Welcome to the third and final part of this series of blog posts where we deconstruct a video I made using frames from a series of star trails images. So far we’ve covered simple time lapse image sequences, we’ve looked at summing sequences and now for something a bit more complex.For the last sequence in my video I wanted the effect of a small star trail appearing to move through the arc of a much larger trail. So we don’t see it add up, we just see a smaller trail move through the sky, like this..
This presents a problem using the techniques we’ve already looked at, using a photoshop action. We want to see a sequence of frames that goes something like…
newFrame 1 = sum[Frames 1-9]
newFrame 2 = sum[Frames 2-10] minus Frame 1
newFrame 3 = sum[Frames 3-11] minus Frame 2
newFrame 4 = sum[Frames 4-12] minus Frame 3
Turns out there isn’t a clever automated way to do this… 😦
Lets reconsider the Photoshop Action we used in Part II…
>Set Current Layer
If we remove the Flatten Image command we are going to end up with every frame available as a separate layer…
*Be warned! I had 277 6 Megapixel images, about 3Mb each, so my computer was able to handle this step. I’ll cover how to break up the sequence into chunks later*
So running the action as we did before in Part II gets us every frame as a separate layer. We need to find the Layer Comps tab under the Window menu next.
Lets define our small trail, say 10 frames. Turn the visibility of everything off except the first 10 frames. Then create a new layer comp (bottom of the layer comp window..). Next turn on frame 11 and turn off frame 11. Make another layer comp.. Then turn on frame 12 and turn off frame 2, and make a layer comp. Repeat till you get bored…
When you are done through all your frames choose the Export Layer Comps to Files, under the File-Scripts-Layer Comps to Files.
You can prefix the frames as you wish and then make an image sequence in Quicktime as we did in Part I.
One way of minimising the number of frames you have open is to to the comps in stages. Import 20 frames and setup the first 10 Layer comps, then export them, delete the invisible frames and import 20 more that are next in the sequence, file management is key here.
So that’s it! You can process timelapse frames like animation frames. Someone may have an easier way to do the effects I’ve described and that would be neat – save me some time on the next one! Chances are there’s an easy way in After Effects for example.. but I don’t have access to that!