STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
MultiDrizzle Status and Development Overview
Anton Koekemoer, ACS+WFPC2 Branch
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Project Overview
– Forum: Dither Working Group
– Software Development Mechanism
– Development Timeline to Date
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MultiDrizzle Requirements
– General
– Instrument-Specific Considerations
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MultiDrizzle Testing
– General Overview
– Instrument-Specific Considerations
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Priorities and Timescales
– Development and Testing
– Documentation
– Community Feedback
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Roadmap for Future Development
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
MultiDrizzle Project Overview

Forum - Dither Working Group (established January 2002):
– Purpose:
 Coordinate development & implementation of fully integrated software
to automatically register, CR clean and combine dithered HST images
(software intended as successor to CL-based STSDAS “dither” pkg)
– Process:
 Provide forum for dialog between INS, SSB, and dither software users
 Define requirements and set priorities for development and testing
 Determine roadmap for implementation, distribution, documentation
– Membership:
 Representatives from INS, SSB, + others attending as needed
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Development Mechanism:
– MultiDrizzle requirements initially developed through discussions
within Dither Working Group and interations with users
– MultiDrizzle prototype (Koekemoer, Fruchter, Hook et al.) developed
to demonstrate desired functionality; beta release under STSDAS
– SSB redesigns the code, reproducing the functionality of prototype
– Continual testing by SSB and INS, and dialog with external users
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
MultiDrizzle Project Organization
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
MultiDrizzle Development to Date

Jan - May 2002:
– Definition of MultiDrizzle requirements in Dither Working Group
– Initial prototype MultiDrizzle (Koekemoer, Fruchter, Hook et al.)
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Jun - Sep 2002:
– Distribute prototype to variety of GOs: GOODS, GEMS, High-Z SNe,
GRBs, APPLES, Helix Nebula; external GOs at GSFC, CfA, Caltech,...
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Oct - Dec 2002:
– Announce general availability to GOs on beta-test basis (Cal Wkshp)
– Initial suite of ACS, WFPC2 test datasets
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Jan - Jun 2003:
– Hand over prototype to SSB for inclusion in STSDAS (Hack et al.)
– More user feedback, improve robustness, refine testing
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Jul 2003 to present:
– SSB redesign of MultiDrizzle code (Hack, Hanley et al.) using
prototype MultiDrizzle as a basis for defining functionality
– Develop formal regression test suites
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
MultiDrizzle Requirements - General

Fundamental Requirements:
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Combine arbitrary collections of images (including single-group)
Automatically calculate required output image size
Determine shifts from headers
[Optionally refine shifts or allow input delta-shifts]
Carry out sky subtraction on input images
Automatically perform CR rejection:
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Drizzle input exposures onto separate, registered output images
Create a clean “median” image
Blot the clean image back to frame of each individual exposure
Run deriv, driz_cr to create cosmic ray masks
Use CR masks in final drizzle combination
– Allow external bad-pixel masks to be imported
– Allow individual steps to be selected when running
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Overall philosophy:
– Allow user freedom in specifying behavior via parameters
– Defaults must enable good results from “one-touch” operation
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
Requirements – Instrument-Specific
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ACS
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WFPC2
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Accurately handle WFC, HRC, SBC imaging data
Single-group images (eg only [sci,1])
Sub-array data
Include new geometric distortion-residual images (Anderson)
Handle 4-group WFPC2 GEIS as well as FITS format files
Single-group images (eg WF3 only)
Sub-array data
Include updated geometric distortion (Platais et al)
NICMOS
– NIC1, NIC2 or NIC3 imaging
– Ability to handle multi-accum datasets
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STIS
– CCD as well as FUV, NUV-MAMA datasets
– Imaging (initially) as well as 2d spectroscopy data (later)
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
MultiDrizzle Testing- General Overview

Basic Functionality:
– Do new versions run successfully for small subset of test datasets?
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Extended functionality:
– Do new versions work for the full range of datasets?
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Functionality tests can be automated by regression:
– Run automatically on a periodic basis
– Comparison performed automatically with reference test images,
and results reported in summary form
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Scientific integrity:
– Do functional versions deliver scientifically valid results?
– Different target types:
 Sparse extra-galactic fields, crowded stellar fields
 Large extended objects or diffuse emission across entire field
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Scientific tests require additional analysis, eg:
– PSF measurements of stars to ensure shifts, etc are correct
– x,y position comparisons to verify correct astrometry
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
Testing – ACS + WFPC2
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ACS WFC, HRC, + WFPC2:
– Basic datasets:
 2-point line dither
 4-point box dither (single-visit)
– More advanced datasets:
 Single-visit, small offsets, higher number of dithers
 Single-visit, large offsets (comparable to chip size)
 Multi-visit, small + large offsets
– Number of images:
 Small datasets (2-3 exposures total)
 Medium datasets (4-6 exposures total)
 Large datasets
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ACS testing lead: Shireen Gonzaga
WFPC2 testing lead: Vera Platais
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
Testing (cont’d) - NICMOS, STIS
NICMOS:
 Imaging - NIC1, NIC2, NIC3:
– Multi-accum datasets
– Different dither patterns (spiral)
– Large-scale + small-scale dithers to account for chip defects
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NICMOS testing lead: Megan Sosey
STIS CCD + MAMAs:
 Imaging:
– Mostly large-scale dithering
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Spectroscopy:
– Dithering along slit
– Dithering along spectral direction
– CTE: CRs, bad pixels are a major issue (since low background)

STIS testing lead: Linda Dressel
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
Priorities and Timescales
Development and Testing:
 Near-term (+ 1 month):
– INS: Identify test datasets and create baseline results
– SSB: Include tests in regression mechanisms
– SSB: upgrade current beta-release MultiDrizzle to fully supported
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Long-term:
– Maintain database of reference results
– Update test database when warranted by code changes
– SSB release redesigned MultiDrizzle: for users and HST pipeline
Documentation:
– Release TIR describing development plans for MultiDrizzle
– Release updated Dither Handbook V3.0 to user community, with full
description of the use of MultiDrizzle
Community Feedback:
– Continue to collect suggestions and feedback from users
– Incorporate into regular prioritization planning
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STScI TIPS, 15 January 2004
MultiDrizzle Overview - Anton Koekemoer
Proposed Roadmap for Future Development

Mar 2004:
– SSB to upgrade original “prototype” MultiDrizzle to a fully supported
version (eg via patch release, and/or from STSDAS website)
– INS to release updated Dither Handbook V3.0 with full description
of the use of MultiDrizzle software
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Jan - Jun 2004:
– INS provide test datasets to SSB (near-term), update as necessary
– SSB to complete the redesigned MultiDrizzle as user software
– SSB to release redesigned MultiDrizzle in Summer 2004 STSDAS
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Jul - Sep 2004:
– SSB, INS work on more robust, streamlined MultiDrizzle for fully
automated use in HST Pipeline Operations
– Continue to incorporate feedback and usage patterns from GOs
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Oct 2004 onwards:
– Continuing algorithmic development to improve software, eg:
 tweakshift (automated catalog-based shift refinement)
 more robust CR rejection techniques for few-exposure datasets
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