This tool can be used to reduce vignetting within an image. Vignetting refers to the reduction of image brightness away from the image centre (i.e. the principal point). Vignetting is a radiometric distortion resulting from lens characteristics. The algorithm calculates the brightness value in the output image (BVout) as:

BVout = BVin / [cos^n(arctan(d / f))]

Where d is the photo-distance from the principal point in millimetres, f is the focal length of the camera, in millimeters, and n is a user-specified parameter. Pixel distances are converted to photo-distances (in millimetres) using the specified image width, i.e. distance between left and right edges (mm). For many cameras, 4.0 is an appropriate value of the n parameter. A second pass of the image is used to rescale the output image so that it possesses the same minimum and maximum values as the input image.

If an RGB image is input, the analysis will be performed on the intensity component of the HSI transform.

## Function Signature

`def correct_vignetting(self, image: Raster, principal_point: Vector, focal_length: float = 304.8, image_width: float = 228.6, n_param: float = 4.0) -> Raster: ...`

## Project Links

WbW Homepage User Manual Support WbW