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New stretching software: rnc-color-stretch released (free, open source)
- Thread starter rnclark
- Start date
Hello Grahame,
The reason for the failure is the data are severely clipped, so there is no low end to stretch:
stretched image to show the clipped data (black). The image is clipped from the center, including the coalsack, to the top.
The stretch program stretches and maintains color from the original. But because it does not yet handle gradients, and assumes a uniform sky glow, any gradient gets magnified and the color in that gradient stays. That means the result with images like this, if not clipped would not be good. But you can do the stretch, you just need to turn off color correction.
Because of the strong gradients, I suggest cropping the image like below. But first you need to redo the raw conversion and not clip the data. The color balance also seems off--be sure to use daylight white balance.
suggested crop.
Try and remove as much gradient as you can, e.g. gradient exterminator, or photoshop with this method: http://www.clarkvision.com/articles/astrophotography.image.processing2/ or other tools.
If you get the gradient reasonably removed, then you can use the stretch program with the color correction. Any remaining small gradient can be subtracted after the stretch.
Also, there seems to be strange holes around stars. Is that too aggressive noise reduction? The noise reduction needs to be dialed back.
Roger
The reason for the failure is the data are severely clipped, so there is no low end to stretch:
stretched image to show the clipped data (black). The image is clipped from the center, including the coalsack, to the top.
The stretch program stretches and maintains color from the original. But because it does not yet handle gradients, and assumes a uniform sky glow, any gradient gets magnified and the color in that gradient stays. That means the result with images like this, if not clipped would not be good. But you can do the stretch, you just need to turn off color correction.
Because of the strong gradients, I suggest cropping the image like below. But first you need to redo the raw conversion and not clip the data. The color balance also seems off--be sure to use daylight white balance.
suggested crop.
Try and remove as much gradient as you can, e.g. gradient exterminator, or photoshop with this method: http://www.clarkvision.com/articles/astrophotography.image.processing2/ or other tools.
If you get the gradient reasonably removed, then you can use the stretch program with the color correction. Any remaining small gradient can be subtracted after the stretch.
Also, there seems to be strange holes around stars. Is that too aggressive noise reduction? The noise reduction needs to be dialed back.
Roger
Thanks Roger,
Plenty of info there to think / play with.
That tut looks real interesting.
The light pollution here is pretty bad, the tut gave a bit of hope I may be able to get rid of some of it.
Will work through it in more detail later on.
Just playing and trying to learn a few more skills at present.
Always fun working out new ways to torture my poor ol SX50
Cheers
Grahame
Plenty of info there to think / play with.
That tut looks real interesting.
The light pollution here is pretty bad, the tut gave a bit of hope I may be able to get rid of some of it.
Will work through it in more detail later on.
Just playing and trying to learn a few more skills at present.
Always fun working out new ways to torture my poor ol SX50
Cheers
Grahame
chris gunn
Veteran Member
You may not have to drive too far to find darkish skies. I go about 75km to the south of Christchurch.
Hi Chris,
Nice to see another "local" lurking here.
Yes we are lucky there are many good options relatively handy.
I'm just starting to play again to try and find a way to make the Sag - Crux area look even better in skyscapes with local landmarks.
It seems to be something I do most winters now.
Just have to find a way of digging through the orange haze we call a sky.
Rogers tut linked a couple of posts above looks good.
Enjoy
Grahame
Nice to see another "local" lurking here.
Yes we are lucky there are many good options relatively handy.
I'm just starting to play again to try and find a way to make the Sag - Crux area look even better in skyscapes with local landmarks.
It seems to be something I do most winters now.
Just have to find a way of digging through the orange haze we call a sky.
Rogers tut linked a couple of posts above looks good.
Enjoy
Grahame
Hi Roger.
I had Davinci for Windows version 2.18, but need to re-install it.
I cannot find that version on the ASU site. Is it still available?
It seems that only very old versions are readily available.
Can it be posted (legally) on this forum?
I am anxious to try the color stretch Windows GUI again.
Fivel
I had Davinci for Windows version 2.18, but need to re-install it.
I cannot find that version on the ASU site. Is it still available?
