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Messages - Simon Hicks

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Tutorials and Processing Examples / Re: Star Elongation?
« on: 2011 July 05 00:04:23 »

Deconvolution with the shape parameters described above will work, but unfortunately can lead to hard edges to the stars. If this happens try using some MorphologicalTransform after deconvolution to soften the edges up again.


Off-topic / Re: Astro Soc Field Trip
« on: 2011 May 09 13:55:10 »
That really does look first class Jack! Thanks

Off-topic / Re: Astro Soc Field Trip
« on: 2011 May 09 00:57:00 »
Thanks for the links guys, I'll check these out.  ;)

Seems bizarre to me. In a marketing sense it doesn't seem to make sense. You're trying to promote the name PixInsight and get that to be the word that people think of when they think of high end, top quality, highest performance astro imaging software (or whatever the desired descriptions are).

Now the message will be confused with a pile of short lived code words. If version 1.7 was going to be the latest version for the next 5 years then that would give time and space for a code name to take hold, and give a reason for a marketing splash (i.e. helped by a new code name) to be used at the release of version 1.8. But I hope version 1.8 is not 5 years away. And secondly, nobody needs to be told (in a marketing sense) when version 1.8 comes out, the software update tells them.

And it makes each code named version sound like a different product....."I use Starbuck"...."Oh I use StarChaser"....."Actually mate that's just the latest release of the same product called PixInsight and if you'd used it in the last month it would have told you."

And when someone on the forum talks about a feature in Starbuck vs a feature in StarChaser I will need to go to my wall chart that shows the code names vs Version Number history to work out which came first.

Sorry to be negative...just my two pennies worth.

Off-topic / Astro Soc Field Trip
« on: 2011 May 07 07:06:52 »
Hi all,

If an astro society (maybe 15 people) based in Scotland wanted to go for a week vacation field trip to an observatory where they could get say 6 nights access to a large scope(s) (maybe 20inch) to do some observing and imaging, where would you recommend?

I'm thinking of something either in southern Europe, or maybe in the USA, somewhere where we can start to see objects that may not be so visible in Scotland (Latitude 55 degrees north) and just have some fun with some really dark skies.

Any thoughts?


General / Re: DSLR HotPixel removal
« on: 2011 April 12 10:23:17 »
If this is true, i.e. that a single hotpixel creates a group of four hotpixels automatically after the debayer, then is this a signature of a hotpixel in a debayered image, i.e. any group of exactly four pixels that are all significantly higher than their surrounding pixels? And if so, can we design a filter to only select out these groups of four pixels and replace them with their neighbouring values?

General / Re: Star Trails - The Intentional Kind
« on: 2011 April 10 14:52:29 »
Enzo, Carlos,

Thanks for the suggestions....I will try them tomorrow when I have some time and report back.


General / Re: Star Trails - The Intentional Kind
« on: 2011 April 10 09:22:29 »
Hi Enzo,

Thanks for the link to the thread that I had read before my holiday...and completely forgotten during my holiday  ???  It was a good holiday  8)

Anyway, your script does a great job of combining the raw images  :D but unfortunately it has the same problem as the StarTrails software, i.e. when it does the MAX operation it ensures that it always adds and maintains the brightest noise spikes from all the frames. So I get the star trails but also specially selected highlights of the worst noise from all 25 frames.

On the other hand if I do a normal stack with sigma clipping then I get a fantastic foreground....all the noise has gone...but so have the star trails.

I'm wondering if there is a way to get the best of both worlds?

General / Re: Star Trails - The Intentional Kind
« on: 2011 April 10 06:56:10 »
I wonder if there is a way to do two seperate stacks and combine them. The first stack would be a normal stack with sigma clipping etc to get a nice clean background and foreground....whilst largely washing out the star trails.

The second stack would be a 'difference maintaining' stack. This would take the difference between one image and the next...the difference being the star trails and the noise. This second image would have nice star trails, loads of noise and not much background / foreground.

The trick would be to select a mask for the second stacked image that only selects the star trails and not the rest of the noise / background / foreground. Star trails are typically long thin lines, slightly curved, with roughly equal intensity along their length. Is there a way to create a mask that will just select these features?

