Review: AstroStack 3.1

Product Name: AstroStack 3.1
Company: InnoStack
URL: http://www.astrostack.com
Category: Image processing software
Price:
- Free - Limited Edition
- $39 - full version
- $59 - with plug-in suite 1
Requirements: Any Mac with OS X and JavaM
Rating: 3 Bounces - Lustworthy

Although there have been many accomplished amateur astrophotographers using Macs, the majority relied upon Windows computers, in part because of the availability of sophisticated image processing applications like Registax and AstroStack. While Registax remains a Windows-only program, the latest version of AstroStack is a Java application designed to run equally well on Windows, Mac, and Linux machines.


AstroStack was previously available only to Windows users.

Installation

As with most Java applications, installation is straightforward. The actual Java engine comes built into OS X, and unlike the situation with OS 9 and earlier versions of the Macintosh operating system, Java applications are fast and stable under OS X. Don't confuse well written Java applications like AstroStack with the often flaky little Java doodads built into web pages.

You can run AstroStack from anywhere on your hard drive. When you register AstroStack creates a file in your Home folder called "as3init.png". Despite the name, this is not a picture file, and it contains your license code, so that if you delete or move this file, AstroStack will ask you for this information again. I am not a fan of programs that clutter up my Home folder, and I'd have preferred it if the program had placed this file either in the Preferences directory or in the AstroStack folder itself.

Usage: step by step

AstroStack has a bizarre interface that will surprise and confuse virtually any Mac user. Unlike true Mac applications, Java programs ignore the main menu bar, and instead menu items are placed at the top of each of the application's three windows. In this sense, it resembles a standard Windows or Linux program. However, this isn't the main obstacle to using AstroStack. What really sets AstroStack apart is the way it needs to be used. If you think about a program like Photoshop, each time you employ one of its functions, you see the file change immediately and cumulatively, in other words, each time you do something, the image in the window is updated. AstroStack is different, since it is built around a series of plug-ins that needs to be configured before it will be implemented, and in many cases, you need to use the plug-ins in a specific order for them to work.


AstroStack works by taking a stepwise approach to implementing different tools, such as unsharp masking, but the result is an awkward and unconventional interface.

To try to make this a bit clearer, we'll run through using AstroStack on a set of images of Saturn. In this instance, I've extracted a set of 50 PNG files from a QuickTime movie.

First, launch AstroStack by double-clicking the Java file icon. Assuming you've registered the program, you are presented with three windows. Two of these have pictures of the Moon in, these are called monitor windows and are effectively the "input" and "output" windows, allowing you to interact directly with images and view the results of any changes. One shows the original file (the raw data) and the other the output (the result of any image processing).

The third window is the "interface", and consists of a series of tabbed sections. The main tabs divide the process into the sequence of steps, for acquiring the image, pre-processing, stacking, and so on. Subdivisions to these give access to the settings for specific plug-ins; the bits of software that actually do the work. AstroStack is therefore best thought of as an application that acts as an interface between the user and all the little applications that operate behind the scenes.


The AstroStack interface is awkward, and involves navigating a large number of tabbed panels in a specific order.

To load up the image files, we use the first main tab ("Acquire") and click on the "File List" subdivision. Clicking on "Build File List" brings up a load window, and you need to navigate across to the folder where the image files are stored. Note that there are some differences to the standard Mac interface even here; for example, you cannot use Command-D to go straight to the Desktop. Shift clicking will allow you to choose multiple files, which will normally be what you need to do. When you're done, click on the "Open" button, and the load window closes and you are returned to the main AstroStack interface.

AstroStack now has a list of files to work with, and you will see the first image in the list displayed in both of the output windows. The next step is to crop the images down to a specific "region of interest" (ROI). By throwing away bits of the image you're not interested in, you speed up processing time by getting the computer to work on the parts of the image containing information, i.e., the object being imaged. In this example, we can crop away much of the empty space around Saturn. By clicking once in the input monitor window, a marquee is created that can be dragged across the image. A bull's-eye marks the centre of the image.

By default, the input and output windows scale the images up or down so that they fit, but for the rest of the process, you probably want to see the images at full size. This is achieved by unchecking the "fit to monitor" boxes on the monitor windows.

Moving on from the "Acquire" panel to the "Pre-Processing" panel, we have a pair of sliders that allow us to change the brightness and contrast settings. To be honest, I rarely use these in any image processing application, and my recommendation here is to skip over them for now. I like to leave brightness and contrast adjustments to the very end of the process, in which case it's easy enough to make these changes in a standard graphics program like Photoshop.

It is the third panel that holds the most interest for me, the "Align and Stack" options. Aligning and stacking is central to successful astrophotography, because it allows you to use compensate for a webcam's weakness (sensitivity under low light conditions) using its strength (collecting lots of images within a short space of time). What AstroStack does is superimpose the series of images so that noise is cancelled out while the detail is enhanced. The value of image processing software in astrophotography depends on just how successfully it does this. Many photographers work with hundreds of images at once, and good software will align and stack these quickly and, just as significantly, ignoring any blurry ones.


Aligning the images is the first step to building a detailed composite image.

