[Libva] [PATCH] Fix the quality factor.

[Xiang, Haihao]

Applied, thanks for the patch.

Haihao

> The following are added in this commit:
>     1) Added lower bound to the quality factor.
>     2) Added extensive comments on scaling and normalization of the quality factor.
> ---
>  src/gen8_mfc.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/src/gen8_mfc.c b/src/gen8_mfc.c
> index a329288..9304b97 100644
> --- a/src/gen8_mfc.c
> +++ b/src/gen8_mfc.c
> @@ -2720,10 +2720,20 @@ gen8_mfc_jpeg_fqm_state(VADriverContextP ctx,
>          qmatrix->load_chroma_quantiser_matrix = (pic_param->num_components > 1) ? 1 : 0;
>      }   
>  
> -    if (quality > 100)
> -      quality = 100;
> +
> +    //As per the design, normalization of the quality factor and scaling of the Quantization tables
> +    //based on the quality factor needs to be done in the driver before sending the values to the HW.
> +    //But note, the driver expects the scaled quantization tables (as per below logic) to be sent as
> +    //packed header information. The packed header is written as the header of the jpeg file. This
> +    //header information is used to decode the jpeg file. So, it is the app's responsibility to send
> +    //the correct header information (See build_packed_jpeg_header_buffer() in jpegenc.c in LibVa on 
> +    //how to do this). QTables can be different for different applications. If no tables are provided,
> +    //the default tables in the driver are used.
> +
> +    //Normalization of the quality factor
> +    if (quality > 100) quality=100;
> +    if (quality == 0)  quality=1;
>      quality = (quality < 50) ? (5000/quality) : (200 - (quality*2)); 
> -    quality = (quality == 0) ? 1 : quality;
>      
>      //Step 1. Apply Quality factor and clip to range [1, 255] for luma and chroma Quantization matrices
>      //Step 2. HW expects the 1/Q[i] values in the qm sent, so get reciprocals