nu_corrector is a tool for correcting intensity non-uniformity artifact of image. Here, non-uniformity refers to image artifacts of vignetting and bias (e.g. intensity inhomogeneity, illumination etc.). This tool is an implementation of our single-image based vignetting or bias correction systems based on the sparsity property of image gradient distribution.
nu_corrector can correct vignetting with about 0.7 second and bias with about 0.9 second for an image in size of 750x580 through my experiments using a common computer.
"Definition of vignetting and bias":
Vignetting refers to the phenomenon of brightness attenuation away from the image center, and is an artifact that is prevalent in photography. Vignetting is generally assumed to be radially symmetric.
Bias of image denotes the spatial variations of intensity/color caused by illumination changes for images taken by a digital camera, by in-homogenious magnetic field for MR images obtained with an MRI machine, or by non-uniform X-ray beam for CT images acquired with a CT scanner. Bias is a smooth field in any format, which can be represented by for example a bipoly model, B-Spline, etc.
"Harm of vignetting and bias":
Vignetting and bias can significantly impair computer vision algorithms that rely on precise intensity data. They include photometric methods such as shape from shading, appearance-based techniques such as object recognition and image mosaicing, and many other applications such as image segmentation, image registration, and feature extraction.