One of the reasons for Photoshop's popularity is the huge number of third-party plug-in filters available for it. The chances are that whatever effect you want to achieve, there's a plug-in that can do it, or one is in development. The downside to this constant supply of impressive effects is that Photoshop's standard filters get overlooked, especially innocuous-looking ones like High Pass, a well-kept secret in the backwaters of the Others sub-menu.
At first sight, High Pass appears fairly mundane - all it seems to do is flatten and desaturate an image. But once you understand how it operates you'll appreciate the tool's extreme versatility. It's part of a family of filters that enables you to manipulate the different frequency ranges of information that compose an image.
Over the next few pages, we'll explain exactly how High Pass works. Using practical demonstrations, we'll look at how High Pass can be used as a more flexible alternative to Unsharp Mask for sharpening images, and as a tool for removing any distracting background patterns present in tiled textures.