Colourspace Confusion (UK)

[Incast]

For over a year I've watched DVB-T through the hardware decoding of my ATI card, at the 601 colour spec.

However, having assessed my recordings with DGIndex and G-Spot I've found there is actually no colorimetry flag.

I have a Nova-T USB2, and to my knowledge the .mpg files it records are as close to a raw feed you can get from it. I've read elsewhere that recording in .pva or .ts adds another conversion for this particular hardware.

Upon analysis of the untouched recorded .mpg files these also lack a colorimetry flag. G-Spot records no colorspace information (all boxes are grey), and DGIndex goes to the default 709.

According to a strict interpretation of the MPEG2 specification this, theoretically, means that they should all be in a colourimetry of 709, which is deemed the default. However, I'm fairly certain I've read that all SD DVB is in 601.

As a result I'm enormously confused as to what is going on. I'm certain my stream is losslessly recorded, and there would be no stripping of data.

Is the UK's DVB being broadcast in 601 or 709 colour?

My hunch is that this area of the MPEG2 specification is largely ignored, and that decoders largely treat SD MPEG2 as 601 and HD MPEG2 as 709 if no colourimetry flags are present. But I can't find any further evidence on this.

Does anyone have any further thoughts?

[dukey]

most of the time when you
'record' this just simply means saving the stream dump to your hdd. No colour conversion happens. Unless.. of course you use some hardware recorded with re-encodes the mpeg2 stream.

[ronnylov]

It is the same thing here in Sweden, no colorimetry flag on my DVB recordings. Anyway it does not look bad when opening them i VirtualDubMod so I just assume they are 709. So you think they actually are 601? Try open it through avisynth and test different settings with colormatrix filter.

Maybe you can ask BBC? I guess they know what format they send.

By the way I found this thread (see last post):
http://forum.doom9.org/showthread.php?t=103530
If you have demuxed with projectX this flag may have been changed by projectX.

[ronnylov]

Well I have done the test myself and my conclusion was that it really is Rec.601 and not Rec.709. So if trusting the hints from DGIndex this will get a wrong picture...

I tested following scripts and then probed the colours on the test patterns that the TV channel sent:

LoadPlugin("C:\Program\AviSynth 2.5\plugins\DGDecode.dll")
MPEG2Source("J:\DVB Capture\Testbild SVT2\07-21_07-57-31_SVT2_Testbild.d2v")
ConvertToRGB(matrix="rec601", interlaced=true)

Result:
http://h1.ripway.com/ronnylov/TestpatternRec601.png


LoadPlugin("C:\Program\AviSynth 2.5\plugins\DGDecode.dll")
MPEG2Source("J:\DVB Capture\Testbild SVT2\07-21_07-57-31_SVT2_Testbild.d2v")
ConvertToRGB(matrix="rec709", interlaced=true)
Result:
http://h1.ripway.com/ronnylov/TestpatternRec709.png


EDIT: Are there any tool available to patch the colorimetry flag in the MPEG-2 stream without reencoding the stream?
I feel I need to patch my recorded streams to make the look correct when decoded in my DVD player.

[RedDwarf1]

Maybe you can ask BBC? I guess they know what format they send.

I would love to see the answer that someone got from that question. lol

TVRipper: Can you tell me what Colourspace the BBC uses when transmitting Digital DVB-T broadcasts?

BBC: We could do, but if you are just watching it as your TV license allows, then why do you require that information?

TSReader shows UK DVB-T broadcasts as being 4:2:0 Chroma Format. But I don't know whether that is any help at all.

[pandy]

Generaly all SDTV are 601, all HDTV are 709, EDTV (480p59.94, 480p60,576p50) some are 601 some 709.
Anyway inside video elementary stream You have proper color space flag so this is no problem at all.

[ronnylov]

But there is no flag in my elementary stream and therefore DGIndex report it as Rec. 709 but it really is Rec. 601. So if other decoders do the same I have a problem because I normally do not reencode my elementary stream. I just use it as a source to make a DVD.

[Incast]

Firstly, thanks for all the responses.

Looking at those test screens it confirms without a shadow of a doubt that 601 is the correct colorimetry. The RGB values are each individually at around 190 for each of the rectangles above 7:57:30.

In contrast 709 has significant fluctuation.

EDIT: Are there any tool available to patch the colorimetry flag in the MPEG-2 stream without reencoding the stream?
I feel I need to patch my recorded streams to make the look correct when decoded in my DVD player.

TMPGEnc DVD Author 3 automatically assigns unflagged SD material with a BT.470 (Same as 601) flag. However, if you use this software take care with the settings to avoid it re-encoding the MPEG2 source.

Anyway inside video elementary stream You have proper color space flag so this is no problem at all.

That's the precise problem that we're seeing over DVB. This MPEG2 flag is being left null, for reasons which aren't clear.