Removing dust from scanned slides with an infrared channel

Processing
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1

Hello,

I’m scanning old family slides and negatives with a plustek 8200i scanner. The file format is 64
bits RGBI tiff where the I in RGBI is an infrared channel that can be used to remove dust.

I was wondering if I could use GMIC to “easily” remove the dust with inpainting and using the information in the infrared channel. The algorithm would basically the following

  • select a threshold for the infrared channel (alternatively divide the IR channel by the red channel)
  • use what is over the threshold as a mask for the other channels
  • inpaint the other channels with the mask
  • save as 48 bits RGB tiff

I think GMIC has all the tools for that, but problem is that I don’t know to start.
Can someone give me some hints ?

thanks !

2

Hi, perhaps you can start here: Scanned image scratch removal with “ICE”

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thanks I will have a look !

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Shameless plug :wink:: G’MIC even has a plugin for that purpose: see Scanned image scratch removal with “ICE” - #69 by chris or maybe even start this thread from the beginning, it has e.g. some interesting comparisons of inpainting methods.

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Whoops, I didn’t mean to link to post #79, I meant to link to the start of the thread, lots of good stuff in there. post 79 may or may not be good, I don’t know :smiley:

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Can I ask what scanner you are using?

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Thanks it would be great if I manage to be able to use it !

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It’s a plustek 8200i

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The reason I asked was that I was surprised you were not using the software during the scan to remove the scratches. I am interested if you find any advantage in working with the RGBI files post scanning. I have an Epson V850 and could do the same, but am not sure if there would be an advantage. I am generally happy with the scratch and dust removal obtained during the scan. BTW, if you scan true black and white negatives the infrared option does not work for removing scratches.

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It’s because some of the slides I have need to be processed in 48 bits and the software provided by the scanner (silverfast) provides only 24 bits files when the dust removal function is used. Also some preliminary tests shown me that vuescan is faster to scan but the dust removal much less efficient. So I’m trying another way

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I have silverfast software and I just checked a scanned negative file I have saved and it is a 16bit per channel tiff file. Maybe there is a setting you are missing because I agree that I don’ want a 8 bit per channel scan for the post-scan editing.

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Thanks I will check, maybe I missed something. What version of silverfast are you using?

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Personally I bought Silver fast but I wasn’t the one doing the scans so I couldn’t trust the person properly check each slide and clean it up with optimal settings.

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Some thoughts …

While I do not have silverfast, I would always store the raw data including the IR channel and not the corrected image, as you may discover flaws of the correction later and without the original data it will be hard to discover or fix.

E.g., the VueScan inpainting is much less efficient for particular scratches than other solutions, here is the VueScan result and here a comparison of different inpainting methods from G’MIC for exactly the same scratches/dust spots.

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Silverfast is much better than vuescan on this point, but I will do a comparison with your script as soon as I can

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Since this topic isn’t about G’MIC but about processing scans, I changed the category to #processing with #gmic #scanner tags. Add more tags if you wish.

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I have Silverfast SE 8. I am generally happy with the scratch and spot removal. But I also use GIMP healing and clone tools if needed. I haven’t explored G’MIC so I am unsure what is available through that.