It seems that only very old versions are readily available.
Can it be posted (legally) on this forum?
I am anxious to try the color stretch Windows GUI again.
Fivel
Apparently not
I am not sure. It was taken down apparently because of some bugs. So probably best not to use it.
Download the next available version, 2.07. It works fine except you must use 16-bit png files, not tiffs.
Roger
Roger, thank you for the verification and suggestions.
I will install version 2.07 and re try some of my images.
Now that I have a 64 bit version of Windows 7, I'm hopeful for improved functioning of the GUI.
On another subject, Bryan mentioned you might be at the Space Symposium next week.
I was hoping to be there and meet you, but some health issues prevented me from attending-darn!
Maybe we'll meet another time.
Fivel
I will install version 2.07 and re try some of my images.
Now that I have a 64 bit version of Windows 7, I'm hopeful for improved functioning of the GUI.
On another subject, Bryan mentioned you might be at the Space Symposium next week.
I was hoping to be there and meet you, but some health issues prevented me from attending-darn!
Maybe we'll meet another time.
Fivel
starman1969
Senior Member
A fellow astronomy society member was showing one of his images at our meeting last week which he said was stretched using your program.
Domokos Molnar
New member
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Hi Roger,
I've read in the documentation of your tool that you also hit the issue of CFA (Bayer) induced 'plotchy artifacts' and recommend either 'exposure dithering', 'raw denoising' or '-setmin' to fix the problem.
I have an image where none seem to help to the extent I would like so I looked around a little bit and eventually came across this paper: https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/267_lowlight.pdf
This seems very interesting in fighting the 'plotchy artifacts' - as they call it - and actually present evidence that the phenomena is caused by the demosaicing part of the raw conversion process.
My question is if you have any experience with/it or have you seen an actual implementation of the algorithm they propose.
Regards,
Doma
I've read in the documentation of your tool that you also hit the issue of CFA (Bayer) induced 'plotchy artifacts' and recommend either 'exposure dithering', 'raw denoising' or '-setmin' to fix the problem.
I have an image where none seem to help to the extent I would like so I looked around a little bit and eventually came across this paper: https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/267_lowlight.pdf
This seems very interesting in fighting the 'plotchy artifacts' - as they call it - and actually present evidence that the phenomena is caused by the demosaicing part of the raw conversion process.
My question is if you have any experience with/it or have you seen an actual implementation of the algorithm they propose.
Regards,
Doma
Yes, the color blotchiness is definitely due to demosaicking algorithms. That is well known. You can tune the noise reduction in photoshop/lightroom during raw conversion. Rawtherapee has more advanced algorithms and should do a better job (more difficult program to understand). Another way people mitigate the problem is by dithering--shifting the field of view a few pixels between frames.
But astrophotographers usually push the limits trying to extract ever fainter detail until they hit a wall like this problem. Then the setmin parameter can mitigate the problem some.
Roger
Domokos Molnar
New member
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Hi,
thank you. I actually use Rawtherapee.
I wil try a convolution network based approach, which seems pretty close to the approach outlined in the paper. Namely this one: https://groups.csail.mit.edu/graphics/demosaicnet/
Doma
Rudy Pohl
Veteran Member
I'm trying to install rnc-color-stretch on my Windows 7 machine and I can't find the download link for the latest version of davinci on the davinic web site.
All the "download davinci for windows" links lead back to a web page with only very old versions (2008-2011).
Can someone direct me to the proper link for the Windows download please?
Thanks,
Rudy
All the "download davinci for windows" links lead back to a web page with only very old versions (2008-2011).
Can someone direct me to the proper link for the Windows download please?
Thanks,
Rudy
Loading…
davinci.asu.edu
is the most current, and is version 2.07 (Feb 2011).
It works fine, but the that windows version does not read 16-bit tiffs. Just convert to 16-bit float and it will works fine.
Roger
Rudy Pohl
Veteran Member
Please ignore above request.
I just read through this thread and saw that they removed the latest 64-bit version and that we should stay with using the older 2.07 versions which I have now done.
Rudy
GFamily
Well-known member
Thanks for this, it's really giving a lift to my images. They're much punchier now.
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