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Once you have a set of images loaded as a stack in Photoshop you can apply some of the other Stack Modes. Each one produces a different result, and some of them seem like magic. My favorite is the Median Stack Mode, especially for scenes in which there are too many people to get a clear shot. Median removes things that do not appear in every image in the stack, such as people and cars. For this to work well, some of the subjects in your image must be static (these are the items that will appear in the final image) and you need to allow enough time between the exposures for the items that you don’t want to appear in the final image to move. For example, if you take a series of 20 images over 10 minutes and some of the people in the scene don’t move, they will not be removed from the final frame. The streets in the opening photograph have no cars on them. The only vehicles that show are those that were parked the whole time the series of images was made.
Creating a stack in Photoshop
- 1 Open [File > Scripts > Load Files into Stack]. In the Load Layers dialog, select the files you want to use and check the two boxes at the bottom of the window: Attempt to Automatically Align Source Images and Create Smart Object after Loading Layers (Figure 36.3). Smart Objects allow you to do nondestructive editing on the layer, which is key when applying a Stack Mode in the next step.
- 2 Choose [Layer > Smart Objects > Stack Mode], and then select one of the modes from the submenu.
This trick works really well when you’re photographing scenes with a lot of people in them and you want to make the people disappear. It can be really tough to get a clean shot if you’re at the beach or a park where there are lots of people moving around. For example, The photo below shows what a normal shot of a busy area in Balboa Park in San Diego looks like.
By shooting multiple exposures and creating an image stack, I was able to automatically get rid of the people that I didn’t want in the final photograph. As I said, any object that does not appear in every image is removed, which means that all of the people are gone. The baby stroller on the lower left side never moved while I shot the frames, so it appears in the final image.
Because Photoshop’s Stacks feature uses a set of images combined into a single Smart Object, you can edit the original images that make up a stack at any time. Choose [Layer > Smart Objects > Edit Contents], or just double-click on a layer thumbnail. After you save the edited Smart Object, the stack is automatically updated with the last rendering applied to the stack of images.
If you want to convert the Smart Object to regular layers to preserve the rendering effect, select [Layer > Smart Objects > Rasterize]. Once you do this, you will not be able to edit the individual layers nor will you be able to apply other Stack Modes. If you make a copy of the Smart Object first, you will have the ability to edit the stack and you will have a copy of the final rendered version.
There are many other Stack Modes besides Mean and Median, and I recommend you play around with them to see what effects they have on the image stack
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