Transform Your World (Or Warp It, If You Prefer)
I mentioned last week that I wasn't a fan of software that claims to correct the distortions caused by shooting with a fisheye lens. It just seems that it defeats the entire point. But sometimes even a well composed "pure" fisheye shot can benefit from a judicious tweak via software. Not to remove any evidence of what kind of lens was used or anything, but just to transform it slightly to stop some trees from falling over perhaps. Or, as Adobe Photoshop calls it, "warp" it a tad.
There are a lot of useful options under the Edit menu in Photoshop. In some ways I think Adobe should have called it the "Miscellaneous" menu instead to be more descriptive. After all, apart from opening your photos in Photoshop just to look at them, isn't everything you do to them "editing?" One of those miscellaneous options on whatever you want to call this menu though is called "Transform." And it is here you will find Warp and all its friends.
To begin with, let's review what each of the various Transform sub-options do.
Scale will change the scale an image which is to say it will make them bigger or smaller. Grab one of the handles around the edges and drag on it as desired or enter numbers directly into the options bar. Use the corner handles to keep the aspect ratio the same or the ones in the middle of each side to freely scale each dimension independently.
Rotate allows you to spin your image around its center. As with Scale you can rotate using either the handles around the outside of your selection or via direct numerical entry using the options bar. Want to rotate it around some other point? No problem. Just move the center marker with your mouse to reposition it before rotating.
Skew will let you push your image so it looks like a parallelogram leaning over. To do so, grab one of the handles in the middle of a side and slide it along the side. The opposite side will stay where it was, but the rest of the image will shift along with your mouse cursor. If you'd rather move only one corner rather than a whole side, use that corner handle instead.
Distort works reasonably the same as Skew except that it doesn't constrain your actions. You can still make everything lean over using the side handles, but with Distort the corner handles can be moved anywhere you want rather than only moving along one dimension or the other.
Each of these is of minimal value for fisheye shots but it's when we get down to Perspective that the good stuff starts. Most photographers are familiar with the problem of parallel lines appearing to converge when the camera isn't pointed directly perpendicular to their center. It's evident in most photos of tall building as well as tall trees when the camera is pointed in an attempt to frame them. To correct for this using Edit >> Transform >> Perspective, grab one of the corner handles and drag it sideways to expand or contract that edge of the image. As you do, the opposite corner on that same side will move to match. Move the top right corner further right to stretch the top of the image relative to the bottom and the top left corner will move further left all on its own to keep things balanced. This is what makes Perspective different from Skew when grabbing the same corner handle.
Warp is where the real action is for tweaking fisheye shots. When you select the command, you don't just get handles just along each edge and attached to each corner. Instead, the image will be overlaid by a mesh that you can grab and drag from any point. You many need to play with this a bit to get the hang of things. To get you started, try selecting some of the Warp styles in the dropdown list on the options bar to see what is possible. For real work, you'll likely want to stick with the default Custom style and manually manipulate the warp. Just grab the image or an edge where you need to straighten things out and have at it. Don't overdo it though. A little bit goes a long way.
At the bottom of the Transform list you'll find the standard rotate and flip options to round things out. You can probably guess what these do already.
There's also a Free Transform menu option directly above Transform on the Edit menu that will let you do pretty much any combination of Scale, Rotate and such all at once. But not Warp.
There are a few entries on the Filter menu such as Pinch and Spherize that perform somewhat similar manipulations but most operate on 8-bit images only and don't provide as much control as the Edit >> Transform tools. The temptingly named "Lens Correction" will work in 16-bit mode but operates on the entire image even when only part of it is selected making it useless for localized edits. Lens Correction does have its uses of course, but this isn't it in my opinion.
Time to go explore the world a bit more with a fisheye....