Stitch HDR Panoramas in Photoshop Elements
Stitching your high dynamic range panoramas together in Photoshop Elements isn’t that hard. You might need a few run-throughs before you get totally comfortable with it, but it’s mostly automated.
Elements is a little goofy when it comes to working with 16-bit images. If you open tone mapped files that are 16 bits per channel, Elements prompts you to convert the bit depth before you begin. However, Photomerge tends to get stuck after the first image and refuses to continue opening and stitching images together (no matter how many times you curse at it), so it’s rather pointless.
Instead, open 16-bit images in Elements and convert them to 8 bits (when you save them, consider renaming the files if you want to preserve the 16-bit images for some other purpose), or save the tone mapped images as 8-bit JPEGs or TIFFs directly from your HDR application.
After you have all the brackets you want to stitch together into a panorama saved as 8-bit images, follow these steps:
Open Photoshop Elements and start Photomerge by choosing File→New→Photomerge Panorama.
As this figure shows, the Photomerge dialog box appears, beckoning you toward panoramic greatness.
Click the Browse button, and in the Open dialog box that appears, browse to the folder containing the tone mapped frames of the panorama, select them, and then click OK.
The Open dialog box closes, and the selected files appear in a new, untitled image document as a stitched panorama.
Choose a layout by selecting one of the radio buttons in the Layout section of the Photomerge dialog box.
Auto: You’re telling Elements to go for it, allowing it to choose between Perspective and Cylindrical layouts.
Perspective: The center of the panorama remains unchanged, and the outer areas are distorted so that horizontal lines parallel to the ground remain parallel to the ground.
The major side effect of this layout is the bow-tie effect, in which the center of the panorama looks normal, but the corners are heavily distorted. You lose this area when you crop the final image. This figure shows what happens when perspective goes bad. This is how you know to choose another method. Elements can’t properly configure this panorama as a perspective.
Cylindrical: This projection eliminates the bow-tie effect on the corners and results in a panorama where the corners aren’t distorted up and out. In fact, the corners are allowed to do the opposite — that is, creep in. This figure shows that the sky can balloon up. Everything that isn’t a nice, tidy rectangle gets cropped out at the end.
Reposition Only: This layout aligns each frame (based again on matching reference points) but does not transform them in any way.
This option, contrary to what you might think (we often fall prey to the notion that correcting for perspective is always better), can produce very good-looking panoramas that do not suffer from undue amounts of distortion. This figure illustrates this layout in action. Overall, it looks good, but the horizon looks a little too wavy.
Interactive Layout: This is the do-it-yourself option, as shown. Elements opens a lightbox with your panorama stitched for you (the images it can do so automatically, at any rate), and gives you the control to override the existing layout.
You can zoom in and out, click and drag frames to reposition them, rotate individual frames, and change the settings from Reposition Only to Perspective. If you select the Perspective radio button, you can even set the Vanishing Point of the image.
Elements aligns and processes the images and eventually creates the panorama as a new image. Each frame occupies a separate layer, with portions masked (hidden) to blend together well. Note: This is one of the few times Elements allows you to work with masks.
Save your panorama!
It's best to save the raw panorama as a Photoshop file (.psd) now for future reference before you tweak frame blending and make other adjustments. Then save the finalized panorama image as a separate file.