How AUTO KNEE wrecked everything and ruined my life (almost)

M

mcbob

Veteran
Discovered a delightful new glitch today.

I was shooting a simple white-screen talking head, lit everything well enough, rolled a few takes, then popped into playback mode to let the first head review their performance. All looked good, they went on their way and tweaked the set up for #2... didn't change any light ratios, just moved camera and mic boom height. After rolling his first take, something seemed... off. The background didn't look white any more. I checked the WFM and sure enough, there was a solid bar at 90%IRE. The subject was still lit fine, but the background had gone light grey. Aperture hadn't changed. Lighting hadn't changed. Opening aperture didn't raise the background above 90%. Weird.

Not letting the client know I was minorly freaking out, I thought for a moment and remembered that "ready for broadcast" scene file I was using incorporated an auto knee to help control highlights. I switched scene files to a cine-V style and the background went white again. OK. Switched it back to the auto-knee scene and the background was white again. um... ok....

...then on a whim and a hunch I switched to playback mode, then went back. BAM... background was back down to 90%. Switching out of that scene file and then back to it brought them back to white.

Last bit of the puzzle: I switched that scene file to high knee, and the behavior disappeared... I could go back and forth from playback to record modes without altering the background's IRE reading.

I remembered back to an earlier shoot I'd done for this client where I set up the background correctly, checked the WFM, then started to roll (letting the client check the first shot), but in the edit bay the background was light grey and it took a crapton of work to render it white without blowing out the subject. I wondered if the same bug had bit me back then. Might also explain why sometimes on those quick jobs where I use that scene file, I get back footage on the AF that just seems darker than it should be.

Anyway... just an extra little thing for you all to worry about. Have a nice day!
 
wow... that's kinda spooky. I know there are some gamma settings do not enable knee. Would you share the "ready for broadast" settings? Thanks for the heads up. That was a good catch, especially on set with the inevitable rush and all.
 
Strange though that it acted one way immediately after switching from playback mode and then another at every other time
 
I have had the exact same issue but it was the drs setting that set it off for me. I was on high knee and drs 1, swich to play bak and get the same problem. My solution was to turn off n on after ever time i switch to playback :)
 
I have a question. I don't use auto anything but with the AF100 I can not understand why it isn't WYSIWYG, meaning why is the footage sometimes darker in post (even with the monitor adjusted) than it was live or even in playback sometimes? Can it be the dynamic range of the computer monitor in editing?

I do a lot of doc shooting and looking at a waveform doesn't cut it when moving fast.

Thanks

Thanks,
 
AF100 footage looks identical in recording and in post, so if you're seeing a difference, it's in your monitoring somewhere. Perhaps your on-camera LCD is set too bright, so you're thinking the footage is brighter than it actually is? Use your zebras and WFM to verify where the brightness levels are, because you cannot rely on any on-camera LCD to give you an accurate representation.
 
Thanks Barry. I was referring to my Panasonic 9", I had it calibrated by a video engineer since I am dangerous around knobs. Perhaps the brightness is set too high.
 
Not sure if anyone has tried the Datacolor Spyder 4 color calibrator designed for your monitors, laptop screens and even ipads but I highly recommend it. It will take in account the brightness of your room level and make sure your monitor brightness level is setup properly as this is important. Moreso it will actually calibrate your R G B values so that white is actually white and black is black. I've never had more "true" colors on my monitors and I will never ever use an uncalibrated monitor for my work on video after seeing how great this thing is.

Cheers,
 
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