Posted by
karenacollins on
Jun 24, 2015; 8:35am
URL: http://astroimagej.170.s1.nabble.com/Reducing-data-failing-tp272p277.html
Hi Peter,
As you have discovered, cropping unfortunately does not adjust the WCS
coordinates to match the new image. The only straight forward work
around at this time is to plate solve the image again. AIJ's plate solve
will remove the WCS solution and update the headers with a new solution.
However, this process could be slow since I think you are processing
lots of images.
Here is another possibility: If you can find a way to adjust data in the
image's "info" (see Toobar->Image->Show Info...), the values that need
to be corrected are CRPIX1 and CRPIX2. The image "info" contains the
FITS header information for FITS images. You would need to adjust CRPIX1
by the number of pixels you crop from the left side of the image, and
CRPIX2 would need to be adjusted by the number of pixels you crop from
the bottom of the image (in FITS coordinate space). Maybe this post in
the ImageJ forum is useful:
http://imagej.1557.x6.nabble.com/add-edit-a-comment-and-store-it-with-an-image-td3685672.htmlSince a crop with WCS correction would be generally useful, I have added
it to the feature request list. However, it will probably be a month or
two before I can find time to publish a new version of AIJ the supports
a WCS aware cropping feature.
Regarding cosmic ray removal, are you using the "Remove outliers"
feature on the Data Processor (DP) panel, or something else? I wouldn't
expect the "Remove outliers" feature to blur the image. It should only
replace a pixel with the median value of the surrounding pixels if its
actual value differs from the calculated median by more than the
"Threshold" setting (in ADU). If you are using that feature and entering
"10" as the threshold, it is likely that most or all of the pixels in
the image are being replaced with the neighboring pixel's median value,
resulting in the blurring effect. In that case, I would recommend
experimenting with threshold values in the range of 100-1000 ADU to see
if cosmic rays are corrected without replacing any of the other pixels.
This feature also exists in the AIJ toolbar at Process->Noise->Remove
Outliers if you want to include it to the cropping routine you mentioned.
Hopefully some of these ideas will be helpful,
Karen