Next: Introduction
Compensation for Read-Out Noise in HST Image Restoration
Donald L. Snyder
Washington University, Department of Electrical Engineering,
Box 1127, St. Louis, MO 63130
Carl W. Helstrom
University of California, San Diego CA 92037
Aaron D. Lanterman and Mohammad Faisal
Washington University, St. Louis, MO 63130
Richard L. White
Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore, MD 21218
Abstract:
Data acquired with the charge coupled device camera on the HST are modeled as
an additive Poisson-Gaussian mixture, with the Poisson component representing
cumulative counts of object-dependent photoelectrons, object-independent
photoelectrons, bias electrons and thermoelectrons, and the Gaussian component
representing read-out noise. Two methods are examined for compensating for
read-out noise. One method is based upon approximating the Gaussian read-out
noise by a Poisson noise and then using the expectation-maximization (modified
Richardson-Lucy) algorithm for Poisson distributed data to effect the
compensation. This method has been used for restoring HST images. The second
method directly uses the expectation-maximization algorithm derived for the
Poisson-Gaussian mixture data. This requires the determination of the
conditional-mean estimate of the Poisson component of the mixture, which is
accomplished by the evaluation of a nonlinear function of the data. The second
method requires more computation than the first, but modest improvements in the
quality of the restorations are realized, particularly for fainter objects.
Keywords:
read-out noise, charge-coupled device camera, image restoration