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Old 02-06-2016, 02:20 PM
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Shiraz (Ray)
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Join Date: Apr 2010
Location: ardrossan south australia
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Quote:
Originally Posted by RickS View Post
Very interesting result, Ray. I've often wondered what contributes to star bloat and halos.

What effect does the brightness of the star have? Does it have the same proportional effect on the centre and the skirts?

Have you thought about applying a non-linear stretch, say a PI style MTF stretch, to your results and then plotting a linear result?

BTW, those stars look pretty soft to me... though the log scale helps

Cheers,
Rick.
These are normalised to the peak, so the same profile will apply to any star, but the absolute value will vary.

When you stretch an image to reveal, say, a galaxy, you may be expanding a region of perhaps 2 orders of magnitude so that it covers the whole dynamic range of the image. If you have moderately bright star, that 100:1 band may now be aligned somewhere around the middle of the the star profile, where there is precipitous fall and the star will vary very little over the 100:1 intensity range of interest. Thus, the star edge will be fairly sharp and the core will be saturated - even though the core did not start out saturated. If the star is dim, the band of interest will align with the top end of the profile and you will see a distorted Gaussian profile in the core and a fairly sharp edge. If the star is very bright, the band of interest will be down the bottom of the star profile and the star will have a large soft skirt and a large saturated core (again, even though the core did not start out saturated).

Doing a PI-type stretch is a great idea - much better than the words above. Now to figure out what types of functions are used for stretching - any ideas?

regards Ray

Last edited by Shiraz; 02-06-2016 at 03:38 PM.
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