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Barth, A. J. 2001, in ASP Conf. Ser., Vol. 238, Astronomical Data Analysis Software and Systems X, eds. F. R. Harnden, Jr., F. A. Primini, & H. E. Payne (San Francisco: ASP), 385
ATV: An Image-Display Tool for IDL
Aaron J. Barth
Harvard-Smithsonian Center for Astrophysics
Abstract:
The IDL language offers a powerful environment for reduction and
analysis of astronomical data. While there are numerous libraries of
publicly available IDL routines, one major drawback has been the lack
of an image-display program optimized for viewing astronomical images.
ATV is a display program written entirely in IDL and designed to
emulate the SAOimage and DS9 programs. It works equally well under
the Unix, Linux, Windows, and MacOS versions of IDL, and includes
features such as interactive control of color stretch, zoom, and image
scaling; image blinking; and creation of publication-quality
PostScript output. It also includes a simple photometry package
suitable for quick-look reductions. The program is freely available
via the Internet.
Interactive Data Language (IDL) is an increasingly popular tool for
astronomical data reduction and analysis. One long-standing drawback
of IDL, for astronomical applications, has been the lack of a
high-level display routine optimized for viewing astronomical images.
IDL's built-in image display routines are primitive, and it is
difficult to integrate stand-alone programs such as SAOimage and DS9
into an IDL session. ATV is an image-display program designed to
solve this problem. It is written entirely in IDL and offers a range
of features similar to the stand-alone image viewers.
Figure 1:
The main ATV display window and the ATV photometry window.
![\begin{figure}
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\end{figure}](img1.gif) |
ATV takes advantage of the IDL widget interface, which provides a
simple mechanism for creating graphical user interfaces, as well as a
number of preexisting routines in the IDL Astronomy User's Library.
Thus, the ATV code itself is fairly compact, and in some respects it
simply acts as a graphical front-end for various library routines.
The initial release of the program in 1998 contained basic features
such as control of image scaling and color stretch, blinking, and
zooming, and since then the program has grown to include other
features such as photometry, coordinate tracking, and creation of
PostScript output. For IDL users, the major benefit of ATV is that it
works within an IDL session, so the user can pass data or FITS
filenames directly to ATV from the IDL command line. ATV can be
customized to pass data to other IDL routines, and its internal data
are stored in common blocks so that they can be accessed or modified
by the user.
Since ATV is distributed as IDL source code, it can easily be modified
for specialized use. For example, it has been adapted for displaying
data from the FUSE satellite
(http://fuse.pha.jhu.edu/analysis/sw), and a modified
version of ATV is being used as part of the CEDAR software suite for
the HST Cosmic Origins Spectrograph (Béland & Penton, this
volume).
The main ATV window is designed to look similar to SAOimage and DS9,
with a panning window, a zoom window that tracks the cursor motion,
and information boxes that track the pixel coordinates, pixel value,
and world coordinates (Figure 1). ATV's features include:
- Ability to read in FITS images, including FITS extensions, and
non-standard data types such as HST WFPC2 arrays.
- Image input via pull-down menus or from the IDL command line.
Data arrays in memory can be passed directly to ATV from the IDL
command line.
- Interactive control of zoom, color table, brightness and
contrast, and data range mapped into the color table. As in other
display programs such as SAOimage and DS9, brightness and contrast
stretching are done by dragging the cursor over the main display
window.
- Choice of linear, log, or histogram-equalized scaling.
- Tracking of the cursor position in pixel units and coordinate
units if the image header specifies a coordinate system. User can
choose RA/Dec, Galactic, or Ecliptic coordinates. For 2-D
spectroscopic images with wavelength information in the header (such
as HST STIS images), the wavelength at the cursor position is
displayed.
- Ability to overplot text, contours, or arbitrary line graphics
over the image.
- Ability to plot a compass and scale bar for images with
coordinate information in the header.
- Ability to create publication-quality PostScript output, and
output in Tiff image format.
- Image blinking with up to three saved images.
- Row, column, surface, and contour plots.
- Point-and-click aperture photometry, including radial profile
plots. In the photometry window, the user can control the sizes of
the photometric and sky apertures, the centering box size, and
photometric zeropoint. Output is in counts or magnitudes.
- Ability to view the image header in a separate window.
- ATV works in 8-bit and 24-bit color. (IDL currently does not
support 16-bit color for the X window system, but may do so in the
future.)
- ATV works equally well under the Unix, Linux, Windows, or MacOS
versions of IDL. Some features require the use of a 3-button mouse
(for example, storing 3 blink images), but the program has been
designed so that almost all features can be accessed with a 1-button
or 2-button mouse.
Development of ATV continues with new versions released every few
months. Some areas for future development include:
- Improvements in speed and memory management.
- A more complete photometry package, including saved results in
a log file.
- Ability to read and display multi-CCD mosaic images from
various telescopes.
- Ability to handle extremely large images.
- Better user control over pixel ranges and plot details for line
plots, and PostScript output for line plots.
Some important sections of the ATV code were written and contributed
by David Schlegel, Douglas Finkbeiner, Michael Liu, and Wesley Colley.
The FITS I/O, astrometry, and photometry routines used by ATV are part
of the IDL Astronomy User's Library, maintained by Wayne Landsman at
NASA/GSFC1.
ATV also uses a PostScript configuration tool written by Craig
Markwardt2.
Instructions and complete documentation can be found at the ATV web
page: http://cfa-www.harvard.edu/~abarth/atv.
Footnotes
- ...
NASA/GSFC1
- http://idlastro.gsfc.nasa.gov/homepage.html
- ...
Markwardt2
- http://cow.physics.wisc.edu/~craigm/idl
© Copyright 2001 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
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