Bars, IRE pedestal, DV, analog.... egaad!

[Dave Grey]

Greetings all.

I fear I will have to make this a longish post in order to explain where I am relative to having a clue, appologies in advance for that. Let me go ahead first and ask the straightforward question:

Can I use the SMPTE color bars generated by the GL2 as a tool to calibrate and match my NTSC televison and my computer monitor?
Specifically, what is the significance of the +7.5 IRE analog versus 0 IRE DV black level?

Whew. OK, here is the background... I am new to DV. I have just purchased a GL2. I will shortly be purchasing a DP G4 1.25 and FCP. I will *not* be able to purchase either a reference TV monitor or a new computer monitor. I will be using a 27" Panasonic GAOO TV and a 17" Sony Trinitron computer monitor with component inputs (not sure if the component gets me anything in this setup, but it is there :) both of these were pretty upper end in thier day, but a lot of time has passed since then.

So. Now I have these two old devices I want to use with all this neat new hardware, but I will need to match thier output at least to each other, and ideally with the standard.

I know how color bars work, and I know how to use them with blue filter glasses in an analog environment. Well... my camera outputs bars, so I am ready to move on to the next thing, right? Well... maybe not. I came across this:

"If you're editing DV, the SMPTE color bars actually present a dilemma: they're designed to work properly only in an analog environment with +7.5 IRE pedestal. Since DV uses 0 IRE for black [...] this poses a real problem for using the SMPTE bars. "
-http://www.greatdv.com/video/smptebars2.htm

Reading that sent me running back here (this forum has been invaluable to me since I started trying to puzzle my way through this process, thanks all!) to try a search.

I found an old post by Don Palomaki that confirmed this fact, but as the topic was a comparison of the GL1/XL1 psuedo bars it did not really tell me what to do about it.

Can anyone offer me enlightenment?

For bonus points, do I gain anything by using the component inputs on the SONY monitor? I would be using the DVI>VGA converter from the ATI Radeon 9000 Pro, then a VGA>compenent cable... I already use the VGA>compenent cable with that monitor on one of my PCs, but that was really just because I had it lying around, I don't know if it offers any advantages there either. *shrug*

Thank you everyone for all the terrific information you have contibuted here, and thank you more if you are able to parse the above rant to answer these further quesitons!

lyd

[Jeff Donald]

Why, why does your computer monitor have to match the NTSC video monitor? There is no reason to have them match. If you have clients sitting in on edits they need to be close , so the client isn't wondering why everyone is green. Besides, the monitors exist in two different color spaces, they have different phosphors etc. They can never match, they display color differently. They can be close, and that's it. Myself, I really don't worry about the computer monitor. The NTSC monitor is what it's all about if your work is for broadcast, VHS or DVD distribution. Computer monitors are for your work going to the web. FCP has a waveform/vectorscope built in. They are more important than either monitor.

Rather than rewrite the setup, black level info go to Adam Wilt's page http://www.adamwilt.com/ and spend a couple of hours reading his site. His site will answer many of your questions and probably raise others. Post back with additional questions and I'll try to explain.

Don't waste money on the component inputs. But here is a thought. Why don't you get the dual 1gig mac and with the savings get a new monitor? The little bit extra speed is not that critical (in my opinion) for editing. A new Apple flat screen monitor sure would look nice next to you G4 tower. If you want to impress a client, the Apple flat screens sure do it.

Jeff

[Dave Grey]

Thanks for the response...

I notice this post was moved from the GL2 fourm; I'm sorry if it was inappropriate there. Originally my question was definately GL2 specific, "Are the GL2 color bars 0 IRE or 7.5 IRE?", but it quickly rambled into other things...

I had already read much of Adam Wilt's site, and it is exellent. Returning to it again, however, I couldn't find information specific to this topic. If you have a direct link to that section it would be appreciated.

I did find some good things elsewhere...
http://broadcastengineering.com/ar/broadcasting_color_bars_puzzle/index.htm
http://broadcastengineering.com/ar/broadcasting_inside_color_bars/

The B.E. article answers questions I could never even imagine asking about the nature of color bars. Great stuff.

The apple knowledge base yielded two good basic articles with related links:
http://docs.info.apple.com/article.html?artnum=36779
http://docs.info.apple.com/article.html?artnum=36550

Article number 36779 seems to indicate there may be issues maintaining legal levels when, say, doing a one-off to VHS by outputting computer>firewire>camera>svideo>VHS Deck.
That may be a topic best addressed seperately. If you do not respond to it here I will start a new thread later on.

Finally, I was brought right back home to dvinfo.net when a google search turned up:
http://www.dvinfo.net/sony/articles/article06.php
Bob Stevers has made availiable two .jpg images, a 0 IRE set of bars and a 7.5 IRE set of bars.

I think I now understand what I do, and don't, want to do here. Let me sum up for your approval...

