In modern digital still cameras, noise-reduction is a more and more important issue of signal processing, as the customers demand for higher pixel counts and for increased light sensitivity. In recent years, with pixel counts of ten or more megapixel in a compact camera, the images lack more and more of fine details and appear degraded. The standard test-methods for spatial resolution fail to describe this phenomenon, because due to extensive adaptive image enhancements, the camera cannot be treated as a linear position-invariant-system. In this paper we compare established resolution test methods and present new approaches to describe the influence of noise reduction on images.
A new chart is introduced which consists of nine siemens stars, a multi-modulation set of slanted edges and Gaussian white noise as camera target. Using this set, the standard methods known as SFR-Siemens and SFR-Edge are calculated together with additional information like edge-width and edge-noise. Based on the Gaussian white noise, several parameters are presented as an alternative to describe the spatial resolution on low-contrast content.