Canon PowerShot G12, Advanced Techniques to Explore

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12 years ago

For most of this book, I’ve focused on how to take a great shot—one exposure, one image. But shooting digital opens other options that combine several shots into one better photo. The following two sections, covering panoramas and high dynamic range (HDR) images, require you to use image-processing software to complete the photograph. They are, however, important enough that you should know how to correctly shoot for success, should you choose to explore these two popular techniques.

Shooting panoramas

If you have ever visited the Grand Canyon, you know just how large and wide open it truly is—so much so that it’s difficult to capture its splendor in just one frame. The same can be said for a mountain range, or a cityscape, or any extremely wide vista. Two methods can help you capture the feeling of this type of scene.

The “fake” panorama

The first method is to shoot as wide as you can and then crop out the top and bottom portion of the frame. Panoramic images are generally two or three times wider than a normal image.

Creating a fake panorama

To create the look of the panorama, zoom out to the camera’s widest focal length, 6.1mm.
Using the guidelines discussed earlier, compose and focus your scene, and select the smallest aperture possible.
Shoot your image. That’s all there is to it, from a photography standpoint.
Open the image in your favorite image-processing software and crop the extraneous foreground and sky from the image, leaving you with a wide panorama of the scene.

Figure 7.16 isn’t a terrible photo, but the amount of sky at the top of the image detracts from the dramatic clouds below. This isn’t a problem, though, because it was shot for the purpose of creating a “fake” panorama. Now look at the same image, cropped for panoramic view (Figure 7.17). As you can see, it makes a huge difference and gives much higher visual impact by drawing your eyes across the length of the image.

Figure 7.16 This is an okay image, but the sky occupying the top half detracts from the clouds.

Figure 7.17 Cropping adds more visual impact and makes for a more appealing image.

The multiple-image panorama

The reason the previous method is sometimes referred to as a “fake” panorama is because it is made with a standard-size frame and then cropped down to a narrow perspective. To shoot a true panorama, you need to combine several frames. Although the camera can’t stitch the photos together, it does contain a Stitch Assist mode that aids in lining up the images to be merged together later.

The multiple-image pano has grown in popularity in the past few years; this is principally due to advances in image-processing software. Many software options are available now that will take multiple images, align them, and then “stitch” them into a single panoramic image (Figures 7.18 and 7.19). The real key to shooting a multipleimage pano is to overlap your shots by about 30 percent from one frame to the next. I’ll cover the Stitch Assist mode, but I’ve also included instructions for doing the job manually. Also, it’s possible to handhold the camera while capturing your images, but you’ll get much better results if you use a tripod.

Using the Stitch Assist Mode

Mount your camera on your tripod and make sure it is level.
Choose a focal length for your lens that is somewhere in the middle of the zoom range (a wide angle can distort the edges, making it harder to stitch together).
Turn the Mode dial to SCN and then turn the Control dial until you’ve selected the Stitch Assist scene. (There are actually two Stitch Assist scenes: One helps you shoot left to right, the other helps you shoot right to left.)
Take the first photo.
Carefully pan the camera, using the portion of the previous shot as a guide to align the next shot (see below). When the two images overlap, capture another photo.
Repeat steps 4 and 5 until you’ve captured the entire panorama. Then switch to another mode to exit Stitch Assist.

Shooting properly for a multiple-image panorama

Mount your camera on a tripod and make sure it is level.
Choose a focal length for the lens.
In Av mode, use a very small aperture for the greatest depth of field. Take a meter reading of a bright part of the scene, and make note of it.
Now change your camera to Manual mode (M), and dial in the aperture and shutter speed that you obtained in the previous step.
Switch to manual focus, and then focus your lens for the area of interest. (If you use autofocus, you risk getting different points of focus from image to image, which makes the stitching more difficult for the software.) Or, use the autofocus and remember to set the lens to MF before shooting your images.
While carefully panning your camera, shoot your images to cover the entire area of the scene from one end to the other, leaving a 30 percent overlap from one frame to the next.

