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UltravioletPhotography

Removing dust spots, etc., from images


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There's a discussion in another thread about techniques for cleaning sensors, but what if it's too late and you've already made an image and it's got dust spots on it? The Spot Healing tools in software products like Photoshop and GIMP are great for individual spots but become less usable if there are lots of spots or they're in difficult places to edit. Is there any software to do the job?

 

I had a look round and there are two dust and scratch removal products that get a lot of mentions:

  • Silverfast SRDx. This costs about $/EU 50 - which wouldn't be a problem if it does the job, but it comes as a plug-in for PhotoShop (inc. Elements v13 or later) - which I don't have.
  • Polaroid Dust and Scratch Remover - from back in the day when Polaroid made things rather than just being a trademark that anyone could buy. This is available as a free download (https://polaroid-dus...n.softonic.com/) but was intended for Win 98 or earlier. Like Silverfast, it was aimed at the blemishes brought across with scanned negatives and slides, but I though I'd give it a try with blemishes arising from sensor dirt.

Although being written for obsolete verions of Windows, it installed and ran on Win 10 without any problem. (If you search you'll find references to later versions of Windows, and someone saying that Ken Rockwell has a link for a Mac version, but these must be mods. that someone other than Polaroid made.)

 

Does it work? Yes, to a good degree. But it's not a perfect solution, and doesn't get around the need to keep your sensor clean.

 

Basically the software operates by creating a mask of defects (which can take quite a long time) and then applying the mask to create a clean image. When using the Auto Create Mask tool, there are 4 options, and the best settings for me were:

  • Tile Size = 8 (minimum)
  • Defect Level = 100 (maximum)
  • Mask Size = 16 (maximum)
  • Adaptive Filtering On

The higher value of Mask Size is needed to remove the blemishes arising from sensor dust, but it does have some impact on the image if there is a lot of detail. However, the dust problem is typically most noticeable in areas which are flat and lacking detail. So if possible it is better to use the Select tool to select the areas of the image which have the dust problem, and then the Auto Create Mask tool works only in these areas. This also has the benefit of reducing the time taken to create the mask. You can repeat the Select+Create Mask operations multiple times before creating the clean image.

 

An example of the results is given below. When entering the parameters for the Auto Create Mask tool, you can also specify whether the blemishes are dark or light. Sometimes (esp. with extreme macro images), you may need to run the process first for light blemishes and then again for dark images: this is because the blemishes may consist of a dark core with a light outer surface, presumably caused by diffraction.

 

In the three images below:

  • the first image is the original. with lots of crud in the sky area.
  • the second image used the Auto Create Mask tool to generate a mask for the whole image. The dust spots have been removed, but you can see that the trunks and branches in the tree have been degraded - although the more detailed houses have come out OK.
  • the third image used the select tool to pick up just the sky and tops of the waving trees. So the dust marks have been removed from these areas, and the rest of the image has been left as in the original.

This example is in monochrome, but the tool works fine in colour as well.

 

post-245-0-67602600-1593527093.jpg

 

post-245-0-13836800-1593527093.jpg

 

post-245-0-61953800-1593527092.jpg

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The Polaroid program is 32-bits thus no surprise the website claims it is compatible with Win10, which it in fact is. I think probably best to run it as a plugin in PS to avoid cluttering up the work flow too much.

 

My momochrome NEX-5N has a lot of sensor dirt and crud on it and certainly would benefit from some kind of retouching tool. Whether the Polaroid option is the way to go remains to be seen. I'll experiment and come back later.

 

For Nikons, you can make a "blank" for automated noise reduction in Capture NX-D. would be nice to have something like that for the Sony..

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For Nikons, you can make a "blank" for automated noise reduction in Capture NX-D. would be nice to have something like that for the Sony..

 

Canon has a similar idea but specifically for dust (rather than noise), called Dust Delete Data. You take a shot of a plain background, and the camera then sees where all the dust is, and attaches dust deletion data to each JPEG and RAW file thereafter. Then you process your image using Canon's Digital Photo Professional, which reads the dust deletion data and automatically does a spot healing process for each bit of dust. And you can set this up for a batch of images - great for focus stacking.

 

Perfect. Except I can't get it to work, at least not for extreme (i.e. using bellows) macro shots, which is really what I need this for. I always get the message "Cannot apply Dust Delete Data".

 

I use a Sony A6000 for UV & IR, and that doesn't have this facility. But anyway I've decided to give up on extreme UV and IR macro because the image quality is so poor - far worse than for visible using the same lens. So I'll only be doing extreme macro in visible, using Canon kit - so it would have been really neat if Canon's Dust Delete Data worked.

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Bernard, thank you for the review of these tools.

 

I have spent a lot of time cleaning sensors. And I have spent a lot of time using healing tools to click away dust spots. It was ever thus on both counts!

 

I had trouble with the old Nikon Capture dust delete mask also. Never could get it to work properly. (Not sure what it was called.)

 

In the old Nikon Capture app, it was possible to save their healing brush clicks as a preset. This helped with a lot of photos where the healing clicks were on a background or on a non-detailed area of the photo. It did not work quite as well when the dust spots were on a detailed subject - similar to what you have mentioned for the tools under review.

 

I suppose our only recourse it to continue to try to keep sensors clean. Such a pain though!!

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