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126. Vertical Lines Appearing On Scanned Documents

When you scan documents and you see a vertical line down the image that is not on the physical document, this is often caused by a contaminant like dirt or dust build-up on the scanning lamp/lens assembly glass. 

A customer often calls and say they have black lines, grey lines, or different coloured lines on their scanned images. Why are the lines on the images different colours? Well it depends whether you are scanning in B&W mode, greyscale mode or in colour mode. B&W mode would have black lines. The greyscale mode would have different shades of grey lines... Colour mode will often have different colour lines (red and blue seem to be quite common).

When scanning in colour mode the lines are different colours because the dirt/dust/sticky tape on the lamp/lens is often slightly transparent (i.e. it allows slight to pass through it) and the contaminant causes the normally flat scanner lens glass surface to act more like a prism that scatters white light (like raindrops causing a rainbow). So the scattered light may accentuate one colour over others and that is why we see the different coloured lines on the scanned pages.

In over 26 years of dealing with these types of issues, almost every issue is caused by dirt/dust/sticky tape building up on the scanner lamp/lens assemblies that the paper passes over inside the scanner throat. The scanner throat needs to be cleaned several times each day, and definitely before the start of each day's scanning.

I can’t stress enough that it can often take up to 5 attempts to fully clean off the built-up contaminant on the scanning lamp/lens glass surface so that it’s no longer causing unwanted lines on the scanned image. Don’t give up after just 1 attempt to clean it off, please try several times. Take your time, and do it thoroughly as explained below.

We recommend cleaning the scanning lamp/lens assembly glass lens with the scanner vendor-approved cleaning cloth (e.g. isopropyl alcohol pad) to remove any build-up of dust or dirt from it. If you don't have an isopropyl alcohol pad and need a quick fix then a slightly moist Kleenex tissue could be used. Some scanners also require daily wipe-down with staticide wipes. Those wipes help stop the build-up of static electricity as the paper passes through the scanner's throat. The static electricity builds up on the glass lamp/lens assemblies and attracts dirt and dust that over time stick to the lamp/lens glass surfaces.

What’s the best method to locate the offending dirt/dust/contaminant on the lamp/lens glass? Experience has taught us that if you run your fingertip lightly and very slowly across the lamp/lens assembly you will often feel the dirt or dust build-up. This is often a more reliable method of finding the contaminant than just looking at the lamp/lens glass assembly. When you clean the lamp/lens you do need to use some light pressure to dislodge the contaminants from the lamp/lens glass.

Another common issue is not actually cleaning the correct scanner lamp/lens glass assembly. If you have a duplex-enabled scanner your scanner will have 2 scanner lamp/lens assemblies. One lamp/lens scans the front side of the paper, the other lamp/lens scans the rear side of the paper. So you need to make sure you are cleaning the correct lamp/lens assembly that is causing the vertical line on the scanned images. If you are convinced the scanner lamp is clean but you still get the lines, try cleaning the other scanner lamp/lens assembly. 

One fail-safe way of determining where the dirt/dust build up on your scanner is located (i.e. is it on the top lamp/lens or the bottom lamp/lens, or on both) is to create a test page by taking a sheet of A4 or  Letter paper. On one side write the words ‘face up’, with one number from 1-4 written in each corner (top left =1, top right =2, bottom left = 3 and bottom right = 4). Now turn the paper over like turning a page in a book, and write ‘face down’ on the other side, with one number from 5-8 written in each corner (top left =5, top right =6, bottom left = 7 and bottom right = 8). Use a normal black pen to write the words and numbers.

Once you have created the test page, take that page and place it in the scanner in-tray with the words ‘face up’ so you can read them when you look down into the tray. Press scan and look at the resulting 2 scanned images. If the image with the words ‘face up’ written on it has the lines on it, then you need to clean the upper lamp/lens in the scanner throat (i.e. the lens that looks down onto the top of the paper sheets fed in from the in-tray). If the image with the words ‘face down’ written on it has the lines on it, then you need to clean the bottom lamp/lens in the scanner (i.e. the lens that shines up onto the paper sheets fed into the in-tray).

99.9% of the issues of extra unwanted lines appearing on scanned images can be traced back to improper cleaning. Scanners must be cleaned daily, and in high usage situations, several times a day. Keeping the scanner clean is the customer’s responsibility. Service calls for problems caused due to lack of cleaning or infrequent cleaning are considered to be billable by most service companies.

The other 0.1% of issues that cause unwanted lines, are physical scratches on the scanner glass caused by staples or paper clips passing through the scanner throat. It’s very rare to see this. Even when people are convinced the glass is scratched, our service department finds it just dirt/duct/sticky tape built up on the glass surface. Repairs/replacement of scanner glass assemblies due to scratches caused by the customer’s poor document preparation process (i.e. the failure to remove metal staples and paper clips from documents prior to scanning) are considered to be billable by most service companies.

Please check out FAQ 143 if you are having trouble with black edges appearing on your scanned images.

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