Welcome to iraf.net Thursday, March 23 2017 @ 02:13 AM GMT


 Forum Index > Help Desk > Applications New Topic Post Reply
 fconvolve
   
rachanab
 02/10/2017 01:36PM (Read 153 times)  
+----
Newbie

Status: offline


Registered: 02/07/2017
Posts: 1
Hi,

I am trying to convolve my image with a psf and I am struggling with the following two things:

1) It takes a really long time to time to get the output file (~20mins).
2) My input fits file has 0 values outside the field of view, but once this image is convolved with the psf using fconvolve, I can see that it has introduced noise outside the FOV also. The problem I am facing because of this is that when I run Sextractor on it, its detecting this noise also and giving me thousands of detections when there are actually only 200 sources in the image. Does fconvolve introduce noise in your convolved image like this?

Thanks,
Rach

 
Profile Email
 Quote
fitz
 02/10/2017 04:04PM  
AAAAA
Admin

Status: offline


Registered: 09/30/2005
Posts: 3940

1) It takes a really long time to time to get the output file (~20mins).


Without knowing more about the image or hardware being used I can't really comment on the time. FCONVOLVE does use the FFT of both images and requires that the psf image be the same size as the input so perhaps another task such as GAUSS or CONVOLVE would be more efficient and accomplish the same thing.

2) My input fits file has 0 values outside the field of view, but once this image is convolved with the psf using fconvolve, I can see that it has introduced noise outside the FOV also. .....


The GAUSS/CONVOLVE tasks do have parameters for boundary extension but this is different than 0 values outside a FoV. You could try setting the 0 values to something like the image median to minimize the convolution artifacts, but a better approach might be to first create a mask of the input image (either the FoV or the outside region), do the convolution and then apply the mask to reset the values back to 0 before running SExtractor. You can use the command "cl> refer mask" to find suitable masking tasks or see the help page for IMEXPR for a way to create or apply masks.

 
Profile Email
 Quote
   
Content generated in: 0.09 seconds
New Topic Post Reply

Normal Topic Normal Topic
Sticky Topic Sticky Topic
Locked Topic Locked Topic
New Post New Post
Sticky Topic W/ New Post Sticky Topic W/ New Post
Locked Topic W/ New Post Locked Topic W/ New Post
View Anonymous Posts 
Anonymous users can post 
Filtered HTML Allowed 
Censored Content 
dog allergies remedies cialis 20 mg chilblain remedies


Privacy Policy
Terms of Use

User Functions

Login