Reduced dynamic range when scanning at 600dpi or lower (Officejet Pro 8500)

By LoekV
Feb 10, 2014
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  1. Equipment: HP Officejet Pro 8500 (A910)
    OS: Windows 8.1 64-bit
    Software: VueScan and HP Scan (both yield same result)

    I noticed that when I scan a document at a resolution of 600dpi or lower, the dynamic range of the scanner is significantly reduced at the high brightness levels. For example colors that are very bright, but not entirely white, all get mapped to 100% white.

    See for example the figure below (please download and view at 100% to see the details properly): I did two scans, one at 2400dpi and one at 600dpi. I then downsized the 2400dpi version to 600dpi and compared the two. As can be seen, patches with a white level of 36 and lower (almost 54 too) are getting output to complete whiteness when scanning at 600dpi. This is not the case when scanning at 2400dpi (in fact for all resolutions of 1200dpi and higher); the patch with '18' still is light gray instead of complete white.

    [​IMG]

    Download the full resolution picture: https://dl.dropboxusercontent.com/u/38472922/2400dpi_600dpi_comparison.jpg

    Besides the reduced dynamic range, there seems to be some noise reduction and contrast/sharpness enhancement applied for the 600dpi scan (noise reduction because the individual dots (can be seen when the figure is viewed at 100%) are really smeared out compared to the 2400dpi scan, and sharpening can be seen by the bright halos around the '90' and '108' characters).

    Is there a setting that avoids reducing the dynamic range (and the noise reduction/sharpening) for scans at 600dpi or lower? I want the same dynamic range as at 2400dpi, but I want to scan at 600dpi or even 300dpi because that's enough for print output and I get smaller file sizes.


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