Compositing Bracketed Photos

Achieve more control over images and improved dynamic range

By Barry Haynes Back to

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The image Ship Rock Fire Sunset, on the cover of my book Photoshop CS Artistry, is a composite of two bracketed photos created from one original 120 film 6×4.5 shot. In the first part of this two-part article, I’ll show you how to create and work with both digital- and film-bracketed images, and how to line up several images. In part two, I’ll cover how this image was created, how to create masks from channels, and how to separately adjust the colors from each image that went into Ship Rock Fire Sunset.

Bracketing exposures

When you are shooting in a high-contrast situation where either your film or digital camera can’t capture the full brightness range of the scene, you can put the camera on a tripod and shoot two or three exposures of the image. One exposure should be underexposed to get the highlight detail, then a second normal exposure captures the rest of the mid- tone and shadow details. You can also shoot three expo- sures, one for highlights, one for midtones, and one for shadows. This is called bracketing your exposures. When you do this, you want the camera on a tripod so that all the exposures line up once you get them into a computer.

Sometimes you may have only one exposure to work with. When that is highly contrasty on film or in a digital Raw file, you might decide to open that one exposure two different ways from the Raw filter, scan it two different ways, or even process different parts of that same file in different ways within Photoshop. The procedure for doing this, and for working with the resulting layers, is very similar to the procedure for bracketing the original exposures and then working with them to get exactly what you want from each part of the image.

A third option, now available with Photoshop CS2 and later, is to take many exposures, five or more, over the full dynamic range of a very high-contrast scene, then combine those photos into one High Dynamic Range (HDR) image. This new format allows you to produce one image that can capture the full dynamic range in some of the most con- trasty scenes that occur in nature. (See PHOTO Techniques September/October 2007 for more on HDR).

Improving digital capture

With digital cameras, you can use the histogram display in the camera to see if you lost highlight or shadow detail when you took the initial shot. If you see a vertical bar on the right side of the histogram and/or flashing bright areas in your pic- ture preview area, then you lost highlight detail. In this case, shoot another exposure with your camera set to underex- pose by one f-stop. If the vertical bar is still there after that, underexpose by two stops, and so on. If you have a vertical bar on the left side of your histogram display, this means you lost shadow detail and you need to overexpose by a stop or two until the shadow detail returns. Losing shadow detail happens less often than losing highlight detail.

I usually don’t use the autobracket feature on my camera because I seldom need the overexposed shot to get shadow detail.

With the camera on a tripod, you can set aperture priority, then change the shutter speed to adjust your exposure. If you change the aperture setting, it changes the focus and depth-of- field of the scene. That’s why it’s usually better to leave the aperture the same and to vary the shutter speed. Having a tripod is a big help here, and also makes combining the images later in Photoshop much easier—or, in some cases, even simply possible. Sometimes, if you can’t get the range of focus you need in a scene to make everything sharp, you can purposely bracket the focus as well, then combine several images where one has the front objects in focus and the other has the distant objects in focus. Depending on the subject matter, this can get tricky in the places where you blend these images together.

HDR vs. one or two exposures

You may think you’d benefit by shooting for HDR with every exposure. This is not the case! If your digital or film camera can capture the entire dynamic range of the scene without losing information from either end of the histogram, you will probably get the sharpest results by making just one exposure. This is especially true when the entire scene is one type of lighting. For example, when everything in a scene is brightly lit, you often don’t need the extra shadow detail or have the blown-out highlights that HDR could improve on. Also, in an HDR version, things such as a moving truck in the background, moving clouds, or blowing wind can cause problems that don’t exist in a single shot. If you have important shadow and highlight details—even if the histogram seems to span the entire range—it doesn’t hurt to shoot a second exposure for highlights and a third for shadows. You might not need them, but it’s better than having to reshoot. I often do this even if the camera isn’t on a tripod because it’s easy with Photoshop to take small parts from a second or third image and blend them into a main image.

Aligning shots

Next issue, we’ll take a look at the specifics of how I created Ship Rock Fire Sunset. For now, I’ll say that it was made from two separate copies of the same image transparency, each adjusted differently in Photoshop. If the two parts of the Ship Rock image were actually made from two separate exposures, we’d have to line them up in Photoshop. Two separate digital camera exposures automatically line up if they were shot using a steady tripod. If you hand-held them, then they’d also have to be lined up. Two film exposures always need to be lined up, even when shot from a tripod, unless there is a way to line up the two pieces of film in the scanner the exact way they were lined up in the camera. Most scanners can’t do this.

Here’s a generic technique for lining up two shots.

• Move both shots into the same Photoshop layers; I’ll show you how to do this in part two of this article.

• Using the Move tool (V) with the Shift key held down to center the image, drag-and drop the second image on top of the first. Do not lock the position of the top layer until you line up the two images. If the two images are exactly the same and they are lined up perfectly, at 50% inverted, all you’d see would be solid gray. If the images are not lined up quite right, you’d see an embossed pattern formed by the pixels that were off. You could then use the arrow keys to move the top image one pixel at a time up, down, left, or right until the embossed pattern disappeared and the images lined up. If these two images are not exactly the same, you see the embossed pattern and you also see a strange ghost of these two images. Using the arrow keys to nudge the top image, it will be most closely lined up when this embossed pattern is gone or as small as possible.

• Type V to switch to the Move tool. Do not lock the position of the top layer until you line up the two images. If the two images are exactly the same and they are lined up perfectly, at 50% inverted, all you’d see would be solid gray. If the images are not lined up quite right, you’d see an embossed pattern formed by the pixels that were off. You could then use the arrow keys to move the top image one pixel at a time up, down, left, or right until the embossed pattern disappeared and the images lined up. If these two images are not exactly the same, you see the embossed pattern and you also see a strange ghost of these two images. Using the arrow keys to nudge the top image, it will be most closely lined up when this embossed pattern is gone or as small as possible.

• Once the embossed pattern is removed, use Command (Control)-I to again invert the top layer, and type a 0 (zero) to return its Opacity to 100%. Now click the Lock Position icon in the Lock area of the Layers palette to lock this newly aligned layer.

With this foundation in bracketing and lining up shots, you are ready to examine all the steps that went into creating the final image of Ship Rock Fire Sunset, which is exactly what we’ll cover next issue.


About the Author

Barry Haynes
Contributor
Barry Haynes is a photographer and author living in Gibsons, BC, Canada, just north of Vancouver, where he has his studio and photography gallery. See www.barryhaynes.com for info about his Outdoor Photography, Photoshop/Printmaking workshops,Photoshop books, images and gallery. His Photoshop Artistry: for Photographers using Photoshop CS2 and Beyond, from New Riders publishing, is the 8th edition of this series. See also www.maxart.com.