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UltravioletPhotography

Famous Fishing Shack


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Andy Perrin

Hoya UVIR cut, Sony 55-210mm, f5.6 0.016" iso100

post-94-0-53195200-1524493004.jpg

 

Hoya R72, Sony 55-210mm, f5.6 0.016" iso100

(No processing except for removing the window screen pattern and the usual contrast/saturation adjustements.)

post-94-0-78152300-1524493083.jpg

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Andy, I've been there! It is nice to see it again.

 

So colorful! Ports and marinas make interesting subjects in UV/IR work.

 

I always have liked the R72 filter. It's false color can be brought out in more than one interesting way.

 

Is there some app which helps remove window screen patterns?? That could not have been easy!

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Andy Perrin

Thank you!

 

Is there some app which helps remove window screen patterns?? That could not have been easy!

Just that Neat Image plugin that I showed you before. It can be set to remove specific frequencies, so I set it to leave the high frequencies alone and only remove the lowest ones. It worked beautifully.

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Window screen pattern?

 

I have not noticed anything that could be called that in my pictures.

Please show an example so that I can see what to look for.

Is it something seen only in some cameras?

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Andy Perrin
Ulf, it is the pattern you get when you shoot a photo through a window screen! If you avoid window screens you should have no trouble.
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Andy Perrin

I shot the pics through a window screen, yes. Since window screens add an extremely periodic pattern to the image, they are easily removed by denoising software such as Neat Image (or using a Fourier transform, if you don't mind getting your hands dirty in MATLAB).

 

Before:

post-94-0-48788100-1524521282.jpg

 

Neat Image amplifies the noise (on purpose, so you can see what you're removing), so the window screen is clearly visible here:

post-94-0-60832400-1524521331.jpg

 

You can select which frequencies you want to remove. Since the window screen periodicity is a very low frequency, we set all the sliders except the very low ones to zero so the rest of the image will be unaffected.

post-94-0-23085800-1524521513.jpg

 

After noise removal:

post-94-0-97249300-1524521348.jpg

 

(Obviously there was a lot of other processing - this was not the same image as I used above, in fact, but it was better for demonstrating the noise removal because the screen pattern was more obvious.)

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Perhaps a dumb question, but could the same mathematics run in reverse eliminate the MTF smudging of some mirror lenses with large on-axis secondary mirrors?
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Andy Perrin
No idea, because I don't know how they work or what the cause of the smudging is. This method works if you have a single repeating element (the window screen wires in this case) that you want to remove.
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Ah!

 

Window screens are not that common here. I didn't make the connection to real windows.

I just assumed it was a name of an imaging artifact pattern I hadn't seen before.

 

NeatImage is a very competent program.

I used it a lot when it was new, to filter scanned slides and negatives, but have forgotten much how to use it optimally.

Must start using it again.

 

Thank you for the demonstration, fixing this problem.

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