Determining exposure values from HDR histograms for smartphone photography

We present a novel system to assist users in choosing suitable exposure values for photography on smartphones. The user specifies the desired shape of the histogram of the captured image by adjusting the parameters of a function. The system then uses the smartphone's camera and varying exposure values to calculate a high dynamic range (HDR) histogram of the scene. It contains the entire brightness range from the darkest to the brightest area of the scene. For any exposure value, the HDR histogram can be used to synthesize a conventional histogram of a low dynamic range (LDR) image as if captured by this exposure value. This process is much faster than capturing the image itself. By comparing a number of synthesized LDR histograms to the user's desired histogram shape, the system determines an exposure value that best meets the user's preference.