Cepheus Ghost (Nightmare)

[MarkS]

Thanks for the explanation but it was only the position of those sliders and not the method.

I'm not sure what you're asking.  Once you have set the black level then when you play with the Photoshop "levels" slider or the Pixinsight histogram slider you'll notice that the star colour remains the same, no matter what position of the slider you select.  On the hand, as soon as you perform PS curves or Pixinsight stretching, the colour becomes diluted.  This is an indication that something dodgy is being done to the data.

The method of maintaining true star colour?  Arcsinh transform - which in opinion, is the only proper way to perform stretching.  Yes you can simulate this in Photoshop by many iterations of stretching and increasing saturation but all this demonstrates is that the Photoshop method is fundamentally flawed.

Mark

[MarkS]

Well, the Ghost does in fact overlap the Iris image I took 4 years ago:



But the Iris was only 4 hours of data whereas the Ghost was 12 hours.  So the Iris had to be stretched quite a lot.

Bigger version:
http://www.markshelley.co.uk/Astronomy/2014/iris_ghost.jpg

It seems to indicate that I may have inadvertantly neutralised an area of dust in the Ghost image.  Collateral damge whilst removing the background gradients

[Carole]

Well done Mark.

Carole