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

[Loek]

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.

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.

 

[piasabird]

Using a Fujitsu fi-6140z Duplex Scanner.

My guess is for black and white you don't need much over 600 dpi.

There are a lot more possible settings than what your are looking at for scanning. I use some software called Kofax VRS and it lets you adjust the quality of the scan. This is why Scanners are expensive. The software is pricey. Kofax VRS Elite is very expensive. We use an OEM Version. Some scanners come with some version of this or something like this.

There are settings like line weight, brightness, Contrast, Gamma and Speckle size. Then there are setting to auto rotate the image for text. I am not positive about resolution settings (dpi). However, we can also choose B & W, Grayscale and Color. If you select adjust quality you can play with the settings for best quality. I copy a lot of different type of hand written forms with pencil and ink, and some Transcripts and other difficult things to scan.

My default setting:
Line 5
Bright 64
contrast 75
Gamma 17
Speckle 0
Auto Rotate on
Delete Blank Page - Delete

Transcripts
My default setting:
Line 8
Bright 26
contrast 32
Gamma 22
Speckle 12
Auto Rotate on
Delete Blank Page - Off
Adjust Quality - every page
Duplex.

 

[Loek]

Thank you for your reply.

I can only change brightness and contrast using the HP software. Varying these parameters did not make any difference at all (white levels up to 36 are still completely blown out when scanning at 600 dpi or lower).

I know that I would probably get better results using a more expensive scanner. But I wanted to know if it's possible with my HP scanner .