Search found 11 matches

by pcl
2016-11-28T03:12:03-07:00
Forum: Bugs
Topic: Error in `convert': corrupted double-linked list
Replies: 2
Views: 3379

Re: Error in `convert': corrupted double-linked list

Weird. Thanks for checking. It could well be a Heisenbug which goes away when debugging mechanisms such as valgrind are in place. It might be some strange effect of the compilation options on this Gentoo installation. As it has only been noticed for the one image and could well go away with the next...
by pcl
2016-11-27T10:38:20-07:00
Forum: Bugs
Topic: Error in `convert': corrupted double-linked list
Replies: 2
Views: 3379

Error in `convert': corrupted double-linked list

Perhaps this has been fixed in the latest version, but Gentoo only ships as follows pcl@anubis ~/identify -version Version: ImageMagick 6.9.6-2 Q16 x86_64 2016-11-16 http://www.imagemagick.org Copyright: Copyright (C) 1999-2016 ImageMagick Studio LLC License: http://www.imagemagick.org/script/licens...
by pcl
2016-11-23T10:08:52-07:00
Forum: Developers
Topic: Variance computation
Replies: 17
Views: 14009

Re: Variance computation

The standard deviation of a single point is identically zero. Think about it: there are no deviating points and so no deviation. I could have explained that rather better as the reasoning goes to the heart of this topic. There are no deviating points only if you've already used the sole point to de...
by pcl
2016-11-23T02:34:32-07:00
Forum: Developers
Topic: Variance computation
Replies: 17
Views: 14009

Re: Variance computation

One problem with doing that. A 1 pixel image will have an undefined std, due to a divide by 0 (1-1=0). So you will need to trap for that special case and report NAN or inf or some other value. This is fine for identify and %[standard_deviation], but may cause issues with -statistic and -fx. NO! The...
by pcl
2016-11-18T14:36:46-07:00
Forum: Digital Image Processing
Topic: Removal of coma from an image through cepstrum?
Replies: 7
Views: 17557

Re: Removal of coma from an image through cepstrum?

It looks like it has chromatic aberration also (the cyan on one side)? Yup. That's why I tried CLEAN on all three RGB channels separately rather than converting to HSV, deconvolving the H channel, re-adding the HS to the clean H image and then back to RGB. Thinking about it, I may have made an erro...
by pcl
2016-11-18T14:09:39-07:00
Forum: Digital Image Processing
Topic: Removal of coma from an image through cepstrum?
Replies: 7
Views: 17557

Re: Removal of coma from an image through cepstrum?

Have you tried deblurring with an ellipse shaped PSF whose diameter are the radii in the cepstrum? I am not sure if the orientation of the ellipse PSF image should be the same as the cepstrum or orthogonal. But you can try either way. You can try that using my script fftdeconvol I haven't but will ...
by pcl
2016-11-18T03:07:35-07:00
Forum: Digital Image Processing
Topic: Removal of coma from an image through cepstrum?
Replies: 7
Views: 17557

Re: Removal of coma from an image through cepstrum?

fmw42 wrote:Perhaps you would provide an example image. You can upload to some place such as dropbox.com and put the url here.
The 256x256 sample is Image and the cepstrum is Image.
by pcl
2016-11-17T18:37:57-07:00
Forum: Digital Image Processing
Topic: Removal of coma from an image through cepstrum?
Replies: 7
Views: 17557

Removal of coma from an image through cepstrum?

Reminder: coma is an optical aberration which typically arises from misalignment of optical components and which results in a point source producing a comet-shaped image (hence the name). Users of fast Newtonian telescopes will be all too familiar with this bane. I have a star-field image which show...
by pcl
2016-11-17T18:01:29-07:00
Forum: Digital Image Processing
Topic: Detection of Noise quantity in an image
Replies: 5
Views: 15839

Re: Detection of Noise quantity in an image

For examples of these histograms (but not in the context of noise), see my "Multi-scale pyramids" page. I expect an internet search with suitable keywords will find references. A search with multi-scale pyramid "noise estimation" produced four results, the first of which, http://mcolom.perso.math.c...
by pcl
2016-11-16T10:06:24-07:00
Forum: Developers
Topic: Variance computation
Replies: 17
Views: 14009

Re: Variance computation

See https://en.wikipedia.org/wiki/Variance. Using n and not n-1 (or n+1 or n-1.5) is the population variance. It is also the variance of a set of n equally likely values. With images with large numbers of pixels the difference between n and n-1, is probably not significant. If you want the unbiased...
by pcl
2016-11-16T09:09:18-07:00
Forum: Developers
Topic: Variance computation
Replies: 17
Views: 14009

Variance computation

I'm new here and although I've used the search button to see whether the issue described below has been discussed in the past, I've not found anything. Apologies if it's an old one. The identify utility can be persuaded to give statistical information about the channels in an image, specifically the...