Table of contents:

1. VFGS - Versatile film grain synthesis
2. FGC designer

VFGS - Versatile film grain synthesis

Software model of hardware-friendly film grain synthesis, supporting FGC SEI message and AOM-registered ITU-T T35 metadata (also called AFGS1).

This software implements a film grain synthesis method that supports both frequency-filtering and auto-regressive modes of the FGC SEI message, as well as AFGS1 metadata (an other auto-regressive model), while reducing hardware implementation costs compared to SMPTE RDD-5 by doing a sample-based local adaptation, rather than based on a local 8x8 average (which requires line buffers).

The intent is to provide a "one for all" solution, using a single hardware module while supporting different grain models.

Details of design considerations regarding film grain synthesis can be found in JVET-AC2020 (committee draft of ISO 23007-2 technical report), section 8.

Compared to FGC SEI message, AFGS1 specification supports a larger number of AR coefficients, but does not support local adapation of grain size/shape; it can also specify a chroma grain strength local adaptation from a color mix, which is not implemented in this software.

This software is designed as a model for hardware designers; it uses the C language, and is organized in separate layers:

• the hardware layer (in vfgs_hw.c), which performs the actual grain synthesis process, based on grain patterns memory, local adaptation LUTs, and a few other parameters. This is the piece that is potentially implemented in hardware.
• the firmware layer (in vfgs_fw.c), that converts input model parameters (e.g. FGC SEI) to hardware configuration. This part can be easily modified to adapt to other grain metadata formats, to generate grain patterns in a different way, etc.
• the outer layer, made of the main program and YUV I/O routines.

Usage

This programs takes an input YUV video and a configuration file, and generates an output YUV video.

The configuration file reflects the contents of an FGC SEI message, and follows the same syntax as in the VTM; for AFGS1 metadata, a similar syntax is used. Test configuration files can be found in the cfg/ subfolder. A default FGC SEI configuration is used if none is provided.

An SEI text dump as output by the VTM or HM can also be ingested instead of a configuration file, an example of which is also found in the cfg/ subfolder. Only the first FGC SEI found in the dump is retained. For AFGS1, the .tbl format used in AOM reference software is also supported, but taking only the first configuration found (an example is provided in the cfg/ subfolder).

When the --gain option is used, new valid grain parameters are computed internally before further processing.

Full help is provided when typing vfgs --help, with default option values indicated in angle brackets [ ]:

Usage: vfgs [options] <input.yuv> <output.yuv>

   -w,--width    <value>     Picture width [1920]
   -h,--height   <value>     Picture height [1080]
   -b,--bitdepth <value>     Input bit depth [10]
      --outdepth <value>     Output bit depth (<= input depth) [same as input]
   -f,--format   <value>     Chroma format (420/422/444) [420]
   -n,--frames   <value>     Number of frames to process (0=all) [0]
   -s,--seek     <value>     Picture start index within input file [0]
   -r,--seed     <value>     Random seed
   -c,--cfg      <filename>  Read film grain configuration file
   -g,--gain     <value>     Apply a global scale (in percent) to grain strength
   --help                    Display this page

Compilation

Compilation is performed either using cmake or typing gcc src/*.c -o vfgs.exe -mavx2 (adapt -mXXX to your machine)

Contributing

Please use fork and pull requests. Examples of welcome contributions:

• SIMD and GPU acceleration (HW layer)
• HDL code / HW design (HW layer)
• Further improved FGC SEI message support (FW layer)

License

A BSD 3-clause-clear license is applicable. See the LICENSE file.

FGC designer

A python script called fgc-designer.py is present at the root of the repository. This is a graphical interactive tool that can be used to display and adjust film grain parameters.

After loading an FGC configuration file (currently, only FGC SEI in frequency-filtering mode is supported), and selecting the color component, the mouse can be used to adjust intensity interval boundaries, gain and frequency cutoffs (just click and drag). An interval is removed by making it zero-length, and is split by double-clicking.

External dependencies are matplotlib and numpy.

License

A BSD 3-clause-clear license is applicable. See the LICENSE file.