While the Gaussian Blur filter is well-known, the High Pass Filter is a little stranger, less user friendly and not so easily understood. It is often used for various sharpening moves. Depending on the radius, it reveals fine detail against a 50% gray background. The larger the radius, the more detail is exposed.

When used as a sharpening tool, the idea has been to combine the resulting layer with the underlying image in one of the modes that both lighten and darken, based on the value of the pixels on the top layer. The usual modes are Soft Light, Overlay and Hard Light, modes for which 50% gray has no effect and so only work on the level of detail revealed.

While the Gaussian Blur filter is well-known, the High Pass Filter is a little stranger, less user friendly and not so easily understood. It is often used for various sharpening moves. Depending on the radius, it reveals fine detail against a 50% gray background. The larger the radius, the more detail is exposed.

When used as a sharpening tool, the idea has been to combine the resulting layer with the underlying image in one of the modes that both lighten and darken, based on the value of the pixels on the top layer. The usual modes are Soft Light, Overlay and Hard Light, modes for which 50% gray has no effect and so only work on the level of detail revealed.