Scanning and noise

 The Canon 8800f scanner has made noises since I brought the scanner home. There is a youtube video on disassembling and cleaning a Canon 8600, which is similar to the 8800. There seemed to be no effect on scanned images, so I put the repair effort off.

Noise. There are several types of noise associated with scanners and scanning. 

Each scan injects some random noise into the image. The noise is different for each scan. 

The solution is averaging several scans of the same image. More scans is better than fewer. Realistically, the effect after four scans is minimal and three scan work in most cases.

There is a free astronomical imaging software program titled StarStax. This programs takes multiple scans of an image and 'stacks' them, mathematically. Corresponding pixels from each image have the values averaged an the result placed in a new image. This removes most of that type of noise.

With this in mind, I began the process of scanning the archive film. After a long session of scanning, I began the averaging process. I examined one of the finished images and found a blur. On closer examination, The multiple scans were not registered. They were misaligned. Eventually, I pinpointed the scanner as the problem. That's when I decided to attempt the repair.

The disassembly went well. The youtube video of an 8600 scanner was close enough to get me through.

Once I had access to the interior, I ran test scans to locate the origin of the noise. There were two lubricants used: 3-in-1 Oil and WD-40 spray lubricant. The oil was applied to the transport shaft and the spray applied to the other moving parts, excluding the belt area.

Re-assembly went smoothly. I ran several test scan to allow the lubricants to penetrate and spread. The repair was successful. All multi-scans were now correctly registered.

The next averaging task resulted in an improved image, one with less noise.

There is another form of noise, a bias in the scans. A solution is to scan a dark image. Cover the platen or lid platen with a black cover. This is called a dark scan  and is subtracted from an image to neutralize the effect of scan bias.


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