Chapter 9
Image Reduction and Processing
Abstract Image processing is the process that turns an image from a science image
to something more pleasing to the eye or highlights a structure of interest. Many
image processing techniques render the image unsuitable for photometry. In this
chapter, we discuss image processing techniques such as stacking, sigma clipping,
drizzling, stretching, as well as the application of image processing filters. We touch
on how to make colour images from black and white astronomical images using
commercial packages.
9.1 Introduction
In this chapter, we will discuss the processes by which you take your raw light
image or images and create an image that has been modified either for aesthetic or
scientific reasons. Although these two goals are not always in opposition, most of the
processing required for the production of high quality glossy astronomical images
renders them all but useless for scientific purposes. Hence we should distinguish
between image reduction, which we can consider the process required to turn a
light frame into a science frame, and image processing, which goes beyond image
reduction to produce an image that is pleasant for the viewer.
It is therefore important to understand your final goal. If you wish to perform
photometry or astrometry, you will not be making coloured images, nor will you
apply highly sophisticated mathematical filters to your image. However, if you wish to
look at the structure of the object, then coloured images and filtering are useful tools.
Likewise, if you are looking at producing spectacular images, then your stacking
technique will be different than that employed for stacking photometric images. If
you wish to process your image, you may wish to use processing software such as
Adobe’s Photoshop or The Gimp to tidy up an image.
Observational astrophysics rather than astronomical imaging is the principal subject of this book; therefore, this section concentrates mostly on image reduction
rather than image processing. However, most image reduction and image processing
techniques are the same. We will, however, touch on image processing and the pro© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_9
135
Image Reduction and Processing
Abstract Image processing is the process that turns an image from a science image
to something more pleasing to the eye or highlights a structure of interest. Many
image processing techniques render the image unsuitable for photometry. In this
chapter, we discuss image processing techniques such as stacking, sigma clipping,
drizzling, stretching, as well as the application of image processing filters. We touch
on how to make colour images from black and white astronomical images using
commercial packages.
9.1 Introduction
In this chapter, we will discuss the processes by which you take your raw light
image or images and create an image that has been modified either for aesthetic or
scientific reasons. Although these two goals are not always in opposition, most of the
processing required for the production of high quality glossy astronomical images
renders them all but useless for scientific purposes. Hence we should distinguish
between image reduction, which we can consider the process required to turn a
light frame into a science frame, and image processing, which goes beyond image
reduction to produce an image that is pleasant for the viewer.
It is therefore important to understand your final goal. If you wish to perform
photometry or astrometry, you will not be making coloured images, nor will you
apply highly sophisticated mathematical filters to your image. However, if you wish to
look at the structure of the object, then coloured images and filtering are useful tools.
Likewise, if you are looking at producing spectacular images, then your stacking
technique will be different than that employed for stacking photometric images. If
you wish to process your image, you may wish to use processing software such as
Adobe’s Photoshop or The Gimp to tidy up an image.
Observational astrophysics rather than astronomical imaging is the principal subject of this book; therefore, this section concentrates mostly on image reduction
rather than image processing. However, most image reduction and image processing
techniques are the same. We will, however, touch on image processing and the pro© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_9
135