Let me come clean before we even begin this Chapter - I am not an image-processing expert, in fact I just about get by. However, what you will learn from this section of the book should provide you with the basis of getting some very good-looking results from your hard won data. I will also give you the process by which I transform the raw FITS data into a file ready for image processing. This procedure is by no means meant to be definitive. I have found that it works well for me, but I am sure that there are better procedures to follow, and better ways of processing your images. There is however one very important observation I have made that should help you in getting the best out of your data and it is this: there is no set processing sequence that you can apply for all your images! You must treat every image as unique and worthy of its own special attention, because it is unique. The noise characteristics will be different from any other image you take, the background signal will be different, the light pollution (gradients) if any will differ, in fact just about every aspect of every image you take will differ from every other image in some subtle (or not so subtle) way. This inability to apply a "wrote procedure" for processing images is, I find, very annoying. It means there is no formal "scientific approach" to deep-sky image processing; it is very much a black art. This is fine if you are blessed with some artistic talent, and an eye for what looks good to the general public, and it is a curse if you are not so blessed. This is why you will find that an American collaborator based in Florida, Noel Carboni, has processed all but one of the deep-sky images in this book. Noel has probably used Photoshop on a daily basis for the past 10 years and therefore has more practical knowledge of the use of this package than I can ever achieve. He has also created a set of "actions" to be used in conjunction with Photoshop that allows the user to run complex sequences of image processing functions at the click of a mouse button. For example, a couple of mouse clicks will remove background light pollution effects (gradients) by setting off a sequence of Photoshop actions that effectively create an inverse background which is subtracted from the light polluted background to give a final resulting flat background. Digital image processing is the present day equivalent of yesterday's photographic darkroom. It is in this digital dark room that your hard won images are turned into awesome works of art, or are effectively destroyed! It is an unpleasant fact of life that the image processing side of deep-sky imaging is every bit as important as getting the photon data in the first place.
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