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Sharpening is one of the most commonly misused processes in Photoshop. When you are editing a photograph, you should almost never sharpen until the very last step. If you sharpen the occasional layer or adjustment, the image will have varying layers of sharpening artifacts that will be impossible to go back and edit without undoing some progress. There are three things which you should always keep in mind when sharpening an image for printing or for web use.

1) A printer outputs significantly more dots per inch [dpi] than a standard computer monitor. When printing, you should generally aim for 300 dots per inch minimum, while a computer monitor generally only has 72 dots per inch. This means that if you are looking around you ten megapixel print at a 100% view in Photoshop, you are wasting your time. Considering 300dpi is just over 4x the resolution of your computer monitor, it is advisable that you only sharpen while viewing the image at 25% [or one forth] to compensate.

2) For small images and outputs, a smaller radius will give the appearance of a sharper image. Rather than using 40% or 50% and a radius of two, take it down to a radius of 0.5 or less. Here’s an example of an image sharpened using the following settings.

100%, 0.4 radius

3) Know your website’s maximum dimensions. Photoshop’s bicubic resizing algorithms are significantly more powerful than a website’s automatic resize function. If you are using Wordpress, the limit is usually 500 horizontal pixels. If you are using Facebook, the limit is 604 pixels in either horizontal or vertical aspect ratios.

Note how poorly your browser resizes images

To prevent the aliasing you see in this image, resize the image in Photoshop before uploading to the web. No matter how sharp the image, it will be represented poorly by the web browser.

4) Try sharpening in LAB mode. LAB mode is a more specialized color space (a method of storing information about a photograph’s data). Where as RGB stores values in red, green and blue channels, LAB stores values in “lightness”, “a” and “b” channels. When you adjust the lightness channel, you are not effecting colors. This lets you sharpen without causing as many artifacts, as it essentially only has to sharpen one third the amount to get the same result. To switch to “LAB” mode, go to “Image > Mode” and select LAB. If you switch, adjustment layers will be flattened, so be careful. It is best to do this at the final step before printing when you can completely flatten a document.

Other than that, sharpening is the same process as before: for smaller documents, use a smaller radius, for larger documents use a large radius and if printing zoom out to 25%.

This post is tagged lab, lab color, lab color mode, sharpen, sharpening