First, it makes perfect sense (after you bonked me on the nose with it) that trying to match the SVGA monitor with the NTSC monitor is a pointless excersize. My personal experience is with matching many SVGA monitors in a digital still image production environment, and "all the displays must match" was kind of a knee-jerk reaction.

That said, I still want each display to be representing the most accurate color and brightness possible. Leaving the SVGA monitor out of it for the moment, would I want to:

1. Assume that the color bars generated by the GL2 are in fact 0 IRE setup.
2. Use 7.5 IRE bars (not the ones generated by the camera) to adjust the Panasonic NTSC display.
3. Use the bars generated by the camera to adjust the flip out LCD (is this of any value?) and any other display I might use at aquisition time to check exposure, color, etc.

Finally, your suggestion to get the slower G4 and use the difference on a flat panel is a good one, and something I have considered. The reason I am leaning toward the 1.25 and the older monitor at this point is that I would like to get the 22" cinema display. The savings I would appreciate by going with the 1GHz would still not allow me to buy it now.

Thanks very much for your input.

lyd

[Bill Ravens]

This can be a very confusing issue. The DV standard requires a 0 IRE, that is to say, there is no such thing as "setup" as far as digital video is concerned. The problem comes when you load that DV info into your NLE for display. The NLE massages the info to give you some black to white level. That level is, again, modified by the RGB color mapping in the monitor. The object of calibrating your monitor is to try to match the standard NTSC color map, so that you know that you're looking at the same thing as another monitor set up to the NTSC monitor standard. Your NLE app should also give you the option to "clamp" the color mapping to NTSC standards, which are 7.5 IRE for black, to 100 IRE for white. If you don't clamp it, your final output will probably be out of spec. Don't worry about what your DV camera is doing in the codec, just be concerned with what you're outputting from the NLE. If you're outputting back to DV tape, be sure the tape house knows what IRE level you used in the NLE....ie, clamped or not.

[Andre De Clercq]

People claiming that colorbar calibration/verification is only valid when setup is OK, did never calibrate monitor signals...Setup is just minor part in the game and if "wrong" it's simply corrected by adjusting the "brightness" of the TV. As long as the brightness setting of the TV (monitor) has not been (optically)calibrated it rules out any setup discussion...Colorbars' most important purpose is to verify saturation, hue and component balance after color decoding. The pro's do it by verifying the decoded colorbar RGB signals with an oscilloscope. I you are used to "see" and interprete colorbars there is a good chance that the "calibration" can be done without the pro stuff (eventually using filters..). Whether you can use the GL signal depends on the internal colorbar generator precision. Not only the digitally generated baseband signals, but also the encoding process (NTSC or PAL) should be OK...Maybe it is OK...or it has to be verified first with a vectorscope/waveform generator.. Can be a computer based one if the (software based) decompression/visualisation algorithm is OK.

[Peter Wiley]

Someone once said that NTSC actually stands for Never The Same Color -- old joke.

I used to agonize over all this and then I bought an Ikegami color production montior. Now I calibrate the monitor with bars laid down at the head of whatever tape I am working with and don't worry -- it is a very good predictor of what one will see on consumer TVs.

When I started using the monitor I could suddenly see much more clearly than ever before the impact of color temprature. Daylight looked bluish, incandecents yellowish, floursecents greenish. The inexpensive consumer TV I had been using as a monitor really distorted colors far more than I imagined. The experience made me question the value of trying to calibrate a consumer set. I also realized that LCD screens can't be trusted for any kind of asthetic judgement.

With the monitor I can also actually see the impact of decisions about exposure far more clearly.

I suppose what I am saying is that a good monitor is well worth cost.

[Andre De Clercq]

Well...I designed and later on headed several designs of color TV's , projectors and Class1 broadcast monitors including NTSC versions (Barco). My experience is that modern TV's, most of them, include advanced digital decoders and signal processing and are quite performant and stable. Times have been changed... also for the "never twice the same color" world.

[Charles Papert]

Gaahh...oy vey.

I've just finished a project in FCP that has a variety of kinds of media in it, and I've been battling the setup issue.

I've read a bunch of posts here as well as the section on setup in the FCP manual, and I think I get it. But then again...

I've set up my broadcast monitor to the bars output from FCP and then adjusted all my clips so they observe the proper baseline (black at 0 IRE), which required dialing down the blacks in the color corrector. Everything looks lovely on the monitor; absolute blacks in the image correspond to the picture black created by a fadeout in FCP. Much higher, like 7.5 IRE, and the blacks look washed out. So far so good.

I output to tape (DV via firewire) and watch it on my regular TV--and it's noticeably crushed compared to any other source like cable, DVD etc. Sure, it's easy enough to adjust the brightness...but I can't ask the many viewers of this particular program to do that to their own sets!

