IRE has to do with TV signal strength, more specifically the amplitude of the video signal, much as dB is a measure of preceived loudness for audio. IRE stands for Institute of Radio Engineers so that's how it got it name. The value for black instead of being 0 as you would expect is really set at 7.5 on a scale of -40 to 120 with the part we see as a picture between 0 and 100.

Now this I found interesting when I read it sometime ago. What does broadcast TV have to do with the very odd frame rate in NTSC video?

Before the arrival of color television the horizontal frequency was a nice simple easy to remember 60 herz. Anyhow room had to be made to carry the color part of the signal.

So for NTSC TV signals (USA) were dropped to 59.94 herz. Divide that by two. Guess what... its that goofy 29.97 we've wondered about in other threads! Since TV is interlaced, two frames A, B (even and odd) scan lines, together end up at 59.94 herz or roughly the whole picture you see is redrawn 30 times a second or 30 A frames internlaced with 30 B frames.

Now you know the rest of the story. Unless my memory is more faulty than I think it is.

Now more back on point... should you care?

Well a guy named Joe that apparently uses FCP came up with a pretty good site that shows the relationship. Keep one thing in mind. That's for the Apple platform, which has a different default gamma setting for computers than PC's do as does TV.

Kind of gets confusing, don't it.

http://www.joesfilters.com/joesbroadcastlegalizer.php

Joe has some nice tips... just remember to transalte back to the Windows word.

Say don't some of those filters look familar? LOL!

First- IRE is an arbitrary unit used to describe the amplitude characteristics of a video signal. White is defined to be 100 IRE and the blanking level is defined to be 0 IRE.

7.5 is the analog reference for optimum black levels and 0 is the digital reference for optimum black level... These are the exact same set up or black level the only difference is the measurement used-analog versus digital. I will even go a step further- if you recoed 0 black in the digital world (Digital Beta) and then play that back in an analog world- it will be 7.5 IRE black level.

As others explained- the black level increases copntrast so to say-- as you lower black levels- you also lower video levels the same amount- you would want a time base corrector to have optimum levels...
Hope this helps

Basically it works like this:

If you shoot in DV it should be at 0 IRE throughout the edit and mastering process. If you want to make a transfer to a VHS or other analog tape you should add 7.5 IRE set-up to the signal for the black levels to look right. Note: Some DV decks add set-up to their analog outputs (I believe JVC does this). My Sony does not - I add it with a proc amp or my Storm card depending on where I'm editing.

Check this article out for a good explanation http://www.adamwilt.com/DV-FAQ-tech.html#Setup

How about when you are doing A/D conversion with lets say, the canopus advc-100. If i start with VHS going to convert it to digital and throw it on my hard drive, should it be set at 0 because the final digital format or should it be set to 7.5 since the source material is VHS?

Then the next question is just the opposite. If after i am done editing in the digital world and would like to make a few VHS copies, using the canopus A/D as the bridge between my VCR and computer, should the device be set at 7.5 because it is going to be outputted to VHS (analog) or should it be set at 0 because of the digital source material?

anytime you're gonna display on a TV monitor, the Ire should be set to 7.5
if your display is intended for a computer monitor, set it at 0.

Adding to the great posts so far - neat stuff isn't it BillyBoy? ...

Related to the 601 you might encounter, the reason for the clamping filters in VV3, broadcast filters in 4c, to my knowledge the origin was actual voltage levels in the signal. In practice, video shot at 7.5 might have a bit more headroom as the range from ~16 - ~ 235 leaves room for super black and super white, when and where equipment accepts this.

Prob. arrise when transferring from one spec to another, as when you have footage from different contries/standards, different equipment using different standards, going to the PC environ, even among software apps as some automatically assume 7.5.

A *while* back there was an excellent article in DV on this including tips to account for it in ae by Chris Meyer if you can find it (just went to their site and couldn't). I did find an article in their archive that touches on it, particularly with DV and it's std 0 IRE: http://www.dv.com/features/features_item.jhtml?category=Archive&LookupId=/xml/feature/2001/jackman_legalstills_pt1_1201

As always, adam wilt is a great source of info: adamwilt.com

If you just want the quick answer, in the US go by what Bill just posted.

Oh no... super white? That's a new one on me. Sounds like a tag line for a laundry detergent.

Ok ive read the articles and i am still confused. A majority of my finished worked is shown on a projector which is connected to either a portable DVD player or a computer w/ DVD drive which is connected by svga. Displayed on a large white screen. What would the IRE have to be in this scenario so that i could take it to one setting to another without everything looking different (i do use a lot of black colors in my work.)

The other question has to do with the Canopus ADVC-1000. It has dip switch setting in the conversion process. If converting FROM ANALOG->DIGITAL would it have to be set to 0 or 7.5? The Canopus device is confussing me with regards to settings and conversions.

