0 VS 7.5 ire REMIND ME!

Hey all you veterans, (Koz, Ian, etc...)

Remind me on this one again...

FCP at DV resolution is operating at 0 or 7.5 ire for black levels?
Is this a preset/choice in the Sequence Settings?
This affects the Color Bars output VIA firewire to NTSC monitor right?
(I use the built in color bar generator to set-up my NTSC monitor).

So the output of the color bars should match the NTSC monitor and be carefully followed so things aren't too dark or too light right?

Can someone point me to a primer on this as it related to Final Cut Pro? I'm trying to verify I'm setting all my bars properly through the chain...

THANKS THANKS THANKS!!!

-Joshua

IRE is for analogue video. DV is digital. There is no IRE in digital video. FCP does not know, and does not care about IRE as it only works on digital video. The only things in your system that care about IRE are analogue to digital and digital to analogue converters. It is the settings of these devices that determine black leves in your system.

In FCP, your blacks should always be at 0%, and whites should stay below 100%. These are not IRE numbers, but refer to rec601 standard digital levels of 16 for black and 235 for white which are the standards you need to worry about for digital video.

Graeme



[www.nattress.com] - Plugins for FCP-X

Hey Graeme,

Gotcha...

My chain goes FCP -> Firewire out to DSR-11 -> S-Video Analog out to NTSC

So if FCP is using 0-100 digital than everything in my analog chain should be set to 0 ire as well right?

My NTSC Monitor is set-up is at 7.5 ire right now, which I gather from what you are saying is wrong. It should be 0 correct?

I'm also curious what the "color temperature" should be set at. It allows me to select 6500 or 9300. Should this reflect the color of my studio lights?

THANKS>

I know this is a weird series of questions but I want to make sure my stuff looks consistent...

And to answer the other question, if you shot your digital show normally (not got it from an analog conversion) then yes, the colorbars from the effects tab and the show video should match.

You can open up the Waveform Monitor Scope and look to see that your video doesn't stop short of zero on the bottom and doesn't go too far over 100 at the top.

If you're in 4.5HD,you can switch the scope to "Luminance" and it makes everything a little ealsier to see. The two critical levels are clearly marked.

Blacks are very sensitive things. A 7.5 error at white is, for all practical purposes invisible, but a 7.5 error at blacks is immediately visible as muddy pictures or milky bright blacks depending on the direction of the error.

These scopes will show you problems like that and help you keep your show looking good.

Take a regular scene from nature that you shot and beat it up with the two color correctors while you're watching the scopes and see what happens when you apply the different controls.

Pull down this still:

[www.kozco.com]

...and watch what happens when you manipulate it. This is easier to see what's going on than live video. Watch on a good monitor while you fool around.

Also, to air my favorite complaint, note that if you import that gray graphic, the mid point isn't at 50. I created it that way, but FCP distorts imported stills so things are brighter than you think they should be.

Koz

So... when whites go above 100 ire on an analog signal the tv set at home gives out a buzz. what happens when blacks go below 7.5 ire in a broadcast?

Koz? Does the set explode?

Because black is set at 0 ire in europe and japan I've always wondered why the fuss here over 0 ire blacks.

Joshua - you're mixing things up there. The scale of 0% to 100% in FCP has nothing to do with, and bears no relation to the 0IRE to 100IRE scale in analogue video, however, that does not mean that the two scales will not match numbers with each other in particular circumstances, but that has more to do with humans numbering scales from 0 to 100 than anything else.

Your DSR-11 deck is either PAL or Japanese NTSC. The NTSC ouput on it is not North America NTSC. That means it's digital to analogue converter will translate REC601 Digital video code 16 (what FCP calls 0%) to 0IRE, and code 235 (which FCP calls 100%) to 100IRE.

The 0IRE / 7.5IRE switch on your monitor should be set to 0IRE, and the brightness (more properly called black level) should be calibrated to the FCP bars running through your deck to your monitor.

Graeme



[www.nattress.com] - Plugins for FCP-X

<<<My NTSC Monitor is set-up is at 7.5 ire right now, which I gather from what you are saying is wrong. It should be 0 correct?>>>

The trip in and out of analog land is fraught with perils.

Most decks and unless somebody contradicts me including the DSR-11 do not translate between video levels correctly when used as a pass-through converter.

Given that, the DSR-11's output is going to be too dark and you should probably use the "zero" setting on the monitor.

More better than that, however, is to use the monitor's brightness (black) user control and Effects Tab Colorbars to calibrate the monitor correctly by eye for normal room lighting. Set the two dark gray stripes in the lower right so you can only see one of them.

Koz

Although why the USA didn't ditch 7.5IRE in the 80s like Japan did I'll never know. Then again, you only have to look at their botched HD introduction to see that they couldn't organise a piss-up in a brewery...

Graeme



[www.nattress.com] - Plugins for FCP-X

THANKS KOZ/GRAEME!

That confirms my suspicion!
I had been calibrating with the monitor set at 7.5 ire.

And yeah I realize the two were separate issues, but you both hit it on the head...I wasn't sure what was happening when the signal went to analog land and hit my monitor...

One last question...

The monitor also has color temperature settings of 6500 or 9200. I'm guessing here...but I want to choose the color that most reflects the temperature I'm working at right? This is a basic indoor/outdoor scenario and related to white balance essentially?! 6500 indoor and 9200 outside or on location?

THANKS!!

-J

<<<when whites go above 100 ire on an analog signal the tv set at home gives out a buzz.>>>

The whites will be caused to not do that by the video processing at the transmitter. They will be clipped off at 100 and any video higher than that will be lost. This gives you pasty-looking highlights and weird sparklies on shiny things.

