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38 Special: photographic special effects > Stitching Panoramas Together

Stitching Panoramas Together

You don’t need a $500 stand-alone application to stitch together simple panoramas because you can do it in Photoshop. You can, however, make the process dramatically easier if you follow these two simple rules before you shoot your pano: (1) Use a tripod. That’s not to say you can’t shoot panos handheld, but the consistency a tripod brings to panos makes a world of difference when you try to stitch the photos together. And (2), when you shoot each segment, make sure that part of the next segment overlaps at least 15% of your previous segment (you’ll see why this is important in the tutorial).

Step One.
Open the first segment of your pano. The photo shown here is the first of three segments that we’ll be stitching together.


Step Two.
Next, go under the Image menu and choose Canvas Size. In the capture shown here, you can see the Width of the first segment is 5.014 inches. We’re stitching three segments together, so we need to add enough blank canvas to accommodate two more photos of the same size, so make sure the Relative check box is turned on, then enter 14 inches as the Width setting. This extra blank canvas needs to be added to the right of your first segment, so in the Anchor grid (at the bottom of the dialog) click the left center grid square (as shown here).

Step Three.
Click OK and 14″ of white canvas space is added to the right of your photo (if it doesn’t look like the capture shown here, press Command-Z [PC: Control-Z] to Undo, then go back and check your Anchor grid setting and make sure you clicked on the left center grid square).

Step Four.
Now, open the second segment of your pano. Notice that the rocks on the far right of the first segment also appear in the second segment. That’s absolutely necessary because now we have common objects that appear in both photos, and we can use the rocks as a target to line up our panos.


Step Five.
Press the letter “v” to get the Move tool from the Toolbox and click-and-drag your second segment into the first segment’s document window. Drag the second segment over until it overlaps the first segment a bit. I’ve zoomed in here so you can see the two segments overlapping.

Step Six.
Go to the Layers palette and lower the Opacity of this second segment’s layer to 50% (as shown here). This is pretty much the secret of stitching together panos. As long as there’s a common element in both photos, you can lower the Opacity of the top layer, and drag it with the Move tool until the two objects line up perfectly together.

Step Seven.
As the two rocks (your target objects) get closer in alignment, it’s easier if you take your hands off the mouse and do the final aligning using the Arrow keys on your keyboard. Start nudging the top layer with the Left Arrow key to line them up. Because the Opacity has been lowered on the top layer, things look kind of blurry (almost out of focus), but as the two target objects get closer to each other, the blur lessens.

Step Eight.
Keep nudging with the Arrow keys, and when the rocks don’t look fuzzy anymore and are perfectly clear, your two segments are lined up right on the money (as shown here).

Step Nine.
Now, go to the Layers palette and raise the Opacity of the top layer to 100% (as shown) to see how your stitch looks. The two images should look like one (that is if you shot them using a tripod and didn’t bump the camera along the way). If you see a hard edge along the left-hand side of the top layer, switch to the Eraser tool; choose a 200-pixel, soft-edged brush; and lightly erase over the edge. Since the photos overlap, as you erase the edge, the top photo should blend seamlessly into the bottom photo.

Step Ten.
Now, open the third segment of your three-segment pano (as shown here).


Step Eleven.
Repeat the same technique of dragging this photo into your main pano, lowering the Opacity of this layer to 50%, and dragging the segment over your target object. (In this example, we’re using overlapping rocks again. Hey, it’s not like we’ve got a lot of other options here, eh?)

Step Twelve.
Don’t forget, as you get close to lining up the rocks, take your hands off the mouse and use the Arrow keys on your keyboard to perfectly align the two segments (as shown here where the two versions of the rocks line up perfectly). Again, after you raise the Opacity of the top layer back to 100%, if you see a hard edge between the two, use a soft-edged Eraser to erase away that seam.

Step Thirteen.
Here are the three segments stitched together in Photoshop. As you can see, by guessing that we’d need 14 inches, I overestimated a bit, and there’s some blank canvas space to the right of my pano. No sweat. There’s a quick way to get rid of it without even using the Crop tool.

Step Fourteen.
Go under the Image menu and choose Trim to bring up the Trim dialog (shown here). The area we no longer need is on the right-hand side (the extra white area), so in the dialog, under Based On, choose Bottom Right Pixel Color and it will trim away everything outside your photo that is white (which is the color of your bottom-right pixel).

Step Fifteen.
Click OK in the Trim dialog, and the excess Canvas area is trimmed away and your pano is complete (as shown here). Now this was an ideal situation: You shot the panos on a tripod, so the stitching was easy; and you didn’t use a fisheye or wide-angle lens, so there wasn’t much stretching or distorting to deal with. (Incidentally, we use Free Transform’s Distort and Perspective functions to deal with segments that appear to bow upward or outward.)

Step Sixteen.
However, one thing that will absolutely happen from time to time is that the colors of each segment won’t precisely match. Technically, they should match— they’re shot at the same time, under the same lighting conditions, using the same camera settings, yet—it happens. Luckily, Adobe’s own Graphics Guru (and Photoshop Hall of Famer) Russell Preston Brown came up with a great technique for dealing with that common occurrence. Here’s how Russell does it: Open the first segment (this will be just a two-segment pano) and add the Canvas size as shown previously.


Step Seventeen.
Open the second segment, drag it on top of the first segment, lower the Opacity, and line up your photo using the common target object (in this case, it’s the house in the center).


Step Eighteen.
After the segments are lined up and the Opacity is raised back to 100% on the top layer, you can see the problem—although the two segments line up perfectly, the tone of the right side differs from the tone of the left side (as shown). Your goal is to make the photo on the right (the top layer) match the tone from the photo on the left (the Background layer). You do this by making simple grayscale edits to the top layer’s channels.

Step Nineteen.
Make the Channels palette visible, then click on the Red channel (as shown). Your pano now appears in grayscale (by default, all the channels display as grayscale). As you can see, the tonal difference is very visible here in the grayscale Red channel as well.

Step Twenty.
Next, press Command-L (PC: Control-L) to bring up the Levels dialog (shown here). What you’re going to do is drag the midtone Input Levels slider (the center one, directly under the histogram) to the right (as shown) to balance the Red channel of your right image (your top layer) with that of the left image (your bottom layer). When they match, click OK to apply the adjustment.

Step Twenty-One.
Go to the Channels palette, and click on the Green channel (as shown).

Step Twenty-Two.
Press Command-L (PC: Control-L) to bring up the Levels dialog, and drag the midtone Input Levels slider until the two sides match (as shown), and then click OK to apply the adjustment.

Step Twenty-Three.
Go to the Channels palette and click on the Blue channel (as shown).

Step Twenty-Four.
Press Command-L (PC: Control-L) to bring up the Levels dialog, drag the midtone Input Levels slider until the two sides match (as shown), and then click OK to apply the adjustment.

Step Twenty-Five.
Go to the Channels palette, and click on the RGB channel to see your adjustments. As you can see here, if you matched up each channel, the color image now matches up as well. Here’s the final pano after removing the excess Canvas area using the Trim command and using a soft-edged eraser to hide the edge between the two segments.



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