[Libva] [PATCH 6/7] shaders: vpp: gen7: use yuv to rgb matrix to compute rgb values

[Sean V Kelley]

On 11/05/2015 02:22 AM, Lionel Landwerlin wrote:
> On 05/11/15 00:31, Zhao Yakui wrote:
>> On 11/04/2015 11:27 PM, Lionel Landwerlin wrote:
>>> ---
>>>   src/shaders/post_processing/gen7/YUV_to_RGB.g4a   | 626
>>> ++++++++++++----------
>>>   src/shaders/post_processing/gen7/pl2_to_rgbx.g75b | 528
>>> +++++++++---------
>>>   src/shaders/post_processing/gen7/pl2_to_rgbx.g7b  | 528
>>> +++++++++---------
>>>   3 files changed, 909 insertions(+), 773 deletions(-)
>>>
>>> diff --git a/src/shaders/post_processing/gen7/YUV_to_RGB.g4a
>>> b/src/shaders/post_processing/gen7/YUV_to_RGB.g4a
>>> index 24616dc..6af651f 100644
>>> --- a/src/shaders/post_processing/gen7/YUV_to_RGB.g4a
>>> +++ b/src/shaders/post_processing/gen7/YUV_to_RGB.g4a
>>> @@ -386,34 +386,36 @@
>>>           mov   (8) fBUFFER_V(0, 0)<1>    r[a0.0, 1]<16;8,2>:ub
>>>           mov   (8) fBUFFER_V(1, 0)<1>    r[a0.0, 17]<16;8,2>:ub
>>>
>>> -    add   (16) fBUFFER_U(0, 0)<1>    fBUFFER_U(0, 0)<8;8,1>    -128.0f
>>> -    add   (16) fBUFFER_V(0, 0)<1>    fBUFFER_V(0, 0)<8;8,1>    -128.0f
>>
>> As far as I know, the value in fBUEER_U/V is still in [0 255] range.
>> So I think that it still should be extraced by 128 before it is
>> normalized to [0..1].
> 
> Looking at the green component for example, given the following
> coefficients for Y, U and V :
> 
> CY = 1.0
> CU = -0.344
> CV = -0.714
> 
> This is what the current shader does :
> 
> green = ((Y + (U - 128) * CU + (V - 128) * CV) * 0.0039216) * 255
> 
> The shader in this patch does this :
> 
> green = (Y * 0.0039216 + (U * 0.0039216 - 128.0 / 255) * CU + (CV *
> 0.0039216 - 128.0 / 255) * CV) * 255
> 
> This looks equivalent to me given that
> 
> 128.0 / 255 ~= 128 * 0.0039216
> 
> we just distribute the [0..1] normalizing factor earlier.

Ah, that's fine.

Thanks,

Sean

> 
> It's possible to do what you suggest, but it would require more
> instructions.
> Maybe I'm missing some precision stuff that is specific to the hardware?
> 
>>
>>
>>> +        mul   (16) fBUFFER_Y(0, 0)<1>      fBUFFER_Y(0,
>>> 0)<1>             0.0039216f
>>> +        mul   (16) fBUFFER_U(0, 0)<1>      fBUFFER_U(0,
>>> 0)<1>             0.0039216f
>>> +        mul   (16) fBUFFER_V(0, 0)<1>      fBUFFER_V(0,
>>> 0)<1>             0.0039216f
>>
> 
> 
> 
> 
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