The Gimp Ebook
If we combine three optical images in a manner akin to how our eyes would see it, e.g., with similar intensity ratios for red, green, and blue light, the image is called a true color image. As usual, the best way to learn all about color imagery is to experiment yourself. Programs such as The Gimp, XV, Photoshop, and others can be used for this purpose. An excellent account of how to produce color astronomical images including all the factors and intricacies involved, as well as examples, is provided in Rector et al. (2005).
The more frames that are stacked, in general, the better the results, under even mediocre seeing. The signal-to-noise ratio increases proportionately to the square root of the number of images averaged. The best-known piece of software for performing this image stacking operation is a piece of freeware called Registax, developed by Cor Berrevoets, but there are others. Further image manipulation, in various programs, is then normally carried out in order to achieve the finished result. DSLRs can be used with telescopes to record fine wider-field views of open clusters, extensive nebulae, star clouds, the Andromeda Galaxy, etc., but they are rapidly fogged-out by light pollution (and moonlight), limiting exposure in badly-polluted areas to only a minute or so. Various narrowband and broadband filters can mitigate the pollution problem, as they can with CCD cameras. Postprocessing in an image manipulation program can also be used to reduce the effects. (Later in this book, I will...
GIMP GIMP http www.gimp.org http www.gimp.org GIMP (GNU image manipulation program) is a free application with a great deal of functionality. It's well worth downloading even if you already have a full-featured commercial graphics program. GIMP is suitable for a variety of image manipulation tasks, including photo retouching, image composition, and image construction. It can be used as a simple paint program, a high-quality image retouching program, an image format converter, and so on. The program is expandable, designed to be augmented with plug-ins and extensions to perform just about any graphics tasks (Figure 7.9). Figure 7.9. Screenshot from GIMP showing an enhancement of a lunar eclipse observation (photo by Peter Grego). Figure 7.9. Screenshot from GIMP showing an enhancement of a lunar eclipse observation (photo by Peter Grego).
Although there appears to be an abundance of choice in the personal computer market, making the right choice can be a rather complicated process. Your ideal computer's specifications depend on your computing needs (both current and anticipated), and the decision is ultimately tempered by your budget. Graphics work with image manipulation programs such as Adobe Photoshop CS2 requires a fairly fast computer running at least Microsoft Windows 2000 (SP4) or Windows XP (SP1 or SP2), with a minimum of 384 MB of RAM, a monitor capable of 1024 x 768 pixel resolution, and 650 MB of available hard disk space. As of the time of writing (July 2008) a year-old machine with Vista Home Premium OS (32 bit) uses a Pentium Core 2 Duo processor and has 1014 MB of RAM and two internal hard drives with a combined capacity of 500 GB. It is perfectly adequate for writing, desktop publishing, graphics, and image manipulation needs, although with a Windows Experience Index base score of 3 it might benefit...
Take as many exposures os you can for each filter. Capture L sub-frames without binning, but use 2x2 binning far the RGB set. Exposures can be kept shorter (or the binned shots. Calibrate each filtered set as you would For a single CCD image. Combine the RGB shots using image processing software or by loading and aligning each colour into the red, green and blue channel of an RGB image in Photoshop (shown above) or GIMP. Increase the Final RGB image size by 200 For 2x2 binned images. Take as many exposures os you can for each filter. Capture L sub-frames without binning, but use 2x2 binning far the RGB set. Exposures can be kept shorter (or the binned shots. Calibrate each filtered set as you would For a single CCD image. Combine the RGB shots using image processing software or by loading and aligning each colour into the red, green and blue channel of an RGB image in Photoshop (shown above) or GIMP. Increase the Final RGB image size by 200 For 2x2 binned images.
Of course, it's perfectly possible to run older versions of well-known astronomical programs such as RedShift and Starry Night and experience the graphics capabilities of older versions of good drawing image manipulation programs such as Corel's PhotoPaint and Adobe's PhotoShop using, say, an early 2000s machine running Windows 98 SE. Such a machine will also be able to link with a PDA through a cable using the Windows ActiveSync program.