What is photo sharpening? Discover methods of sharpening like the unsharp mask and high pass sharpening. Learn when and why to apply sharpening to your images.
What is Sharpening?
Sharpening is one of the digital photography basics you need to master. Sharpening is a process that’s used to enhance the appearance of sharp edges in your image. It is accomplished through local contrast adjustments, i.e., increasing the contrast along edges to make them appear sharper.
Methods of Sharpening
Unsharp Mask (Photoshop)
Digital Photography Basics:
Don’t overdo your sharpening, or else you will see an unattractive and distinctive halo effect around your edges.
A common software technique in use for photo sharpening is the "unsharp mask." While the name is seems counter-intuitive, it makes sense when you understand how it works. It uses a unsharp (blurred) positive to create a "mask" of the original image. That mask is then combined with the image negative to create the impression that the resulting image is sharper than the original.
High Pass Sharpening (Photoshop)
One problem with the unsharp mask method of sharpening is that it can magnify the noise in an image. Another sharpening technique to use instead is Photoshop’s high pass filter. The steps of the technique are as follows:
- 1. Create a new merged layer of everything below.
- 2. Apply the high pass filter (Filter->Other->High Pass) using a radius of 10 (or to taste).
- 3. Choose a layer blend mode of Overlay (Soft Light, or Hard Light may be used too, creating a slightly different effect – experiment!)
- 4. Zoom in to 100% to see the effect, and reduce the layer opacity until you are no longer over-sharpened.
Another advantage to the high pass sharpening technique is that it allows you to keep sharpening on its own layer.
When and Why to Sharpen
Any time we convert light into pixels, we introduce a degree of softness to the image because we are turning continuous gradations of tone and color into a fixed grid of pixels. We want to correct this with photo sharpening.
We may also want to introduce extra sharpness into our image, or parts of our image, for creative purposes, such as emphasis.
Finally, when we print our image or display it on a screen, the output device we use may also introduce softness (e.g., in converting pixels to ink dots) that we wish to counteract.
My favorite photo sharpening software is a plugin to Photoshop made by Pixel Genius, called PK Sharpener. It splits sharpening into three distinct stages that correspond to the above reasons for sharpening:
Capture sharpening is done immediately on your raw image before any editing is applied. It’s intended to compensate for the softening introduced by the actual process of converting the light to pixels.
PK Sharpener provides varying degrees of edge sharpening that can be applied to the entire image, or "brushed on" to selected areas. The global sharpening can compensate for things like haze or overly shallow depth of field. The local sharpening can be used to add emphasis, for example to eyes in a portrait.
Options for output sharpening depend on the targeted output device: a monitor, matte paper, glossy paper etc., and the resolution of the image.
Next, you may want to:
Return to the next stage of the Digital Photo Workflow.
or, visit a digital photo tips page to learn about the Live View feature of many DSLR cameras, and how it can help with focusing.