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Using our recent tutorial on image stacking it is possible to stack images from both day and night to create a single image of the city skyline over time. The photograph below consists of 8400 images taken using a Go Pro HD with one image every 5 seconds. The streak of light to the left is the moon during the night time sequence, while the right hand light is the daytime sun. The small lights are aircraft during the evening:
You can view a higher resolution version on our Flickr Stream, we will have more on the Go Pro HD next week, including a tutorial to create 24 hour+ timelapses.
Last week we covered creating 'day trails' in Photoshop using the technique in Astrophotography known as 'star trails'. Today we take the same technique and use it to create a view of city activity at night.
Time Taken, 4 to 12 hours to capture, 2 to 6 hours to process.
Setting Up
The concept is simple, set up your camera, webcam or iphone at a suitable location, and capture an image at regular intervals, for our example we captured an image every 5 seconds pointing at the skyline of London. Capturing an image at least every 5 seconds is vital for star/aircraft trails as it allows for closer spacing between the lights in the final image.
We left the camera running for approximately 12 hours capturing 8000+ images, saved into a folder on our computer. Ours captured covered both day and night time, resulting in the following timelapse:
The next step is to open up photoshop, chose the images you want to use, and start stacking.
Image Stacking in Photoshop
The images will be stacked onto of an intially blank image via a simple automated action:
1) Create a new blank black image the same size are your captured photographs.
2) Load the action into the action windows in Photoshop and load the action Startrails.atn.
3) In Photoshop click 'File', 'Automate' and 'Batch'. Select the action you have just loaded and choose your directory with the images as source and make sure you select 'None' for the output directory.
Click 'Ok' and leave it running, our Mac laptop took around an 2 hours to stack the images - resulting in the Start/Aircraft Trail' below:
The line across the centre is a star and the bright line on the left is the moon coming into shot. The rest of the lights are aircraft in the sky above London.
Our previous tutorial on setting up a Waterproof webcam timelaspe system via a torch and USB extension leads also lends itself to capturing star trails or city activity at night. Being Central London based light pollution filters out the stars to a large extent but with very little effort some interesting images can be captured and if you are located in area with lower light pollution it is perfect for capturing star trails.
Step 1: Capture the Images
Use your webcam via our previous tutorial to capture a image in .png format every 5 seconds throughout the night. This will result in approximately 10,000 images which can be stacked to create a simulated night long exposure.
Step 2: Stack the Images
We found by far the best image stacking option was to use Helcion Focus. Available for both Mac and PC Helicon Focus is a program that creates one completely focused image from several partially focused images by combining the focused areas. The program was designed for macrophotography, microphotography and hyperfocal landscape photography to cope with the shallow depth-of-field problem. It also however is one of the best stacking programs around. Other software we tried would crash above 1000 images whereas Helicon has coped well with up to 10,000 so far.
The software is available for a free 15 day fully functional trial.
2) Click 'Add Images' and point Helicon to the folder containing your images saved overnight. The software will now load them in, our iMac took approximately 10 minutes to complete the process.
3) We are not using Helicon for macro photography so we can turn off processing, allowing the stacking to run faster. Click 'File/Preference' and set ReSample Method to 'None'.
4) Click 'Run'
Our image at the top of this post comprises of 8401 separate captures, it took 12 hours to complete the stack, running on our Mac overnight. Star trails will not require such a long exposure, perhaps a few hours and thus a smaller number of images will be sufficient.
In our image the long line is a star with the crescent moon streaking on the left before going behind clouds and finally the rest of the lights detail air traffic over the London skyline. If you are in a low light pollution area you will be able to quickly and easily capture images such as the one below:
