How to properly set black/white points using waveform monitor (bt878) ?

[juhok]

Hi,

I've ran into great deal of headache trying to match the levels on my capture card. Specially with problem tapes which are a bit overexposed.

(Capture card is PDI Deluxe, using latest x64 drivers (WDM 2.0) and capturing 8mm video(Sony EV-S9000E) with VirtualDub)

Most guides that are referred in older post don't exist anymore. My question is what is the proper way to analyze this waveform?

http://www.siluriformes.net/pub/cap_8mm_waveform.png

Should black & white point be set according to luma only, or take R-G-B into account, and if so, what is the philosophy?

I can only set brightness / contrast / saturation / sharpness. Hue / gamma sliders don't work.

[Blue_MiSfit]

That's a tough one.

You're asking how you should adjust your brightness / contrast sliders before capturing, correct?

~MiSfit

[juhok]

You're asking how you should adjust your brightness / contrast sliders before capturing, correctRight. To be more specific, many waveform monitors (like avisynth's histogram()) will show only luma. This would suggest that that's all I'd need. But if I set brightness/contrast(black/white) that way and capture, a lot of highlights gets blown away (which doesn't happen if I view it directly from TV instead of Capture->DVD->TV). I have to just keep the contrast down by eye/gut feeling.

Up to this point the best "waveform method" I've used is luma for brightness and luma+green for contrast. This works somewhat ok. Red and Blue always gets blown more or less.

[Blue_MiSfit]

Ahh dynamic range limitations....

I wonder - can you capture in full-range luma? i.e. 0-255?

~MiSfit

[juhok]

I'm capturing YUY2 16-235 (afaik) which is native for this card (Sweetspot aka PDI Deluxe (http://www.pluggedin.tv/sweetspot/specs/index.html)). I've understood that any other capturing format would just be conversion from this in the driver level or so.

[FlimsyFeet]

My method is to set black and white points just based on the luma waveform, saturation setting is adjusted using either the vectorscope or the "hot pixel" view in colortools.

I believe if you extend luma white point and extend luma black point in VirtualDub you can caputre "sub-black", <16 and "super white" >235 YUY2. But of course this would probably get clamped during processing or encoding.

But, looking at your luma waveform on the top of the image, it looks like highlights are blown out already on the source, look at the bright horizontal lines near the top of the waveform. You can't do anything about that, as chaning the contrast/white point will only move those lines up and down, not retriev any detail out of them. Yet you say it doesn't look this way on a TV, so I don't know if there might be a problem with the capture card?

[juhok]

This particular scene has overexposed areas which are those flat parts in luma waveform. If I extend the clipped areas to 235 in luma, red and blue will clip very hard and that is noticeable. I try to play with saturation a bit. Also I need to try different sources, it might be that these particular tapes just "are like this".

Capturing DVD source via s-video for example is pretty ok and easy to set up.