Photoshop For Beginners - How Much Should I Sharpen a Photo For the Internet?

What is USM or Unsharp Masking?

The most common method of sharpening an image in Photoshop is to use the USM or Unsharp Mask filter. The unsharp mask filter has its roots in traditional darkroom printing and involves increasing the contrast at the edges of detail. This increase in contrast produces a perceived increase in sharpness.

How much USM should I use?

Before we get too far let's just establish that there isn't a 'one stop' group of settings for all occasions. Many beginners think you can use just one amount of USM for all images but that is not usually possible. The amount of sharpening has to be done on an image by image basis.

Of course, if you regularly produce images of the same basic size, for example for your internet gallery, you may find that one amount of sharpness works most of the time; for that size of image! To determine the amount of USM required, it is best to look at how we want to use the image.

The Internet

For the internet, where the image is to be displayed only on screen, we usually resize the image so that it produces a reasonable size on the computer monitor. For screen display the 'resolution' of the image shown in the Photoshop image size dialog is irrelevant (this is only used for printing); the only important information is the actual pixel dimensions of the image. Now most monitors display at a screen resolution of 96ppi (pixels per inch) and the commonest screen pixel sizes are 1024x768 or above. So, if you want an image to fill half the screen on a 1024x768 display the width needs to be 612 pixels. This would produce an image of just over six inches wide on the screen.

So, we resize our finished image (and save it as a copy!) to 612 pixels wide. Now we apply USM. Since this image is only destined to be viewed on a computer screen you can simply use your eyes to determine how much to sharpen. Adjust the USM settings visually with the preview box checked. If you get haloes around edges bring it back, you have gone too far!

This is easy as you can see the result instantly, just use your judgement. If your screen size is bigger than 1024x768 adjust the figures for your own screen since you have absolutely no control over other people's screens. Just keep thinking about how big you want the image to appear ON SCREEN and use pixel sizes to get there (or use 96ppi to calculate screen inches). This is all done for you in PS using the Image Size dialog so you don't need the math.

If you are submitting your photos to online libraries or for use on printed products you should follow the guidelines set down by the particular website you are sending the images to. Most commercial websites will have very detailed help to guide you.

By doing some simple tests you should learn all you need to know about USM for Internet photos without worrying about how much or little to use. By the way, this is also getting to know your visual preferences for your Internet based photos!