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How False Color Astronomy Works
StartsWithABang writes: When you look out at the nebulae in the night sky — especially if you're seeing them with your eye through a telescope for the first time — you might be in for a big surprise. These faint, fuzzy, extended objects are far dimmer, sparser and more cloud-like than almost anyone expects. Yet thanks to some incredible image processing, assigning colors to different wavelengths and adjusting the contrast, we can make out detailed structures beyond what even your aided eye could ever hope to perceive. Here's how the magic happens, and what it teaches us.
In the amateur astrophotography community some people image-process to death by using brush tools to selectively enhance specific features. An example: "Paint" a galaxy with a brush tool to make it stand out from the background. In my humble opinion, this is unacceptable. One other example: Wrong color balance in wide-field Milky Way shots, resulting in blue night skies. The night sky can't be blue for any aesthetic reason. At least, inform your viewers that your images are (heavy) processed.
Thierry Legault, an acclaimed astrophotographer says about image processing:
Furthermore, an astronomical image is something fragile, and it is dangerous (and unuseful) to torture it to extract details. Image processing softwares are now so powerful that they look like Ferraris...but don't drive them like Ayrton Senna ! Actually the best is to process an image as little as possible: the first quality of an amateur in this field is its moderation. Just take a look at the planetary images of the HST: they are detailed but very smooth and natural, no trace of the over-processing that damages so many amateur images. If a raw image is good, a slight processing must be sufficient for showing its contents. And if a processed image shows too few details, it is not a problem of processing but a problem of acquisition.
(From http://www.astrophoto.fr/ip.html)