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04-02-2007, 11:45 AM   #1
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What post-processing trick for visible sensor dust?

I have a nasty piece of dust sitting on my sensor.
I tried hard to remove it and did eveything suggested. No hope!
As the particle chose to sit on the right upper quadrant of my images it is annoyingly visible when there is a bit of homogeneous sky in my pictures.
I am not asking for a remedy for its removal (though I would appreciate condolences!). What I am asking is this:
- What tool do you use to remove those speckles (clone stamp and the like)?
- Is there a way in any of the commonly used raw file processors (PhotoLab, Silkypix, LightZone etc.) to handle this issue "automagically"?


Last edited by bc_the_path; 04-02-2007 at 10:57 PM. Reason: misprints
04-02-2007, 03:17 PM   #2
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Clone it out
I haven't heard of any prog that does it auto......
04-02-2007, 03:46 PM   #3
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QuoteOriginally posted by bc_the_path Quote
- What tool do you use to remove those speckles (clone stamp and the like)?
- Is there a way in any of the commonly used raw file processors (PhotoLab, Silkypix, LightZone etc.) to handle this issue "automagically"?
Any photo editors allow you to use clone or healing stamp to remove it.
Although not automatic, Bibble can apply the same healing tool in the same area for all your image files during batch processing.
04-02-2007, 06:19 PM   #4
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Nosnop: wrote-
"Any photo editors allow you to use clone or healing stamp to remove it."

Lightzone will alllow you to spot edit or clone multiple points on a black frame image and save the adjustment as a non-destructive adjusment layer that can be applied to any subsquent image. Other editors may have the similar functions.

Be aware that what you think arre hot pixels May be just high noise in a specfic image and will not occur in subsequent images.

You should shoot some black frame images to make sure your are dealing with dead or hot pixels. The test: shoot with the lens cap on and the eyepiece covered at 1/2, 1 and 2 sec at the highest ISO and the look at the results to identify the problems.


Last edited by dmdctusa; 04-02-2007 at 06:41 PM. Reason: spelling and syntax
04-02-2007, 06:35 PM   #5
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Hmmm... No astrophotographers here? To remove those flaws in astrophotos we all use flat frames. If you take a photo of a flat white surface (I use a light box on my telescope) and divide it into the image you eliminate spots in the light path, usually dust on the sensor. Also removes vignetting.

Much better than a clone tool since you replace it with what should be there, not what is nearby. I could produce some examples with my K100D if you'd like. I have not cleaned the sensor in a few weeks.
04-02-2007, 06:50 PM   #6
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Leo,

I had overlooked white frame as a mean to the same end. It would would be helpful to non-astro types to detail the steps you use. I ssume you are using layers to make the adustment and are using Photoshop or another layer enabled or stacking type program to make your edits. I think most of us here are non-astro photograpers.
04-02-2007, 07:49 PM   #7
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It seemed this started about dust and is now about hot/stuck pixels???

For hot/stuff pixels, Adobe RAW processing tools automatically fix them, so can bibble (though I have gone off bibble of late as it seems to be slowing down with every new version for me).. Try Adobe Lightroom, it is 100% auto.

For dust the clone tool is the easiest solution IMO..
04-04-2007, 02:53 PM   #8
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dmdctusa requested:

<It would would be helpful to non-astro types to detail the steps you use.>

OK, here goes!

I use Images Plus, which is written for the astrophotography crowd but can be used on daylight images. I assume the more expensive programs, such as Adobe, can do flats as well. It was raining this morning when I took a demo shot so ignore the poor quality. I wanted a lot of sky so the spots would show, and they did. Presuming my upload works you should see the original photo of the top of one of our evergreens with dust spots all around. As mentioned, I have not used my Rocket in a few weeks. Next is a shot taken of my lightbox, a device I made to fit on the business end of my telescope. It has white LEDs that shine indirectly at milk glass. I can count two dozen spots in the original 6 MP image.

I converted the raw PEFs to TIFs.

In Images Plus I select Automatic Image Set Processing, tell it where my image and flat are located, and click process. The result is the bottom image. There is some alignment error since a couple of spots in the upper right are not completely erased. I don't see this in my astro images, but then I combine dozens of images to make one final.

Down side of removing spots with a flat is:
You need to take the flat with similar focal length, soon enough that the dust has not changed. new dust will remain dark, dust that falls off will be white.
You need a flat source such as a light box, photo lab flat white panel, grey or twilight sky.

Up side of using a flat is:
You remove all spots at once. You replace the dim spot with whatever SHOULD be there since the color, texture, etc peek through the dim spot. Using a clone tool brings over whatever is nearby. Flat sky is easy but what about complicated things like the spot on the needles of the tree?

It is not for everyone. I'll rarely use it for daytime photos but I always use flats darks, and bias images to calibrate for Astrophotos.

Attached Images
 

Last edited by LeoTaylor; 04-04-2007 at 04:36 PM. Reason: Fix spelling
04-04-2007, 03:07 PM   #9
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The original file I uploaded was 600 pixels wide, but too tall for the forum. Here is a link to the 600 * 1200 flat demo:

http://pages.cthome.net/astroleo/flatdemo1.jpg

If you tell your browser to show it actual size you can see the spots clearly.

Last edited by LeoTaylor; 04-04-2007 at 04:37 PM.
04-04-2007, 10:06 PM   #10
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those spots look very detailed and contrasted. are you sure that they are not under filter specks?
04-05-2007, 05:35 AM   #11
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QuoteOriginally posted by skaktuss Quote

those spots look very detailed and contrasted. are you sure that they are not under filter specks?
I don't think so. After reading your letter I blew the sensor off with my Giotto Rocket Blower and removed about 2/3 of the spots including the most offensive ones. I acquired a particularly dark blob on the right edge, so cleaned again and the new one is now gone as well.

Software used for amateur astronomy is designed to bring out subtle details. It will automatically set the white level just above the grey and black level just below the spots. I also used a manual Sigma lens at 210mm f8 on a cloudy day which will accentuate the spots.
04-05-2007, 05:57 AM   #12
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May not be as effective with the K10D as the dust specs have a knack of moving from shot to shot.
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