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Old October 11th, 2005, 06:23 PM   #1
Major Player
Join Date: Oct 2003
Location: Grand Rapids, MI
Posts: 286
Problem With Black Setup


I shot the footage in question on a Panasonic DVX100a. I was in 30p mode, using cine-gamma and the cine color setting. I know that this can throw the black level off a bit, and requires color correction... but I am afraid I might have gotten the IRE setting to 7.5 instead of 0 in the camera menu. Long story short, I have alot of questions. I'm learning the ropes of the 7.5IRE to 100IRE Analog = 0% to 100% Digital = 16 to 235 Digital. I think I got that right.

The first question to my problem is whether or not my ntsc monitor is even calibrated correctly. Well it isn't a professional broadcast monitor, but it is a Sony Trinitron set. It is connected via:

PowerMac 1394 --> VX2100 Y/C --> Monitor

I calibrated my monitor using the FCP5 NTSC Color Bar Generator. Do these bars work for calibration when outputing them to my monitor using my current configuration? Are they ment to have setup added to them before getting to the NTSC Monitor? If I adjust my monitor to these bars using my current configuration, am I going to be looking at an accurate representation when viewing DV footage that has no black setup (but will look like it does / or look how it will look off of a DVD when the player adds setup - If the final cut pro bars actually work how I have been assuming and am hoping they do)?

** I have read the SignVideo article on Setup, the chapter on calibrating analog video equipment in the FCP5 manual, and an article regarding DV black setup on Adam Wilt's website, and seen the JVC video on black Setup**

---- How I Calibrated My Monitor ----

I calibrated the monitor by turning chroma down... adjusting the brightness so the first two pluge bars were the same, then adjusted contrast so the third was just barely visible. Then, because I don't have a blue only switch, I used a piece of blue lighting gel (read to do this in a tutorial somewhere) and adjusted my chroma and phase settings until the alternating color bars matched. I'm sure it isn't perfect but... could/should it be close?

---- How I Calibrated My Monitor ----

Now from my understanding the VX2100 does not add 7.5% setup to the analog output signal. So theoretically I would see crushed blacks on my NTSC Monitor -OR- The blackest black should have an analog level of 0 IRE. (If the monitor were calibrated for video with a setup level of 7.5IRE.... But since I setup my monitor to the FCP bars, with no added setup, does this mean that the DV video should look like it has setup added because I adjust the tv to basicly add the setup? or do the FCP5 bars maybe have setup already added?)

Secondly I am wondering if I had the DVX set to 7.5IRE setup... would this have any influence on the camera generated color bars recorded to the beginning of my tape?

When looking at the waveform monitor, in FCP5, of the color bars recorded from the DVX to tape and transfered over firewire to FCP5 I see Black levels below 0. Here is a screenshot of what I am seeing in the FCP5 waveform monitor.

Can anyone draw any conclusions from this?

When viewing my footage on my NTSC monitor it looks ok... but I'm afraid it is not correct and that when it is played back from DVD, and the DVD Player adds setup things will be really messed up.

When looking at a frame from my video that looks as though it would contain a pure black, the waveform monitor seems to level off at 7.5 to 10. Here is a frame exported from my timeline and the waveform screenshot that goes with it.

The Frame:

The WaveForm:

If anyone has any input or solutions, or needs more information, or has things for me to try it would all be very helpful.
Matt Trubac
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Old October 11th, 2005, 08:57 PM   #2
Inner Circle
Join Date: Jun 2003
Location: Toronto, Canada
Posts: 4,750
Here's my explanation. I'm not a video engineer by any means and there's lots of confusing and conflicting information out there. So, big bags of salt.

Analog levels (NTSC, non-Japan):
black level should be at at 7.5IRE
white level should be at 100IRE

Digital levels (DV is Y'CbCr format, where Y' is luma):
black level should be at a Y' value of 16.
white level should be at a Y' value of 235.
FCP doesn't show Y' values. You have to figure out where levels are supposed to be. Y' value of 16 corresponds to 0 on the FCP waveform. Y' value of 235 corresponds to 100 on the FCP waveform.

Digital to analog conversions:
Y' value of 16 should go to 7.5IRE, Y' value of 235 should go to 100IRE.

TRAP #1: A lot of prosumer equipment like the DVX100 doesn't put Y' values of 16 at 7.5IRE. Instead, it puts it at 0 IRE.

TRAP #2: Some cameras will record "fake" setup, putting digital black level higher than it's supposed to be (Y' value of 32). When you go digital-analog, black levels end up at 7.5IRE (two wrongs make a right in that particular scenario). But in FCP that can screw you up.

I think what you should do is to drop the color corrector filter on, and lower video black level until it hits 0 on the waveform. You can apply that to a nested master project, or copy and paste attributes to a bunch of clips.

2- Monitor calibration: The blue gel trick isn't particularly good at setting hue/saturation, but it could be better than nothing. Regardless, hue/saturation isn't related to video levels.

3- If you feed color bars from FCP and calibrate your monitor to that, then you will be able to monitor your video with the right levels. This doesn't mean your levels will be right (it just means you're monitoring right, and see the levels properly).
That doesn't matter if your DV-analog converter has setup or not.

4- DVD players add setup, so you should aim for proper digital levels (your levels will get converted correctly). Video should hit 0 on the FCP waveform.

5- The waveform has two modes. One just shows luma, which are brightness levels.
This is similar to the lpass (low pass) setting on a real, external hardware waveform.

If you enable the saturation setting, then it shows the composite signal.

It's because the color subcarrier (which carries chroma information) rides on top of the main signal (which contains the luma information). The low pass setting gets rid of the color subcarrier so you can just see luma. The luma values would show your black and white levels (the composite signal, which is both luma and chroma, doesn't).
Glenn Chan is offline   Reply

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