How to simulate long exposure with Adobe Photoshop

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A simple way to simulate the smoothness of a long exposure using Photoshop is to use a time stack. Instead of one long exposure, stacking uses many shots over time. The post-processing technique helps overcome bright lighting conditions that prevent normal long exposures. Additionally, stacking applies to a number of other areas of photography, most notably capturing star trails in astrophotography.

However, achieving the desired results in post takes preparation and planning ahead of time.

No intravalometer? No problem!

Some people use an intervalometer. If that is not an available feature on your camera, one can be purchased that plugs into your camera for around $20 on Amazon. An intervalometer is device that triggers the shutter at a regular set intervals. These are good for also doing time-lapse photography.

For this demonstration I’m just pressing the shutter manually to accomplish the same thing. A tripod and a remote trigger will also work keep everything steady and ensure all images will align properly. It’s not unusual to run 100, 200 or even 300 shots into a single stack. For brevity I’m using only nine. The more shots you stack in the image the smoother your image will be.

Stacking images in Photoshop

It’s a lot simpler before starting if all the shots use are located in one folder, especially if there are hundreds of shots. Open Photoshop and in File use Scripts -> Load Files into Stack…

Scripts > Load files into Stack
Creating the image stack with Photoshop. Files -> Scripts -> Load Files from Stack.

In the ‘Load Layers’ dialog box Browse to find and load all the shots. Check the ‘Attempt to Automatically Align Source Images’ if shots handheld or there is potentially any camera shake. Otherwise, leaving it unchecked is fine. Check the ‘Create Smart Object’ after ‘Loading Layer’ box and click OK.

Browse to find the files
Load Layers dialog window.

After all the layers load and are converted into a smart object in the menu, choose Layer -> Smart Objects -> Stack Mode -> Mean.

Layer > Smart Objects > Stack Mode > Mean
Blending the Stack

Simulate long exposure with Path Blur

Again, the more shots put in the stack the smoother the smoother the smart object image will be. If there is a big stack this might be the end outside of a normal editing process. If only a few shots were used in a stack more can be done by flattening the image. Then copying the background layer and add more blur by going to Filter -> Blur Gallery -> Path Blur.

Filter > Blur Gallery > Path Blur
Use Path Blur to smooth the water

Run the path in the direction the water is flowing using the points and set speed to somewhere between 38 and 48. Change the End Point Speed up to 230. Press OK. Add a filter mask to the blurred layer and invert it. Using the brush tool and white, with an opacity of 20%, paint over the white areas of water. If you get too much change the color to black (X key) to remove some of the blur. When done merge the layers.

merging the layers after adding path blur
It’s getting smoother

Duplicate the layer again and set the layer blend mode to Screen. Add a layer mask and invert. Using the brush with an opacity of 80% now paint white on areas of the waterfall and water you want to lighten. As you do this the effect will become apparent and you can add more or less using the X key changing back and forth between white and black. Remember white adds and black removes. When done process the image as normal.

Done
The final image

Stacking images in Photoshop is a good way to simulate a long exposure. The more shots in a stack the less end work needed but the tools are there in Photoshop. Grab your gear and give it a try. Don’t forget to show us the results on the photopigs community pages!

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