How much sharpness needed?
Looking at images on the web, I notice a huge range in image quality. A key factor is sharpness, and many photographs appear less sharp than they ought to be. People often say that my images are bright, punchy and appear to ‘jump off the screen’. The reason for this is careful manipulation of the sharpness.
But what exactly is going on when we sharpen an image on a web page? First of all we have to understand that a computer screen is actually a very low-resolution image display medium – only 72 pixels per inch. Even a low-quality newspaper image has 150 dots per inch
Our eyes perceive the image as sharp because we look at a computer screen from further away than a book or newspaper. Also, because the tiny pixels on the computer screen are emitting light, there is a slight halo effect around each one, making them appear to merge into a smooth area. Sharpening an image for display on a web page can be done in any image-editing software program. You need to increase the contrast between neighbouring lighter and darker level pixels. When viewed from a distance, our eyes perceive this as sharpness.
The amount of sharpness to apply depends very much on the image. If there is a lot of detail already, for example leaves and branches, then only moderate sharpening should be necessary. If there is less detail, then more may be required.
