Design standards for computer-generated teaching slides

Projected digital radiologic images for teaching: balance of image quality with data size constraints

RATIONALE AND OBJECTIVES

The authors performed this study to determine, in the context of a teaching presentation with slides, the information content needed in a digitized radiologic image for it to be equivalent in quality to an analog image.

MATERIALS AND METHODS

Eleven sets of radiologic images were obtained from a teaching file collection and digitized. The images were scanned at high resolution and saved as image files. The information content of each image was then halved repeatedly with repeat sampling of the image. This procedure was repeated nine times to yield a total of 10 images with an information content that ranged from very low (32 kB) to high (12 MB). Each of these image files was made into a 35-mm slide by using a digital slide maker. The original radiographs were subsequently made into slides by using conventional photographic methods. Care was taken to make the images identical in every respect except digitization and information content. The slides were shown to radiologists, who filled out questionnaires to rate image quality.

RESULTS

Digitized slides that contain an average of 416 kB of data (the equivalent of a 750 x 570-pixel matrix with 8-bit gray levels) were equivalent to analog images for 90% of viewers. At 830 kB (1,060 x 800-pixel matrix with 8-bit gray levels), 100% of viewers found no difference between digitized and analog images.

CONCLUSION

Digital images become indistinguishable from analog images if a sufficient amount of information is retained in the digital image. There is a defined relationship between the perception of quality and the information content of a digital image.

Computer-generated slides: outdated technology or state-of-the-art presentation style?

With the explosion of computerization, it appears that the business community is switching to computer-based presentations, projecting onto a screen directly from a computer, instead of the old standard of presenting with slides. However, the dental profession has been slow to follow. Although some speakers have switched to computer-based presentations, slides are still the standard in 1998. With the advent of numerous new computer software programs, clinicians are now able to generate highly sophisticated slides, that can be an equally powerful medium to communicate with the audience. Unfortunately, many clinicians are not taking advantage of the benefits of this technology. This article explains the simplicity of generating professional, high quality slides, reviews the major programs and equipment available to accomplish this task, and previews the multitude of applications this technology offers to practitioners as well as educators.