FORUMS: list search recent posts

75% bars

COW Forums : Broadcasting

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Adam Swaab
75% bars
on Sep 14, 2005 at 6:20:01 pm

**Duplicate post in After Effects Forum**

Hi,

I've been asked to deliver a spot using 75% bars as my limit for chroma/luminance. Normally, I just deliver with the after effects broadcast filter on top of everything, knocking my spot down to 110 IRE, and there are no problems. We gave them (the network) a test this way, and they said it was too hot.

So, I have no idea what I should be setting my colors/whites at for 75% IRE. Can anyone explain this in layman's terms and tell me what settings I should be using?

Thanks!
Adam


Return to posts index

Dave LaRonde
Re: 75% bars
on Sep 14, 2005 at 6:59:14 pm

I can't explain 75% bars, but I can tell you how to fix it in AE so you'll NEVER have trouble with it again.

1. Don't use AE's Broadcast Safe effect, or whatever they call it. It stinks. Sorry, but that's the fact.
2. Get an AE plugin called Scopo Gigio. The cost is about $75, and it comes in Mac and Windows versions. It'll save your life.

Scopo Gigio is a software vectorscope and waveform monitor, and in tests we've run at our station, its readings are dead solid perfect according to our Tektronix scopes. You can apply Scopo Gigio to a single layer in an AE comp, or you can open a window and look at the entire comp, all layers. It doesn't work in real time, and it only looks at one frame at a time, but you really don't have to be Einstein to figure out where your trouble spots may lie.

The catch: you have to set it up for it to work properly. It's under Options. On my machine, it's set up thusly:

Color system: Analog NTSC
Black Level: 7.5 IRE
Luminance Range: D1 (16-235)
Vectorscope Ref: 75% Color Bars

So how do I use it? I do a LOT of comp work in AE, and if I see an offending level, I try to fix it on individual layers. Why on individual layers? If there's a logo that's too hot, I only have to fix it and I don't have to suck all the chroma or luma out of my comp to do it. I use the Levels filter and the Hue & Saturation filter, in that order.

Scopo Gigio: for AE users, it's a cheap and accurate way to make sure things are right for broadcast, as long as they know how to read a vectorscope and waveform monitor.

Now, If we can get Charlie King to jump in on this thread, I bet he'll be able to school both of us on why there are 100% bars and 75% bars, and what the difference is... and the answer we seek is NOT 25%, Charlie!


Return to posts index

Dave LaRonde
Re: 75% bars
on Sep 14, 2005 at 7:02:19 pm

Oh, and another thing... once you start using Scopo Gigio, I can pretty much guarantee that you'll never, ever try to eyeball levels on your computer monitor again.

Another bad habit bites the dust!


Return to posts index


Charlie King
Re: 75% bars
on Sep 14, 2005 at 7:09:09 pm

Dave,

This brings up a big point. When we went color at our station in the late 60's. The chief engineer said, "The first person I find setting or matching cameras to a monitor can pick up his check."

At that time we all learned how to use a scope to it's fullest extent. I have never regretted that learning process. I do all color correction to a scope, all setup to a scope. I look at the monitor to see what I have after it is all setup and corrected.

Monitors can drift or need setup. Once calibrated correctly, a scope is GOD.

Charlie


Return to posts index

Dave LaRonde
Re: 75% bars
on Sep 14, 2005 at 7:17:39 pm

I agree. I bet I could benefit from those scope-reading lessons you got.

Now, the big question: why are there both 100% bars and 75% bars, and what's the difference... besides 25%? Any thoughts?



Return to posts index

Charlie King
Re: 75% bars
on Sep 14, 2005 at 7:29:48 pm

Why? I have no idea. Standard color bars have the white bar at 100%. SMPTE bars are the best since they have the upper part same as 75% bars with the white bar at 75%, plus adding the bottom section with white at 100%,with I and Q on each side and 7.5% black with the little black stripes at 10% and 5% which gives you a nice monitor black setup.

Originally there was only color bars with the white bar at 100% and black at 7.5 IRE.

