chroma problem

Widetrack wrote on 2/15/2006, 1:41 PM
((Sorry for multiple bogus posts. Weird connectivity problems with satellite. WT))

I recently submitted a hour-long progrm to a TV station for broadcast. Before rendering, I added the Broadcast Colors filter with a "conservative" setting.

FWIW, I rendered to disk and burnt the file to a mini DV tape, which I then transferred to Beta SP (the stastion's requirement)

They sent back the tape saying there were "often" chroma levels that were too hot.

I spoke to a local service bureau who said they could use Final Cut Pro to automatically find any areas of the program with out-of-spec chroma, then filter each one individually.

I'm concerned that they found problems despite my using the filter (Potential reasons ranging all the way from I don't know what I'm doing to They don't know what they're doing. No good answers here.)

Can Vegas Find problem areas automatically? I'd like some confirmation that there really are problems, and to be sure I get it right without going through the whole program repeatedly, trying to guess what they saw.

Any good techniques for handling this problem?

Thanks for any help.

Comments

Jimmy_W wrote on 2/15/2006, 2:11 PM
You should see it with the video scopes tool in Vegas.
Jimmy
winrockpost wrote on 2/15/2006, 2:24 PM
Could be the dub to Beta was the problem,,,not set up correctly, did you do it, or a dub house,, check the beta to your master DV
farss wrote on 2/15/2006, 2:26 PM
Ditto the above.
The problem with using the BC FX is that it simply clips the video. It should be legal but depending on the content may look not too pretty.
I use the Color Curves with a custom curve to remap the levels back into legal.
Again though you do need to use the scopes to see wht you're doing, there's no one shoe fits all solution.
Bob.
Widetrack wrote on 2/15/2006, 3:07 PM
I was ticked when this FCP guy went on about how his software could find and flag any problems in a couple of minutes. That's the first time I've seen FCP trump Vegas for ease of use.

The dub happened at a friend's (fairly rudimentary) studio.

What's it take to make acustom Color Curve? A lot of deep technical voodoo involved?
farss wrote on 2/15/2006, 3:22 PM
No not really.
Hard to explain without being able to post a picture and the silly CC things doesn't have any number attached to I cannot give you values.

Anyway first thing you need to do is open the scopes and set them to Studio RGB, Waveform. Check to see that your levels are between 0 and 100, find the highest contrast scene in your video.

Most likely if this was shot with a typical Sony camera then the whites are over 100%. To fix that you need to drag the upper right node down until the peaks in the waveform are JUST kissing 100.
Now the problem is that this will also push your blacks down, assuming they were just around 0 to start with.
To prevent that add a node near the bottom of the curve and drag it a little to the right so the curve runs horizontal. Keep watching the scope while doing this, you should be having no effect on the bottom end of the waveform. In fact what that straight section will do is to clip anything below 0 to 0, not normally desirable however as I doubt you've got anything down there normally not a bad solution.
Hope this helps.

Bob.

PS, If anyones gots better info on using CC PLEASE pass it on, I find the way you drive them totally confusing, there seems to be some glitches in how you can move nodes around.
farss wrote on 2/15/2006, 3:26 PM
One other thing of course, anything could have happened during the transfer to SP, does the guy who did this have a hardware scope in his lineup. Pretty dangerous working blind in analogue land.
I think the SP decks are pretty safe, not that I've worked with them much, but there's good reasons why bars were added to analogue tapes and watching the old hands working with 1" and 2" tapes, every time a tape is loaded for playback several pots get tweaked while watching the scopes.
Widetrack wrote on 2/15/2006, 5:11 PM
Thanks for the tips. I ll try them all.

The GOOD NEWS is that the FCP guy called back chagrined and admitted he was wrong and FCP couldn't actually find illegal segments with a simple search. He has to watch the scope and search just like we do!

HA!!

Doesn't help me, but at least I don't have to apy some snotty FCP guy to find my f***ups.



FrigidNDEditing wrote on 2/16/2006, 8:34 AM
Yea - use the scopes - Though I'm kidna suprised the broadcast filter (am asuumting that's what you used) didn't fix it.

Dave
Widetrack wrote on 2/16/2006, 6:31 PM
Better believe I was surprised and embarrassed when I got the news, too.
I'm thinking the "field" dub to beta may have lacked some appropriate control.

I got the scopes up and am going through the program. There certainly are several points where Chroma goes over 100 (reds, usually)

And it looks like I need to use the "extremely conservative" setting. Should I cut the threshold to below 100 IRE if it looks like the signal is bumping into it too hard?

I'm also trying to figure out whether to check 7.5 setup and "Studio RGB" whatever that means.

Really appreciate everyone's help.

WT
GlennChan wrote on 2/17/2006, 6:49 PM
1- The betaSP deck may have proc amp controls which can alter your video levels. You should make sure these are set to not mess with your video. So even if your digital levels are correct, the deck can screw things up for you.

The way to be sure about your analog levels is to rent a hardware vectorscope and waveform monitor.

Tektronix has some information on its website about reading vectorscopes and waveform monitors.

http://www.tek.com/Measurement/cgi-bin/framed.pl?Document=/Measurement/App_Notes/NTSC_Video_Msmt/wfmmonitor.html&FrameSet=television

2- The 7.5 setup setting (this is pretty confusingly labelled):

This controls where proper digital black level will be displayed in Vegas's waveform display.
UNCHECKED: Proper digital black level should be at "0" on the waveform display.
CHECKED: Proper digital black level should be at "7.5".

This is somewhat poorly designed, as you need to check the settings to see what the waveform is set at (i.e. someone else may sit down and get confused).

This setting also affects how things appear on the vectorscope.

3- Studio RGB:
The correct setting depends on what codec you're using.
If you are on Vegas 6 and using the Sony Vegas DV codec (the default for Vegas 6), then pick this.

If you are using a waveform + vectorscope, I recommend you use a codec that uses Studio RGB color space (and not computer RGB). The test pattern (SMPTE bars) is correct for studio RGB, and not computer RGB.

4- The waveform in FCP actually only scans every several lines, and it only scans the title safe area (it excludes the overscan area). It also does not display superblacks correctly. The broadcast safe filter in it is a little better than Vegas'.

In any case, the best solution is to get an external hardware waveform monitor + vectorscope.