Black Level´s for Broadcast TV use

[Thomas Wagner]

Hello
I am really confused about the black level setup for broadcast use. Can you please explain it to me.

Flash animation about black levels (very cool but confusing me even more)

http://pro.jvc.com/pro/attributes/pr...p/JVC_DEMO.swf

Thanks for your help

Greetings from Germany

Thomas

[Graeme Nattress]

Germany is PAL. Black level is 0IRE for analogue video.

"Setup" or 7.5IRE only applies to North American NTSC, and only to analogue video.

If you have an all digital workflow, black is alway at 16 and white at 235 in 8 bit video levels, which, for instance FCP shows as 0% to 100%.

Graeme

[David Lach]

I must say I'm a bit confused too with the setup on the XL2. I come from film, and never had to worry about that before. I understand that analog video is 7.5 IRE and digital 0 IRE, but I'm still not sure...

1- What values to select on the XL2 for SETUP and PEDESTAL if my goal is digital screening and DVD authoring. I can figure out the knee and black settings by looking in the XL2 manual at the graphical representation of what it affects on the curve, but the SETUP and PEDESTAL settings I have no idea if I should leave at the default position or increase/decrease. If I record at 0 IRE, can I adjust the blacks in post in the event I need to transfer the footage to analog?

2- When I have my answer to the first question, I still need to know how to set the XL2 so it corresponds either to 7.5 or 0 IRE. Do I change the PEDESTAL value? SETUP value? Both? And since the adjustment is just done via an unmarked sliding scale, how do I know where to put it?

Still very confused about that aspect of video.

[Barry Green]

Always leave it at zero. All digital recording should be done at zero. The only time setup enters the picture is when transferring from digital to analog, and pro decks will be configured to add that setup for you.

For DVD authoring, you still want it at zero. DVD players will add setup to their analog outputs for you.

[Chris Mills]

From what I know of video and checking in my AC Video Manual 3rd Edition - NTSC has its black set at 7.5 IRE whereas PAL is at 0 IRE.

If you are talking about digital signals then a value of 0 will correspond to the appropriate IRE based on which standard you are using - PAL (0 IRE) or NTSC (7.5 IRE).

You don't get to change the format of your XL-2. It is either PAL or NTSC and that will determine where it minimum IRE level is.

Pedestal will adjust the contrast of your image.

Setup will increase the exposure - or lighten your image - but clamps the lights so that they don't over-expose.

[David Lach]

So should I understand that no matter what I do to the PEDESTAL and SETUP settings on the XL2, the IRE value that corresponds to absolute black will remain the same?

[Chris Mills]

I'd be happy to have someone either validate or correct me, but AFAIK yes, that is the way it is.

[Barry Green]

Not as familiar with the XL2 yet, but on the DVX and the PD150, there is a menu option for "setup", which can be set at either 0% or 7.5%. I'm assuming the XL2 has it as well, but that's only an assumption.

On the DVX and the PD150, the 7.5% setup option does not function the way it does on professional broadcast equipment, and should never be used (except in the rare circumstance of using the camera as a camera head only, recording through s-video onto an analog deck, or other similar circumstances).

For digital recording, that type of menu option should always be set at zero.

[David Lach]

There's a setup option on the XL2, but it is not adjustable between 7.5 and 0 IRE. It is a sliding scale that you can increase and decrease by 6 discreet steps in every direction. It seems to create deeper shadows when decreased (less sensitivity to light). The Master Pedestal option functions the same way. There's no option clearly meant to choose between 7.5 and 0 IRE. That's why I'm a bit confused as to how to set the blacks on the XL2.

The questioning could be pushed one step further, if we assume the IRE level cannot be adjusted and is set according to the system (PAL vs NTSC), by asking if the XL2 records 0 IRE (16 units) to tape but converts to 7.5 IRE when the signal is sent via the analog connections for monitoring.

[Graeme Nattress]

IRE is not a digital phenonema and has no meaning what-so-ever in terms of digital video. In digital video black is always at 16 and white at 235 and that's the end of it. You can't adjust that.

However, in the digital realm you can lift or crush your blacks, but that is altering the image that gets recorded to tape in such a way that it looks like the blacks have been raised or lowered, but if you raise the blacks to, say 32, then the recorder still wants to record black at 16, but there's no black black in the image as it's all grey up at 32. Hence you now have a tape which is incompatible with any NLE, and you've burned your effect into the video, so there's no going back. You've probably lost some colour resolution because you're now no using 16 shades of colour in the recording.

Any such adjustments can be done in post, but only if you're doing them for artistic effect. If you're trying to add 7.5IRE setup in your NLE, then not only are you wrong, because digital video has no IRE and no setup either, but you're reducing quality by removing 16 levels of brightness that could have been used to store pictoral detail, and adding a render to boot.

The only correct place to add NTSC 7.5 IRE setup is on the analogue outputs of the digital to analogue conversion. If your camera or deck does not do that, then use an external proc amp please! Or take it to a pro dub house.

Graeme

[David Lach]

Still, it would be useful to know if the XL2 automatically converts the DV footage to 7.5 IRE via its analogue connectors, because you want your blacks to look right when viewing, say, on an external LCD monitor via the S-video jack.

[Greg Boston]

I watched the flash animation on JVC's site. It is VERY informative. I suggest that everyone take a look at it. Apparently, some cameras can add setup to the firewire port while others will always have the firewire at the same level regardless of the setup selection. In some scenarios, it was mentioned that even when recording digital, you have to adjust setup to check lighting of the scene and then return it to zero before recording.

This confusion is going to remain until the analog broadcast methods have become obsolete and everything is digital. By the way, the presentation is done in an informative but humorous way. I enjoyed it.


regards,

=gb=

[Chris Mills]

<<<-- Originally posted by Graeme Nattress : IRE is not a digital phenonema and has no meaning what-so-ever in terms of digital video. In digital video black is always at 16 and white at 235 and that's the end of it. You can't adjust that.

Graeme -->>>

Are you saying this is for both PAL and NTSC? It's my understanding that PAL goes the full range from 0 to 255 and that NTSC goes from 16 to 235.

[Graeme Nattress]

Greg, Setup is never added to a firewire signal as that is digital and digital never has setup.

Chris, 8bit digital video levels are always 16-235 the world over, that's so that you can dub superblack and superwhite footage to digital video and have it accurately preserved. PAL is not 0-255, and the 16 is not a setup level above black like 7.5IRE setup is in analogue NTSC.

Graeme

[Chris Mills]

I think I am seeing the light now. Or the black, as the case might be. Thanks.