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I digitize B/W photos using an old CanoScan FB630U scanner and VueScan under Mac OS X. I scan these photos as 600 dpi tiff files. Some files show a longitudinal banding (in the same direction as the scan unit is moving). I cleaned the scanner several times (not on the inside), the problem persists.

What is source of this banding and why does it affect just some of the image (same kind of photos, same settings)? How do I fix it?

Thank you for your help.

sample image 1sample image 2

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1  
I think I had a comparable problem with negative scans on a Canoscan 8000F. The source of my problem was that the negatives were curved a bit. This resulted in them not lying on the glass evenly and flat. The parts that were pushed to the glass more than the rest showed a comparable banding. I had to flatten the negatives such that they lay evenly on the glass to minimise this problem. As I'm not sure that this is the solution, I'm not posting this as an answer –  Bart Arondson Aug 22 '13 at 22:21
    
@BartArondson Thank you for your comment. I tested your hypothesis with several scans. No matter where I moved the photo or how I pushed it onto the glass I could not achieve different results. –  lejonet Aug 22 '13 at 22:36
    
If you scan the photos in the opposite orientation (portrait vs landscape), does the banding change direction? If so I suspect it is a mechanical artifact of the scanner. –  Patrick Hurley Aug 22 '13 at 23:54
    
@PatrickHurley When I change the photo’s orientation, the banding changes its orientation on the photo as well. –  lejonet Aug 23 '13 at 0:23
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@MichaelClark I am sorry, my previous comment was mistakable (I am not fluent in English): With the photo turned, the banding doesn't change it direction relative to the scanner, but to the photo's content. –  lejonet Aug 23 '13 at 12:10

3 Answers 3

up vote 6 down vote accepted

Such banding is not uncommon, you have a a few choices on how to proceed.

Option 1: try and fix the root cause of the problem -- the scanner.

Odds are there is a (very small) bit of dust on the scan head, try opening up the scanner and using a rocket blower or similar along the scan sensor. Of course this involves opening the thing up and depending on you and your experience this may not be something you want to try.

Option 2: fix it in post

Scan a completely black sheet of paper (or better yet get a print of an image of the same size and finish as the photos you are scanning filled with the black point from one of the photos). Bring both scans into photoshop with the "black scan" as a layer on top of the original. Change the blending mode to overlay (also try linear burn and soft light) and adjust the opacity down until the banding disappears. You will probably have to push up the contrast after as this will flatten the look.

Option 3: pick up a new scanner :-)

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Thank you for your answer. I started disassembling the device and removed the two plastic parts on both sides of the glass (they are glued to it and jammed between the plastic on the other sides of the glass). I am not sure how to proceed, the glass is still kept in place by the plastic body which seems welded(?). Unfortunately the device is to old for disassembling instructions on the internet. Adjusting it in post-processing is no option for me right now, scanning is already time consuming. –  lejonet Aug 23 '13 at 12:05
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Well you may want to try scanning at a lower resolution, it may help (or make it worse, depends on the scanner and software). You can also try opening a hole in the side of the scanner with a dremel and using flexible tubing (like from an aquarium) to try and blow the scanning mechanism, used this scanner is going for ~$20 so the risk is not too large :-) –  Patrick Hurley Aug 23 '13 at 13:25

Your scanner ought to have some sort of calibration tools to help reduce this effect. You have a row of individual sensors that scan out the length, or in your case the height, of the original. Adjacent sensors have different sensitivities.

I wouldn't necessarily say that your scanner is faulty, just that it needs to be recalibrated.

Check the documentation that came with the scanner. There should be some calibration tools for it.

Googling 'scanner calibration' could lead you to some tutorials and possibly even some software.

Here's a link that might be helpful: http://fullypsyched.com/calibrate-canoscan-scanner-remove-lines/

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Thank you for your answer. There is no support for current Mac OS X versions anymore, so I won't be able to run this software. If I found an older Windows installation, could I calibrate the scanner using this system and use it afterwards calibrated with VueScan under Mac OS X? –  lejonet Aug 23 '13 at 22:01
    
@lejonet8, I added a link I found that might be helpful. I'm not sure if it applies to your model. –  Octopus Aug 24 '13 at 4:53
    
If the problem always occurs in the same areas on the scan -- not the print -- then it is likely a calibration issue. However if it is tonal in nature -- effecting dark areas more than light, regardless of location -- I am going to stick with the sensor dust theory (especially given the age of the scanner). –  Patrick Hurley Aug 24 '13 at 12:12

Those bands look to me like uneven movement of the scan head. There may be a sticky part on the rails on which the scan head moves, like lubricant dried off or similar. There could be just an accumulation of dust somewhere inside, the scanner being so old, and the clump of dust (or other particles) makes the scanhead momentarily stutter, like jumping small distances over the sticky part.

Whatever, it looks similar to what I got 20+ years ago with a handheld scanner. It was of crucial importance to keep it moving steady. Uneven movement causing banding, similar to what you now have.

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