Handheld Exposure Techniques
While the best way to make exposures for panoramic merges is to use a dedicated panoramic head on a tripod, this may not be practical—or necessary. (There are three significant benefits to using panoramic tripod heads: one, they keep the camera level and without rotation throughout an exposure sequence; two, they calculate the number of and overlap between exposures; and three, they pivot the camera around a lens’ nodal point, minimizing parallax.) Today’s software packages work miracles, making what was once impossible possible. Several practices can help you make better handheld exposures for panoramic merges.
Keep the horizon level in all the exposures. Varying rotation can cause improper alignment and/or excessive cropping and/or retouching.
Shoot a little loose. Perspective correction in these types of photo merges often results in irregular borders that beg cropping—or retouching, if this is appropriate. The extra wiggle room you gain from shooting loose will allow you to crop the final results more precisely.
Don’t shoot the separate exposures edge to edge. Instead, overlap your exposures by a third for medium lenses, a half for wide-angle lenses and two-thirds for fisheye lenses.
Make exposures with the opposite orientation as the final image orientation. If you’re making a horizontal composition, shoot with a vertical camera orientation; if you’re making a vertical composition, shoot with a horizontal camera orientation. This does two things. One, it increases the number of frames, and thus, vanishing points, reducing the tendency for the required perspective correction to produce distortion artifacts. Two, it increases resolution, a tendency that becomes compounded with each added pass in multi-column or multi-row exposure sequences.
Once focus is set, turn off auto-focus during the bracketing sequence. Unwanted shifts in focus may ruin an exposure sequence. For this same reason, consider shooting all exposures in a single sequence at the same aperture setting, as significant variances in depth of field between frames may be challenging to merge convincingly.
Consider using manual exposure. While software can convincingly blend exposures with significantly varying exposures, if brightness across a scene remains fairly constant, keeping the same exposure settings between different shots can aid the blending process. (The same is true for white balance, which can be set either during exposure or during RAW processing.) On the other hand, if brightness varies dramatically, bear in mind that simultaneous HDR exposure bracketing isn’t out of the question; it just increases the number of exposures needed.
Stitching & Merging
The processing of merging separate exposures is reasonably straight-forward. In Bridge, select the files you wish to include in a photo merge and then go to Tools > Photoshop > Photomerge. Alternately, in Lightroom, go to Photo > Edit In > Merge To Panorama In Photoshop. Whether you start in Bridge or Lightroom, Photoshop will do the merging. (Beside Photoshop, there are other photo-merging software options, such as PTgui, which offer alternative solutions necessary only for the most challenging jobs such as precise architectural convergence.) In Photoshop, you’ll encounter the Photomerge dialog. In most cases, you’ll want to use all three options it offers—Blend Images Together, Vignette Removal and Geometric Distortion Correction—but any of them can be unchecked before producing the final merged file.
Photoshop offers five Layout
(or blending) options: Perspective, Cylindrical, Spherical, Collage and Reposition. The default Auto lets the software select the method it deems best for the images included. Perspective favors the center of the final image, allowing both horizontal and vertical distortion to become more extreme on the edges. Cylindrical favors maintaining horizontal alignment across all included frames, useful for keeping horizon lines straight. Spherical warps images in both horizontal and vertical directions. Collage repositions and rotates without distorting them. Reposition only repositions without rotation or distortion.
As a general rule of thumb, choose Perspective for images with an angle of view of less than 140 degrees, Cylindrical or Spherical for images with wider angles of view, and Collage or Reposition for scanned (moving the camera parallel to the subject) rather than panned (pivoting the camera around a central axis or nodal point) exposure sequences.
While Auto usually delivers good results, to choose an optimal final solution may require making a comparison between several methods. When evaluating the final results, in addition to determining how convincing the merge is, pay close attention to the relative distortions within the frame that each method creates. Variances in shape, proportion and line angle all can make a significant impact on an image.
Photoshop will place separate exposures on separate layers, transform and align and mask them, then
selectively adjust color to create seamless transitions between them. It’s magic! If you’ve ever done this by hand, you’ll appreciate how much work is being done for you and how well it’s done. Because the results are saved in a layer stack, you can fine-tune the results manually at anytime, now or in the future.
Once a merge is complete, you can create further variances by using one or more of Photoshop’s powerful distortion tools: Free Transform, Puppet Warp and the filters Lens Correction, Adaptive Wide Angle and Liquify. These can be used for functions as obvious as straightening a horizon, whether uniformly on nonuniformly bowed, or as subtle as subtly adjusting shape, proportion and line angle. While this step is often overlooked, it can produce substantial differences. To apply one or more of these effects to all layers at one time, you can merge them into a single new layer by simultaneously tapping Shift, Option, Control and E.
Cropping And/Or Retouching
The distortion necessary to align and fine-tune image information within the frame also distorts the frame. To restore a rectangular shape requires one of two moves—or a little of both. One, crop. This eliminates some image information along the edges. Again, ensure that significant information isn’t lost in the final merged image by framing loosely during exposure. Two, retouch. Using the Clone Stamp tool, Healing brush or Content Aware Fill synthesizes convincing image information to fill gaps left by distortion, often in a way that can’t be ascertained by the uninformed viewer, but it nonetheless changes the nature of the photograph created, either subtly or substantially; it’s a practice that may or may not suit your intention.
Regardless of whether you use panoramic aspect ratios, the practice of extending format through photo merges can help you perfect many compositions in ways that are often challenging and in some cases impossible to do otherwise. It can help you choose a better angle of view without eliminating essential information or include essential information when you either can’t or don’t have time to change angle of view. When this skill becomes second nature, you’ll find that you’ve become visually more versatile, flexible and accomplished.
John Paul Caponigro, author of
Adobe Photoshop Master Class and the DVD series R/Evolution, is an internationally renowned fine artist, an authority on digital printing, and a respected lecturer and workshop leader. Get his enews Insights with access to hundreds of lessons at www.johnpaulcaponigro.comand see more of his panorama tips at www.johnpaulcaponigro.com/downloads/technique/exposure.php.