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MultiDrizzle vs PyDrizzle

MultiDrizzle resulted from the efforts to automate the process of applying distortion correction solutions to images and to remove cosmic rays.  The tasks drizzle and PyDrizzle represent different aspects of this process. The following descriptions provide the functional relationship between the various tasks, as well as each task's unique capabilities.

The task MultiDrizzle, found in the Dither package within STSDAS and also distributed as a separate task with STScI_Python, automates a cosmic-ray rejection algorithm based on PyDrizzle.  It can be run without performing the cosmic-ray rejection steps, in essence, as a replacement for PyDrizzle.

The task PyDrizzle, found in the Dither package within STSDAS and also distributed as a separate task with STScI_Python, automates the use of the 'drizzle' task to not only correct multiple images for distortion in one step, but also automatically determine the size of the output image to be created from all the input images.  The 'drizzle' task in STSDAS only works on one input chip at a time, while PyDrizzle can process whole associations or lists of images in one step.
The alignment of the input images used by PyDrizzle relies primarily on the WCS information contained in each input header. Additional corrections to the alignment can be provided by a 'shiftfile' to accurately combine images taken at different times.

This Python task uses the same code (converted to C) which create the STSDAS 'drizzle' and 'blot' tasks. It also understands the IDCTAB reference file for describing the distortion model and translates the model automatically for use with the 'drizzle' and 'blot' tasks.

The task 'drizzle' as found in the Dither package within STSDAS represents the most basic operation: application of the distortion model to a single chip.  The user must provide all inputs for this task including an ASCII file with the distortion, the size of teh output frame, and the linear transformation terms to place the image in the output image.  It also only works on a single array (chip) at a time.

The various tasks in the Dither package in STSDAS all implement the drizzle algorithm in Fortran (as compiled into an IRAF executable) to apply the distortion model ('drizzle', 'wdrizzle') to an image, to recreate a distorted input image from a distortion-corrected image ('blot', 'wblot') and perform coordinate transformations based on the distortion model ('traxy', 'wtraxy', 'tranback', 'wtranback').

MultiDrizzle news
Improved distortion solutions for ACS

Resetting DQ bits


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