GreyCStoration: Differences at 16 vs. 32 bit

[andyschlei]

I am working (first pass really) with some image data and got to noise reduction.

There was a fair amount of noise but I got a good result with 3 iterations of GreyCStoration noise reduction.  When I went to save before processing the whole image (I was testing on a preview) I noticed that the image was at 16 bit integer -- I had forgotten to move to 32 bit floating point earlier in the process.

I had my processing history, so I started over.  When I got to noise reduction, the results were entirely different.  The same noise reduction that worked at 16 bit integer totally blurred the image when working in 32 bit floating point.

Why would otherwise identical images have different noise reduction results due to different bit depths?  Does the lack of precision prevent the excess blurring that occurs in the more precise data space?

I am confused.

--Andy

[Juan Conejero]

Hi Andy,

Of course there should be no difference, other than small ones due to roundoff errors.

Could you please save your processing as a PSM file and post a link to it? Also, we'd need to have access to at least a significant crop of the original 16-bit image.

Thanks

[andyschlei]

I'll post the PSM and images tonight.

[andyschlei]

Here is the data documenting my problem.

PSM file:ftp://ftp.obsballona.net/NRProblem/GREYCstoration.psm

Note that I only changed the iterations to 3 and set it to do the channels separately.

16 bit integer before (link is the FITs)



16 bit integer after



32 but floating point before



32 bit floating point after



All of the files are available at ftp://ftp.obsballona.net/NRProblem/

--Andy

[andyschlei]

One other thought.  The problem of over blurring occur when the number of iterations is greater than 1.

[David Serrano]

I can confirm this behaviour, in both images and previews. It may be normal but I think it's worth pointing out that it takes nearly 3 times as much time to process the 32 bit floating point image.

Edit: oops, forgot to mention that I tested it with version 01.00.45.337.


[I don't get annoyed when corrected, english corrections are welcome as private messages, if you like ]

[Juan Conejero]

Hi Andy and David,

Indeed this was a bug - thank you for catching it.

I have fixed it; please refer to this thread on the Announcements section.

[David Serrano]

Fixed here. Good job .

[andyschlei]

I'm happy that I was able help by finding this problem.

Great to see it fixed....