1. A method comprising: receiving an image, where a plurality of pixels of the received image have input red, green and blue (RGB) values that depend on a sensor used to acquire the image; expanding, by an image processor, the input RGB values of the plurality of pixels using a nonlinear base, where terms of the nonlinear base correspond to functions f(R,G,B), where each of the functions f(R,G,B) has an associated value and f(kR,kG,kB) equals k times the associated value, for any scalar k>0, such that each term of the nonlinear base scales linearly with exposure of the image or brightness of a scene depicted in the image; and adjusting, by the image processor, the image by transforming the expanded input RGB values of the image to output RGB values that are independent of the sensor used to acquire the image and scale linearly with the exposure of the image or the brightness of the scene depicted in the image.