comp.lang.idl-pvwave archive: archive

Home » Public Forums » archive » CCD saturation

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: CCD saturation [message #63117 is a reply to message #63031]

Mon, 27 October 2008 06:43

MichaelT
Messages: 52
Registered: May 2006

Member

A couple of years ago I did something like this to remove the streaks
(can't find the program any more, though...):

First label all stars in your image (img) which have pixel values
above a threshold value

lab = Label_Region(img gt threshold)
h = (histogram(lab))[1: *] ;[1: *] removes background pixel count

dims = Size(img, /Dimensions) ;image dimensions

So h now contains the pixel count for each identified area. Saturated
stars with streaks usually have a pixel count above a certain value
(their area is larger). In a loop I then checked which area is larger
than other_threshold and then determined the aspect ratio of each of
these areas:

;Areas larger than 100 pixels probably have streaks (or whatever
threshold is best in your case)
other_threshold = 100

w = Where(h gt other_threshold, n_areas)

;limiting aspect ratio, example: 1.2 (or whatever you like) considered
to be a streaked star
a_threshold = 1.2

For i = 1, n_areas - 1 Do Begin

wa = Where(lab EQ w[i] + 1) ;+1 to compensate for the removed
background count

wx = wa Mod Dim[0] ;Find the x- and y-locations of the pixels
wy = wa / Mod[0]

;If your streaks are vertical, otherwise reverse wx and wy
aspect_ratio = (Max(wy) - Min(wy) + 1.0) / (Max(wx) - Min(wx) + 1.0)

If aspect_ration GT a_threshold Then Begin
;Do something to remove the streaks
EndIf

EndFor

I can't remember exactly how I removed the streaks. I think I
substituted the streak's pixels by pixel values that were found just
adjacent to the streak (left and right). I also added some random
noise to the pixels to make them less obvious.

I hope it helps.

Michael

Report message to a moderator

[Message index]

		CCD saturation By: Wox on Fri, 24 October 2008 02:54
		Re: CCD saturation By: Wout De Nolf on Tue, 28 October 2008 02:42
		Re: CCD saturation By: MichaelT on Wed, 29 October 2008 08:07
		Re: CCD saturation By: Wout De Nolf on Thu, 30 October 2008 01:31
		Re: CCD saturation By: Wout De Nolf on Tue, 28 October 2008 01:56
		Re: CCD saturation By: MichaelT on Mon, 27 October 2008 06:43

Previous Topic:	why the variable become -NaN?
Next Topic:	Re: why the variable become -NaN?

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Oct 10 07:42:46 PDT 2025

Total time taken to generate the page: 0.00714 seconds