Quote:
Originally Posted by astronobob
Cryyppeeeezzz Greg, , ,  |
Cheers Bob!
Quote:
Originally Posted by RickS
I've got 30+ hours of boring old M16 and 40+ hours of Helix, Mike.
Greg: sorry for the thread hijack. May I ask how you do your colour calibration? I notice that your colours are quite different to Mike's image of the same object.
Getting decent colour is a process that vexes me greatly! I sometimes wonder if we build up a false expectation of what some objects should look like based on previous images we've seen.
Thanks,
Rick.
|
Thanks Rick. Colour is a tricky subject. I correct for any colour bias, remove any green noise which throws off colour usually, try to keep some nice colour in the stars (often a bit tricky). Otherwise I eyeball it.
Selective colour is a good tool to massage colours to the shade that you want that matches good posted images. The blues in galaxies are often hard to achieve. The blues often have too much cyan and not enough yellow which gives that nice lightish ocean blue. Rob Gendler often achieved those shades and I wondered also how he got it.
Excess green is the usual enemy and comes from light pollution and also air glow. You can use the G2V star calibration method (I never have) but the top guys often do. That's where you have a list of G2V stars (a free list on Astrodon's site) and find one in your image. When you process the colour that star should be white if its high in the sky. Others correct for colour extinction as the angle of the scope lowers, blues extinct first and reds last. In your acquisition routine you should try to capture the blue subs when the scope is at a steep angle. If you are using CCDSoft this annoyingly means you have to wrongly label the filter name so even though you can select blue as the colour in the red filter dialogue box it will be labelled as red in the saved file - annoying little point. I read somewhere you can change it with some dive into the code - I never did. Just be sure to remember to rename the files the next morning or you are in for some really challenging processing!!
Quote:
Originally Posted by alpal
|
I do some minor stretching in CCDstack (click auto) and process the callibration, the data rejection and the registering and combine into masters and the initial colour combine. I don't see much evidence of a dark ring around it on my monitor but I can a slight one in the thumbnail.
I don't use DDP for stretching of my images but rather curves and levels.
In Photoshop that is 16 bits. Do you think 32 bit files in Photoshop would help?
Unfortunately this was shot low in the sky where I have the most light pollution. I then use a few gradient handling techniques to get rid of that. That's probably some minor residual of that routine. If you saw the process along the way its a mile from where it started. Yes the background being a bit darker is part of that process as well. At a dark site I would allow the background to be a bit lighter like Mikes - a dark grey My image is also only 1/3rd of exposure time of his and he is now in a dark site area. If the object were higher or past the Meridian and I was imaging to the west where I have little light pollution it would be a nicer result.
So in summary I don't think it came from the stretching process but the gradient handling process - Gradient Xterminator requires you to lasso the object and invert the image before running.
Quote:
Originally Posted by Joshua Bunn
Cool result Greg.
|
Cheers Josh. I was happy with it considering everything.
What I am realising is the gain from the 17 inch aperture is also the shorter total exposure time to get a good signal to noise ratio and the fact it also picks up Ha areas even without imaging some Ha.