Sharpening a digital image

Whenever you resize or edit a digital image, you should consider sharpening your image as a final step. If you sharpen first, and then edit your image further, you are likely to exaggerate the "artifacts" created as part of the sharepening process. Make sure you save your edited image with a different file name, or in a different folder than the original, in case better sharpening algorthims come along in the next few years - I burn my Original images to CD and store locally in an "Original Photos" folder, and place the edited versions in a "Photo Editing" folder.

Unsharp Mask

There are many techniques for sharpening a digital image, each with pros and cons. The following steps and ideas for using Unsharp Mask apply to Adobe Photoshop and Adobe Elements.

Radius: In general, if you have a low resolution image (fewer dpis) then you need a lower Radius - try setting it to 0.3; if you are working on a high resolution image, then you need a higher Radius. To avoid creating coloured halos around edges of things in your image, reduce your Radius. If you make the Radius too high, you may lose detail in light areas

Threshold: For "busy" images, set this value to 0. As soon as you have large areas of a similar colour (e.g. blue sky), you should increase this setting to reduce introduction of noise in otherwise smooth areas.

Amount: This value will typically depend on the two settings discussed above. To reduce the constrast introduced by sharpening, try setting this value to its maximum (500%) and then find the smallest Radius at which sharpening is adequate (e.g. start at 0.1 and increase slowly). Be sure you view your image at 100% its actual size.

For More Information...

If you're interested in purchasing only one book as reference, then I highly recommend the PhotoShop CS book by Scott Kelby (editor of Photoshop User Magazine). I use it as reference frequently while editing photos and trying to correct for mistakes I made during my latest photo-shoot.

He gears his reference material toward amateur photographers who don't care to know the detailed ins-and-outs of PhotoShop CS, but who instead want to know how to correct common problems with digital images. For example, he covers cropping and resizing tricks, corrections to common image problems (over-exposure, under-exposure, bad mix of colours, etc), masking techniques, fixing photos of people to look more flattering, and much more. I even learned to straighten a building that suffered from fish-eye distortion!

I've added a link to Scott Kelby's book on amazon.ca, which is where I purchased my copy, since it has the best price anywhere - either locally or online. It's about $40 Cdn, and ships within a day or two, but the shipping is free!