[theora-dev] Higher quality video - supporting greater than 8 bit color depth

Maik Merten maikmerten at gmx.net
Sun Mar 14 10:31:00 PST 2004

Disclaimer: I´m not a theora-developer. Some information in this mail 
may be plain wrong. You have been warned ;-)

KarasevAS at aol.com wrote:
> 1. Ability to support greater than 8 bits per RGB or YPrPb channel color 
> depth, either arbitrarily defined (preferred) or as a selection of 
> "good" values or "green or luminance"/other color depth pairs, to have 
> say 12 bit Y and 8 bit Pr, Pb. You be the judges what would be the good 
> values to support; I'd sure love to see e.g. 8, 12, 16, 24 bits per channel.

My limited understanding of _lossy_ video compression makes me think it 
is not possible to think of "8, 12, 16, 24 bits per channel". Theora 
uses YV12 colorspace. Every plane is transformed via Discrete Cosine 
Transform (DCT) and compressed using quantization. How much information 
is thrown away is determined via a psychovisual model. There is no fixed 
"color resolution" AFAIK.

For video-editing a lossless video codec is a wiser choice anyway IMO.

> 2. Ability to specify the "authoring" gamma value and color temperature 
> in the video header.

Perhaps a metadata-stream could contain this information.

> 3. Robust internal support for interleaved subtitles, so each word is 
> tied to a section of a video. Header could include "recommended" font / 
> color / text field size & position within frame / text alignment within 
> field / modification (bold/italic/underline/outline/strikethrough) / 
> transparency / merging type (direct/add/subtract/multiply).

This belongs into a subtitle-stream seperate from the video-stream. No 
need to change video-coding for that. :-)

> 4. Speaking of subtitles, would be good to have multiple streams of ... 
> EVERYTHING! I mean, multiple angles of video; multiple audio 
> tracks; multiple subtitle tracks.

It´s already possible to mux several logical audio- and video-streams 
into one physical Ogg-stream.

> 5. Would be very forward-looking, I think, to support ability to qualify 
> the video components in the video header (i.e. in RGB terms, "what kind 
> of green is this, really"). This means defining filter's median wave 
> length and breadth. Something even more elegant to scal eto scientific 
> applications perhaps would be, for each channel, specify the filter 
> curve and response curve. ... and support potentially more (or less) 
> than three channels such as our plain (R G B or Y Pr Pb). There may be 
> applications incluing IR or UV channels, or simply additional channels 
> at specific other wavelengths. It would be up to the player to interpret 
> these in a user-defined way, by ignoring or mixing them in as specific 
> colors or applying threshold or logical operations.

I´m not sure if _lossy_ video compression is suitable for scientific 
applications at all... at least the files will be very small as the 
psychovisual model will make sure all IR and UV channels will be 
completely thrown away ;-)

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