IMAGE STACKING NOTES (brief version) ------------------------------------ Compiled MJI April 2001-2002 Issues relevant for stacking and mosaicing [Observe=Image*PSF*Shah] * = convolution x = multiplication NB. defect rejection simplest if already done by "local" stacking PSF not varying --------------- 1. Lauer, T, 1999 PASP, 111, 227 - coaddition in Fourier domain (solve matrix equation to recover Nyquist sampling), requires precise fractional pixel offsets cf. WFCAM interleaving 2. Projection onto convex sets eg. Adorf, H,-M, ADASS IV 456 - iteration technique (similar to drizzle in a way) promising for automatic PSF generation 3. Drizzle technique - used for HST, ESO ESI - benchmark method, works, well, review of this and others: Fruchter & Hook astroph 980887, see also Hook, Pirzkel & Fruchter, also worth checking ADS publs. 4. Standard approach - resample to align and "average" - many different interpolation schemes; precis: nearest pixel bilinear (similar to 1:1 drizzle) sinc interpolation (textbooks) hyperbolic tangent eg. Devillard, N. ESO Messenger ++ bicubic spline eg. Alard & Lupton 1998 APJ 503 325 interpolate with optimum weights Fischer & Kochanski 1994 AJ 107 802 PSF varying ----------- 1. Image coaddition and restoration using Lucy-type methods (iterative deconvolution eg. IRAF acoadd). Bayes/ML MEM argument non-linear iterative methods, trade off is S:N -v- resolution, issues local flux conservation. Enormous literature on subject. CPU intensive. 2. Nic Kaiser approach based on optimal image detection, form: Y = sum_i W_i x X_i * S_i ith weight image seeing define Z * sum_i W_i x S_i = Y solve for Z interesting if only want optimal image detection 3. Also relevant are adaptive kernel matching techniques (devised for difference imaging viz transient phenomena detection SNe, NEOs....) eg. Alard C., and also Alard & Lupton 1998 APJ 503 325 4. Magain ESO messenger, and Magain, Courbin & Sohy, 1998, ApJ 494 472 deconvolution with correct sampling plus application for stacking images with different seeing