Must be odd. Default is 15. The path must already exist. The gain factor for the contrast increase is given by -k factor which defaults to 1.0. The actual increase factor is limited when -a lower upper is given.
Clipping is done with the -c option.
With this option off it is easy to visually see over and under range clipping. With clipping enabled over and underload is handled in a more visually pleasing manner. The overall gray level may be controlled by the -m factor . Values of factor larger than 1.0 give a brighter image and vice versa. Large kernal values -n kernel give more smoothing of the contrast enhancement.