A method of generating a tone scale function for a sparsely sampled extended dynamic range digital image, includes the steps of: providing a sparsely sampled extended dynamic range image sensing device having fast photosites with a predetermined response to light exposure interspersed with slow photosites with a slower response to the same light exposure; using the image sensing device to produce a sparsely sampled high resolution digital image having fast pixel values produced by the fast photosites and slow pixel values produced by the slow photosites; and generating the tone scale function using only slow pixel values from the sparsely sampled high resolution digital image.