Thanks for any help in advance.

For sure it is confusing. If you're going to project and not use a TV, off the top of my head I would think you would want zero. The IRE scale is mainly for broadcast TV. So you'd get a bit richer blacks using zero. What would be interesting to learn is if this is taken care of by the projector... or the Canopus box automatically. I don't think so, but I don't know don't have one.

From what I have seen on my own DVD players they seem to add their own set-up to the DVD analog output. For this reason I always master by DVDs at 0 IRE and it seems to work fine. I've tried it by bringing the blacks up to 7.5 and it looked washed out. My VHS copies do get set-up added to them when transfering from DV masters.

With a projecter you could always increase the brightness slightly if it was a problem. It's not a perfect fix but it would work I'm sure. I've plaved DV tapes through projectors with no problems and they we're at 0 IRE.

Marc

The standard for NTSC black in the United States is 7.5 IRE. In Japan it's 0. It's important that one sticks to the standard if at all possible because if you master your video to 0 IRE, and it gets shown on a display device that is set up (no pun intended) for 7.5 IRE, your detail in blacks will be lost.

There are several things that complicate the discussion however. Most LCD projectors, even DLP ones don't have very good black levels wherein their blacks are more of a very dark gray. Also many DVD players are poorly configured. In theory, you should be able to take smpte bars from Vegas, render them as mpeg 2 (DVD), burn them to a disc and then play that disc on a properly configured DVD player and see proper smpte bars almost as good as that seen from a signal generator.

I haven't tried the latest version of the mpeg encoder but the last one was not bad except that the 11.5 IRE pluge bar was at about 14 IRE I think.

I would suggest that folk stick to the standard wherever possible. NTSC is pretty awful but if everything is adjusted to the standard it can be bearable at least.

Sorry to chew your ears off...

Al

This discussion has cleared up a few questions I had regarding using the broadcast filter in Vegas and the reason for doing so. Just wondering how this relates to PAL footage...what is the legal IRE for PAL broadcast footage? I tend to use the conservative setting in the broadcast filter just to be safe, but have noticed that the on parts of my videos that have almost entirely black backgrounds(especially cg generated stuff) , the blacks don't look quite black enough on TV...thoughts from the PAL world anyone? Cheers...

PAL uses 0 IRE as black.

Al

"Oh no... super white? "

Same as super black - not quite NTSC broadcast legal color values between 235 and 255 captured by some cameras, and if not careful, lost when transfered.

Not familiar enough with projectors to say more then they vary quite a bit in their capabilities.

Control what you can control is not a bad philosophy, and in this case trying to specify somehow that the source is played back on a pc or laptop feeding the projector, maybe even going to a format that forces the issue, you'd at least have the PC Player color controls. Then again if the presentor is colorblind?...

Going pretty far afield here, but sounds like it might be worthwhile to create a calibration CD or DVD with some simple screens as idiot proof as one could make them.

"The other question has to do with the Canopus ADVC-1000. It has dip switch setting in the conversion process. If converting FROM ANALOG->DIGITAL would it have to be set to 0 or 7.5? The Canopus device is confussing me with regards to settings and conversions. "

IMO I think a lot depends on the camera... If it's recording at IRE 0, might keep it there on your box when transferring - if it's 7.5, might leave it there. In theory your PC is much more capable of capturing the nuance going to 7.5 or 0, as it's a bit more then just expanding or clamping colors during conversion, and you'll have some control of the curves used.

hope something there helps...

Sorry for beating this thread over the head but is it safe to say to produce/ master video in IRE 0 then depending on the situation (ie. Projectors, TV, Foriegn Countries) Carry SMPTE disc with me to do calibration on site before the showing?

I just want to set up some guidelines for when i master my movies and leaving IRE set to 0 and changing it depending on the scenario seems easier than having to take 7.5 setting into consideration since of the variance of where i show my movies.


Let me know if this sounds acceptable or if im on the right track.

Thanks Jumbotech, that is good to know! What is a safe preset for broadcast PAL tv....I tend to stick to "extremely conservative"...is this a wise choice?

The use of "setup", having 7.5 IRE instead of 0 is just a convention used in the U.S. NTSC market. Someone once told me that years ago when TV was sent over land lines long distance, there was so much noise on the cables that using 0 IRE didn't raise the threshold of black enough for it to clear the noise. Remember that IRE levels are voltage levels. That story could be nonsense of course. It all depends on what your display device expects. Some TVs now have a switch or embedded menu option to switch from 7.5 IRE to 0 IRE. Some folk think that in the U.S. we settle for a different color of black but if we had cameras and monitors which we both could set for 50 IRE or whatever then that would be our "black" provided that we both stuck to our "standard". The point is that if you set 0 IRE as black, anything that is slightly brighter, say 4 IRE will be invisible on a correctly set up U.S. TV monitor. If you're in Europe or Japan, you should be using 0 IRE since that is what your display device expects.

