Film-Tech Forum ARCHIVE: White Flashes

This is topic White Flashes in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Paul Willmott (Member # 3904) on 01-06-2013, 07:58 AM:

We have a Barco DP2K-15C and a GDC SX2001A server. Occasionally we get a flash of white noise (often looks like half a frame) between clips e.g. between 2 trailers.

After a lot of investigation I narrowed it down to only clips that we have made ourselves (using a variety of software). And further, I now think it's where the frame rate changes. We often show videos made at 25fps (or 30fps) and to ensure they run smoothly we let the projector show at that rate rather than convert to 24fps.

Has anyone come across this and is there a solution (other than converting everything to 24fps)?

Posted by Bajsic Bojan (Member # 4928) on 01-06-2013, 09:03 AM:

using barco 19b / doremi 2000 and mxf mpeg2 files, we occasionally get green flashes at beginnings of clips.

I hide it by closing dowser at 1s before the end of clip and opening 1s after beginning of new clip. Since these are files we do ourselves, we always add 3-5 seconds black before the first picture so no issues of unneccessarily cutting images.

Posted by Steve Guttag (Member # 268) on 01-06-2013, 09:57 AM:

In ANY of the DLP projectors...at the moment...when you change frame rates...you will get some form of noise/flash...dousering down just prior and opening just past is the only solution. The flash is happening in the ICP as it changes rates...so it is going to be brand independent. If possible, try to master in 24fps (or 25fps if that is what the rest of the content will be). Use blanks of the same rate you want to transition to so you can open the douser on the blank and have a clean transition that has already adjusted the speed.

Posted by Randy Stankey (Member # 64) on 01-06-2013, 10:18 AM:

If you are making your own content, why are you not making it at 24 fps?

Or, at least, you ought to group all your 25/30 fps content together so that it can play together without frame rate changes. Then, when you go to the feature or whatever other 24 fps content you are playing, you will only have one transition to contend with.

I haven't made any content for DCP yet but, for other types of media, I have always been conscious of keeping the frame rates consistent even if that means I have to do some sort of frame rate conversion.

I know that quality can suffer when you make such conversions but you seem to be facing a "Hobson's Choice." (Is the cure worse than the disease?). In such a case as yours, you might be better off leaving the frame rates as they are and dealing with the problem as others have advised above.

However, in the future, I might suggest that you do some testing to see whether can can either produce your content at the correct frame rate or convert existing content to the correct rate without suffering too much loss of quality.

Posted by Antti Nayha (Member # 4980) on 01-06-2013, 01:40 PM:

Here’s my solution. You just need to create a one-second black clip in all the framerates that you use.

Frame rate conversion from 25 to 24 fps, and vice versa, can be an acceptable solution. Not so with 30 fps.

Posted by Randy Stankey (Member # 64) on 01-06-2013, 10:32 PM:

quote: Antti Nayha

Frame rate conversion from 25 to 24 fps, and vice versa, can be an acceptable solution. Not so with 30 fps.

A choice between something that might be unsatisfactory or taking nothing at all... A Hobson's choice.

As I said, I haven't edited video for DCP but I have made video for presentation on-screen by other formats and I have done some video for broadcast. Like you said, depending on source frame rate and target fame rate, it might work. It also depends on the conversion method or algorithm you use.

My point was not to discuss methods of conversion but to mention that it is one possibility which might work. If it works, as determined by testing, then okay. If not, then another method must be used. It can be done by the way you suggest, by using black lead-ins and lead-outs then covering with the dowser.

If you are the one who is making the video in the first place, why didn't you create it at the correct frame rate in the first place? As I alluded to, I have had many heated discussions over this
in the past. I have ended up redoing projects because of mismatched frame rates. Yes, it's a PITA but, if you want your material to look right, ya' gotta' do what ya' gotta' do.

Posted by Antti Nayha (Member # 4980) on 01-07-2013, 06:07 AM:

Agreed. And even 30 fps to 24/25 conversion will work fine, if your footage is eg. a static pre-show still image.

Posted by Paul Willmott (Member # 3904) on 01-09-2013, 08:21 AM:

Thanks for all the advice. Looks like I'll have to go the closing the dowser/blank clips route.

Our pre-show slides are created as videos directly from Powerpoint which uses 30 fps, but as they are all at this frame rate there is no problem.

We often show video from external sources where we have no control over the frame rate - most of the videos supplied are 25 fps and I've never had much success converting to 24 fps. At least I now have a workround!