Customized embedded processor design for global photographic tone mapping

Tone-mapping (TM) aims to adapt high dynamic range images to conventional display devices. TM algorithms are usually implemented on general purpose processors and graphics processing units. Such platforms may not meet performance, area, power and flexibility constraints imposed by the embedded system domain. This paper presents the design and implementation of a customized processor for a global TM algorithm. Using an architecture description language, three custom instructions to calculate luminance, logarithm and maximum luminance were added to a 32-bit RISC-based processor. The logarithm was computed using an improved Mitchell approximation. Experimental results demonstrate a 169% performance improvement when adding all three instructions, with a hardware overhead of only 22%.