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Author Topic: Improving I-mag quality  (Read 353 times)

Craig Hauber

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Improving I-mag quality
« on: December 07, 2019, 01:01:11 am »

I have an ATEM switcher
Running SDI wiring
JVC 4K semi-pro camcorder with SDI output
Toshiba projector with HDMI input using a blackmagic mini-converter from SDI
Everything set to 1080i 59.97

Noticing a slight lag between real-life and the image right above them -is there any way to mitigate this or is it just something you are stuck with?

Also how to get a decent color rendering -looks great in viewfinder and ok on the switcher's multi view screen but too yellow on projector -There just doesn't seem to be any adjustment on that unit and the slides look great so any adjustment would throw them off then.

Stupid old sound guy here trying to make my touring Christmas show look it's best.  Is there some piece of gear I should be using instead for this or adding into the signal chain?
Last real experience in this was with analog composite back in the 90's so amazed I actually got this newer gear up and running!

Still have 23 shows on the tour and would love a bit of improvement, any advice would be appreciated
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Craig Hauber
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Keith Broughton

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Re: Improving I-mag quality
« Reply #1 on: December 07, 2019, 05:55:07 am »

I can't speak to the colour rendering but as for the delay, there is at least 1 frame of time per process in the video chain.
Considering 1 frame is appx 33 ms, it doesn't take much processing to show a noticeable lag.
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Mike Caldwell

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Re: Improving I-mag quality
« Reply #2 on: December 07, 2019, 08:35:51 am »

With any digital video processing, switching, conversion your going to have lag/delay.

What do color bars from the camera look like projected, what do colors bars from the switcher look like.

By chance are the slides all off and the system re aligned to make the slides look good.

You need to get a known true color reference to calibrate the projector to and start from there.

Caleb Dueck

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Re: Improving I-mag quality
« Reply #3 on: December 07, 2019, 12:05:30 pm »

I can't speak to the colour rendering but as for the delay, there is at least 1 frame of time per process in the video chain.
Considering 1 frame is appx 33 ms, it doesn't take much processing to show a noticeable lag.

True, and to add a bit - like with audio, you have to add the latency of each device to get total number of frames, then using frames per second calculate total latency in ms.

From there - find out how much latency is acceptable to you (camera to projector, analog, as reference), and evaluate every device in the chain, as well as potential excessive devices.
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Tim McCulloch

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Re: Improving I-mag quality
« Reply #4 on: December 07, 2019, 12:58:07 pm »

Every conversion takes time, everything with a buffer adds time (so that's almost everything digital).

I had a corporate event a few years ago - outdoors for a major aerospace concern.  I was given precisely measured AutoCAD drawings of stage and video wall placement.  The video wall was a huge semi-trailer thing (hydraulic rams to raise it) and the corporate creative team insisted on 1920x1080 HD resolution.  This resulted in approximately 12-15 frames of video delay which was quite amusing to watch behind the presenters.  The other issue was that the corporate creative team's boss insisted that the audio sync up for the VIPs in the front rows, so I added almost a half-second of delay to the lectern mic send to PA, which had predictable implications for the presenters (like singing the anthem at the ball park).  Why? Next paragraph...

They moved the stage and video wall truck from the locations in the plans given me, so the presenters got a full blast of PA (in the original design the stage was in a null of coverage).  No amount of foldback could overcome the PA without feeding back.  And for good measure the winds were 25MPH all day so there was a huge amount of wind noise that could not be magically removed from the lectern mics.  Nobody was completely happy with the final result although the audience would have never known.

Oh, and all these changes happened while I was on vacation - I came home early and found a train wreck I could do nothing about except try to say "yes" to as many suits as I could.  I didn't bother explaining why the "cure" was worse than the disease because after the first suit said "you just don't want to help me..." it was all over.  I don't handle passive-aggressive bullshit well so it's easier to smile, lie, and move on to the next person with a completely contradictory request.  I gave them exactly what they asked for.

I did suggest changes to reduce video latency but was ignored because "you're the audio guy".  Fine.  I hope your CEO and the political dignitaries are sufficiently embarrassed.
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Keith Broughton

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Re: Improving I-mag quality
« Reply #5 on: December 07, 2019, 03:51:46 pm »

12-15 frames!!!!! Yikes!

We were trying to mitigate at least some of the delay with a 4 camera iMag setup and I was informed that the video cable to the farthest camera was the longest so that's why there was more delay! :o
This is someone who is "educated" and I had to explain the difference between the speed of sound in the air and the speed of electricity in a wire. (sheesh)
I had him watch the video from the back of a 250' room and guess what....it was OK. ;D
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Erik Jerde

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Re: Improving I-mag quality
« Reply #6 on: December 07, 2019, 04:32:15 pm »

you can measure your video delay through the system by putting a timecode display on stage with the camera trained on it.  Route that to screens then snap a picture of the timecode display and the screen (in the same shot).  Use a high shutter speed.  Faster than video frame rate at minimum.  Compare the two read outs, do math, bam thereís your real world latency.  If itís just 3-4 frames you live with it.  Beyond that you can track things down by isolating and using the same method.
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Mike Caldwell

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Re: Improving I-mag quality
« Reply #7 on: December 07, 2019, 07:08:46 pm »

You could go all old school, analog component video switching and distribution all the way to the projectors. For fun get three tube cameras and dedicate someone to tweak the camera registration every day.

Craig Hauber

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Re: Improving I-mag quality
« Reply #8 on: December 08, 2019, 10:39:02 am »

With any digital video processing, switching, conversion your going to have lag/delay.

What do color bars from the camera look like projected, what do colors bars from the switcher look like.

By chance are the slides all off and the system re aligned to make the slides look good.

You need to get a known true color reference to calibrate the projector to and start from there.

I think that's my underlying problem.  I just arrived as TD and was confronted by a pile of used video gear from previous runs of the tour
Semi-pro at best with very little available for detailed settings.  The projector just has a "tint" slider for example.  The preview monitor is samsung and way too "consumerish" to have any real settings.
I tried yesterday swapping cameras around (we have 3 in the pile) An older sony looked far superior with color but had the nice "SDI Output broken" label on it so yet another blackmagic convertor to go from HDMI to SDI.  Overall the lens is far better on it and getting good low-light performance and color accuracy.
It's amazing that the JVC cam has an over 500 page manual yet still no clarity on exactly how to use the white balance system correctly.

As for the latency it's good to know it is normal and I'm not really doing anything wrong. 
(Musical show with backing art-shot imag so hand motions were noticeably lagging)
Now that we are on the road with a very busy schedule there's really no time to be tinkering with the video rig -especially in the middle of nowhere ND -So it will be re-evaluated all next year well in advance of the tour.   (I was brought on board way too late this year to deal with it all properly)

Thanks much for the insight
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Craig Hauber
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brian maddox

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Re: Improving I-mag quality
« Reply #9 on: December 08, 2019, 04:41:16 pm »

Yeah, the latency thing is inherent in Digital Video, which basically at this point just means Video.

The only "trick" is to minimize views that have both the actual stage talent and the screen in the same eyeline.  Obviously this is easier said than done, but yes, screens upstage or over the stage are gonna be especially problematic.  And while you can improve the problem somewhat by minimizing the processing steps, etc., hand movements on stage will ALWAYS look wrong no matter how low you can get the latency.
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Re: Improving I-mag quality
¬ę Reply #9 on: December 08, 2019, 04:41:16 pm ¬Ľ


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