In part one we saw how to use Quicktime to turn still image sequences in video, now lets manipulate some still images using some batch techniques.
Part II – Manipulating frames with Photoshop Actions
To make some of the effects in my Star Trails video I needed to use Photoshop actions. Some of you may be familiar with the stacking technique for star trails, where you take a number of shorter shorts and then stack them up into a composite image (if you haven’t come across this technique, then you haven’t been reading this blog very carefully!).
Most people will have used the PC program “Startrails.exe” but there are some Photoshop actions than can be used as part of a batch import, which achieve the same thing.
The Star Trails action (found here) looks like this..
>Set Current Layer
To break it down, it takes an image, copies it, closes it, then pastes it into another (already open) picture with the blending mode set to ‘Lighten’. This mode allows only things that are lighter in the new shot to show through – so is perfect for star trails – the lighter stars moving through the dark sky show up with increasing frames. Then the image is flattened to prevent massive build up of frames.
This action is best used as part of a batch import process, found under the File-Automate-Batch menu in Photoshop, operating on a folder of successive frames, as shown below.
To use it, create an empty, transparent (this is important) image that is the same size in pixels as your frames and then automate with the action as shown above. The result is a single flattened image, similar to the effect of running the frames through the StarTrails.exe program.
Which of course is no good for us because we want the individual frames!!
What we can see is that if we add in a ‘Save as’ command before the Flatten Image, each time we add a frame we will create a new frame that is the build up of the trail as it happens.
Making the above additions to the action means that we will create new frames as an output that are the sums of the previous frames, so we see a trail build up, not just the passing stars. Note the destination settings in the above batch. we create new frames titles 01,02,03 e.t.c into a new folder.
Then we can output a movie in the same way as we covered in Part I of this series. Which gives us…
But the next part will cover the question, what if we want to move a small trail across the whole sequence. For this we need to investigate Layer Comps.
Part III Coming soon!