Captured Videos are green (BT601 colorspace issue?)

[alvy]

Hi,
I try to backup old family videos from VHS-C (PAL). I had the idea that I could get a reasonable result with an old video scaler (Kramer VP 419xl). This is capable of giving whether RGB (800x600 and other VGA resolution in 60 HZ) or YPbPr (576p and others) output is on VGA only. I try to capture with Startech usb3hdcap. The Startech unit is recognizing a BT601 colorspace. However everything I get in Virtualdub (or other Capture Software) is just green (RGB output works).
I would much prefer 576p (800x600 is cropped 10% of frame). Is there a way to convert this back with virtualdub or avisynth? I am lost here... (tried also VGA to RCA cable but don't get a signal).

I would appreciate any suggestion/idea.

Cheers
alvy



[Attachment 46068 - Click to enlarge]

[jagabo]

VGA is RGB, not YCbCr. Doesn't you're capture card want YCbCr rather than RGB?

[alvy]

Thanks for your reply. Well I think it's the other way round (wants rgb gets YCbCr). I think I currently can't fix it with hardware so I thought it might be possible to convert by with software by applying a colormatrix (or something like that).

[JVRaines]

On the Kramer unit, have you selected OUTPUT = PC in the SETUP menu?

[jagabo]

You won't get any useful colors out of that green image. It's not a rec.601/709 type of error. You need to get the hardware working right and agreeing on the signal system.

[alvy]

Ok thanks. I will give it one more try with a VGA to RGB cable (Capture unit has this as input as well (I understand from documentation that this might work with YPBRT). Otherwise I guess I will deinterlace with software and don't use the Kramer unit...

@JVRaines. Yes this works but the picture is cropped on the corners (~12 pixel per boarder)

[jagabo]

QTGMC() in AviSynth is a far better deinterlacer than any piece of hardware.

I was able to get a little color out of the green image:



This was done by treating the green channel as luma and the red and blue channels as chroma.

[JVRaines]

That may be an interesting exercise in AviSynth, but unless you live in the Emerald City, sending a YPbPr signal to an RGB input is just plain wrong.

[jagabo]

Of course.

[pandy]

That may be an interesting exercise in AviSynth, but unless you live in the Emerald City, sending a YPbPr signal to an RGB input is just plain wrong.

Why? This is usual way of mapping YPbPr on RGB (or more commonly GBR/GRB color space) common in nowadays consumer electronics but not only - also software like for example ffmpeg use frequently GRB/GBR, GPU commonly organize memory as GRB/GBR...

See nothing wrong in sampling YPbPr with RGB frontend (YCbCr 4:4:4 with oversampled chroma).