What is Image Sharpening?
Image sharpening is a process of emphasizing the structure of elements in the image by increasing the local contrast.
Digital camera sensors and lenses always blur an image to some degree, which cannot be avoided; thus we use photo editors to (re)sharpen our images..
Image sharpening is a delicate process. When too much sharpening is applied, images may appear too textured, which is even worse than a slightly soft image.
On the other hand, when done correctly, image sharpening can noticeably improve image quality.
How does it work?
Sharpening tools work by improving the local contrast along the edges in the image. This means that the post-processing software recognizes edges in images by analyzing a swift change in brightness or colour of pixels. It then makes the bright pixels along the edge even brighter and the dark pixels even darker.
Although sharpening is a great way to improve quality of your images, it won’t help with motion blur. If your image is very unsharp, there’s no saving it, other than retaking it.
I (almost) always turn to Lightroom for image sharpening.
There are few reason why.
Firstly, it’s part of my workflow. I always import images into Lightroom first, do the basic adjustments (Lens correction, Remove Chromatic Aberration, Basic panel adjustments, and Sharpening), then import image into Luminar.
Secondly, I love how much control Lightroom gives me with image sharpening. I especially enjoy using Masking slider (more on that later) with Alt (Option on Mac) key + Left mouse button.
Thirdly and lastly, I started my photography career with Lightroom and I’m used to it – it feels like home.
Problems with Image Sharpening
While sharp images look more aesthetically pleasing than soft or blurry images, applying too much sharpening in post-processing introduces all kinds of problems, such as:
- Over-sharpening: when too much sharpening is used, it results in harsh, visible lines on edges (halo). Such images look “textured”.
- Noise: excessive amounts of image sharpening can add noise to an image. This effect is even more noticeable with high ISO photos.
- Zigzag lines: straight lines become zigzags, and circular shapes can become cubic when using excessive amounts of sharpening with a large radius
Settings for Image Sharpening
Lightroom boasts with a powerful image Sharpening tool which can be found within the Develop module, under the Detail panel. It works similarly as Photoshop’s Unsharp Mask, but it gives you extra controls.
This is a procedure you should follow when you try to sharpen photos in Lightroom.
Lets do it together:
- Navigate to the “Develop” module which you can find in the top right part of the Lightroom, or press “D” on the keyboard.
- Expand the “Detail” panel on the right.
The detail panel will look like this:
Lightroom tip: You can press Alt (Option on Mac) key + Left Mouse Button when hovering over the sliders, which will temporarily switch the image to black and white. This also works in Basic panel and Split toning.
Amount slider controls the overall strength of the sharpening effect. It is usually listed as a percentage, but in Lightroom the amount range is 0-150 (for whatever reason).
This is the slider you will set first. A good technique is to start with 150 (max) and then keep lowering it until the halo around the edges disappears.
My final values are around 30 to 60 for most images, but anywhere up to 100 is acceptable, depending on the situation.
Radius controls the size of the edges you wish to sharpen – a smaller radius enhances only smaller detail. This is a tricky setting to get right and usually take some experimenting to find the right value.
Lightroom’s default value is 1.0, which means that sharpening over 1 pixel around the edge will be applied. If you increase the radius to a maximum value of 3.0, sharpening will be spread over 3 pixels around the edge, resulting in a thicker sharpening radius.
Most of the time, the default 1 is just fine.
Details slider controls the amount of sharpening on the edges or details of the image. Smaller values sharpen only large edges, while higher values sharpen every edge – at 100 sharpening is applied to virtually the entire image.
For this one, I urge you to zoom into the photo and check for the noise. I usually leave the Detail slider at the default value 25, or even decrease it in some low-light cases.
This is in my opinion the most important slider in the Detail panel. It masks out areas that you do not want sharpened. This tools takes care of the noise produced by Amount and Detail sliders.
It works the best with images that have isolated subjects, with soft and less defined background. I usually use values between 40-70 for “Masking” slider, but this heavily depends on the image you are editing.
Local Image Sharpening
Sometimes only a part of the image needs sharpening, for example, you want your main object to stand out from the rest, so you would apply a local filter and use sharpening.
How to do that?
In Lightroom, there are 3 different local filters: Graduated filter, Radial Filter, and Adjustment Brush.
Lightroom Tip: You can use shortcuts to quickly access filters: Graduated filter (Shortcut: M), Radial Filter (Shortcut: Shift + M), and Adjustment Brush (Shortcut: K).
Graduated filters, as the name suggests, can be used to a gradually sharpen an image.
These are great when you’re trying to sharpen (or blur) a relatively uniform foreground or background.
When used properly, you can achieve a larger (when sharpening) or shallower (when blurring) depth-of-field, both of which can help lead the viewers eye into the frame.
Lightroom Tip: Use shortcut “O” to show the masked part (red).
Radial filters excel in situations where the object of interest has a circular shape.
Make sure to properly feather radial filters, otherwise you will create an abrupt border or sharp vs unsharp area.
When you’re in a need for a very precise image sharpening, Adjustment brush comes into play.
You can change feather radius, opacity, and site of the brush, making it extremly versatile.
It can be best used when you want to sharpen irregularly shaped objects.
Lightroom is a very powerful piece of photo editing software. It has every feature you will ever need for image sharpening.
To get the most out of it, your photos should already be sharp straight out of the camera, and then improved in Lightroom to make up for the aforementioned shortcomings of camera sensors and lens.
Matic is a landscape photographer from Slovenia and creator of Photutorial.