Undesired blur in a photograph is annoying. It can take a great image and ruin it, either because of an operator error or subject movement that couldn’t be controlled. While blur can be used to great artistic effect when employed intentionally, accidental blur is far less desirable. Some of this blur can be fixed with image-editing programs, like GIMP and Photoshop.
What Counts as Blurry?
When you describe a photo as “blurry,” that’s a fairly broad category. It means that the subject isn’t sharp, yes. But there are several kinds of blur. Identifying the type of blur is important to knowing how to fix it.
- Motion blur results from the subject or the camera moving during the exposure.
- Focus blur comes from focusing on the wrong part of the subject.
We will focus on improving focus blur in this tutorial. Motion blur can also be fixed to an extent. However, it requires different techniques and more advanced tools to get the best results.
Fix a Blurry Photo with Unsharp Mask
The classic way to sharpen photos is with a filter called “Unsharp Mask.” The history of the counter-intuitive name is interesting, but rest assured: it does sharpen images.
1. Open your image in GIMP or Photoshop. We will use GIMP for this example.
2. Select “Unsharp Mask” from the “Filters” menu. In GIMP 2.10 this is under “Filters -> Enhance -> Sharpen (Unsharp Mask).” In Photoshop you’ll find it in “Filters -> Sharpen -> Unsharp Mask.”
3. This will pop up a pane with some default settings. You can adjust these settings to better sharpen your image.
- Amount controls the strength of the mask. The higher the amount, the more edge contrast will be added to the image. It’s important to set this value properly. Too low and you’ll see no effect; too high, and you’ll see hideous effects.
- Radius controls what counts as an “edge” for sharpening purposes. Small radius values will sharpen fine detail, while high radius values will apply to larger edges. Radius is easy to set too high, so keep a steady hand.
- Threshold defines how many luminosity levels must change from one pixel to the next to define an edge. The higher the value, the less it counts as an edge. Smaller values will sharpen more edges, while higher values do the opposite.
Because each image is different, the optimal settings for each image will also be different. There is no “best” setting. You’ll gain experience through practice. Applying too much sharpening will lead to an unappealing high-contrast look that you’ll probably want to avoid.
4. Apply a mix of settings that you feel best sharpen the image. This is an art and not a science, so experiment.
While experimenting, you may want to see a comparison of your sharpened and unsharpened images. By ticking the “Preview” box on and off, you can toggle between the two images. You can also click “Split View” to see a side-by-side comparison. The split view tool is only available in GIMP.
Fix a Blurry Photo with the High Pass Filter
Another method of sharpening is the high pass filter, which applies a different method of detecting edges.
1. First, duplicate your layer by right-clicking the layer and choosing “Duplicate Layer” from the context menu.
2. With your new layer selected, choose “Filter -> Enhance -> High Pass” in GIMP or “Filter -> Other -> High Pass” in Photoshop.
3. Adjust the settings until you can see the edges you want to sharpen, then click “OK” to apply.
4. Change the blending mode for the layer to “Overlay” from the dropdown menu.
For more detailed control, you can adjust the opacity of the high pass layer after changing the blending mode.
Newbies frequently oversharpen images. Use the image above as a guide. The image should be less blurry, but not distressingly high contrast or haloed. Try for the middle eye and avoid the bottom.
Fixing blur in photos is an art. It requires a careful and patient hand. Despite the incredible power of today’s computers, not all blur can be fixed. Extreme blur will remain unfixable, likely forever. When there isn’t enough data to create a sharp image, the computer can’t just imagine one. But light blurring can be recovered in many cases.
Image credit: Ru_dagon