Steve McGanity, a reader from England (or do you prefer UK?) asked a question regarding sharpening in response to my article on tips for sharper photos. In the article, I briefly mentioned that photographers need to sharpen photos that will be used on the web differently than photos that will be printed. Steve wanted to know how to properly sharpen for the web and print, and why they need different sharpening techniques.
Whether Steve knew it or not, he was asking about output sharpening. Output sharpening is the sharpening that is applied to a photo after it has been determined what medium the photo will be used in. This happens after the camera itself sharpens the photo (capture sharpening, as with a JPEG) and after any creative sharpening is applied selectively to only certain portions of the photo (such as to make eyes or hair stand out).
Output Sharpening for the Web or Screen
When output sharpening is applied to a photo that will be displayed on the web, you first need to determine the size at which the photo will be viewed. For example, your 18 megapixel file may be sent to Facebook. In this case, Facebook will display the image at approximately 1000 pixels on the longest edge. When you resize the photo, fine detail will get smudged together. For example, if your photo of a tree showed all of the individual leaves clearly, the leaves at the top of the tree may blend together into just a green color. When you see the fine details being lost from resizing, you know you need output sharpening.
Only a slight amount of output sharpening is needed for publishing a photo to the web. Because screens display images in perfect pixels without any bleed between the pixels, the photo will naturally appear sharper on a screen than in print.
Output Sharpening for Print
Output sharpening for print is performed differently. Unlike the perfectly square pixels of a computer screen, when a printer places a dot of ink on a paper, the color of the ink bleeds slightly into the regions surrounding it because the paper is porous. Therefore, the photo will appear less sharp.
To combat the lack of sharpness achieved in the printing process, a significantly increased amount of sharpness must be applied to the photo. I like to sharpen the photo to the point that it looks slightly oversharpened on the screen. I know that this oversharpened look will go away once the photo hits the paper.