I'm all perplexed: video scopes

[Bill Ravens]

Yes, I use the following workflow...I do all my work with 0 IRE setup. In POST, when you are ready for the final render and PTT do the setup based on the final distribution, analog or digital. This means your monitor should be set to whatever your final output will be in order to get the right color balance hi-lite and shadow. After applying the Broadcast color filter, since it remaps the blacks, you may also need to apply a color correction filter to fix the contrast and brightness issues Rob mentioned. Be sure to play with the smoothness sliders to minimize these contrast and brightness effects.

A note on the XL1s black level(pedestal) setting. I've been playing with the black level and seem to notice that changing the knob has an affect on the blacks in the viewfinder. I question whether it also affects the black level on the DV tape. I don't think it should have any effect on what gets layed down to tape. As we discussed yesterday, DV pedestal is 0 IRE by definition. You should not be able to reset that during capture. I beleive the black level setting on the camera affects the analog output, but, NOT the DV output. If, in fact, the DV black level is changing, Canon made a BIG mistake.

[Rob Lohman]

Well, that's a long story Bill. Canon didn't make a mistake at all
and yes, the level is changed digital on tape as well. You are
correct in the matter that DV by definition is 0 IRE. That's only
true since it allows the pixels to start at 0. But why couldn't
a camera manufacturer only use the 16 - 235 range of that if
they wanted to?

That's what the setup level of the XL1S. It simply moves the
line up. So depending on where the slider is set it will not encode
completely black as 0,0,0 (if it was RGB) but as 15,15,15 for
example.

Why would this be a big mistake? You are asking the camera to
change the setup level, that's what it does.

[Bill Ravens]

Rob...

yes, I see. It was confusing me that I was seeing a change in DV black level, but now I understand what you're saying. In tests I've done, it seems that a black level slider setting of -2 sets 7.5IRE. So, you're saying that a slider setting of -4(minimum, whatever that is) is 0 IRE? That would make sense.

[Rob Lohman]

That seems to be the case. I've got mine all the way to the left
and I'm getting nice deep blacks (I'm in PAL land).

[Don Donatello]

to add some confusion ..

just where are these 0 blacks ?
and 0 what ? 0 rgb ? 0 ire ?
on scale 16-235 then 16 rgb is 0 ire so is that the 0 black ?
16rgb is the middle pluge which is black level at 7.5 ...
0-255 so is 0 the 0 black ?

i use GL 1 and elura .. i see no 0 blacks .. the only way i see a zero black is with Vegas waveform scale set to 16-235. but 16 is not 0 rgb it is 16rgb which in analog is set up 7.5 ... change the vegas scale to 0-255 and my 0 black moves to 7 ...

HOWEVER !! if i switch Vegas to use the microsoft Dv codec ..
now on a 0-255 scale my blacks are 0 ire ...add set up and the blacks are now 7 ire ... move the scale to 16-235 and the black is now -7 ire add set up and blacks are now back at 0 ire ...

it appears that Vegas codec supports NTSC 601 mapping .. the microsoft dv codec does not ...

my question is what is meant by 0 black .. is that 0 rgb ? or is it 16 rgb ?

[Bill Ravens]

In DV speak, 0 black is 0 IRE. In RGB speak, 0 IRE is 16 RGB in a correctly calibrated NTSC system. If your system is erroneously calibrated, 0 IRE could be 32 RGB or 0 RGB.

In analog speak, 0 black is 7.5 IRE. Yes, I think you're right. Vegas4 is referenced to NTSC601.

[Rob Lohman]

Are you sure 0 IRE is 16 RGB? I always thought 0 IRE was 0 RGB
and 7.5 IRE was 15-15-15 RGB (basically). Now I'm not from an
NTSC country, so I haven't weaved through all the techincal stuff
on this. But 15 for 0 IRE seems a bit high to me. I could be very
wrong on this ofcourse. You can CALL 7.5 ire 0 black, but I'd
rather not since it is actually grey. So shall we call it 0 grey? <g>

How confusing! I am glad we don't have that in PAL land. Pfff.