In trying to remember, it seems that 75% bars came about roughly the same time as 3/4 acquisition. Now don't quote me on this, cause been too long for my feeble brain to remember but I believe it was so you could setup the 3/4 playback easier since the tapes had a tendency to clip at 100%. There may be someone out there that remembers better than I do, and if there is I would love to hear either confirmation or difference with my memory.

Anyone remember exactly?

Charlie


Return to posts index


Adam Swaab
Re: 75% bars
on Sep 14, 2005 at 7:37:53 pm

Hey guys,

Thanks for the feedback. I'll be sending over another test to the station later today. Hopefully, it will work out allright.


Return to posts index

Charlie King
Re: 75% bars
on Sep 14, 2005 at 7:39:28 pm

[Adam Swaab] "Thanks for the feedback"

Oh! I forgot we were supposed to be helping you.
Only kidding. hope our rambling helped in some way.

Charlie


Return to posts index

Adam Swaab
Re: 75% bars
on Sep 14, 2005 at 9:09:24 pm

Yes. You helped. :) I hope you didn't interpret me thanking you as sarcasm.

I also posted on some other boards and got a few other responses that I'll summarize here:

RESPONSE 1

Try using the Color Finesse Filter instead of the Broadcast colors, it has Luma and Chroma Limiting and some software vectorscopes where you can see how hot the video is, and how the histograms are responding.Setting it to something like this:

Soft Clip Knee Level: 60
Soft Clip White Level: 80
Soft Clip Max Leve: 110
Luma Hard Clip Level: 75-80

Chroma Max Limit: 100
Chroma Min Limit: -20

Should keep you within 75 IRE
Experiment a bit to see what those sliders do.

Chroma should not be an issue at such faded levels, but I threw in a little limiting.




RESPONSE 2

75% IRE white is RGB 191, 191, 191. However, on a SEMPTE 75% bars there is a 100% white square. So the scope will read the high end. 110 IRE is too hot... if that is what you sent them. 255 RGB?

Just go into your curve outputs and clip your spot down to 200 or so RGB and then out 75% bars on the head, I'll bet they will accept it and it will look fine



RESPOSE 3
At PBS, white is considered 90 IRE for graphics, so don't assume it's always 100%.
The broadcast colors effect is only dealing with chroma amplitude, not luminance. The waveform monitor measures brightness, the vectorscope measures chroma phase and amplitude. In other words, you'll want to develop a method for controlling colors that is specifically tailored to your system. It will probably consist of an adjustment layer with the levels effect to control brightness (black and white output points set to 16 and 235, for example) and the broadcast colors effect to control chroma amplitude - you might decide to throw in "reduce interlace flicker" set to either .5 or .8 depending on your output hardware.

Oh yeah, the 75% bars means the white flag is supposed to be set to 75 instead of 100. Synthetic Aperture has an application that generates such test patters, I believe it's free.
http://www.synthetic-ap.com/products/tpm/index.html

If you need software scopes, check Synth. Ap. or Scopogigio.


Return to posts index


Charlie King
Re: 75% bars
on Sep 14, 2005 at 9:17:35 pm

Looks like most everything is covered for you, and I didn't think of any answer as sarcasm, I just didn't want you to think we got so carried away we forgot you.

Hope everything works well for you.

Charlie



Return to posts index

Frank Otto
Re: 75% bars
on Sep 14, 2005 at 9:53:52 pm

Wow...just like the 3 blind guys describing an elephant...each has a different "view" and is correct yet....

A common misconception is to mistake the percentage number as applied to the color bars as percentage of color saturation. Color bars are always 100% saturated.

The number refers to the amplitude of RGB into the encoder. One hundred percent color bars put an undue strain on transmission systems in that the subcarrier peaks for yellow (which sits atop the highest luminance value) go to 130 IRE. Blue, the lowest in brightness has subcarrier that sinks below blanking. But the math for 75% amplitude color bars works out to a signal that reached to just 100 IRE for the positive peaks of the subcarrier signal for both yellow and cyan.