The worst problem with blacks will be too high--gray, filmy looking shadows. Digital video can't go much lower than digital 0 (although colorbars do that as a desirable distortion for testing).

<<<Because black is set at 0 ire in europe and japan I've always wondered why the fuss here over 0 ire blacks.>>>

Back in 1938 when we were first doing video, transmitters would only work right when the blacks were *not* at 0. 7.5 was a patch job to get the television system out the door. Only later was the system refined enough to not need that. Everybody who came later just adopted the 0 standard. We were stuck with thousands of TVs working the other way.

Same with 30 frames and color. We'll just push the frame rate around a little to get color to work. Who's going to notice 29.97?

Koz

<<<The monitor also has color temperature settings of 6500 or 9200>>>

6500 is the color of outside at high noon on a sunny day. 9200 isn't found in nature.

All of our monitors are balanced to 6500. You can check your monitor. Go down to the bottom of this. It's a cheap and dirty way to check yourself against a sunny day.

[www.kozco.com]

Koz

Koz, it's not the transmitter that needed 7.5IRE, but the reciever to allow it to discriminate easier between black and the signal that trigger flyback I think. Basically, pushing the blacks up put a buffer in to make the control signals easier to notice, and to make sure black in the picture wouldn't confuse the reciever. It was totally unnecessary very early on, and should have been ditched way back. Japan ditched it in the 80s though.

The 30.00fps to 29.97fps was done with the intro of Color to NTSC to stop the color subcarrier interfering with the audio. This should have been ditched with the advent of digital video IMHO.

Graeme



[www.nattress.com] - Plugins for FCP-X

<<< it's not the transmitter that needed 7.5IRE, but the reciever to allow it to discriminate easier between black and the signal that trigger flyback I think.>>>

Perfectly true, but saying it the other way has a lower MYGO* factor.

<<<to stop the color subcarrier interfering with the audio.>>>

You may get an argument from me there. I think it was the other way 'round. The FM carrier is very robust (and can't move), but the color carrier is suppressed carrier semi-double sideband AM and had troubles with the wavy sound leaking in.

Koz

*My Eyes Glaze Over.

so... legal black broadcast limits at 7.5 ire are dinosaur laws that drive us crazy but don't hurt the transmission of the signal at all.

can't wait for that to change.

kevin

I think "interference" is a bi-directional concept, in that if two signals interfere with each other, you can say A interferes with B, or B interferes with A, but because, in this case, audio was the "old" signal and the color "new", the new interferes with the old, as in it's introduction of the new signal that causes problems. The fact is that either on their own would have worked makes the order of A interferes B, or B interferes A irrelevent IMHO, and as it's a quiet friday evening, I hope you don't mind the mindless drivel I've expunged.

I don't think the USA will ever change the 7.5IRE nonesense because they've had ample time and chance in the past and not taken it. Instead they're moving to digital broadcasting where IRE is irrelevent.

Graeme



[www.nattress.com] - Plugins for FCP-X

<<<7.5 ire are dinosaur laws>>>

They have one thing going for them. They made me a great many house payments over the years.

In broadcasting, the measurements go from -40 to +120. This is at the transmitter up on the hill.

-40 is where the sync signals live so the TV in your house can tell where the top, bottom, and sides of the picture are. The official name for these signals is "Blacker Than Black" since obviously, picture black in the US stops at +7.5. Anything lower than that is, or should be, invisible. See Nattress, above.

Our zero is the home of the color reference signal called the burst. It's a little bit of bright yellow-green which is the master reference point for our whole rainbow. Our "Tint, Hue, or Phase" control (purple people) messes with this signal.

Working up, 7.5 is the black level for luminance. 100 is the white level for luminance. All luminance video must fit between these two values. Color can legally exceed both of these values, but it's a poor idea, especially going up.

110 is usually where the transmission equipment brick-wall clips the video. Nothing is ever allowed to exceed this number.

120 is extraordinarily magic. Early transmitters I worked on would actually hit this value if we weren't careful. This is the number where the visual carrier pinches off and either the transmitter explodes or it starts interfering with other television channels, or both. No simple audio buzz, here, this can cause serious damage.

I've had both of these things happen--if briefly. The tower equipment becomes intensely upset when we try to broadcast on other channels and in at least one case an exploding power supply caused me to leave a perfectly good cup of coffee on the ceiling.

Koz

Important point missing in all of this -

If you are monitoring on a real world monitor (or passing a digital signal through to an analogue device (DV to BETA SP for example...or DV through an AJA Box to BETA...or even VHS) ....

You need something in that chain that changes digital 0 to analogue 7.5 IRE.

Most DV decks DO NOT do this...some of the better ones have a menu driven switch that allows the conversion...

Had this problem at ABC News producing earlier spots for them on FCP...where they played everything back in a DVCPRO machine ...and never bothered to flip the 7.5 set up switch so the blacks didn't looked crushed as it went from digital to analogue....they complained FCP was a toy that didn't conform to legal limits. I assured them it wasn't and dug through the menus to show them them the switch...and golly....wouldn't you know it, the scopes finally read the way they were supposed to!

So yes, if you keep everything digital from beginning to monitoring and that's they way it will play out to the masses - 0 DV is black.... (and don't go boosting it with a proc amp in FCP to make it 7.5 on that scope...because if it gets played back with a set up added machine - your blacks will be nearly white they'll be so washed out.)

JVC has an excellent tutorial on how this all works at this address:

[pro.jvc.com]

And this is also a very good primer:

[www.signvideo.com]

Enjoy - Andy Field