Asked by Jim Collins
Most things in space are pretty drab, so space images are normally enhanced by a bit of post-production. Now, that’s not to say the images we see of distant objects aren’t spectacular; rather, the cameras that are used in space often take images in a specific wavelength, so they can’t see all the different variations in an object. So, to get an image that’s visually appealing, variations in the visible spectrum are amplified to differentiate between different parts of an object (like the arms of a galaxy or the rings of a supernova explosion).
For example, most Hubble photos start life as three separate ones. The telescope takes three images at different wavelengths, using filters. Each wavelength represents a colour and a technician must combine all three. This process can be a lengthy one, as the images will need to be scaled and moved and cropped so they line up properly. Then the three images will need to be balanced against each other to ensure an accurate portrayal. Once the composite has been made the image will have any defects like bad pixels removed, it will be cropped and scaled and then it is ready to be shown off to the world.
Answered by Josh Barker from the National Space Centre
Image courtesy of NASA/JPL