Does that help?

Al

Other points:

0 black (or super black) is used for keying in analogue edit suites. The difference in luminosity between 0 and 7.5 IRE gives the switcher the headroom to do keying.

Another point: TV broadcasters amplify their signal threw a transmitter and send it to your television set in your house. A transmitter works very hard to transmit blacks and the contrary is true for whites. The difference between 0 IRE and 7.5IRE is lots of $$$ of electricity and maintenance on their transmitters.

Gilles

"is it safe to say to produce/ master video in IRE 0 then depending on the situation (ie. Projectors, TV, Foriegn Countries)"

My personal opinion would be probably, but I'd run a test or two using a projecter to make sure, and just in case I think I'd try to compose so that anything in the 0 - 16 range wasn't absolutely critical so that if it got muddied a bit wouldn't matter [applying the clamping filter in Vegas & previewing might be a good test to make sure nothing important got lost]

My reasoning is that DV, PCs, and the rest of the world are based on 0 = black. TVs can handle it as PC output to a TV using video at that level works, and DVD players sometimes offer black enhancement, ie. bringing levels down. And I've burned discs using full color range and they've played fine [a caveat being that with letterboxed anamorphic, you might see a lighter black strip from the TV, and a true black one from the video, *depending* on the TV settings]

If the projector just acts like a TV, accepts what it's given by the PC or DVD player, then don't see why it wouldn't work. Having full color range in countries where it's a standard would I think beat trying to compensate, especially as your viewers will be expecting, trained to expect full range color. In the US viewers should be extra pleased.

I think the caveat I mentioned above, plus multi purposing concerns re: cable broadcast & ppv, is the reason that at least the one commercial movie DVD I just checked was in the 601 color space. I know there are no if's when it comes to NTSC broadcast legal, but you're not so limited.

trivia FWIW, From what I've read, I believe Al (Jumbo) is right about the early land lines and voltage requirements... Think they were experimenting with various amplification setups inline every so often and came up with the current scheme.

If anyone has calibrated their computer monitor properly, you can easily see the contrast difference between 0 IRE, 7.5 IRE and 16 IRE on the NTSC Pluge Bars. I submit that the difference is so slight as to be noticeable only by the trained eye and on very close inspection. Given that fact, a video tuned to 0 IRE will crush the black contrast by this amount when shown on an NTSC monitor. Likewise, a video tuned for 16-90 IRE looses a little bit of dynamic range. For a DV camera, the loss of dynamic range in a system that already has limited dynamic range(by the nature of CCD's) exacerbates a problem with image contrast. Therefore, as a matter of practice, I always shoot at max dynamic range, i.e. 0 to 90 IRE. If I eventually determine that my output is destined to meet NTSC requirements, Vegas 4 will remap the colors to be NTSC legal, i.e. IRE 16. So where's the beef?

Well the "black" pluge bars aren't 0, 7.5 and 16 IRE, they're 3.5, 7.5 and 11.5 IRE and with the greatest of respect, the difference between 0 and 7.5 can be critical. To give an example that I mentioned once in another posting, the place that I work at bought a large outdoor display screen (Japanese). It was used in a big night-time show in which at a certain point, the lights all went dark, the music suddenly stopped and as the big screen went black, the whole stadium was plunged into darkness - except that because the screen was calibrated for 0 IRE, it didn't go black, it went a horrible noisy gray that looked awful. It saw 7.5 IRE which was what our equipment was sending it as gray so that was what we got. When you get several Directors coming up to you after the show and asking why the x.x million dollar screen won't go black when it's supposed to, there's the beef!

Once your work is mastered to mpeg 2 for instance, it's a bit late to remap, that's why I urge people to follow the standard.

Of course, if you are working solely in the amateur world and your work is intended just for family and friends then I'd say go with what looks best to you. Your work is just as valid as a professional's, but you don't need to conform to any NTSC standard.

Regards...

Al

Jumbotech-

Okay with what you just said about the Japanese screen situation, would having mastered at 0 IRE corrected this problem? The IRE info of ntsc video equipment is not easily available so i assume most consumer dvd and the like are set to 7.5ire in the USA NTSC land.

I can imagine a scenario you presented happening to me. Is there any devices out there for the traveling projectionist (such as myself) that would adjust PAL/ NTSC and IRE settings? Perhaps hook it up to a video mixer, or even the dvd player itself.

You said your recommend following the standard. What IRE standard are you applying the 0 IRE for mastering to DVD or 7.5 for broadcast?

Since i dont consider my audience the immediate family and plan on showing my work in a professional setting, what would you recommend the IRE setting should be set?

REcap:

Constantly Traveling possibly to Japan
Mainly used combination Video Mixer, Dvd Player, and Projector