Non-linear image contrast enhancement

Disclosed is a method for enhancing the contrast in an image. The method starts by applying a gain to a received image by multiplying the pixel value of pixels in the image by a ratio of a target mean output pixel value and a mean pixel value for the pixel values of the pixels in the image 201. Then adjusting the distribution of pixel values of the gain-adjusted image by, determining a pixel difference value by calculating the difference between each gain-applied pixel value and the target mean output pixel value 202. Then determining an output image by mapping the pixel difference values into output image pixel values, using a mapping function that expands the distribution of pixel difference values close to the target mean output pixel value and compresses the distribution of pixel values far away from the target mean output pixel value 203. The method may calculate a histogram of the values of the pixels in the image, such that the mean value for pixel values is calculated using the histogram.