Contents:

• Introduction
  
• List of features.
• Known weirdnesses.
• Currently known bugs.
• Disclaimer.
• Comments, complaints, suggestions?

Introduction.

Back when I started using IDL a lot, around 1998, one thing I wanted which didn't really exist at the time was an interactive image-display tool optimized for viewing astronomical CCD images.  There are a lot of nice image viewing programs out there, like SAOimage , which are usually designed to work with IRAF or as stand-alone applications (see here for a list of other image viewers), but for working in IDL it would be far easier to have a display routine written as an IDL procedure.  In order to learn how to use IDL widgets, I started writing an image viewer which would do some of the things I wanted.   It seemed like something that would be useful to other IDL users, so I made it available here.  The program is written entirely in IDL.  It's very easy to use within an IDL session and it's also very simple to add new routines, buttons, menus, or whatever.   It looks a lot like SAOimage or DS9, so if you're used to using those programs, then you'll probably get used to ATV quickly.  

For detailed instructions on how to use atv, see the instructions page .

ATV requires IDL version 6.0 or greater.  This makes it possible to use some very helpful new widget features that appeared in IDL 6.0. 

One nice thing about ATV is that you, the user, can easily add new features or link your existing IDL programs to ATV.  For example, you can easily define a keyboard shortcut that will pass the current cursor position in data coordinates to an external IDL routine.  Also, all of the ATV internal variables are stored in common blocks, so you can have another program access the ATV variables by declaring the ATV common blocks in your program.

What atv can do for you.

A quick list of atv's main features:

• Display of 2-d images with a variety of scaling, color map, color stretch, zoom, and rotation options
• World coordinate system information is displayed if available
  
• Labeling and overplots to annotate images
  
• Image output in a variety of formats
• Display of line plots, surface plots, and histograms of data regions
• Quick photometry and image statistics
• Simple spectral extractions
  
• Image blinking
  

If you're used to using DS9 with IRAF, you'll notice that ATV has some great advantages:

• It shows you actual pixel values as you move your cursor around the image, not interpolated approximations like what you get when you use the "display" task in IRAF
• It's very easy to change the image scaling parameters such as the minimum and maximum pixel values that get mapped into the color table
• The asinh scaling works really well for most images
  
• The autoscaling routine is done by estimating the sky value and sky sigma, so the default autoscaling parameters work pretty well- this means you can often read an image into ATV and it will just show up pretty much the way you want to see it, withouth having to do a lot of mucking around with the image scaling parameters
• Working with large images, ATV can be a lot faster and more responsive than DS9
• While ATV is not as feature-rich as DS9, ATV's menus are a lot simpler and easier to use
• One-click photometry and spectral extractions can be handy for quick-look analysis
  

Known weirdnesses.

These are peculiarities of the program that can't really be classified as bugs.  Some have to do with inherent limitations of IDL widgets, and others have to do with how IDL behaves differently under different platforms.

• If you're using a system that has fewer than 3 mouse buttons, you may not be able to access all features of the program.  I've attempted to make many features for buttons 2 and 3 accessible in other ways (i.e. keyboard shortcuts), but some features require having 3 buttons.  For example, if you've only got 1 button, then you can only use 1 blink image.  If you are using a Linux machine that has 2 buttons and emulates a 3-button mouse by holding both buttons down, then blinking may not do exactly what you expect for the second and third "blink" images.
• The way IDL widgets work, the best thing to do is to define the widgets using the default fontset, rather than to specify a particular font, since different platforms may have different fonts installed.  The result is that the layout of the buttons and windows in the ATV window will depend somewhat on your platform, window manager, and default font size.  This snapshot gives you an idea of what the ATV window is intended to look like.  If your window manager uses really big fonts, you can just resize the ATV window to make things fit better.
• The inner workings of ATV are based on IDL event handlers.  If you have another IDL routine running from the IDL command line prompt, or from a blocking or modal widget, then the ATV event subroutines may not be accessible until the other routine finishes what it's doing.  For example, if your main IDL prompt is waiting for input at a "read" statement, or something like that, then ATV won't be usable until after that read statement takes its input.  There's nothing that I can do about this; it's just how IDL widgets work.  So if your ATV window appears to freeze, the most common reason is that there's another IDL program running which is blocking the ATV event routines from executing.  ATV will also freeze if you have another IDL program that hits an execution error or a "stop" statement.
  
• Fractional pixels are handled in a very simple way, which forces the lower left corner of the viewport to display a complete pixel.  You might notice this when displaying an image with a very high zoom factor.  This is a direct consequence of my own laziness.  Fractional pixels might be handled better in a future version, but this isn't really a high priority.
• In some window managers, window resizing can be a little finicky.  I've gotten it to work pretty well in Linux with the metacity window manager, and in Mac OS X.   If you resize the main window and things come out looking a little funny, just give the corner of the ATV window another little nudge to resize it just a bit, and that usually sets things straight.
  

Since I don't have all that much time to debug and test ATV, it's likely that there are some bugs hidden in the program which I haven't discovered yet.  If you find a bug, send me an email and tell me what went wrong, and please be as specific as possible about what you were doing and what IDL version and platform you're running.  Currently known bugs are listed below.

• A few Mac OS X users have reported that ATV will crash with a "bus error" when compiling.  This isn't an ATV bug- it is most likely a result of running an out-of-date version of IDL that doesn't work well with Mac OS.  If you get the bus error when compiling, upgrading to the current IDL version will probably solve the problem.
  

Disclaimer.

This software doesn't come with any warranty.  It may contain bugs.   Please bear in mind that this program is a work in progress, and it is gradually being updated and improved. 

The photometry and spectral extraction routines in ATV are intended primarily for quick-look analysis and not for publishable results.  They work very well in many circumstances but users should be aware that they are not as sophisticated, or as rigorously tested, as some other available tools for photometry and spectroscopy.

Comments, complaints, suggestions?

If you've tried atv and have any complaints, comments, bug reports, or suggestions for further improvements, write to me at barth [at] uci [dot] edu.    I don't promise to add every feature that people request, but I do keep a list to keep track of suggestions and I try to handle bug fixes relatively quickly.

If you'd like to be on an email list for occasional announcements about new releases of the software, just send me an email and say that you'd like to be on the ATV mailing list.

Last update:  May 22 2009
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