color bars questions

[Bob Zelin]

REPLYS below

1) There are several color bars that we can find, the FCP bars, the Test Pattern Maker/EchoFire bars, the Blackmagic bars. In your experience, what bars are accurate/correctly calibrated? Which ones should I start to constantly use?

REPLY
Color bars are color bars – they should all be EXACTLY the same. FCP bars are dead accurate, and Blackmagic, Echofire, and FCP bars should be EXACTLY the same – you should see NO DIFFERENCES between levels. Most people use SMPTE or 75% saturation bars – not 100% bars, which have a 100% saturation level in the Pb Pr levels.

2) should I use the color bars with set-up or without set-up? Again, I will finish on digital (that would say NO set-up) but I am monitoring on an analog device (that would say use setup).

REPLY – SMPTE color bars have NO SETUP on them. Let me make this clear, because it is confusing. The exact same NTSC color bar signal passing thru a Digi Beta VTR will have setup on the analog outputs at 7.5 IRE and zero setup (at blanking level 0 IRE) on the SDI output. This is why people say “hey I shot this Beta tape, and now the black levels looked crushed when I look it on an SDI monitor”. Good reason – the SMPTE committee never considered that people would be mixing and matching analog and digital source material. There is no way to resolve this – digital SDI signals (and HDSDI) have zero setup, and analog has 7.5 IRE setup in the US. Which is correct – they are both correct. How do you explain to a client that it looks different when you look at the analog or digital signal – good luck – tell em to sue SMPTE.

Plus, when I try to calibrate based on the pluge, with set-up I can see the 3 small black bars and I can easily calibrate, while when I use no set-up everything is black all-over and is harder to differentiate.

Reply – PLUGE was developed to help assist you in setting up the brightness control (black level control) of your TV monitor. The bar to the left in pluge is considered “blacker than black”, and the bar to the right is “whiter than black”. You turn your brightness control until the blacker than black bar disappears, but the whiter than black bar is still visable. This is the reason it was invented. But nothing beats having a waveform monitor to see all of this.

Bob Zelin

[Mike Medavoy]

Thanks so much for your answer, and some issues are now clear for me. However, I am still confused on some points:

1) Are indeed all color bars the same? When I output FCP bars, then Echofire bars, then Blackmagic bars, they all look different on my monitor (and I don’t re-calibrate the monitor, of course). They never look exactly the same. And I remember reading in several places (including the Synthetic Aperture manual) that most color bars you can find are “wrong”, I mean not properly calibrated. They said theirs are ok so it could be marketing :-)))

But back to the set-up, then why in the Blackmagic folder after installing there is a Test Pattern subfolder containing SMPTE bars WITH setup and SMPTE bars WITHOUT setup? Now I am really confused.

2) But what I’ll do I will just use FCP color bars since this is my editing platform and calibrate my monitor to it, using all the known steps, and using the pluge at the end. This should give me peace of mind the calibration is accurate, right?

Thank you again.

[Bob Zelin]

1) Are indeed all color bars the same? When I output FCP bars, then Echofire bars, then Blackmagic bars, they all look different on my monitor (and I don’t re-calibrate the monitor, of course). They never look exactly the same.

REPLY – the physical spacing of the bars, and the I/Q may be different, but the lumanance/chromanance of the bars should ALL BE THE SAME levels – that is for 75% bars, or 100% bars (you should only be using 75% bars for 99% of the work out there). These measurements are made on a Waveform Monitor, which is the only thing you can trust – you can’t trust a TV monitor for levels, and color bars is the test signal for this calibration process. The ONLY way to tell who is correct, is to put the video out from the Decklink into a Waveform monitor, and look at them and measure them. I can assure that the FCP NTSC bars thru a Decklink card are 100% correct. You will not learn engineering theory on a forum like this – someone must show you, or you must study the Tektronix and Leader websites.

And I remember reading in several places (including the Synthetic Aperture manual) that most color bars you can find are “wrong”, I mean not properly calibrated. They said theirs are ok so it could be marketing :-)))

REPLY – I find it hard to believe that Synthetic Aperture said that most color bars are wrong. This is a foolish statement. You can only evaulate what is right and wrong on a waveform monitor.

But back to the set-up, then why in the Blackmagic folder after installing there is a Test Pattern subfolder containing SMPTE bars WITH setup and SMPTE bars WITHOUT setup? Now I am really confused.

REPLY – Digital bars that follow SMPTE 259M DO NOT have setup level. RS-170A color bars (the original analog color bars) have setup. ANALOG has setup, Digital has no setup. THE SAME DAMN IMAGE or the SAME DAMN COLOR BAR SIGNAL passed thru a VTR that can show analog and digital outputs will show the ANALOG output to have setup, and the Digital output to have NO setup. This is typical of the Sony DVW-A500 VTR. This means that the SAME SIGNAL looks DIFFERENT on a monitor that can display both analog and digital, depending on if you look at the ANALOG signal, or the Digital signal. It looks different becuase the digital signal has NO SETUP on it, so it looks “darker” or more contrasty. There is NOTHING you can do about this – this is the nature of the mistake not taken into account by the SMPTE committee when these standards were developed.

If you use a color bar pattern with NO SETUP (0 IRE black level), and do an analog project, the blacks will be elevated to 7.5 IRE on the analog outputs. You can’t appreciate any of this unless you look at a waveform monitor. Just looking at your TV will confuse you.

2) But what I’ll do I will just use FCP color bars since this is my editing platform and calibrate my monitor to it, using all the known steps, and using the pluge at the end. This should give me peace of mind the calibration is accurate, right?

REPLY – you will NEVER have peace of mind until you observe these signals on a waveform monitor. PLUGE is just a convenience tool to setup the brightness control on your TV – it is not a way to calibrate your signal.

I remember the first time it “clicked” about the difference between analog and digital – with setup, or no setup – and my only reaction at the time was “how can this be – what the hell were these guys thinking – how could they have expected no one using D1 machines to ever use an analog Beta VTR or 1″ source in the same session”. You get over it, you eventually don’t care.

Bob Zelin