Appendix D:
Techniques for Dithering, Background Measurement and
Mapping

D.1 Introduction

D.2 Strategies For Background Subtraction

D.2.1 Compact Objects

D.2.2 Extended Objects

D.3 Chop and Dither Patterns

D.3.1 Dither Patterns

D.3.2 Chop Patterns

D.3.3 Combined Patterns

D.3.4 Map Patterns

D.3.5 Combining Patterns and POS-TARGs

D.3.6 Generic Patterns

D.4 Examples

D.5 Types of Motions

NICMOS patterns have been created to enable observers to perform dithering, chopping, and mapping, and these patterns are significantly different than those described in earlier versions of this handbook.