The Poisson and Normal probability distributions poorly match the dark current histogram of a typical image sensor. The histogram has only positive values, and is positively skewed (with a long tail). The Normal distribution is symmetric (and possesses negative values), while the Poisson distribution is discrete. Image sensor characterization and simulation would benefit from a different distribution function, which matches the experimental observations better. Dark current fixed pattern noise is caused by discrete randomly-distributed charge generation centers. If these centers
shared a common charge-generation rate, and were distributed uniformly, the Poisson distribution would result. The fact that it does not indicates that the generation rates vary, a spatially non-uniform amplification is applied to the centers, or that the spatial distribution of centers is non-uniform. Monte Carlo simulations have been used to examine these hypotheses. The Log-Normal, Gamma and Inverse Gamma distributions have been evaluated as empirical models for characterization and simulation. These models can accurately match the histograms of specific image sensors. They can also be used to synthesize the dark current images required in the development of image processing algorithms. Simulation methods can be used to create synthetic images with more complicated distributions.
A new method for testing the resolution of digital cameras has been developed. The new method is an extension of the ISO 12233 Slanted-edge Spatial Frequency Response test. The new method computes the spatial frequency response along the edge of a circle. It is especially well adapted to inexpensive imaging systems with rotationally symmetric blur and lens distortion. In addition to presenting the new method, a set of practical improvements, which can be applied to both the slanted-edge and circular-edge methods, is described.
This paper presents a comparison between primary (RGB) and complementary (CYMG) CCD color filters arrays, as applied to digital photography. Our analysis is based upon the measured spectral characteristics of the primary and complementary color versions of the Matsushita MN3776 CCD. The important role of the color correction matrix on the quality of the image is considered both in terms of noise and color saturation. Our calculations show that there is a tradeoff between color saturation and ISO speed, when complementary filters are used. Complementary color filters only gain an ISO speed advantage when the color saturation is low. When the color correction matrix is chosen to make the ISO speeds of the two filter systems equivalent, the well capacity of the complementary CCD must be significantly higher because of the higher overall transmission of its color filters. Our comparison includes ISO speed calculations and plots of the color gamut for primary and complementary color filters with various color correction matrices. We conclude that primary color filters are superior for digital photography.