Making a 360° pseudo-stereographic projection from an ordinary panorama
Those cool "little planet" 360° stereographic photographs are often described as being made from dozens or hundreds of photos. But that ain’t necessarily so. We’ll see here how it’s possible to create images like these from relatively ordinary 360° panoramas.
Step 1 – Make a Normal 360° Panorama
For shooting your panorama you want to use the widest angle lens you have available. The wider the lens the better because a large angle of view reduces the width of the final panorama in relation to its height. Ideally, you want to be able to get the full 360° in 8 or fewer photos, even allowing for a generous overlap between shots. In the example shown here I used a 12mm lens on an APS-C format camera.
You also need to be sure to cover more than 360° in your photos because that gives you some overlap that will come in handy later in this process. This usually isn’t a problem because most full-circle panoramas go over 360°, but be aware that if you happen to come in under the full 360° you’ll have problems. You’ll also benefit from using a tripod and, if possible, a proper panoramic head. You can get by without either, but it might make your life difficult later. As with most things in photography, getting it right at the very beginning pays big dividends later.
When you’ve assembled your panorama in Photoshop’s Photomerge utility you should have something roughly like this:
Step 2 –Match Left & Right the Edges
Now, for our stereographic version to work properly, the far left edge of the photo and the far right edge must match perfectly because they’re going to be joined later. That means the final panorama must cover 360 degrees exactly and the image content at the two edges must line up perfectly. The reason for making the original panorama more than 360° is that it gives some choice of where to make the join.
Use the Marquee Tool to make a Selection of the left half of the image (it doesn’t have to be exactly half) and then press Cmd+J (Mac) or Ctrl+J (Win) to make that Selection into a new Layer.
Cmd-click (Mac) or Ctrl-click (Win) on the thumbnail of the new Layer in the Layers Panel to load it as a Selection. Choose Select > Inverse from the main menu to invert the Selection. Now target the Background Layer and press Cmd+J (Mac) or Ctrl+J (Win) to make that Selection into a new Layer.
You should now have your image divided into two parts, each one in its own Layer, that together make up the whole. Hide the Background Layer at this point. Now move the right half to the left side and the left half to the right. Your Layers Panel should look like the image at right.
Step 3 – Fix Where the Two Halves Meet
Now you know for certain that the (new) left and right edges match perfectly – because they were joined at the center of the image a few seconds ago. The trouble is, zooming in will show that there’s now an ugly, obvious join in the middle where the two Layers meet – because your panorama (if you did it properly) exceeds 360 degrees.
The first step in fixing the center is move the two halves closer together to make up for the overlap (which will depend on how much more than 360° you got in your panorama). If you’re very lucky the two halves will match neatly when this is done – use of a tripod with a panoramic head makes this much more likely. If you’re not lucky you’ll need to do some work to blend the two halves together. First, try swapping the stacking order between Layer 1 and Layer 2 to see if one works better. Mask out or erase parts of one Layer. Next try the Clone and Healing Brush tools. If things are really amiss you may have to transform one or both Layers to get them to blend seamlessly. If you try to use a Transform be very careful not to let it affect the far edge of the image after we just took so much care to insure that it matches the opposite edge of the image! Don’t get too fanatical about making the join perfect because the final step in generating the pseudo-stereographic rendering will hide a multitude of sins. It’s also worth noting that this process becomes much more critical with large images. If you’re using a high-megapixel camera and intend to make big prints, you’ll need to be more fastidious.
When you’re satisfied that the seam is unnoticeable, merge the two Layers and name the resulting Layer "Merged".
If your blending resulted in any gaps at the top or bottom of the image, clone/heal them away now (or use Content-Aware Fill). If you need to trim the image be sure to do so only off the top or bottom (since we’ve just gone to great lengths to make the left and right edges match exactly!)
Step 4 – Crop to 360 Degrees and Flatten
When you’re satisfied with all the previous steps you should have a panorama that covers exactly 360 degrees and which has left and right edges that match perfectly (because they were originally the middle).
Cmd-click (Mac) or Ctrl-click (Win) on the thumbnail of the "Merged" Layer in the Layers Panel to load it as a Selection. From the main menu choose Image > Crop. Now choose Layer > Flatten and you’re ready for the interesting bit…
Step 5 – Make it Square & Flip it Over
The final result is going to be a square image. It’s certainly possible to make it square at the end of the process, but it’s usually quicker to do it now (especially with very large images). Open the Image Size dialog (Image > Image Size…).
• Make sure the Resample box is checked
• Un-check the link icon that keeps height & width proportional
• Increase the height to 150-200% its initial value
• Decrease the width to exactly the same value you just entered for image height
• Click OK
Obviously, every image will have different dimensions. Mine started as 1000px height and 3200px width so I Increased the height to 1500px and then set the width to 1500px. The result will look a little weird but then the final product we’re aiming for is going to be even weirder so don’t worry about it.
Now flip the image by choosing Image > Image Rotation > 180° from the main menu (this is necessary because the next step uses the top of the image as the center point).
At right is the image I had after resizing and rotating 180°.
Step 6 – Convert to Polar Coordinates
Now we’re ready for the "little planet" conversion. From the main menu choose Filter > Distort > Polar Coordinates…
Make sure the "Rectangular to Polar" option is active and click OK.
Now you should have your own "little planet" image without needing to take "hundreds of images". Have fun with this! My result is shown below.
