Small digital camera modules such as those in mobile phones have become ubiquitous. Their low-light performance is of
utmost importance since a high percentage of images are made under low lighting conditions where image quality failure
may occur due to blur, noise, and/or underexposure. These modes of image degradation are not mutually exclusive: they
share common roots in the physics of the imager, the constraints of image processing, and the general trade-off situations
in camera design. A comprehensive analysis of failure modes is needed in order to understand how their interactions
affect overall image quality.
Low-light performance is reported for DSLR, point-and-shoot, and mobile phone cameras. The measurements target
blur, noise, and exposure error. Image sharpness is evaluated from three different physical measurements: static spatial
frequency response, handheld motion blur, and statistical information loss due to image processing. Visual metrics for
sharpness, graininess, and brightness are calculated from the physical measurements, and displayed as orthogonal image
quality metrics to illustrate the relative magnitude of image quality degradation as a function of subject illumination. The
impact of each of the three sharpness measurements on overall sharpness quality is displayed for different light levels.
The power spectrum of the statistical information target is a good representation of natural scenes, thus providing a
defined input signal for the measurement of power-spectrum based signal-to-noise ratio to characterize overall imaging