Image content impacts how you sharpen images. There are essentially three types of image content: low-frequency, high frequency and a mix of both. (Well that was interesting. This got published in error, my error of course.) Oh well, moving on.
low-frequency image
The above image is all about smoothness and yet still has a graphical quality. This makes this a low-frequency image.
High-Frequency Image
The image of the tree and rocks is considered high-frequency. It has lots of different edge details and lots of edges requiring sharpening.
Medium Frequency Image
This image is a mix of low-frequency sky and clouds and high-frequency trees and grass. Therefore, this is referred to as a medium frequency image.
You images will fall into one of these categories. The point to take away here is that one stop sharpening does not always work. I know there are many who disagree, but read on and you’ll see what I mean.
Digital image sharpening is done to pixels. By “sharpening” the pixel you create a halo around the pixel to increase or decrease its contrast compared to the pixel next to it. The size of the halo determines the degree of sharpness. And in Lightroom and Photoshop the Radius setting determines the pixel’s halo size.
Therefore, when sharpening a digital image you need to consider a couple of things. Image content impacts the Radius selection. Image capture affects sharpening (image noise, poorly focused lens, chromatic aberration and camera movement). Remember, sharpening cannot repair an out of focus image. Also, you need to consider image enlargement before sharpening.
A high frequency image requires a Radius setting of 0.8 – 0.6. Now these are not absolutes, but guidelines.
A low frequency image requires a Radius setting of 1.5 – 2.0.
The Amount setting affects the intensity of the sharpening.
Given that your computer monitor has a very low resolution, it is really difficult to judge image sharpness by only looking at the monitor. Running a test print is the only true way to judge if the sharpening is adequate or too over the top. Like you, I look at the monitor with an image at 1:1 magnification and “judge” the quality of the image’s sharpness. I then run a print. Sometimes an image looks really great on-screen and the print is too sharp. Sometimes the reverse is also true. So make a test print to evaluate your sharpening.
Also consider setting up some sharpening defaults within Lightroom. It saves a lot of time.
