# Clipped Projections

When projections are rotated or skewed, the projection region can extend outside the boundary of the image, particularly if the projection region is close in size to the image. The following figure shows a projection region that extends outside the image; the clipped area is shown in grey.

The Caliper tool automatically adjusts the projection region if it detects clipping. The Caliper tool detects clipping by computing a weights image when it computes the projection image. The weights image is a one-dimensional image in which each pixel is set to be the number of pixels from the input image which contributed to the corresponding pixel in the projection image. The following figure shows how the weights image is computed.

The Caliper tool resizes the projection image so that no pixels with weights of zero are included.

When the Caliper tool produces the filtered image and performs peak detection, it automatically normalizes the projection image based on the number of source image pixels that contributed to each projection image pixel.