About a month ago, Johannes and I had a shot at doing a timelapse of the sunset behind the Forth Road and Forth Rail bridges. The sequence is about 1200 shots over the space of 1.5 hrs or so, combined in the first video at 24 frames per second using Virtualdub, an excellent free video processing tool for Windows. The result is the first vid below, and apologies for no sound on it.
You can see that there’s a fair amount of flickering in the first video. This is because the camera was set to Aperture priority, which means that with a set ISO and aperture, the camera automatically adjusts the shutter speed based on the internal light metering in the camera (if I understand that right). So, as it gets darker or lighter, the shutter speed gets slower or faster, respectively. Unfortunately, this means that sometimes (or often!) pictures in the middle of a sequence can be darker or lighter than adjacent pictures because the camera’s metering has set a slightly different shutter speed. If one were to do the whole sequence manually, you should be able to get rid of the flickering by making sure that the shutter speed doesn’t jump up and down through the sequence.
Anyway, the result is as you see below. However, a brief internet search revealed that a filter plugin is available for Virtualdub (cunningly called Deflicker filter for Virtualdub). Designed primarily for removing flicker from converting film reels to video, it works just as well with timelapse sequences. I applied the filter to my sequence, using the default settings, and the result is the second video. I think it looks much better, so I’, pretty impressed. Some tweaking with the settings would improve it a little more, and a bit of editing to cut down the time as it’s a long single sequence!