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Drizzle (image processing)
Encyclopedia
Drizzle is a digital image processing
method for the linear reconstruction of undersampled
images. It is normally used for the combination of astronomical images and was originally developed for the Hubble Deep Field
observations made by the Hubble Space Telescope
. The algorithm, known as Variable-Pixel Linear Reconstruction, or informally as "Drizzle," preserves photometry and resolution, can weight input images according to the statistical significance of each pixel, and removes the effects of geometric distortion on both image shape and photometry. In addition, it is possible to use drizzling to combine dithered images in the presence of cosmic rays.
According to astrophotographer David Ratledge, "Results using the DRIZZLE command can be spectacular with amateur instruments."
Camera optics generally introduce geometric distortion of images.
Undersampled images are, for example, common in astronomy because instrument designers are frequently forced to choose between properly sampling a small field of view and undersampling a larger field. This is a particular problem for the Hubble Space Telescope
(HST), where the corrected optics may provide superb resolution, but the detectors are only able to take full advantage of the full resolving power of the telescope over a limited field of view. Fortunately, much of the information lost to undersampling can be restored. The most commonly used of these techniques are shift-and-add and interlacing.
Drizzle was originally developed to combine the dithered images of the Hubble Deep Field
North and has since been widely used for the combination of dithered images from both HST's cameras and those on other telescopes. Drizzle has the versatility of shift-and-add yet largely maintains the resolution and independent noise statistics of interlacing. Drizzle has the advantage of being able to handle images with essentially arbitrary shifts, rotations, and geometric distortion and, when given input images with proper associated weight maps, creates an optimal statistically summed image. Drizzle also naturally handles images with "missing" data, due, for instance, to corruption by cosmic rays or detector defects.
Drizzle is freely available as an IRAF
task as part of the Space Telescope Science Data Analysis System
(STSDAS) package and can be retrieved from the Space Telescope Science Institute
(STScI) web site. In addition to Drizzle, a number of ancillary tasks that assist in the combination of Hubble Space Telescope
imaging data are available as part of the "dither" package in STSDAS.
Drizzle was developed as a collaboration between the Space Telescope Science Institute
and the Space Telescope European Coordinating Facility
.
Digital image processing
Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing...
method for the linear reconstruction of undersampled
Undersampling
In signal processing, undersampling or bandpass sampling is a technique where one samples a bandpass filtered signal at a sample rate below the usual Nyquist rate In signal processing, undersampling or bandpass sampling is a technique where one samples a bandpass filtered signal at a sample rate...
images. It is normally used for the combination of astronomical images and was originally developed for the Hubble Deep Field
Hubble Deep Field
The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, two parts in a million of the whole sky, which is equivalent in angular size to a 65 mm tennis...
observations made by the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
. The algorithm, known as Variable-Pixel Linear Reconstruction, or informally as "Drizzle," preserves photometry and resolution, can weight input images according to the statistical significance of each pixel, and removes the effects of geometric distortion on both image shape and photometry. In addition, it is possible to use drizzling to combine dithered images in the presence of cosmic rays.
According to astrophotographer David Ratledge, "Results using the DRIZZLE command can be spectacular with amateur instruments."
Overview
Undersampled images are, for example, common in astronomy because instrument designers are frequently forced to choose between properly sampling a small field of view and undersampling a larger field. This is a particular problem for the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
(HST), where the corrected optics may provide superb resolution, but the detectors are only able to take full advantage of the full resolving power of the telescope over a limited field of view. Fortunately, much of the information lost to undersampling can be restored. The most commonly used of these techniques are shift-and-add and interlacing.
Drizzle was originally developed to combine the dithered images of the Hubble Deep Field
Hubble Deep Field
The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, two parts in a million of the whole sky, which is equivalent in angular size to a 65 mm tennis...
North and has since been widely used for the combination of dithered images from both HST's cameras and those on other telescopes. Drizzle has the versatility of shift-and-add yet largely maintains the resolution and independent noise statistics of interlacing. Drizzle has the advantage of being able to handle images with essentially arbitrary shifts, rotations, and geometric distortion and, when given input images with proper associated weight maps, creates an optimal statistically summed image. Drizzle also naturally handles images with "missing" data, due, for instance, to corruption by cosmic rays or detector defects.
Drizzle is freely available as an IRAF
IRAF
IRAF is a collection of software written at the National Optical Astronomy Observatory geared towards the reduction of astronomical images in pixel array form. This is primarily data taken from imaging array detectors such as CCDs...
task as part of the Space Telescope Science Data Analysis System
Space Telescope Science Data Analysis System
The Space Telescope Science Data Analysis System is an IRAF-based suite of astronomical software intended primarily for processing data from the Hubble Space Telescope. STSDAS is produced by Space Telescope Science Institute .-External links:...
(STSDAS) package and can be retrieved from the Space Telescope Science Institute
Space Telescope Science Institute
The Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
(STScI) web site. In addition to Drizzle, a number of ancillary tasks that assist in the combination of Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
imaging data are available as part of the "dither" package in STSDAS.
Drizzle was developed as a collaboration between the Space Telescope Science Institute
Space Telescope Science Institute
The Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
and the Space Telescope European Coordinating Facility
Space Telescope European Coordinating Facility
right|The Space Telescope - European Coordinating Facility is an institution which provides a number of support and service functions primarily for European observers of the NASA/ESA Hubble Space Telescope...
.
External links
- The Dither/Drizzle Page at the Space Telescope Science InstituteSpace Telescope Science InstituteThe Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
- Linear Reconstruction of the Hubble Deep Field, by Fruchter and Hook. An accessible version of the paper published above.