Interlace flicker works magic

JJKizak wrote on 10/12/2004, 5:38 AM
A friend sent me a tape of an old documentary taken from a projector with a 4 bladed shutter which caused constant "blinking" throughout the entire tape. I captured it and rendered it out using the interlace flicker switch and it removed about 95 % of it. The result was staggering. The only negative was the increased time of rendering from 2.5 to 8.5 hrs.

JJK

Comments

taliesin wrote on 10/12/2004, 6:29 AM
If blinking means altering luminance then it's real magic. Because all that "Reduce Interlace Flicker" does is adding a very small amount of blur to the video. It does not touch the luminance of the video.

Marco
farss wrote on 10/12/2004, 6:51 AM
Although I doubt this switch did anything for the flickering from the projector I can assure you it does far more thna add blur.
It can for some odd reason stop serious artifacts when resizing video. I've had no explaination as to why this works, makes no sense to me at all but it damn well works!

To get rid of the flicker the best thing seems to be the deflicker filter for Virtual Dub. However not all flicker is due to shutter strobing. First off you need to get the shutter speed on the camera to 1/50th or 1/60th of a second. Other issue I've found seems to be the automatic exposure control in the film camera in the first place. The things must have hunted quite a lot causing a very slow variation in exposure. Annoying and I've found no way to fix it.

Bob.
JJKizak wrote on 10/12/2004, 9:36 AM
I don't see how blurring could have reduced this constant change in brightness which as far as I can recollect it was about every 1/8th second. (guessing) The constant variations were really irritating, almost like constantly blinking your eyes. Unless the resampling had something to do with it. However, without the interlace flicker switched in the flicker did not change after render. So it had to remove it somehow. I also did not notice any focus change. It sure did work.

JJK
RalphM wrote on 10/12/2004, 10:05 AM
JJK,
Interesting phenomenon. Next time I transfer some film, I'll purposely slow the transfer machine enough to introduce the strobing effect of a projector-camera shutter mismatch, then try the interlace flicker reduction.

Farss,
I wish there were a way to lock the video gain on prosumer cameras to further reduce any flicker. I don't know whether the automatic aperature control can also cause some "pumping effects" but I usually run with it in manual control to reduce the flare that often happens when scene to scene lighting varies widely.
taliesin wrote on 10/12/2004, 10:50 AM
It's not that I don't believe but I can't explain what going on there. Cool if it works. Will try that on my own by chance.

Marco
farss wrote on 10/12/2004, 3:44 PM
Ralp,
I was referring to the cheaper Super 8 film cameras!
Running video cameras in manual is a bit of a two edged sword. Unless you've got zebra I advise people against it unless they really know what they're doing. I've had so much footage where the cameraman went to sleep on the job resulting in under / over exposed footage. This is a big problem with long shoots of live events, in one there were serious problems with clouds passing over the event and then almost total loss of natural light. So the WB shifted from daylight to tungsten and the light dropped dramatically. With a camera in manual everything and the ND2 filter still on the results were well, near useless.

Bob.
RalphM wrote on 10/13/2004, 7:41 AM
Bob,

Oh! Yes, I do see that word "film" in your posting now.

While I do have zebras, I generally don't use them on film transfers. The reason being that most of the film I transfer is amateur, and the lighting is far from ideal.

I take the viewpoint that the customer wants most to see the people in the frames. If the subject has been backlighted and I have a choice of silhouettes of people or blowing out the window whites, I'll lose the window. More common is that little Jimmy walked up to the film camera with the 600 watt SunGun and the "Casper the Friendly Ghost" effect appears. I always crank the aperature down to try to rescue any facial detail that may be there.

I know there are more sophisticated ways to deal with esposure problems, but most of my customers are not interested in spending the money to do so.
Now if video just had the same contrast range as film........