[Bill Ravens]

The DV "standard" defines the RGB level to extend from RGB16 to RGB 235. While RGB 0 may be possible with some cameras, it's officially an unofficial (re: non-standard) capability. The whole secret to NTSC 601 standard pedestal of 7.5 IRE correction in Vegas4 , is that it remaps the DV luma signal so that 7.5 IRE or lower is 16 RGB. Therefore, in the remapping process, all DV signal levels between 0 IRE and 7.5 IRE are moved to 16 RGB. So, if you have a monitor setup at 7.5 IRE, you still get blacks. If you've left the setup at 0 IRE, all the values between 7.5 and 0 get clipped off, resulting in muddy blacks.

Yeah, it IS confusing. Probably better discussed over a cold beer.

Think this way:
DV signal is 0 IRE to 100 IRE
DV color space is 16 RGB to 235 RGB.

Analog signal is 7.5 IRE to 100 IRE
Analog colorspace is 0 RGB to 255 RGB (that's why you'll see 110 IRE on a waveform scope.

[Rob Lohman]

I'm assuming that it isn't doing this for a PAL project since I've
got below 16 values and they are pitch black.

[Josh Bass]

Beer. . .but I'm a nerd. . .I don't even drink. . .


When you "NTSC system," in reference to black being something other than 16 if not properly set up, what do you refer to? The camera? The NLE? I thought the NLE just took in whatever the camera gave it? There's no way to set up anything during capture, like there is with AVID (or at least the Avid I used--you could pump up brightness, audio, whatever before you captured). I don't have a DV deck or anything.

[Bill Ravens]

Josh...

just what you've been thru. if you do everything right, for example, but feed a 0 IRE pedestal to your NTSC monitor(which is expecting a 7.5 IRE pedestal), you won't see the right color blacks. There's a zillion ways to mess this pedestal thing up, just in POST, alone.

here's a little lab exercise that demonstrates a LOT about your NLE and display monitor.

Download a black step wedge off the internet, use the step wedge provided as "generated media" in Vegas 4, or better yet, make your own black step wedge in Photoshop. Be sure to start at RGB 0,0,0 and makes wedges all the way up to RGB 255,255,255. Be sure to include a wedge at 16 and a wedge at 235.

Now, import this step wedge into vegas 4, turn on the waveform monitor, insert a Broadcast Color filter on the clip and play with the settings. Be sure to always have the checkboxes set in the waveform monitor match the settings in the Broadcast filter, otherwise the waveform you're looking at means nothing. Also, compare the white and black wedges to what you see on the monitor to what you see on a CRT screen. You'll learn a lot.

[Josh Bass]

Just had an exhaustive talk with a friend of mine who owns a rental house and functions as a video engineer on the sets of some its clients.

He told me basically that 1) once the product leaves my hands, there's a million ways it can go wrong until it's broadcast

and 2), the change between 0 and 7.5 when going from digital to analog is AUTOMATIC, that is, black levels are automatically raised up to 7.5 from 0, or an additional 7.5 units (?) from whereever they are. Messing with them in post, then, is a bad idea because it'll result in an additional 7.5 bump from whereever I've raised them to. Basically then, if shoot at 0, edit at 0, and output the same way, keeping my deepest blacks above 0, then I'll be okay, provided there are color bars from which to set up. Since the NLE I have generates them, should be no problem.

[Bill Ravens]

wrong...sometimes right...but, mostly wrong. If you follow this policy, all I can say is BE SURE to label your final tape as to what the setup level is.

[Josh Bass]

But wait. . .if I've been setting my black pedestal on the camera recently to -2, then I AM using a 7.5 pedestal, no? All the way to the left would be 0, right? So then I should set the monitor to 7.5 too?

[Glenn Chan]

and 2), the change between 0 and 7.5 when going from digital to analog is AUTOMATIC, that is, black levels are automatically raised up to 7.5 from 0, or an additional 7.5 units (?) from whereever they are. Messing with them in post, then, is a bad idea because it'll result in an additional 7.5 bump from whereever I've raised them to. Basically then, if shoot at 0, edit at 0, and output the same way, keeping my deepest blacks above 0, then I'll be okay, provided there are color bars from which to set up. Since the NLE I have generates them, should be no problem.

Consumer equipment doesn't do that when converting from DV --> analog. It's supposed to. You can compensate, but then you'll make out of spec DV that would be too bright with equipment that does things right.