4 Replies Latest reply on Nov 25, 2012 11:32 PM by jhex66

    Repair flicker bands on DSLR footage?

    jhex66

      Before I start, I'm aware that this problem has been posted a few times before, that there isn't an easy fix and that it's best to reshoot. I have no option of reshooting and am happy to spend a bitter time trying for a solution, however partial. Any comments on my attempts so far would be greatly appreciated!

       

      So the problem is horizontal lines of flicker resulting from a clash between shutter speed and lighting frequency. In this case I tried changing shutter speed but flicker persisted. I didn't try changing the frame rate from 25 to 24 and am not sure if this would've helped.

       

      Here's a sample of footage:

       

      So it first looked to me like undulating lines of darkness and brightness. So I made a gradient mask and key-framed it to the movement of the flicker bands.

       

      Here's the gradient mask:

       

      I then tried using the mask as a luma matte for an adjustment layer. So far I've tried changing the brightness, but it looks to be more than that.

       

      Does anyone have a better idea of the way the bands change the "original" image? And am I completely barking up the wrong tree or wasting my time? I've not had that much experience with grading but have access to Colorista if that helps.

       

      Many thanks!

        • 1. Re: Repair flicker bands on DSLR footage?
          Mylenium Most Valuable Participant

          That#s normal temporal aliasing because your shutter frequency didn't match the frequency of the electrical lighting. It would have had to be fixed by adjusting the camera's shutter phase on the spot. Post facto you will have to split the channels and smooth out the luminance, then re-assemble them, e.g. using the Channel Combiner effect to convert to YUV or HLS, use a blur or create a temporal accumulation using Timewarp or Echo, then using Channel Combiner again to convert back. You may need multiple layers, also. The bad news is, that despite your best efforts it won't go away completely. There's only so much blurring you can do without ruining your footage...

           

          Mylenium

          • 2. Re: Repair flicker bands on DSLR footage?
            jhex66 Level 1

            Thanks for your reply Mylenium, although I think it'll take me quite a while to get to grips with Channel Converter and "temporal accumulation".

             

            In the meantime I'm going to give virtualdub's tempsmoother a go as I've heard it works pretty well. Will let you know how I get on.

            • 3. Re: Repair flicker bands on DSLR footage?
              Rick Gerard Adobe Community Professional & MVP

              That's one of the hazards of shooting 24 or 24p. You're a lot more likely to run into phase problems with lighting. Shooting 50Hz land with NTSC gear or in 60Hz land with Pal equipment can also cause problems with high frequency lighting like fluorescents and metal halide (discharge) lighting.

              • 4. Re: Repair flicker bands on DSLR footage?
                jhex66 Level 1

                I was actually shooting at 25, and tried changing shutter speed to suit NTSC to no avail. I've been told that using 60hz light on a 50hz supply can result in lighting frequency of neither 50 or 60 hz, could this be true?

                 

                In terms of trying to fix it in post I haven't had much luck. Mylenium, I'm not really sure quite what your proposed method entails. I've tried adding another layer of 50% opacity, directly out of phase to counteract the bands. Then of course I have to mask out the movement of the musicians so they don't all look like Ganeshes. I've had limited success with the masking but the bands are looking better than any other method I've tried so far.

                 

                I've got a feeling that the gradient of the band interference isn't even, ie they are weighted toward the top or bottom, making it pretty tricky to fix with any delay or sequenced colour correction.

                 

                I'd love a filter that detected this problem and fixed it but there doesn't seem to be one. Could anyone help me reduce the contrast on the most affected area, the back wall? I know how to select a colour region with Colorista but don't know the way to reduce the impact of the interference bands for that region.

                 

                Thanks