DigiTrail Effect

By Andrew Shanks

I remember when I first got into the television industry back in the early nineties, a bright-eyed student with wonderful ideas but a lot to learn, I used to have free rein of all the DVE and vision mixer equipment in that facilities online suite after hours, ...one of the funky old effects on one of the toys I used to love playing with (a relic of the early eighties) was the old DigiTrail effect, also refered to by some people as video strobing (although it does not really strobe in the traditional sense of the word). This effect was used in a lot of old Music videos and can still be used today if you want a bit of a weird psychedelic feel to a clip or sequence. The effect you get is that moving objects within a scene end up having this ghostly trail following them.Its a weird effect, but someone might find this useful. Now the technique I'll list below is not the best way of getting this effect (better results can be had by playing with the Echo filter in After Effects for example, or indeed just layering in AE using different modes, such as Sift Light to get the right look for the trail), but its about as good a way you can get it from Cinestream as I can think of.

Okay, down to the nitty gritty.

  1. First thing is a little planning when you shoot your footage, it pays to lock your camera off on a tripod to keep it steady while the action takes place in front of it, ...this leads to a better over all effect as the background will remain sharp and normal with only the moving object getting the ghostly trail treatment, ...however if the camera is hand held everything will be moving which means everything will have some form of trail on it (depends what you're going for though I guess)

  2. Place the clip you wish to treat in a new timeline (if you want to treat a series of clips, I suggest you edit the sequence together into its own composition then edit this composition clip into this new timeline sequence, ...just to save on work). At this point I recommend that you have about a second or so of extra footage on the head and tail of your clip (this is because the effect will not start and stop cleanly, ...having the extra footage means that you can use this new composition as a clip within your main edited program sequence later on and set new in and out points that work right)

  3. Decide how many ghostly echos you want trailing out behind your moving object (this may require some experimenting, as it really does depend on what the object is, how fast its going, and the look you're going for). In my example I am going to have a trail of 4 plus my original object. So in order to do my example effect I will need a total of 5 video tracks. Create as many new video tracks as are needed.

  4. copy the clip you wish to effect (or the composition clip) onto the other video tracks

  5. now we want to stagger them out, each having a little more delay than the previous one, again this will take some experimenting, in my example I have decided to go with 2 frames difference between each. So in my example I have moved all the clips on the video tracks so that each one is starting 2 frames after the layer above it in the timeline.

  6. next we want to divide up our opacities for each layer as we wish the clip that starts first to be at 100% opacity and every following one in the trail to become more and more transparent. In my case I am opting to have V1 at 100%, V2 at 40%, V3 at 30%, V4 at 20% and V5 at 10%. Note this is again a bit of a hit and miss thing, ...you generally don't want the trail to be too visible, play around and see what works for you. Use the PZR filter to set the master transparency for each clip. NOTE: due to this layering occuring, you will find that the video is likely to quickly over-expose, so you will most likely have to play around with adding a colour adjust filter to each layer and tweak the brightness/contrast to get the best results.

  7. Now if you render the VP track you should end up with a DigiTrail effect. Note how the start and end are a little weird, ...don't worry about this, if you have put this in its own composition and have included a bit of extra footage at the start and end, you can just trim this composition footage (to get rid of the strange start and end) in the source monitor and cut it into the main sequence.

There you have it, its not the most elegant way of doing it, but its something. For a better result I recommend trying the Echo filter under Time in After Effects, that gives good results.

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