I Made a PQ to HLG Converter

wswartzendruber · 13th April 2020, 05:44

I wrote a small utility for converting raw video streams from PQ to HLG. It's available on GitHub.

Code:

USAGE: pq2hlg [format] [nits] [width] [height] [input] [output]
  format - The raw pixel format to use. Supported options are:
           rgb48
  nits   - Luminance value of the brightest pixel in the input.
  width  - Width of the video stream in pixels.
  height - Height of the video stream in pixels.
  input  - Raw RGB48 input file; use - for STDIN.
  output - Raw RGB48 output file; use - for STDOUT.

My motivation was that I wanted to rip my 4K UltraHD library, but wanted to do so in a viewing format that is as universal as possible, even if that entails some amount of compromise. I quickly settled on HLG after reading about it, but couldn't find a conversion utility to do this. I learned that ffmpeg supports the use of lookup tables, but couldn't find any such thing for cheaper than a couple hundred dollars. Others were available from the BBC under license.

All in all, I got quite fed up with the situation and started researching PQ, HLG, metadata, gamma curves, etc. until I got nauseated and started work. Then I studied some more and then went back to coding. Wash, rinse, and repeat a few times. I'm at the point where I'm comfortable with releasing my work to the public. Principally, it uses, to the best of my understanding, the algorithm published by BBC Research & Development.

Future improvements may include passing dynamic metadata in for variable PQ->HLG tone mapping. I definitely want to add YUV10 support as soon as I can figure out how the U and V components are encoded.

This is also the first thing I've written in Rust, so it's probably not going to be as idiomatic or as proper as it could be.

EDIT: Attached a screenshot from Alita: Battle Angel using this utility, taken from a nightly build of VLC 3.0.9 on a SDR monitor. The video codec in use is VP9 Profile 2.

EDIT: I also forgot to mention: This isn't really suitable for any brightness value aside from 1,000 nits. If a PQ video has a peak brightness of less than 1,000 nits, pass 1,000 nits in as the second argument anyway. If any pixel ever exceeds 1,000 nits, then external tone mapping really needs to be applied to the PQ source before passing it into this utility. A peak brightness of other than 1,000 nits can be specified, but this will cause reference white to be pushed up or down. This addendum is in accordance with ITU-R BT.2390-8 Section 7.2.

13th April 2020, 05:44	#1 \| Link
wswartzendruber hlg-tools Maintainer Join Date: Feb 2008 Posts: 413	I Made a PQ to HLG Converter I wrote a small utility for converting raw video streams from PQ to HLG. It's available on GitHub. Code: USAGE: pq2hlg [format] [nits] [width] [height] [input] [output] format - The raw pixel format to use. Supported options are: rgb48 nits - Luminance value of the brightest pixel in the input. width - Width of the video stream in pixels. height - Height of the video stream in pixels. input - Raw RGB48 input file; use - for STDIN. output - Raw RGB48 output file; use - for STDOUT. My motivation was that I wanted to rip my 4K UltraHD library, but wanted to do so in a viewing format that is as universal as possible, even if that entails some amount of compromise. I quickly settled on HLG after reading about it, but couldn't find a conversion utility to do this. I learned that ffmpeg supports the use of lookup tables, but couldn't find any such thing for cheaper than a couple hundred dollars. Others were available from the BBC under license. All in all, I got quite fed up with the situation and started researching PQ, HLG, metadata, gamma curves, etc. until I got nauseated and started work. Then I studied some more and then went back to coding. Wash, rinse, and repeat a few times. I'm at the point where I'm comfortable with releasing my work to the public. Principally, it uses, to the best of my understanding, the algorithm published by BBC Research & Development. Future improvements may include passing dynamic metadata in for variable PQ->HLG tone mapping. I definitely want to add YUV10 support as soon as I can figure out how the U and V components are encoded. This is also the first thing I've written in Rust, so it's probably not going to be as idiomatic or as proper as it could be. EDIT: Attached a screenshot from Alita: Battle Angel using this utility, taken from a nightly build of VLC 3.0.9 on a SDR monitor. The video codec in use is VP9 Profile 2. EDIT: I also forgot to mention: This isn't really suitable for any brightness value aside from 1,000 nits. If a PQ video has a peak brightness of less than 1,000 nits, pass 1,000 nits in as the second argument anyway. If any pixel ever exceeds 1,000 nits, then external tone mapping really needs to be applied to the PQ source before passing it into this utility. A peak brightness of other than 1,000 nits can be specified, but this will cause reference white to be pushed up or down. This addendum is in accordance with ITU-R BT.2390-8 Section 7.2. Attached Images Last edited by wswartzendruber; 13th April 2020 at 07:05. Reason: Clarifying brightness setting.