How to retain correct star colour during processing

[sharkmelley]

A question that often arises is how to retain star colour during processing since it is so easy to wash out those colours.  So I've created a synthetic test image that you might like to experiment with and discuss.

You'll find it contains 3 sets of stars: white, orange and blue.  Each set of stars has identical colour balance (except that the cores of the brighter stars are deliberately saturated). Each star is 1.4x brighter than its neighbour and has the same FWHM (the same Gaussian shape).  There is a muddy sky background typical of mild light pollution and the RGB balance needs adjusting - as is typical for a RGB or one shot colour image.  The file is in "linear" format i.e. no stretching has been applied.  As far as possible it is typical of a raw stacked image. You can assume the white stars are G2V stars and are therefore suitable candidates for defining the white balance. 

This is the kind of result I would expect to see after processing, though I'm not claiming this to be perfect!

I'd love to know how you get on with processing it and what software and workflow you used.  Post your results!  

The 16-bit TIF file can be downloaded from here:

https://docs.google.com/file/d/0B3Ky5pyZvsINeFI2NVprcnpMUUE/edit?usp=sharing

Choose "Download" from the "File" menu.  The preview that appears is pretty ropey and is not at all a good representation of the image.

Any comments welcome.

Mark

[Quatermass]

Interesting, I will try this later but mostly I select my stars and expand and feather the selection. After this I increase the saturation and apply a gentle gussain blur to bring out the stars colours which tend to be on the outer edge of my stars.

Sent from my Nexus 7 using Tapatalk

[sharkmelley]

One thing I forgot to mention is that the little panels that say "Can you read this?" correspond to some very faint nebulosity in the image which you want to bring out as much as possible (and separate from the noise background) without oversaturating the brighter stars.

Mark