How to sharpen a blurry photo
Smart Sharpen, Unsharp Mask and High Pass sharpen soft photos in Paint by Zaweba, and Shake Reduction estimates camera shake and reverses it.
How you sharpen depends on why the photo is blurry. For general softness, Paint by Zaweba has Smart Sharpen, Unsharp Mask and High Pass sharpening. For blur caused by the camera moving during the shot, Shake Reduction estimates a straight line of shake and reverses it by deconvolution. Neither can rescue a photo that's badly out of focus, but both can make a soft one look crisp.
Sharpening works by increasing contrast along edges. Done well, the picture looks clearer. Done too hard, you get bright halos, crunchy textures and noise that wasn't visible before. The aim is to stop just before the effect becomes noticeable.
Which kind of blur
Look closely at the photo at 100 percent. If everything is slightly soft in all directions, that's general softness, from the lens, a small focus miss or resizing. If edges seem doubled or smeared in one direction, the camera moved during the exposure. Fixing the first is ordinary sharpening. Fixing the second is a job for Shake Reduction.
Smart Sharpen
Smart Sharpen is the most flexible choice for photos. It can treat the blur as Gaussian, as lens blur or as motion blur, which lets it target the real cause. It also has shadow and highlight fade settings, which hold back sharpening in the darkest and brightest areas where noise and halos show up first.
Open it, zoom the preview to 100 percent on an area with fine detail such as eyes or text, and raise the amount until the detail looks clean. Then back off slightly.
Unsharp Mask and High Pass
Unsharp Mask is the classic. Amount sets the strength, radius sets how wide the edge effect is, and threshold stops it sharpening fine noise. Small radius values suit detailed photos, larger ones add punch to softer pictures.
High Pass sharpening is a layer based method. Duplicate the layer, run High Pass, and blend it in with a contrast mode such as Overlay or Soft Light. Because it's a separate layer, you can lower its opacity or mask it to sharpen only the subject, which makes it a favourite for portraits.
Shake Reduction
For camera shake, Shake Reduction estimates the path of a straight shake from the photo and deconvolves it, working backwards to recover the sharper picture. It handles the common case of a slight jolt in one direction. It won't fix a moving subject, or a curved, jerky shake, and it can add ringing around edges if pushed. Use it on the part of the photo that matters most and judge it there.
Getting a good result
Sharpen last, after resizing and other edits, and sharpen for the final size. A picture for a phone screen needs different sharpening from one for a large print.
Reduce noise first if the photo is noisy, because sharpening will make noise more visible. Then sharpen through a mask so smooth areas like skin and sky stay smooth while eyes, hair and texture get the detail.
Don't sharpen a JPEG that's already been sharpened in the camera too hard. Check edges for white outlines and back off when you see them.
The simpler filters
Sharpen, Sharpen More and Sharpen Edges are also in the menu, with no settings. They're fine for a quick touch, but the adjustable filters give far better control. For most photos in Paint by Zaweba, Smart Sharpen is the place to start.