General / Star Trails - The Intentional Kind
« on: 2011 April 10 06:27:38 »
Hi all,

Whilst on holiday I took a couple of sets of star trail images. I'm now trying to get some nice star trail images out of them. They are a set of maybe 25 x 4 minute exposures with an 18mm camera lens with a cottage and some trees in the foreground.

The question is really 'is there a way to combine them in PI?' I can't do a straight stack of the images because this enhances the S/N of the background  :) , but washes out the star trails.  :'(

I've tried the excellent little program at Firstly this only accepts 8bit images :( . But if I convert all my raw images to jpeg and put them into this program then I end up with quite noisy images at the end. I guess that it detects the differences in each image (i.e. the star trails in different positions) and makes sure they maintain their 'full' intensity (i.e. they don't get diluted by subsequent additional images)....but I guess that this means that all the noise in each image also gets maintained at its full intensity. Noise is a difference just like a star trail in a different position.

So has anyone got any good ideas as to how to get all the benefits of normal stacking of the background and foreground, whilst also not washing out the actual star trails by stacking?


Off-topic / Re: Strange colored halo
« on: 2011 March 22 13:14:59 »
Hi Georg,

My first thought is to take the derivative of the image...this gives the slope. The saturated parts will have a slope of zero....and not have any noise on that slope, which should make it very obvious from any other flattish unsaturated areas in the image...because these will have noise on them. So even if channel X has been multiplied by 0.5, the 'flat tops' will still be detected. This assumes that the images are still linear.

This can be used to generate a mask of the saturated parts of channel X....Mask1.

Then you need to 'sample' the halo to find its unsaturated colour. Do this by expanding Mask1 (MorphologicalTransform?) to give Mask2. Then do something in PixelMath (my brain hurts at this point) so that you end up with Mask3 which is just the halo area that is exposed in Mask2 but not in Mask1, i.e. a halo ring looking mask.

So Mask3 will show the halo parts of the image, i.e. the true(???) unsaturated colours of the stars.

Now you need to somehow 'correct' all the channel X pixels inside the saturated core so that they are in the same ratio with the other channels as they were in the halo. If you had a single saturated star in the image it would be easy. You just take the ratio of the three channels through Mask3 and then apply that to channel X through Mask1. But the problem is that there will be many saturated stars in an image, all with different colours. So you somehow have to apply this on a 'local' basis. I have no idea how you could do that, but I guess there are people here that do.

This might be problematic if there is a nebula behind the star...depends on the halo definition I guess.

Anyway, that's my thoughts. I hope it helps, or maybe its the wrong track to take?



Off-topic / Re: Strange colored halo
« on: 2011 March 22 06:37:48 »
Hi Georg,

I've just noticed this thread....sounds like a good idea. I'll just add some thoughts.....

The red response of my DSLR is way higher than the blue and green since its been modded. This means that 'white' stars often have the red channel saturated in the centre whilst unsaturated in the blue and green. This means that when I do colour calibration, by applying factors to each channel, the halos are white or whatever colour they should be (as expected) and the centres are blue/green, because the red channel has 'flat topped' at some intermediate value.

What would be good is a way of detecting the 'flat top' in a star in a channel, and from there to the centre replacing that channel with the same channel mix that was detected in the halo, but following the intensity curve of the other one or two channels that don't have a flat top.

Maybe this is what you are trying to do?


Gallery / Re: Half Moon
« on: 2011 February 23 05:09:03 »
I really like these colour saturated images of the moon, they really show the different geology and features...maximum information content. After all, that's the methodology often applied to the colour and contrast rendition of nebulae.

And to my taste you have got it just right, definitely not overdone.

Announcements / Re: PixInsight Magazine
« on: 2011 February 16 11:09:36 »
Yes...they are there!....even on my lowly laptop running a brain damaged browser.  ;)

Do you reckon any of this Microsoft stuff will ever catch on?  >:D

General / Re: What is a wavelet?
« on: 2011 February 14 09:02:50 »
Wow... Looking forwards to the appearance of these new tools in PI!

Me too! lets see them soon.   :D

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