Robert's Web Resources Guide:
Scanner Resolution Tests

Optimal scanner resolution for WWW display

Suggestions for the inclusion of additional resources may be sent to: Robert Hershoff.

Purpose

In preparation for the Ronstadt Digitization Project, I wanted to determine the best methods for reproducing images from print format originals for viewing on the World Wide Web. A lack of documentation and the divergence of personal opinions on the "best" scanning resolution led me to conduct a series of tests for the variety of image types that might be encountered in the project.

Method

Tests were conducted in April 1997 using a Hewlett Packard ScanJet 4c flatbed scanner with DeskScan II scanning software. The hardware platform is a Dell P133 IBM PC clone with a 17" monitor. Images were scanned at 75 dpi and 150 dpi resolutions. The digital images were adjusted and formatted using Adobe Photoshop 4.0. Only automatic or preset adjustments were used to prepare the images, in order to maintain the consistency of the data. The goal of this study is to compare the general effects of scanning resolution on screen image quality, not to produce the optimum image for each example. Further adjustment in Photoshop would have improved the quality of these images.

Conclusion

Based on the tests, I have concluded that a scanning resolution of 75 dpi is appropriate for the preparation of most image types for display on the World Wide Web. One notable exception is the scanning of newspaper black and white line screen illustrations, which are best scanned at 150 dpi. (Though 75 dpi scans for newspaper black and white illustrations will produce acceptable images. Another area of potential inquiry concerns the potential beneficial effects of noise filters, Gaussian blur, and other Photoshop editing features on the moire pattern in lower resolution screen prints.

Individuals with additional information, different conclusions, or suggestions for further study are encouraged to contact Robert Hershoff.

Scanner Resolution Test Study Examples:

Note: some of these pages contain large image files, most conveniently viewed via an Ethernet connection
Click here to view the summary results

Black & White photographic images test page
Color Photographic images test page
Black & White Screen Print (from Newspaper) images test page
Black & White Screen Print (fine screen) images test page
Color Screen Print (from Newspaper) images test page
Color Images (continuous tone and fine screen) test page
Black and White Line Art images test page

Return to the Digital Image Information resources page

Return to Robert's Web Resources Guide Home Page