Sharpening images using the unsharp mask

Introduction

This page aims to demonstrate how to sharpen photographs using the unsharp mask with a practical example. A far more rigorous description of this and other techniques for improving your scans can be found on Wayne Fulton's site www.scantips.com.

The problem

When images are scanned they appear to be hazy and rather blurred e.g. the photograph of Buttermere below.

This photograph was scanned at 2400dpi using a Minolta Dimage Scan Dual film scanner and was then resized to fit on the page. The image above does not appear particularly sharp even though the original slide looks fine. The apparent sharpness of the image can be improved by applying an unsharp mask. What this does is to detect the edges of the image and increase their contrast.

Using the unsharp mask in Paintshop Pro

To sharpen the image in Paintshop Pro first display the Unsharp Mask dialog (using the Image->Sharpen->Unsharp mask... menu). I don't understand exactly what all the settings do and so I won't try to explain them. You will need to experiment to find the best settings as these vary from photograph to photograph (if you select the "Auto Proof" option you can see what effect you changes have). I've found the ones shown below useful. If the sharpened image appears too grainy try reducing the strength. Conversely increase the strength if the image is not sharp enough. I generally use values between 50% and 100% and occasionally up to 200%. Note: this is a contrast enhancement technique and it can't compensate for an out of focus image.

Here is the final image shown beside the original image for comparison (click on the images to compare the larger versions):

chris.breeze@iname.com