All the recent publicity in the popular Press has sent a torrent of comments in my direction. Quite a few members of Joe Public made dismissive comments about the images saying they were simply “Photoshopped”. I guess I should not expect the general public to understand the process that goes into creating these images, so I think it is timely to say a few words on the subject here.
By “Photoshopped” these members of the public mean that the images were somehow created, painted almost with unreal heightened colours perhaps. Nothing could be further from the truth! Everything you see in the deep-sky images was present in the raw data (straight from the camera) – absolutely NOTHING has been added. Photoshop is simply a tool – albeit an extremely powerful image processing tool. The functions that are mostly employed are nonlinear stretches to pull out the faint data – whilst at the same time keeping the stars under control (it’s very easy to get the stars bloating if you’re not careful). So all that Photoshop is doing is enhancing the image by bringing out faint objects already present in the data. In fact it is a huge part of the processor’s time and effort to make sure that what is seen in the final image is “real” and not some artifact produced by careless or improper processing. That’s why – if you compare the Star Vistas images with those from professional observatories (or other dedicated amateurs) you will find the images all very similar.
With regards to the colour you see in these images – to keep it short – the colours are “real”. Real in the sense that the red in the emission nebulae really is that colour red, and any coloured stars are really that colour. Once again, a great deal of time and effort is put in by the image processor (Noel in the case of all Star Vistas images) to make sure the colours are “real” and consistent. The fact that you don’t actually “see” those colours when looking at these objects through small telescopes is due to the physiology of the eye. Basically the eye is not good at discerning colour when the light intensities are low – that’s why things look like various levels of grey when you go out at night. We know what the colours really are because spectroscopy tells us at what wavelengths hydrogen (for example) emits – and it tells us to a very high degree of accuracy.
So in summary – in all these deep-sky images – Photoshop is simply a tool to enhance the data which already exists – NOTHING is added. Secondly, the colours you see in all these images are real. If the physiology of the eye was different so that you could discern colour with low light intensities – these are the colours you would actually see.
A quick edit! Noel correctly pointed out that sometimes something is added 🙂 Star spikes are occasionally added (even though they occur naturally in the Hyperstar III images) for added effect.