Today’s Question: I just bought a fisheye lens that makes true 180-degree circular images. Is there any way that Photoshop (or other software) allows or enables perfectly circular cropping? If not, how to accomplish this?
Tim’s Quick Answer: No, Photoshop and other photo-editing software does not enable you to crop to a circular image. Instead, you’ll want to use a layer mask to create a mask around the circular image created by the fisheye lens.
More Detail: A full circular fisheye lens is generally able to capture a full 180-degree hemispherical view, which would naturally translate into a circular image area. However, most cameras capture an image with a rectangular aspect ratio, which means the circular image you are intending to capture will actually be framed within a rectangular photo.
With this type of situation, the camera is capturing an image that extends beyond the actual image area projected by the camera. That means you are actually including the interior of the lens at the outer edges of the photo you’re capturing with a fisheye lens.
Naturally, in the final result, you really only want to include the circular image. But photo-editing software doesn’t enable you to crop to a non-rectangular shape, so you’ll need to improvise. I generally use Photoshop for this purpose, adding a Solid Color adjustment layer along with a layer mask so the selected color will only appear outside the circular image.
To get started, I generally use the Elliptical Marquee tool to create a selection that perfectly aligns with the circular border of the actual image area. Then invert that selection by choosing Select > Inverse from the menu, so everything except the circular image is selected.
With this selection created, you can then click the Add Adjustment Layer button (the half-black/half-white circle icon) at the bottom of the Layers panel and choose “Solid Color” from the popup menu. In the Color Picker dialog that appears, select the desired color. I would generally choose white if the image is going to be printed, or possibly black if the image will be shared online. Click OK to finalize the effect.
The result is a color surrounding the circle that defines the edge of the actual image area. You can always modify the color by double-clicking the thumbnail for adjustment layer (which will have a name of “Color Fill”) to bring up the Color Picker dialog. You can also modify the layer mask for that adjustment layer if needed.
You can see a sample fisheye photo that I’ve applied this type of color border effect to on my Instagram feed here:
https://www.instagram.com/p/BHmiuOegicU/