[x265] [PATCH] Implementation of low-pass subband dct approximation

[Mont3z Claros]

Hi,

thanks for you comment and thanks for accepting my contribution.

I did so many tests using constant QP that I forgot about the other
more important rate-control modes. We could relax this by just ORing
it with limits for those other modes. However I understand that
ideally the application of this transformation is a function of QP and
the blocks mean deviation. I've tried to do this indirectly by fixing
the QP's limit and by using the transformation only on 16x16 and 32x32
blocks.

I'll try figure out a better way to best add those limitations.
Please, let me know if you can think of anything that might help.

Humberto

>> +
>>  void setupAliasPrimitives(EncoderPrimitives &p)
>>  {
>>  #if HIGH_BIT_DEPTH
>> @@ -256,6 +271,11 @@
>>  #endif
>>
>>          setupAliasPrimitives(primitives);
>> +
>> +        if (param->bLowPassDct && param->rc.qp > 20)
>> +        {
>> +            enableLowpassDCTPrimitives(primitives);
>> +        }
>
>
> Essentially this means that you enable lowpass-dct only when doing constant
> QP encodes. You could consider relaxing this to enable the option for other
> rate-control modes as well (ABR/CRF) and have some directives in your docs
> as to when the feature is better to use. Hard-coding the limits in the code
> isn't a great idea, IMO.
>
>>
>>      }
>>
>>      x265_report_simd(param);
>> diff -r 6a310b24c6a2 -r 893b36b82133 source/common/primitives.h
>> --- a/source/common/primitives.h        Thu Nov 02 12:17:29 2017 +0530
>> +++ b/source/common/primitives.h        Sat Oct 14 09:19:03 2017 -0700
>> @@ -259,8 +259,12 @@
>>       * primitives will leave 64x64 pointers NULL.  Indexed by LumaCU */
>>      struct CU
>>      {
>> -        dct_t           dct;
>> -        idct_t          idct;
>> +        dct_t           dct;    // active dct transformation
>> +        idct_t          idct;   // active idct transformation
>> +
>> +        dct_t           standard_dct;   // original dct function, used by
>> lowpass_dct
>> +        dct_t           lowpass_dct;    // lowpass dct approximation
>> +
>>          calcresidual_t  calcresidual;
>>          pixel_sub_ps_t  sub_ps;
>>          pixel_add_ps_t  add_ps;
>> diff -r 6a310b24c6a2 -r 893b36b82133 source/x265.h
>> --- a/source/x265.h     Thu Nov 02 12:17:29 2017 +0530
>> +++ b/source/x265.h     Sat Oct 14 09:19:03 2017 -0700
>> @@ -1505,6 +1505,11 @@
>>
>>      /* Disable lookahead */
>>      int       bDisableLookahead;
>> +
>> +    /* Use low-pass truncated dct approximation
>> +    *  This DCT approximation is less computational intensive and gives
>> results close to
>> +    *  standard DCT for QP >= 23 */
>> +    int       bLowPassDct;
>>  } x265_param;
>>
>>  /* x265_param_alloc:
>> diff -r 6a310b24c6a2 -r 893b36b82133 source/x265cli.h
>> --- a/source/x265cli.h  Thu Nov 02 12:17:29 2017 +0530
>> +++ b/source/x265cli.h  Sat Oct 14 09:19:03 2017 -0700
>> @@ -282,6 +282,7 @@
>>      { "force-flush",    required_argument, NULL, 0 },
>>      { "splitrd-skip",         no_argument, NULL, 0 },
>>      { "no-splitrd-skip",      no_argument, NULL, 0 },
>> +    { "lowpass-dct",          no_argument, NULL, 0 },
>>      { 0, 0, 0, 0 },
>>      { 0, 0, 0, 0 },
>>      { 0, 0, 0, 0 },
>> @@ -543,6 +544,7 @@
>>      H1("-r/--recon <filename>            Reconstructed raw image YUV or
>> Y4M output file name\n");
>>      H1("   --recon-depth <integer>       Bit-depth of reconstructed raw
>> image file. Defaults to input bit depth, or 8 if Y4M\n");
>>      H1("   --recon-y4m-exec <string>     pipe reconstructed frames to Y4M
>> viewer, ex:\"ffplay -i pipe:0 -autoexit\"\n");
>> +    H0("   --lowpass-dct                 Use low-pass subband dct
>> approximation. Default %s\n", OPT(param->bLowPassDct));
>>      H1("\nExecutable return codes:\n");
>>      H1("    0 - encode successful\n");
>>      H1("    1 - unable to parse command line\n");
>>
>> _______________________________________________
>> x265-devel mailing list
>> x265-devel at videolan.org
>> https://mailman.videolan.org/listinfo/x265-devel
>>
>
>
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