Blur & Sharpen > Compound Blur effect

The Compound Blur effect blurs pixels in the selected layer based on the luminance values of a blur layer, also known as a blurring map. The blur layer, which can be any layer that contains pixels of different luminance values, is essentially overlaid on top of the selected layer, and the pixels of both layers are matched, one to one. Where the blur layer is black, no blurring occurs in the same location in the selected layer. The blur layer is used only as a map; it is not visible in the composition.


Original (left), with the cloud layer set as the Blur Layer; then inverted (center) and cloud layer's Video switch off (right)

Blur Layer specifies the layer in the composition to use as the blurring map. Bright values in the blur layer correspond to more blurring of the affected layer, while dark values correspond to less blurring. Maximum Blur specifies the maximum amount, in pixels, that any part of the affected layer can be blurred. Stretch Map to Fit stretches the blur layer to the dimensions of the layer to which it is applied; otherwise, it is centered. Invert Blur inverts the values, so areas that were previously more blurred are less blurred, and vice versa.

This effect is useful for simulating smudges and fingerprints, or changes in visibility caused by atmospheric conditions such as smoke or heat, especially with animated blurring layers. Compound Blur is especially effective in combination with other effects, such as Displacement Map. (See Distort > Displacement Map effect (Pro only).)