Applying sharpening to photos has many benefits. It helps restore the detail to your image that was lost during the digitization process, especially around the edges of subjects or objects in a photo. It can also help fix photos that came out blurry during your photoshoot due to a shaky camera, missed focus, or myriad other reasons. In the end, adding sharpening during your photo editing workflow is a simple way to improve the look and enhance the quality of your photos.
There are multiple ways to sharpen your photos using GIMP, but the most tried and true method for doing so is using the Sharpen (Unsharp Mask) filter. I’ll discuss how to use this filter in-depth in this article, plus provide tips along the way to help you achieve sharper photos every time in GIMP.
When to Apply Sharpening During Image Editing
For starters, I recommend sharpening your photos towards the end of your photo editing workflow, meaning after you’ve color corrected, retouched, and resized or cropped the photo. This avoids enhancing the details on things you plan on removing from the photo (i.e. wrinkles or artifacts) while also ensuring the final sharpening effect is optimized for the final image.
How to Apply Sharpen (Unsharp Mask) Filter
Keep in mind that this filter was designed to avoid enhancing blemishes or noise in your photos, so it’s OK if the photo still has imperfections when it comes time to sharpen.
To apply the filter, make sure your image layer is the active layer in your Layers panel (blue arrow in the above image), then go to Filters>Enhance>Sharpen (Unsharp Mask) – denoted by the red arrow in the photo.
This will bring up the “Sharpen (Unsharp Mask” dialogue (outlined in blue in the image above), which contains three sliders along with some additional options and settings. Make sure the “Preview” box in the lower left corner of the dialogue is checked (red arrow) before you begin tweaking settings. This will ensure you see a live preview on your image as you apply sharpening.
The first slider, “Radius,” (red arrow in the above image) allows you to increase or decrease the area on either side of an “edge” of a detail in your image for sharpening. Edges are simply the outlines surrounding details in an image – like the outline of the subject’s eyes or eyebrows, the lines in the subject’s hair, or the contour of the subject’s jawbone (blue arrows in the image). Basically, any area where pixels abruptly change their intensity or contrast is an edge. Since this filter works by increasing contrast around edge details, the Radius slider is important because it allows you to set how large or small of an area you want to apply your sharpening to the edges in your image.
Showing this slider in action is more effective when we increase the value of the second slider, so we’ll come back to the Radius slider. I promise it will make sense to you by the end of this article.
The next slider, “Amount,” (red arrow in the above image) let’s you increase or decrease the amount of sharpening applied to your image. The higher you set the value for this slider, the stronger the sharpening effect will be. The lower the value, the weaker the effect will be and thus there will be less sharpening applied to your image. If I click and drag this slider to increase the value to somewhere between 20 and 25 (blue arrow in the image), you’ll see the strength of the effect will be intense and we’ll see way too many details in our image. Increasing the “Amount” value too much also adds noise to the photo, which you can see when you zoom in.
If, on the other hand, I bring the value down to “0” (red arrow in the image), it’ll appear as if there’s no sharpening at all on our image.
Usually, the larger the image you’re editing, the higher you can increase the “Amount” slider without overdoing it. In my case, my image is over 5000 pixels wide and 3400 pixels in height, which is a fairly large image, so I can increase the amount slider quite a bit and get a nice looking result. If you’re editing a smaller image (i.e. 1280×720), you may want to keep the “Amount” set to a lower value to avoid too much sharpening.
With the Amount slider turned up a bit (red arrow), let’s revisit the Radius slider to see how it can alter the sharpening of your image. By default, the slider value is set to 3. If I start to increase the value of the slider (I went to around 7.5 in the image – blue arrow), you’ll notice that all the edges around the details in my image start to have more contrast and become darker in appearance. The colors in my image will also start to show signs of distortion. (Note: these observations are a little harder to see in the image here as I’ve scaled it down for the website/article).
If I continue to increase this value to something more extreme, like a value of around 50, the edges will now have way too much contrast, the colors will be much more distorted, and the image overall looks unsightly.
Again, if you are using a smaller image, you may start to see these effects much sooner when adjusting the slider values.
I recommend keeping your Radius value set to a lower value, and adjust the Amount slider until you are happy with the amount of sharpening applied to your image.
Additionally, make sure you zoom in to 100% of the zoom value to get a closer look at any noise that may be created through sharpening, especially if you intend on printing the image. If you’re going to send this somewhere where the image will ultimately end up compressed, this may not be as big a deal. You may find that the image has too much noise when viewed up close and you may want to tweak your settings to reduce the noise while maximizing sharpening.
The last slider for this filter is the “Threshold” slider. This slider allows you to adjust at which point changes in pixel values are considered an “edge.” According to GIMP, increasing the value of this slider will “protect areas of smooth tonal transition from sharpening, and avoid creation of blemishes in [the] face, sky or water surface.” In other words, if you start to see sharpening around blemishes or in areas where there’s a smooth transition of colors (a.k.a. not an edge), you can increase the value of this slider and it will remove sharpening from those areas.
If I bring the value of this slider up to demonstrate the setting in action (red arrow), you’ll see that my photo will look blurrier overall because GIMP is reducing the number of edges that receive sharpening in my image. GIMP will still retain some sharpening around pronounced edges (like the eyes of my subject).
For this image I don’t need to adjust the threshold, so I’ll drag the value back down to 0.
Split view and Adding Presets
If you want to see what your image looks like before and after the sharpening was applied, you can click the “Split Preview” option in the bottom right corner of the dialogue (red arrow) to see a side-by-side comparison. You can also move the pink dotted line to reposition the preview.
If you want to add your current settings as a preset inside GIMP, click the “+” icon towards the top of the dialogue (red arrow). You can then name your preset (I named mine “Cowgirl Edit” – blue arrow) and click OK to save the preset (green arrow).
Now when you click the “Presets” dropdown (red arrow) you’ll see your saved preset towards the bottom of the list (green arrow). Clicking on the preset will apply your current settings to whatever image you’re working on.
When you’re happy with your settings, click OK to apply your sharpening to your image.