| finding star-like objects in images [message #94858] |
Wed, 08 November 2017 02:12  |
Helder
Messages: 10
Registered: October 2017
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Junior Member |
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Hi,
I'm not an astronomer and I guess that this is something that astronomers have been confronted with quite often in their lives.
I have a detector where particle events generate intensity across some pixels (2-5 x 2-5) [*]. Typically their integral intensity is constant (lets say 100 +/- 20). These events show over a noisy bkg.
Apart from having a constant intensity, these events are similar to stars (that have a varying luminosity).
What approaches are typically used for detecting/locating such events?
Any IDL solution readily available out there?
Thanks for reading so far and for any suggestions.
Regards,
Helder
[*] - threshold methods would not work very well, because the total intensity of 100 may be distributed over 2x2 pixels (~25 per pixel) or 5x5 (~10 per pixel).
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| Re: finding star-like objects in images [message #94859 is a reply to message #94858] |
Wed, 08 November 2017 02:25  |
Markus Schmassmann
Messages: 129
Registered: April 2016
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Senior Member |
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On 11/08/2017 11:12 AM, Helder wrote:
> I'm not an astronomer and I guess that this is something that
> astronomers have been confronted with quite often in their lives.
> I have a detector where particle events generate intensity across
> some pixels (2-5 x 2-5) [*]. Typically their integral intensity is
> constant (lets say 100 +/- 20). These events show over a noisy bkg.
> Apart from having a constant intensity, these events are similar to
> stars (that have a varying luminosity).
>
> What approaches are typically used for detecting/locating such
> events?
>
> Any IDL solution readily available out there?
>
> Thanks for reading so far and for any suggestions.
>
> [*] - threshold methods would not work very well, because the total
> intensity of 100 may be distributed over 2x2 pixels (~25 per pixel)
> or 5x5 (~10 per pixel).
Hi Helder,
just a guess, but have you tried
star=where(smooth(img,[5,5]) gt 100./5^2/2)
you will have to change the threshold value and maybe also how much
smoothing you apply, but it could work.
good luck, Markus
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| Re: finding star-like objects in images [message #94899 is a reply to message #94858] |
Mon, 27 November 2017 03:29 |
Helder
Messages: 10
Registered: October 2017
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Junior Member |
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On Wednesday, 8 November 2017 15:24:00 UTC+1, wlandsman wrote:
> You could try find.pro based on a popular software package(DAOPHOT) used by astronomers
> https://idlastro.gsfc.nasa.gov/ftp/pro/idlphot/find.pro
> The image is convolved with a lowered Gaussian with the approximate FWHM of the stars.
>
> Note, though, that astronomers want to detect stars but not cosmic rays so there are sharpness and roundness criteria (with stars being less sharp and more round than cosmic rays).
>
> --Wayne
>
> On Wednesday, November 8, 2017 at 5:12:06 AM UTC-5, Helder wrote:
>> Hi,
>> I'm not an astronomer and I guess that this is something that astronomers have been confronted with quite often in their lives.
>> I have a detector where particle events generate intensity across some pixels (2-5 x 2-5) [*]. Typically their integral intensity is constant (lets say 100 +/- 20). These events show over a noisy bkg.
>> Apart from having a constant intensity, these events are similar to stars (that have a varying luminosity).
>>
>> What approaches are typically used for detecting/locating such events?
>>
>> Any IDL solution readily available out there?
>>
>> Thanks for reading so far and for any suggestions.
>>
>> Regards,
>> Helder
>>
>> [*] - threshold methods would not work very well, because the total intensity of 100 may be distributed over 2x2 pixels (~25 per pixel) or 5x5 (~10 per pixel).
Dear Markus and Wayne,
thank you very much for your insight. It took me some time implement the above (as part of a bigger analysis) and I'm now very happy with it.
Regards,
Helder
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