Colorspace concepts need more explanation

[KenJ57]

I have read the informative explanation of Colorspace provided at animemusicvideos.org and have a reasonably good understanding of colorspace concepts. But, I would like to pose some further questions.

1. How do we find out what colorspace an AVI is in? I have looked at the detailed header structure of AVI files in abcAVI Tag Editor and get no indication of what the colorspace is.

2. If colorspace conversions are to be avoided, and a video editor such as Premiere operates in the RGB colorspace, shouldn't that fact be prominantly displayed on the box?

According to the article, TMPGEnc, FlaskMPEG and VirtualDub all operate in the RGB colorspace. Only AVISynth is able to operate exclusively in YUV colorspace, as well as RGB.

[edDV]

....

2. If colorspace conversions are to be avoided, and a video editor such as Premiere operates in the RGB colorspace, shouldn't that fact be prominantly displayed on the box?

According to the article, TMPGEnc, FlaskMPEG and VirtualDub all operate in the RGB colorspace. Only AVISynth is able to operate exclusively in YUV colorspace, as well as RGB.

My best understanding of Premiere Pro is that will operate in YUV (YUVA internal) as long as the project format is set to a YUV format (DV, HDV, HD plus the variations of CCIR-601 including 4:2:2 and 4:4:4). If an input is presented in RGB, it will be converted to YUVA. The YUVA channels will all be processed separately internally as components. Alpha is used as a transparency multiplier.

The most important issue is preservation of luminance Y (also Alpha) through the process. U and V pixels may be shifted in position or sample rate as 4:1:1, 4:2:0, 4:2:2 YUY2, 4:4:4 and YV12 material is processed internally but color difference channel processing has minimal visible effect.

Any conversion from native YUV to RGB and back introduces crosstalk between components. Even though conventional conversion formulas may imply a lossless conversion, they fail to account for the asymetric sample bandwidth of Y and the color difference channels. Conversion back from RGB to YUV will result in a bandwidth compromised Y component and other crosstalk errors. There are advanced techniques to minimize these errors but these usually are applied internal to the application.

Some Premiere Pro filters and plug-ins will do a RGB conversion, but these should only affect the portions of the timeline influenced by the filter. It's also possible to play filter tricks such as adding input Y detail back into the processed Y channel.

[celtic_druid]

VirtualDub only requires RGB24 for full processing. Older versions use YUY2 in fast recompress. VirtualDubMod and newer versions can do YV12.

[KenJ57]

Thanks for the replies. I am not finding yet what I need. The basic concepts still elude me. I'm Norweigian, so tell it real slow

1. How do we find out what colorspace an AVI is in?

2. Sorry for being too simplistic here. I have Adobe Premiere Elements 1.0, which apparently is a "light" version of Premiere Pro. No options for selection or manipulation of colorspace. I ASSUME from reading, reading, reading -- other topics, threads and web sites that the colorspace used is RGB. I have no way of knowing that, however. How do I find out?

-- Ken

[celtic_druid]

If you email Adobe they should be able to tell you. Most lossy compressors use YV12. If you open the file via AVISynth you can see what colourspace the decoder serves which is probably more important than the actual colourspace. For instance DivX3 is internally YV12, however from recollection the decoder outputted RGB24, now there would be no point of going to the trouble of making sure that you were editing in YV12 if the decoder had already converted.

[KenJ57]

I appreciate your attempt to help.

If you want to avoid colorspace changes, it seems that you would need to know the source colorspace, the editor colorspace, the filter(s) colorspace and the destination colorspace. All I ever see, for instance in VDub or AVS scripts, are colorspace conversions tossed in seemingly because the author knows what ALL those requirements are. Except for certain filters, I have NEVER seen a specification that says a certain type of file is YUV and needs to be converted to RGB before the application accepts it.

!!!!!!!!!!!!???????????? (newbie alert! patience, please)

BTW, I do have some competance in these matters. I have a print-out of the Microsoft DirectX DirectShow YUV Video Subtypes and RGB subtypes, and I am familiar with the "packed" and "planar" formats. It's just that no one can seem to explain my basic questions!

-- Ken

[KenJ57]

Sigh! I guess I will have to wrap up my own topic.

I can use the 'Info' command (filter?) in AVISynth to find out the colorspace of a video clip. Great! Just what we needed.

All of my DV-AVI captures are in YUY2, a packed YUV colorspace format. If I import them into Adobe Premiere Elements, and then save them out via Save ==> Movie, they are reported as RGB24.

Therefore, Elements must edit in the RGB colorspace. Seems like this should be very commonly known information. --- Seems like

Perhaps this is an example of a company implying to it's customers "Now don't you worry your pretty little head, sweetheart. Daddy will take care of all those nasty little details".

-- Ken

[Wile_E]

I made mistake. I used info() in a avisynth script to show info in virtualdub. I think RGB24 is what colorspace Virtualdub works internally. It is not DV colorspace. DV is YUY2.

[KenJ57]

How did you get colorspace information from VirtualDub?