Figure 7.18 Here you see the makings of a panorama, with four shots overlapping by about 30 percent from frame to frame.

Figure 7.19 I used Adobe Photoshop Elements to combine the exposures into one large panoramic image. I also cropped and adjusted the color of the final image.

Now that you have your series of overlapping images, you can import them into your image-processing software to stitch them together and create a single image.

Shooting high dynamic range (HDR) images

One of the more recent trends in digital photography is the use of high dynamic range (HDR) to capture the full range of tonal values in your final image. Typically, when you photograph a scene that has a wide range of tones from shadows to highlights, you have to make a decision regarding which tonal values you are going to emphasize, and then adjust your exposure accordingly. This is because your camera has a limited dynamic range, at least as compared to the human eye. HDR photography allows you to capture multiple exposures for the highlights, shadows, and midtones, and then combine them into a single image (Figures 7.20–7.23).

There are two ways to get an HDR image with the G12. Switch to the SCN mode and choose the HDR option. Be sure to stabilize the camera on a tripod or other solid surface and press the shutter button to take the shot. The camera shoots and combines multiple exposures into one HDR shot with a complete range of exposures using a process called “tonemapping.”

For more control over the HDR photo’s appearance, capture multiple shots at different exposures and use third-party software to process them. I will not be covering the software applications, but I will explore the process of shooting a scene to help you render properly captured images for the HDR process. Note that using a tripod is absolutely necessary for this technique, since you need to have perfect alignment of each image when they are combined.

Sorting your shots for the multi-image panorama

If you shoot more than one series of shots for your panoramas, it can sometimes be difficult to know when one series of images ends and the other begins. Here is a quick tip for separating your images.

Set up your camera using the steps listed here. Now, before you take your first good exposure in the series, hold up one finger in front of the camera and take a shot. Now move your hand away and begin taking your overlapping images. When you have taken your last shot, hold two fingers in front of the camera and take another shot

Now, when you go to review your images, use the series of shots that falls between the frames with one and two fingers in them. Then just repeat the process for your next panorama series.

Figure 7.20 Underexposing one stop renders more detail in the highlight areas of the sky.

Figure 7.21 This is the normal exposure as dictated by the camera meter.

Figure 7.22 Overexposing by two stops ensures that the darker areas are exposed to get detail in the shadows.

Figure 7.23 This is the final HDR image that was rendered from the three other exposures.

Setting up for shooting an HDR image

Set your ISO to 80 to ensure clean, noise-free images.
Set your program mode to Av. During the shooting process, you will be taking three shots of the same scene, creating an overexposed image, an underexposed image, and a normal exposure. Since the camera is going to be adjusting the exposure, you want it to make changes to the shutter speed, not the aperture, so that your depth of field is consistent.
Set your camera file format to RAW. This is extremely important because the RAW format contains a much larger range of exposure values than a JPEG file, and the HDR software will need this information.
Adjust the auto exposure bracket (AEB) mode to shoot three exposures in twostop increments. To do this, press the Function/Set button and highlight the Bracket setting (third from the top). Next, use the Control dial or press the Right button to select the AEB option (A).
Press the Display button to access the exposure control setting.
Turn the Control dial to the right until the AEB indicators move all the way out to –2 and +2 (B). Press the Set button to lock in your changes.
Focus the camera using the manual focus method discussed earlier, compose your shot, secure the tripod, and press the shutter button once; the camera fires all three shots automatically.

A software program such as Adobe Photoshop or Photomatix Pro can now process your exposure-bracketed images into a single HDR file.

Bracketing your exposures

In HDR, bracketing is the process of capturing a series of exposures at different stop intervals. You can bracket your exposures even if you aren’t going to be using HDR. Sometimes this is helpful when you have a tricky lighting situation and you want to ensure that you have just the right exposure to capture the look you’re after. You can bracket in increments as small as a third of a stop. This means that you can capture several images with very subtle exposure variances and then decide later which one is best.