So now I feel like I need to calibrate my monitor to a set of bars that represent black at 7.5 IRE rather than 0 IRE, and then adjust the picture to eye as well as keeping the absolute blacks in the picture to 7.5 IRE so that it will look correct on a regular TV...? Could this be right??

[Graeme Nattress]

Charles, I think you have it right! You must calibrate your monitor to 0IRE when viewing DV because most DV decks do not add setup on output. You must also keep you FCP blacks at 0IRE because digital video does not have setup.

Yes - when you output to tape - VHS, BetaCam etc. you have to put a proc amp between your DV deck and you're analogue deck to att the 7.5 setup. You should only ever add setup on converting digital to analogue. If the tape is DigiBeta, you should get an SDI digital dub done, and, ofcourse, this adds no setup, and that is correct.

Another alternative is to make a DVD. DVD, being digital has blacks at 0IRE, and the player itself should add setup to it's analogue outputs.

[Graeme Nattress]

Also, the site mentioned in the original post:

http://www.greatdv.com/video/smptebars2.htm

Doesn't seem to make sense....

"middle BLACK is set at 7.5 IRE black, or in the digital realm, 16,16,16."

In the digital realm there is NO SETUP! Black is 16 in digital video. It's up to you to make sure that whatever you have you're analogue black at (0IRE or 7.5IRE, depending where you live) gets correctly mapped to 16 in the digital realm, which in FCP's waveform monitor is at 0!

Also, you should only add or subtract setup when you convert digital to analogue or analogue to digital, and you should only do this conversion at the very point of conversion. You shouldn't add setup in the digital realm of you NLE as that will produce non-standard digital files.

If you're working with DV, I find the best thing to do is calibrate your monitor to your NLE output. You will then produce standard DV digital video, and be able to see it correctly. You should only ever worry about setup if you dub to analogue tape for someone else to view. Or if you have to get analogue video into your system. (buy a proc amp!!)

Graeme

[Norm Couture]

Charles,

Exactly as Graeme just wrote, our DV consumer camcorders may be NTSC, but they are made in Japan where NTSC standards have a 0 IRE black level. So the DV world works with 0 IRE blacks. Your computer monitor should be set to properly display whatever comes out of your GL2.

The problem occurs when you connect your cam's A/V or S-Video output to a North-American TV set or a VHS. Then the blacks will be crushed and the whole picture will look darker.

I don't have a proc. amp, but my no-cost solution is to compress my edited movies to high quality MPEG2 format and burn a DVD. DVD players sold in North-America read MPEG2 digital files and add a 7.5 IRE setup to their analog output to the TV screen or an analog VTR. The DV or D8 camcorders do not (except some pro-series). Copies made from DVD players to a VHS recorder are correct.

NOTE : Your GL2 has a special "cam. setup" menu that allows you to adjust VCR setup (- to + slider). I don't know if it works only in recording mode, or if it can affect playback also. You should try it. The ideal would be to record at 0 setting and playback at +7.5 to your TV or VCR.

Tell us if it works...

[Graeme Nattress]

And to clarify, DV camcorders record at 0 black, not because they're made in Japan where NTSC has 0IRE black, but because all digital video the world over records at 0 black! What is missing from camcorders is the circuitry to correctly (for North American NTSC) add the 7.5 setup on conversion of the digital to analogue. Similarly, most DV decks lack this circuitry, and it's complimentary circuitry on the input side to remove the 7.5 setup from analogue sources being dubbed to DV.

[Chris Hurd]

Just to poke in quickly regarding the desire to have the computer monitor match the video monitor... I agree with Jeff, there's really no way they can ever match perfectly... so why would you need to have them match. On my Canopus DV Rex RT, I've toggled off the video display portion of the editing window so that all I'm seeing on the screen is the timeline, tool bars and clip bins. I'm watching the video output to a small video monitor adjacent to the computer monitor, almost like a dual-screen display.

Also, 27" displays are wonderful for client meeting rooms and such, but in the editing suite? It's a separate topic, I guess, and I don't want to deviate from the excellent discussion here, but to my eye, 13" is plenty big in the close proximities of a cramped editing bay.

[Norm Couture]

Just to add:
2 different scales are used. No to be confused:

The IRE scale goes from 0 to 100%, where North-American NTSC's black is 7.5.

The other scale is based on 256 shades of gray from pure black to pure white, where black stops at level 16 and white starts at 235.

I hope not to confuse...

[Charles Papert]

Thanks all,

Good to know that the DVD players add setup. After posting, I burned a DVD and was DELIGHTED to see that it played properly on my home set. I'll have to test the output to VHS to see if it is crushed. I'm going through a JVC AV selector (JX-S777) which might possibly fix the setup, anyone know? Otherwise I have an old Sima color corrector box that I bought in the early FCP days, before that mind-numbingly great color corrector feature was added.