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Calibrating Secondary Capture Card With AJA Kona

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Jason Freets
Calibrating Secondary Capture Card With AJA Kona
on Mar 14, 2013 at 7:46:02 am

Using AJA Preview, I am able to send out a test pattern to a cheaper secondary capture card that I would like to calibrate. Among the built in test patterns in AJA Preview, is the "75% ColorBars" test pattern.

Using the "75% ColorBars" test pattern, I can output the test pattern out at 720x486@29.97i with "Analog Output" set to "Composite + SVideo NTSC"; it goes out from the AJA card via composite or S-Video. Great so far!

Now, with my secondary capture card, I can then capture this test pattern (generated by the AJA card) via Composite or S-Video inputs on this secondary capture card. And, I can see the test pattern in my secondary capture card.

Up to this point, all is well...

I've noticed that during capture on my secondary capture card, the colors from the "75% ColorBars" are 'slightly' off. Thus my questions are:

1) I am assuming the output from the AJA card is accurately sending out NTSC colorbars correctly. In other words, I'm assuming that that what the AJA card is putting out is MORE correct, then what my secondary capture card 'should' be capturing. Is this a correct assumption to make?

2) Therefore, using the proc amp controls on my secondary capture card, I could adjust them so the capture of the received "75% ColorBars" test pattern on the secondary capture card are at the correct levels.

Is this a way I can calibrate my secondary capture card using my AJA Kona card correctly? Or, where am I going wrong or perhaps not understanding something correctly?


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David Kuhnen
Re: Calibrating Secondary Capture Card With AJA Kona
on Mar 14, 2013 at 1:47:17 pm

Your basic theory is correct.

If we "assume" your AJA card is not defective in any way, and the signal does not pass through any other device between the AJA and "secondary" capture card, then yes, you should be adjusting the proc amp on the secondary card to achieve proper levels. Make sure you are using the waveform and vectorscope displays to confirm proper adjustments.

David Kuhnen
BVK-Milwaukee
Video Editor/Engineer


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Jason Freets
Re: Calibrating Secondary Capture Card With AJA Kona
on Mar 21, 2013 at 8:28:01 am

Excellent David! I appreciate the feedback.

For the AJA Kona card itself, is there a way to adjust it's proc amps? Or, is the only way to adjust the signal into the AJA Kona card by an external video proc amp?

What is the proper way of doing this?

Jason


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David Kuhnen
Re: Calibrating Secondary Capture Card With AJA Kona
on Mar 21, 2013 at 2:18:28 pm

Having control of input video levels depends on the model of AJA card.

I had a LHe that allowed (proc amp) level controls on the analog input. I now have a LHi and they don't allow the same control.

David Kuhnen
BVK-Milwaukee
Video Editor/Engineer


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David Kuhnen
Re: Calibrating Secondary Capture Card With AJA Kona
on Mar 21, 2013 at 2:28:00 pm

Having control of input video levels depends on the model of AJA card.

I had a LHe that allowed (proc amp) level controls on the analog input. I now have a LHi and they don't offer the same control.

If your AJA card does not have level controls for input, you need to adjust levels on the source device (i.e. VTR, camera) or by running the signal through a proc amp. Adjusting the source would be preferred over using a proc amp.

View the incoming signal through the capture interface of the editing software, open waveform monitors and adjust levels using waveform and vectorscope.

David Kuhnen
BVK-Milwaukee
Video Editor/Engineer


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Jason Freets
Re: Calibrating Secondary Capture Card With AJA Kona
on Mar 26, 2013 at 6:10:53 am

Hello David,

You are correct! You earlier wrote:

"If we "assume" your AJA card is not defective in any way, and the signal does not pass through any other device between the AJA and "secondary" capture card, then yes, you should be adjusting the proc amp on the secondary card to achieve proper levels. Make sure you are using the waveform and vectorscope displays to confirm proper adjustments."


I have confirmed that the output from the AJA Kona set at 75% color bars is correctly aligned on my waveform and vectorscope displays. So I am happy that I can use this as a means to calibrate my other capture cards. And, the levels look just perfect on both the waveform and vector scope. I then re-confirmed with another piece of hardware that also outputs NTSC colorbars. And, they both match up. So that's great; there is some consistency!

However, there is one catch! The vectorscope and waveform monitor I have only calibrates to composite. Right? I just confirmed that the composite output from the AJA Kona is correct. And, although it's correct for composite, how do I approach calibrating the signal from S-Video or even component? There must be a technique or something that can help me to approximate a close enough calibration. For example, the AJA Kona will output composite correctly. However, if I am using S-Video or component, how do I know what's being put on those lines are indeed correct? Perhaps pass S-Video or component through a device that outputs composite as well as S-Video or component? Run the composite end through my waveform and vector scope to make sure they are within the proper levels? But would that really confirm that still what ends up flowing down the line through the S-Video or component is also at the proper levels?

Aside from my main question and in answering another of your questions, I have the Kona LHe currently. And, I don't see a way to set the proc amp controls via software. In trying to better understand this, I found others who have struggled with this too in another thread:

http://forums.creativecow.net/thread/150/836522


So, it looks like we're not the only ones who have struggled with this issue. Therefore, I'll need to (and as you said) use a proc amp on my source or pass it through another secondary proc amp to correct the levels prior to entry into the AJA Kona capture card.

Look forward to your input ...


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David Kuhnen
Re: Calibrating Secondary Capture Card With AJA Kona
on Mar 27, 2013 at 7:47:18 pm

The AJA "LHe" had a input Proc Amp menu in the AJA Control Panel in all versions of the LHe Driver thru the final 9.1 driver (see page 38 of the LHe manual). As I browse the "LHe Plus" manual, I see that card does not have a Proc Amp menu.

I feel you may be over thinking your situation. If composite out is acceptable, all other outputs should be in unity (same levels) as composite. You can check luminance (Y) levels for S-video and component using your scope(s). Chrominance (only) levels can be much more difficult to measure when not embedded with the luminance signal.

If you're insistent upon checking all signal levels, my recommendation would be to take the desired signal(s) from your output card and connect them appropriately to the other card and measure using the scopes inside your edit application.

If you must adjust levels outside the edit software, yes, it sounds like you'll need to run thru a proc amp.
But, I'd have to question why you need to adjust levels of the analog signals if you are capturing and editing in the digital realm. Personally, if my incoming levels are at least fairly decent, I'd rather do all my color correction inside the NLE.

David Kuhnen
BVK-Milwaukee
Video Editor/Engineer


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