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Non correlated noise - speckles in scanned photographic images
I've been trying to scan some old black and white photos
( that I was trying to digitally archive) using a HP scanjet 4500c at 300dpi (256 greyscale). Recently, I noticed random white speckles/dots in places where the scanned image should be a uniform dark or black. The original non-glossy photo was old but clean and it did not have not any smudges or stains so I thought maybe it was just a dirty scanner - so I cleaned the exterior surface of the flatbed scanner glass and careful cleaned the interior surface of the glass surface. However, even after the cleaning the scanned images still had a significant amount of white speckles in them. So l researched the topic on the hp.com website. I appears - this type of random scanning error is called non-correlated noise and it is attributed to how light refracts off non-glossy photographic paper; HP.com suggests that one can reduce this type of error by rotating the original source 90 degrees when scanning. I noticed that rotating the original photo did reduce the scanning noise but it did not eliminate it - the white speckled scanning errors just appeared elsewhere in the image. So I tried another scanner, HP 2200c, but I got similar results. So far I haven't found much information on the internet about how to get rid of this type of scanning error...does anyone have a solution to this problem short of fixing the problem in photoshop? |
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Non correlated noise - speckles in scanned photographic images
"drydem" wrote in message
ups.com... I've been trying to scan some old black and white photos ( that I was trying to digitally archive) using a HP scanjet 4500c at 300dpi (256 greyscale). Recently, I noticed random white speckles/dots in places where the scanned image should be a uniform dark or black. The original non-glossy photo was old but clean and it did not have not any smudges or stains so I thought maybe it was just a dirty scanner - so I cleaned the exterior surface of the flatbed scanner glass and careful cleaned the interior surface of the glass surface. However, even after the cleaning the scanned images still had a significant amount of white speckles in them. So l researched the topic on the hp.com website. I appears - this type of random scanning error is called non-correlated noise and it is attributed to how light refracts off non-glossy photographic paper; HP.com suggests that one can reduce this type of error by rotating the original source 90 degrees when scanning. I noticed that rotating the original photo did reduce the scanning noise but it did not eliminate it - the white speckled scanning errors just appeared elsewhere in the image. So I tried another scanner, HP 2200c, but I got similar results. So far I haven't found much information on the internet about how to get rid of this type of scanning error...does anyone have a solution to this problem short of fixing the problem in photoshop? I have not seen the white speckles/dots on any photos that I have scanned on my Canon 8400F. You might try the descreen function and see what happens. If you are scanning a photograph that is on textured paper, Descreening may help. The textured pattern would appear as a halftone screen to the scanner. If the scanner does not have a descreen function in the driver, you can try scanning at a much higher resolution, try 1200 DPI. You can reduce the file in a photo editor afterward if that takes care of the speckles/dots. Moire http://www.scantips.com/basics06.html Manual methods for descreening: http://www.scantips.com/basics6c.html -- CSM1 http://www.carlmcmillan.com -- |
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Non correlated noise - speckles in scanned photographic images
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Non correlated noise - speckles in scanned photographic images
On Nov 3, 8:51 pm, MoiMoi wrote:
In article . com, says... I've been trying to scan some old black and white photos ( that I was trying to digitally archive) using a HP scanjet 4500c at 300dpi (256 greyscale). Recently, I noticed random white speckles/dots in places where the scanned image should be a uniform dark or black. Make a scan. Move the pic to different place on the scanner. Make another scan. Are the speckles in the same place? no. If so, look at surface of print with loupe, and you'll find your speckles. MM I used photo editor zoom function to find the random speckles. |
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