The suspension bridge at Lions Gate in Stanley Park, Vancouver is a magnet for photographers. I was only passing through but, as we watched the traffic moving across the bridge, I was thinking about how to get a shot that didn’t have cars on it. The traffic was steady so there was not way I would get a clear moment. Indeed, while we were there, they changed the lights and reversed the center lane based on the traffic demand.
I didn’t have a tripod but I did decide to experiment with an alternative technique. This is best done using a tripod and a lot of exposures but I figured I would go with shots that were pretty closely aligned and about half a dozen shots. This didn’t work perfectly but it didn’t go too badly. When you get back to the computer, you open up Photoshop. Click on File and Statistics and a dialog opens up. Select all of the files and change the option at the top to Median and check Align Images. Then send it on its way.
If the shots are good and there are enough, the algorithm will look at each shot and see the changing items – cars in this case – as the oddities. It will see what is consistent in each shot and get rid of the odd stuff. If you have it right, the cars will vanish. In this case, there were some overlaps and not enough shots but it still did a reasonable job.