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.
MultiDrizzle
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.
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.
drizzle
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').
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