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.

This paper considers the problem of high-dynamic-range (HDR) image capture using low-dynamic-range (LDR) cameras. We present three different minimal-bracketing algorithms for computing minimum-sized exposure sets bracketing of HDR scenes. Each algorithm is applicable to a different HDR-imaging scenario depending on the amount of target-scene-irradiance information and real-time image processing available at the time of image acquisition. We prove the optimality of each algorithm with respect to its ability to obtain a theoretically minimum-size bracketing set of exposures. We also provide closed-form expressions for computing minimal-bracketing exposure sets for two common types of HDR-imaging systems, those with geometrically varying and arithmetically varying exposure settings. We experimentally demonstrate the advantages of the proposed methods by capturing and processing multiple HDR scenes using minimal-bracketing and 1-stop bracketing methods. The results show that minimal-bracketing can be used to produce high-quality HDR images, while requiring only one third as many LDR images be acquired compared to 1-stop bracketing. We also perform a detailed SNR analysis that quantifies the tradeoff between signal-to-noise ratio and image-bracketing-set size.