FORUMS: list search recent posts

Black Levels

COW Forums : Blackmagic Design

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Christopher DeAngelus
Black Levels
on Apr 7, 2006 at 6:38:16 pm

Currently we have a Sony JH-3 importing into Final Cut Pro with a Decklink HD. Our acquisition camera is a Sony F900. I am not on the production side, but I've asked over there, and they said the camera should capture the blacks at 0%. I'm under the assumption that they are correct.

When I bring the footage in to Final Cut, the blacks are hovering around 5-6% (we can say 7.5, but not quite) according to Final Cut's video scopes. Visually, we can see the blacks in Final Cut, and consequently on our final feed outs, usually to SD, are "up." When you look at a monitor in the field as you capture, and then bring it back here, the footage in Final Cut is noticably more washed out.

Our problem is know how many variables there are in this: Our the field monitors calibrated, are the studio monitors calibrated, is the screen (Apple 23" LCD) calibrated, etc. but the scope in Final Cut seems to support our assumption. If using the 3-Way Color Corrector and I drop the blacks by 7.5, it looks just like it does out in the field.

We bring the footage in HD-SDI from the deck to the card to DVCProHD codec. We'll also, from time to time, bring it in SD-SDI from the deck to DVCPro50 codec. The problem is consistent and exact in both formats.

My question is, am I forgetting something? Is there a switch in Final Cut I may have ignored that is bringing the video in too hot? Is it the DVCPro50/HD codecs doing it? Am I imagining things? I know you don't know my system, and I've been in troubleshooting mode for days, but is there something simple yet out of the way I might be missing, either with the card, the deck or the software? Has anyone experienced anything like this?

I appreciate your time. Thank you.


Return to posts index

Bob Zelin
Re: Black Levels
on Apr 8, 2006 at 12:55:05 am

in the US, analog signals have blacks at 7.5 IRE, and digital signals have blacks at 0 IRE. This is not a Blackmagic, or Sony issue. Blame SMPTE.
If you look at a RS170A color bar signal going into a regular Sony Digi Beta VTR, and monitor on a TV mon that has SDI and analog inputs (think PVM-20L5 or PVM-20M4), and monitor on a scope than has multi function (like a Videotek VTM-200 or Leader LV5100D), you will see that the EXACT SAME SIGNAL looks "darker" in SDI, becuase the analog output black is at 7.5, and the SDI output black is at ZERO. Does this drive you and your clients crazy - YES - has this been an issue since the day SDI was introduced and people had to mix in analog sources with their SDI sources - YES. Do you want to blame someone ? SMPTE in in Scarsdale, NY. Please send all pipe bombs to them.

Bob Zelin




Return to posts index

Graeme Nattress
Re: Black Levels
on Apr 8, 2006 at 12:33:36 pm

You can hardly blame the SMPTE for a mistake made in NTSC many years ago. Japan had the sense to drop setup back in the 80s and PAL has never had it. Neither can you say digital is at 0IRE - that just doesn't make sense. A digital signal has no analogue leve - that's like trying to measure height with a weighing scale.

If a SDI output shows video darker, then whatver is converting that SDI digital signal to analogue is wrong, not the SDI signal. If that's in the monitor, then that monitor is not functioning correctly.

As for the original poster, black should read at 0% on the FCP scopes. That corresponds to an 8bit digital code of 16, which is the correct international standard for digital black. If it's not, and you're in an all digital workflow, there's probably some switch set wrong or some setting wrong on a menu in the HD camera.

Graeme

- http://www.nattress.com - Film Effects and Standards Conversion for FCP


Return to posts index


Shane Chadder
Re: Black Levels
on Apr 8, 2006 at 2:46:10 pm

Graham

There are some decks and cameras (especially Panasonic) that will add setup in the actual digital signal during recording, and strip it off the digital signal in playback if you set them.

It makes no sense as it just compresses your range of digital values.

Just last fall I had a camera op. go through the menus of our Panasonic DVCPro 410 and turn setup on thinking he was correcting us. Of course a firewire capture had all the black high and we had to fix it in post! By the same token if someone plays with the deck menus on our DVCPro50s - 930s and 950s they can add setup or crush the blacks on the recording of an SDI signal by changing setup values in the menu.

It may not be a good way of recording but the machines are made to do it.

Shane


Return to posts index

Graeme Nattress
Re: Black Levels
on Apr 8, 2006 at 5:24:27 pm

There are certainly decks that do so on analogue input and output, but I've never come across one that alters digital bits off tape to an SDI output in such a manner.

Graeme

- http://www.nattress.com - Film Effects and Standards Conversion for FCP


Return to posts index

Bob Zelin
Re: Black Levels
on Apr 8, 2006 at 3:15:51 pm

Graeme writes -

If a SDI output shows video darker, then whatver is converting that SDI digital signal to analogue is wrong, not the SDI signal. If that's in the monitor, then that monitor is not functioning correctly.

Hi Graeme -
this has been an issue from before the AVID was invented. We saw this in digital linear suites in NY that started to integrate "old" analog sources into their D1 suites. This became a HUGE issue when the original SDI AVID was introduced (the original SDI only ABVB board developed by Don Nelsen at AVID), and everyone wanted to get their 1" and Beta sources into this new product. All of a sudden, everything looked "dark" if was a mixed format job. The Videotek VTM's were not developed yet, and the only multi format scope at the time was the "new" Leader LV5100D. This scope allowed you to instantly switch between SDI and analog input. The "problem" was apparant on the scope. ALL SDI monitors showed this "problem" - that included Sony BVM and PVM series, ASACA (popular at the time), and Ikegami. An alternate way of monitoring was to take the output of the waveform monitor, and take the PIX MON out of the SDI scope, and put that into the analog component inputs of the TV monitor, and switch the TV monitor to SMPTE N10, which matches the level of the PIX MON output of the scopes from Tek and Leader. Switch back and forth, and you still see the difference in black levels. IT DROVE CLIENTS CRAZY back then, and it drives them crazy today.

Want to see the problem (got a multi format scope like a Videotek VTM ?) -
Put up bars out of your AVID Adrenaline or Blackmagic Decklink Extreme (you have both, right ?) - now, take the SDI output, and analog composite output, and stick it into the SDI and analog inputs of your scope. Now switch between inputs - LOOK, the 7.5 line goes all the way down to blanking level on the SDI input ! But it's the SAME DAMN SOURCE.


But don't worry Graeme, this is nothing compared to dealing with trying to match legacy analog tapes with HD images, and changing the aspect ratio
from 4:3 to 16x9, and trying to explain that to clients (how come it looks funny). All of a sudden, the black levels ain't that important anymore.
It's like the old saying - " got a headache, hit your hand with a hammer, and you will forget about your headache".

Bob Zelin




Return to posts index


Borjis
Re: Black Levels
on Apr 10, 2006 at 4:27:04 pm

[Christopher DeAngelus] "My question is, am I forgetting something? Is there a switch in Final Cut I may have ignored that is bringing the video in too hot?"

If I'm not mistaken there is a 0 & 7.5 setting in the preferences of FCP if that helps you.

and to throw in a curve, how about the "superblack" -7.5 signal?



Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2020 CreativeCOW.net All Rights Reserved
[TOP]