Image Quality

In this experiment I scanned the same image at a low resoultion (72 dpi), each time using a differnet scan type on a HP ScanJet IIc (Color Photo, Sharp Color Photo, Millions of Colors and Sharp Millions of Colors). The two Color Photo scans are 8-bit, while the Two Millions of Colors scans are 24-bit. While I found quite a range in overall image quality from lowest to highest, I did not find image 1 less readable than image 4. For the purpose of displaying these images on a Web brower such as Netscape or Mosaic, I think that the images with less dynamic range (or bit-depth) are of adequate quality. In most cases the images would be clear enough for most users needs. However, are these images (such as 1 and 2) still of sufficient quality for republication in a digital format? I'm not certain that the grainy quality of images 1 and 2 would be enough to discourage someone from trying to re-use them in an unauthorized way.

The repository should not be too concerned about the user who might want to download a copy of a particular image for inclusion on their personal home page. It is the situation where a user intends to use the image without permission or credit in an electronic publication about Joseph Labadie or American Anarchists that needs to be addressed. Kevin Comerford, of The Dallas Museum of Art, has recieved several requests from CD-ROM publishers and data-base vendors who wish to use the low resolution images from the museum's Online exhibit for commercial purposes. The point he makes is that anything you put on the Internet has potential commercial value to someone else, even when you have gone to some lenghts to protect your property (in this case by using low resolution images and altering the dynamic range).

The examples with a greater dynamic range (3 and 4) are certainly more attractive in terms of clarity than the previous two examples. If I were concerned about the unauthorized re-use of these images, I would not tempt potential pirates with the highest grade digital facsimilies possible. Furthermore, I would identify the image with a label bearing the name of the repository, along with a notice of copyright

See next page for a discussion of labeling.



Image 1

Scanner: HP ScanJet IIc
Scan type: Color Photo
Scanned at: 72 dpi
Mode: RGB Color
Saved format: JPEG (medium quality)
File size: 33K

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Image 2

Scanner: HP ScanJet IIc
Scan type: Sharp Color Photo
Scanned at: 72 dpi
Mode: RGB Color
Saved format: JPEG (medium quality)
File size: 34K

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Image 3

Scanner: HP ScanJet IIc
Scan type: Millions of Colors
Scanned at: 72 dpi
Mode: RGB Color
Saved format: JPEG (medium quality)
File size: 23K

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Image 4

Scanner: HP ScanJet IIc
Scan type: Sharp Millions of Colors
Scanned at: 72 dpi
Mode: RGB Color
Saved format: JPEG (medium quality)
File size: 19K

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Return to Introduction / Go to Labels
Cameron Trowbridge
cambridg@umich.edu