When the NTSC color standard was developed in 1952-53, the transmission concept of analog terrestrial transmission was already established. The basic characteristics were negative modulation with sync (-40 IRE) at 100 percent of carrier modulation, blanking (0 IRE) at 75 percent of carrier modulation, and white (100 IRE) at 12.5 percent of carrier modulation. This allowed for 12.5 percent headroom before carrier cancellation (at 120 IRE video signal amplitude), which was perfectly acceptable. Color television consisted of the addition of chrominance information transmitted as sidebands of two suppressed color subcarriers.

Illegal signals were relatively rare until the appearance of digital character generators that could generate synthetic full-amplitude yellow and cyan colors, leading to transmitter overload and audio intercarrier buzz.

Just some history...

Cheers,

Frank Otto



Return to posts index

Frank Otto
Re: 75% bars
on Sep 14, 2005 at 9:58:17 pm

Y'know, I should have quoted the earlier post...this one:


QUOTE:
Yes. You helped. :) I hope you didn't interpret me thanking you as sarcasm.

I also posted on some other boards and got a few other responses that I'll summarize here:

RESPONSE 1

Try using the Color Finesse Filter instead of the Broadcast colors, it has Luma and Chroma Limiting and some software vectorscopes where you can see how hot the video is, and how the histograms are responding.Setting it to something like this:

(snip)


RESPONSE 2

75% IRE white is RGB 191, 191, 191. However, on a SEMPTE 75% bars there is a 100% white square. So the scope will read the high end. 110 IRE is too hot... if that is what you sent them. 255 RGB?

Just go into your curve outputs and clip your spot down to 200 or so RGB and then out 75% bars on the head, I'll bet they will accept it and it will look fine

(snip)

RESPOSE 3
At PBS, white is considered 90 IRE for graphics, so don't assume it's always 100%.
END QUOTE


I'm not refering to messrs. King and LaRonde...just a clarification

Cheers,

Frank Otto



Return to posts index


Dave LaRonde
Re: 75% bars
on Sep 15, 2005 at 5:22:28 pm

Thanks for the history lesson, Professor Otto! I, for one, appreciate it.


Return to posts index

tony salgado
Re: 75% bars
on Sep 15, 2005 at 5:16:59 pm




Adam,


75% bars refer to saturation when bars are viewed on a vectorscope.

Vectorscopes can be set to display either 100% or 75% saturation.

75% bars are a standard primarily due to NTSC transmission issues with 100% saturation.


You can verify which saturation level your bars are by checking the levels on a vectorscope.




Tony Salgado


Return to posts index

Frank Otto
Re: 75% bars
on Sep 16, 2005 at 9:18:52 am

[tony salgado] "75% bars refer to saturation when bars are viewed on a vectorscope."


No it does not.


Color Bars are always 100 percent saturated. The 75% refers to amplitude.

To repeat: The number refers to the amplitude of RGB into the encoder. One hundred percent color bars put an undue strain on transmission systems in that the subcarrier peaks for yellow (which sits atop the highest luminance value) go to 130 IRE. Blue, the lowest in brightness has subcarrier that sinks below blanking. But the math for 75% amplitude color bars works out to a signal that reached to just 100 IRE for the positive peaks of the subcarrier signal for both yellow and cyan.





Cheers,

Frank Otto



Return to posts index


tony salgado
Re: 75% bars
on Sep 16, 2005 at 3:19:26 pm



Yes Frank you are correct,


I will use the proper term amplitude not saturation.



Tony Salgado


Return to posts index

glenn chan
Re: 75% bars
on Sep 18, 2005 at 5:30:27 am

Frank, is it 130IRE or 133IRE? (I see 133 everywhere.)


Return to posts index

Doug
Re: 75% bars
by
on Sep 19, 2005 at 11:38:12 pm

hehehe....all this discussion and I once worked with an engineer who swore time and time again that color bars are worthless, they don't tell you anything. Until the day our then-owner saw a spot on air that was so hot the video was tearing....it looked good on the editing monitors....and since the owner was the one that conceived the spot he took it personally. The next day we had a waveform monitor and vectorscope installed in the edit bay, the first ever for that station. (And the one in master control was hooked up and checked as well).

Doug


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]