The tradeoff between SNR and exposure-set size in HDR imaging

In high-dynamic-range (HDR) imaging, a radiance map of a HDR scene can be constructed by capturing the scene multiple times with a digital camera at different exposure settings and then digitally combining the images. As we show in this paper, the signal-to-noise ratio (SNR) of the resulting HDR radiance map depends strongly on the number of images that are captured. We present an analytical model for computing SNR as a function of the set of exposure settings used in image capture and the physical noise parameters of the digital camera. We find that the average dynamic range of the HDR image varies as the inverse of the square-root of the inter-exposure spacing. We also find that using a denser exposure set can significantly reduce the inter-pixel variability and spatial variability of SNR in the final HDR radiance map.