post_processing/gen9/pl2_to_rgbx.g9b | 16 ++++++++++++++++
6 files changed, 96 insertions(+)
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