PixInsight Forum (historical)

PixInsight => Tutorials and Processing Examples => Topic started by: Nocturnal on 2008 November 19 06:32:16

Title: M45 Processing Example by Carlos Sonnenstein
Post by: Nocturnal on 2008 November 19 06:32:16

Hi,

thanks very much for publishing

http://pixinsight.com/examples/M45-sonnenstein/en.html

I have a similar M45 image and I tried the HDRWavelet step on it. This tool has been of limited use to me so far because it either does nothing or it corrupts the data so I'm trying to learn more about it. As I understood from earlier discussions wavelets should be run against unstretched data so that's what I tried. I got terrible '+' sign artifacts around the stars. So I did a non-linear stretch like what Carlos showed and then re-did the wavelet processing. Much better. Upon stretching the data some more I did still see unacceptable '+' sign artifacts around stars so I had to undo it again. I then noticed that a mask had been generated in an earlier step and not been disabled. Was the mask enabled for the HDRWavelet process?

Thanks,

  Sander

Title: M45 Processing Example by Carlos Sonnenstein
Post by: Juan Conejero on 2008 November 19 13:44:43

Hi Sander,

Quote

wavelets should be run against unstretched

Yes, but this refers to wavelets applied as an *image restoration* process, i.e., ATrousWaveletTransform applying layer biases. In this case, wavelets act in a way comparable to deconvolution.

However, the HDR Wavelet Transform algorithm usually doesn't work well with linear data. Of course you already know this example:

http://pixinsight.com/examples/wavelets/NGC7000/en.html

Note that I applied HDRWT to the stretched image. In general, HDRWT should be applied with its "Luminance mask" option enabled. This option protects the background and avoids ringing artifacts.

If you upload the image you're trying to apply HDRWT to, I can give it a try if you want.

Title: M45 Processing Example by Carlos Sonnenstein
Post by: Nocturnal on 2008 November 19 13:58:27

Hi Juan,

great, thanks for that explanation. I will give it another go and report back. Thanks for the offer. Should I not be able to replicate the effect I'll upload the image for you to try.