High bit-depth Support with Avisynth

Introduction

Currently, Avisynth (not AvisynthPlus) only supports 8-bit video. Nevertheless, through various utilities, plugins, and scripts, Avisynth can be used to import, process, and export high bit-depth video. There has been some effort to update Avisynth itself to support high bit-depth, but there has been no progress as of 2012 (http://forum.doom9.org/showthread.php?t=162436).

What is Deep Color?

Deep Color refers to using more than 8 bits of data to represent each color channel. It is also referred to as high bit-depth color. Basically, deep color allows finer graduations of color, smoother gradients and more detail. Please refer to this short, easy to understand article: PCWorld: What is 10-bit Color?

Why Use Deep Color?

• Higher internal precision, using high-bit depth color, when processing an image in a filter, gives a higher quality (8-bit) output.
• If a video filter uses linear gamma internally, there can be noticeable differences in the image. A linear gamma representation is best supported with a high bit-depth. See the illustration for ResampleHQ.
• If you encode high-bit depth video, you can get better compression (reportedly up to 30%) and less banding.
• Banding is one of the most serious liabilities of 8-bit depth. Refer to the following references for an explanation of why 10-bit encodes compress better:
  • Why does 10-bit save bandwidth (even when content is 8-bit)?.pdf
  • Using 10-bit AVC/H.264 Encoding with 4:2:2 for Broadcast Contribution.pdf
  • Keeping Video Quality Pristine throughout the Production Process: 4:2:2 10-bit AVC/H.264 encoding.pdf

AviSynth+ Native Deep Color Support

Since r2290 (October 2016), AVS+ supports deep color – 10, 12, 14, 16 and 32-bit (floating point) RGB & YUV color spaces. All AVS+ color spaces are listed here. Support functions include ConvertBits, ConvertStacked, Extract and CombinePlanes. Deep color support has also been added to all internal filters and many external plugins.

This feature greatly simplifies use of deep color and could make much of the information below obsolete.

See the AviSynth+ main page for more information.

Importing High Bit-depth Video into AviSynth

For importing high bit depth video AviSynth 2.6.0 or greater is strongly recommended. AviSynth 2.6 adds the additional planar color spaces (Y8,YV16,YV24, YV411) which makes it that much more compatible with all of the existing formats.

FFMS2

Patched FFMS2 - import DNxHD, ProRes, and other 10-bit videos in their native format (4:2:2 and 4:4:4 are also supported), output greater than 8-bits will always be in the Stack16 format.

• Source code: GitHub repository
• Discussion: Doom9 thread - Importing DNxHD to Avisynth (some of the links may be outdated; see downloads below or SAPikachu's signature for latest versions)

Download

Updated binaries: March 15, 2015 | older versions

• ffms2-6e0d654+a9fe004-ffmbc-FFmbc-0.7.1.7z | mirror - This version uses FFmbc as a decoder; may have better support for professional video formats like ProRes, DNxHD, etc.
• ffms2-6e0d654+a9fe004-ffmpeg-1e4d049.7z | mirror - This version uses FFmpeg as a decoder; may be better for general (more common) formats.
• ffms2-6e0d654+a9fe004-libav-9a60b1f.7z | mirror - This version uses Libav as a decoder; may be better for general (more common) formats.

These versions work just like the official FFMS2, but includes the additional enable10bithack parameter and support for the additional planar colorspaces available is AviSynth 2.6. By default enable10bithack is set to false so it will work just like the official FFMS2; to import high bit depth video set enable10bithack=true, output will be in the Stack16 format. See FFmpeg versus Libav for information on pros and cons and differences between the FFmpeg and Libav.

LSMASHSource

Another source filter to import regular 8-bit and high bit depth video. LSMASHSource includes these 2 fuctions to import video:

• LSMASHVideoSource - This function uses libavcodec as a video decoder and L-SMASH as a demuxer. Recommended for MP4, MOV, ISO Base Media and its derived file formats.
  
• LWLibavVideoSource - This function uses libavcodec as a video decoder and libavformat as a demuxer.
  

VapourSource

Can be used to import VapourSynth scripts into AviSynth. Video can be 8-bit or greater.

ImageMagick

You can also import video or still via 16-bit PNG format pictures with the following ImageMagick command lines.

Examples shown are for Windows. Requires the 16-bit version of ImageMagick; get it here (look for downloads with Q16 in the file name)

• Convert 16-bit to Stack16 (high/low or stack16 format):

convert 16bit.png -depth 16 ( +clone -evaluate and 255 -evaluate multiply 256 ) 
        -append stacked.png

• Convert Stack16 (high/low) to 16bit:

convert stacked.png -depth 16 -crop 100%x50% ( +clone -evaluate divide 256 ) 
        -delete 1 -compose Add -composite -define png:bit-depth=16 16bit1.png

For further explanation of these command lines, please see the thread Image Magick and stacked high bit-depth (doom9.org)

Obsolete

The following methods are obsolete! If you must, only use as a verification or as workaround:

• Readv210mod - Can read uncompressed v210 in .mov container as color. Needs a manual setting skip the file header.

• Sashimi - Sashimi 0.85 has different bit-depth support. Please see OtherFormats/Read_v210.avs included in the package.

• ReadV210 - Can read uncompressed v210 in .mov container as greyscale.

Alternative builds and methods of importing (also obsolete):

• ffms2mod - Can return most 10bit video in the Avisynth high bit-depth convention.

• RawSource with ffmpeg - shows an example of using ffmpeg to convert to a 16bit format which can be read by RawSource in Avisynth 2.6.