In AstroStack, begin by enabling both the "Align", "Stack", and "Combine" options in their respective subsections. Choose the processing technique you want to use, and then return to the "Acquire" panel and hit the "Load whole list" button. This causes AstroStack to run through the frames applying your chosen alignment and stacking criteria. The smaller the region of interest, the faster this will be, but be sure and select a larger region of interest when once you move onto the "Post Processing" panel. Here, you apply a variety of filters that sharpen and enhance the image. How they work is outside the scope of this article, but used carefully these can turn a seemingly mediocre image into something very impressive. Tweaks performed using these filters can be observed in the second monitor window and compared with the input monitor window. If you crop the region of interest too small, these filters can mess up the image by creating artefacts at the edges of the image that encroach on the planet or whatever else you're interested in. For this reason, it's wise to allow a generous margin, by choosing a large region of interest once you reach this step.


AstroStack has an open plug-in system that includes filters for unsharp masking, Lucy-Richardson convolutions, and more.

The final step is saving the image. By default, AstroStack exports images as JPEGs, but by using plug-ins, this can be changed to things like Windows bitmap files and FITS files. Essentially, the user runs through the entire process before saving files. You make sure you're happy with your alignment, stacking, unsharp mask filters, and so on, and then choose the directory where you want to save the resulting image file. Then go back to the "Acquire" panel, and load the whole list again. With luck, you should have your piece of Hubble-busting art saved as a JPEG ready to share with others.

Comparison with other programs

If this review were written more than a year ago, there really would only have been a single competitor for AstroStack in the Macintosh marketplace, Keith's Image Stacker (shareware: $10). A fine program in many ways, Keith's Image Stacker has been criticised by many for having a distinctly awkward interface. Having said much the same thing about AstroStack, in terms of usability alone there really isn't much to choose between them. On the other hand, AstroStack does have some extra high-end features that Keith's Image Stacker lacks, as well as an extensible format that allows for the addition of plug-ins of various types. Further information on the plug-ins and what they do can be found on the AstroStack web site. Plug-in pack 1 costs $25, but if purchased alongside an AstroStack license, you get a $5 discount. Its main shortcoming when compared with Keith's Image Stacker is the lack of QuickTime movie support, necessitating the use of additional software to convert the ubiquitous ".mov" format into one that AstroStack can use, such as a set of PNG or JPG image files. Given that doing this is most readily accomplished using QuickTime Pro to open and export the movie file, the potential user will need to factor in the additional $30 for a QuickTime Pro license. Actually, to be precise, AstroStack can read QuickTime movies, but only those using compression formats compatible with Sun's Java Media Framework. This includes some, such as Cinepak, but not all. If you want to import QuickTime files straight into AstroStack, you need to ensure that you use a compatible compression format.


Additional features such as alternative image processing algorithms can be added on the fly, greatly expanding AstroStack's usefulness to advanced amateur astrophotographers.

Two new kids on the block are Lynkeos (freeware) and Astro IIDC ($50). Lynkeos may well cost nothing to use, but it certainly isn't underpowered, and can be used very effectively. I decided to run some images through Lynkeos alongside AstroStack, and was surprised to find that the resulting output from the two applications wasn't very different at all. Subjectively, my impression was while AstroStack definitely had the potential to produce the better images, Lynkeos was so much easier to use that repeatedly running though different sets of images and testing out different processing settings was much, much easier. Lynkeos also only has a limited selection of image processing algorithms though, and the extensible AstroStack format may well be tricky to understand but it does pay dividends when it comes to using advanced image processing algorithms such as the Lucy-Richardson convolution.


A quick comparison of Lynkeos with AstroStack revealed the latter to be perhaps the better application, but significantly more time consuming to learn and use.

Comparing AstroStack with Astro IIDC isn't nearly such a tough call because while they overlap in parts, they complement one another far more than they compete. Using Astro IIDC to capture a movie and then extract the sharpest frames from the movie gives the user a head start in obtaining the best possible input, while AstroStack can be relied upon to process the frames and turn them into a single bright and detailed imaged.

Bugs

I didn't find many bugs in my use of the program, but there is an AstroStack forum at the web site and as bugs and other problems are noted, solutions and workarounds seem to be offered quickly.

Nonetheless, there are a couple of issues that I'd like to see addressed in later versions of the program. To begin with, while loading plug-ins is easy, they don't seem to 'stick', meaning that I had to load them again each time I launched the application. Plug-ins do 'stick' to particular projects, so if you are working on something, quit, and come back, they should be where you left them. But there's no way to set global preference for plug-ins. I'd also like to see more "tool-tips"; while tool-tips do appear when the mouse is held over certain items, there are many situations where they don't. Frankly, with a program of this complexity, the more feedback the user has, the better, and this brings us on to my final criticism, the manual. Developer Robert Stekelenburg has certainly done a good job of including some files alongside the main application, allowing new users to play a little before getting to work on their own images, but the HTML and PDF format manuals are just too brief. I'd like to see much more discussion of what each button does, what the options mean, and so on.

Conclusion


AstroStack improved a stack of very mediocre images like the one on the left quite dramatically.

By any standards, AstroStack is a complex program, and while the interface is awkward, it isn't actually difficult to use once you've run through the process a few times. As far as results go, has much to recommend it, and Mac using astrophotographers can rejoice that they finally have a heavyweight image processing application to play with. Really, the main downside to the program is its price: at $39, it is considerably more expensive than its competitors in the Mac marketplace, and for casual astronomers the free alternatives such as Lynkeos are not far inferior and much easier to use. Bottom line, casual astronomers will undoubtedly find the alternatives much more attractive, but advanced amateurs looking to squeeze every drop of detail out of their images will find AstroStack a compelling and impressive piece of software.

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