Throughout the history of photography, many photographers have blended multiple exposures into one final image. Obviously, they didn’t shoot the exposures at the same time, but at some interval to achieve something.
One really common purpose is to remove people by shooting several photos and making sure that all areas are covered without any people and then blend all the images into one image. Another purpose of shooting multiple images is bracketing for HDR. Yet a different purpose is to compress a long time into one photo.
In this article, you will learn how to make an image that compresses a long time-span into one image. It is a bit like a time-lapse movie sequence, but instead of making a movie you create one final image.
Like in time-lapse photography you will shoot several photos shot over a period of preferably several hours to see a change in the scenery. To make it more interesting, you shoot the photos during a change of light, like from daylight to nighttime. When you put such photos together, you get something really fascinating.
To be able to make such a photo you must have a camera and a tripod or similar device. While you shoot, you need to avoid touching the camera more than you have to. Therefore a cable release or remote trigger is recommended.
You will be standing still for several hours and the temperature will most likely change quite a bit. Remember to bring clothes for a change of temperature.
Where to Shoot
In theory, you can shoot these kinds of photos anywhere and of anything. But since you are putting a lot of time into one single image, it is recommended that you have an excellent composition of an interesting scene.
When to shoot
You should shoot when the light changes the most, which is from daytime to nighttime or the other way around. It is this change that will make it into a remarkable photo. If you just shoot for four hours around midday, you will get a midday photo.
How to Shoot
When you shoot photos that you intend to blend into one final image, it is essential that you make sure to have an almost identical composition in each frame. You can do that by stabilizing your camera, typically on a tripod. Minor pixel shift differences can be handled later in the post-processing phase, but big differences in the composition will be really hard, if not impossible to blend.
You can either use a remote control to trigger the camera for each shot or put the camera into a time-lapse mode. The advantage of triggering the shutter release remotely yourself is that you can time your shots if something interesting happens.
As the light changes, you will need to change the camera settings.
During the daytime put your camera in Aperture Priority mode at ISO 100 and set the aperture around f/8. This mode makes sure that the images have the same depth of field and therefore are identical, except for the change of light. Do a couple of trial shots to make sure you don’t blow out the highlights or the shadows. If the image is too bright or dark, use the exposure compensation to adjust.
As it gets darker, the camera will make longer exposures and when you hit the 30-second mark, you will need to increase the ISO. You will typically end up at ISO 800 or 1600.
You most likely want to switch off autofocus before it gets dark. It depends on the scenery. City photos often offer good low light autofocus points, while the contrast disappears in landscape photos and makes autofocus impossible. Alternatively, you can use Back Button Focus.
How many photos do you need?
You need at least two different photos, but any number larger than one will work. For my photo of Sydney, I used a couple of night shots. For the morning part, I only used two.
If you shoot the “many people” variation, you will need photos with interesting people in all those areas you want to be populated with people. For the photo of Manarola, Italy I used approximately 60 photos from a batch of around 200.
How to handle high dynamic range?
Some situations are hard or impossible to capture in one exposure because the dynamic range gets too high. Typically this happens in nighttime city photos or if the sun enters the frame. The difference between the strong light source and the shadows is too great to capture in one single exposure.
In these situations, you must either switch to Auto Exposure Bracketing (AEB) or do some manual exposure compensation.
How to blend the photos
You can use any layer-based photo editing tool to blend the photos together. I will demonstrate using Photoshop, but Photo Affinity, GIMP or any other similar photo editing tools can do the same.
The overall process is to pick one of the good photos from the shoot as the base photo. Then you handpick a set of other photos that you want to blend into the base image.
The technique you are going to use to blend is called “Layer Masking”.
Put all the photos you have picked into an empty folder on your computer. JPEGs are fine, but you can also use RAW files.
Pick your base photo and open that in Photoshop.
Pick another photo with different light. Load that in into Photoshop by dragging the file onto the base image. Position the photo and press enter.
Notice that you now only see the top layer.
Add a mask to the top image, by selecting the top layer and clicking Layer > Layer Mask > Hide All. You have now added a Black Mask. Notice that you can now see the lower image layer again.
Select the layer mask by clicking on the black mask and then select the brush tool. Select white as your brush color and set the opacity to around 50% and hardness to 0%. You want to work with a BIG soft brush for most stuff. When you need to do more detailed work, increase hardness to around 50%.
Start painting in some areas and see how the image changes. Each time you click the mouse and paint in an area, the more the top image becomes visible. Play around until you see something you find interesting.
Add more photos by dragging them into Photoshop one at a time and make sure the new layer is the top one. You can drag it to the top of the stack if it is not. Then repeat steps 4-6 again.
The final image
In the end, you will end up with several layers containing photos from which you have used bits and pieces, to create your own unique and quite fascinating image. In the image of the idyllic alp town of Hallstatt in Austria, I used 18 photos to create my image.
Additional things to consider
8-bit or 16-bit?
Normally you should never use 8-bit mode for image editing, but if you are blending 20+ photos, you will run into serious performance issues at 16-bit, even with a high-performance computer. One workaround is to use 8-bit at the cost of image quality. You can change the mode by going to Image > Mode > 8-bit/Channel. The downside of using 8-bit is that you may end up having banding which is when you can see the colors transition from one to the other (they do not graduate smoothly).
You have probably had to adjust the camera while shooting and most likely you will find that the images are slightly misaligned. It may not be more than a pixel or two.
You use the Move Layer tool to micro adjust the misaligned layer using the arrow keys.
Addition tip – try to make more than one final image from the same photos, by switching around the night and day photos.
from Digital Photography School http://bit.ly/2HOobwD