In the Department of Psychology at UC-Davis, I teach a class in Environmental Awareness that attracts many design and landscape students. As one aspect of this course we consider how the physical and visual characteristics of one's immediate surroundings have an impact on perception and behavior; the course thus has a unit that deals with the psychology of color. At the same time, I have also been conducting my own further research on color aesthetics. This research often involves asking classes to rate geometric figures presented on the screen in different hues. Students judge, in quick succession, the relative attractiveness of a green triangle, a brown semicircle, and so on. As crucial part of my teaching as well as my scholarly work, I have therefore relied upon accurate reproductions of colored graphics and photographic images.

Five years ago, I would have made color slides for a carousel projector. Like many of my colleagues, however, I switched to PowerPoint slides in my teaching. I gradually replaced my overhead transparencies and 35 mm slides with digital images—an initial transition that I have described in a previous in this journal (2002). The advantages of PowerPoint are undeniable: less bulk, the ability to do everything from the front of the classroom, the option of showing slides in a lit room, simplicity of revision, and ease of combining words and text on the screen. The only disadvantages I saw were lower image resolution relative to 35 mm slides, the initial investment of instructor time in learning the software, and the resources required for the new technology.

However, it was not until my study of color aesthetics that I became aware of an additional disadvantage that was not being discussed, at least among faculty: the color distortions that are all-too-common in the use of PowerPoint slides with digital projection. In this article, I outline the problem I faced and the steps I took to investigate and remedy it, with recommendations for other instructors who may confront this situation in their classes.

PowerPoint and Classroom Projection

The colored geometric figures used in my research were created by my technologically-advanced partner Barbara Sommer using Adobe Illustrator software with the RGB color palette. I was amazed at how quickly she constructed and edited the figures. In the old days, I would have traced the outlines on colored construction paper, cut them out with scissors, pasted them on white paper, and photographed them using a macro lens or paid a photo lab to perform this last step. With Adobe Illustrator software, however, Sommer created the figures in an hour and gave me choices among dozens of hues. It was a snap to create several random presentation orders in PowerPoint. The colored figures looked fine on my laptop and also on the desk monitor which I use for editing

Yet when I showed the PowerPoint images in class, I was appalled by the poor rendition of some colors. The hues were washed out, the blue which I had carefully selected came out purple, and red was mysteriously transformed into brown. After class, I returned to my office and rechecked the images on my desk monitor. The hues looked fine. I decided that the problem must lie with the projector in this particular classroom. I went to another room to view my PowerPoint slides, and I was amazed to find equally significant but different color distortions in the second room. A visit to a third room produced a third set of distortions, not the same as in either of the other two rooms.

As a psychologist whose interests include perception, I was fascinated with this problem and saw that it would be a relevant issue to discuss with my class. Together, we closely inspected the colors displayed on the screen. The first thing I noticed, now that I was explicitly attending to hue, was that the colors on my screen saver image were incredibly washed out on the classroom screen. This was personally embarrassing as I had painted this scene myself and knew that I had used brighter colors than the students were seeing. I also noticed significant distortions in hue that were less easy for others to observe because of perceptual constancy. This refers to the tendency of people to see the world as they know it rather than as it appears on the retina: Constancy keeps the perceptual world stable amidst a changing sensory panorama. For example, we typically see a white piece of paper as white regardless of whether it is viewed in bright or dim light (color constancy) and a door as a rectangle regardless of whether it is closed or open when its retinal image is trapezoidal (shape constancy). My students had perceived the California hillside on my screen saver as tan and the tree foliage as green, because that is how they knew the world to be, rather than seeing the distorted colors on the classroom screen. I myself had not previously noticed color discrepancies in the case of certain images, whereas I now noticed them in many images. While this unexpected problem allowed for a serendipitous pedagogical illustration of perceptual constancy, I still needed to solve the problem for our other classroom activities.

I first questioned fellow instructors in the Department of Psychology. They hadn't experienced any problems, as they employed PowerPoint primarily to show text and numerical tables. Whether the letters, numbers, or background on a PowerPoint slide appeared on the screen in ultramarine or cerulean blue was of little consequence to them. For the occasional pictures of actual scenes, my colleagues were also subject to the same color constancies that had kept me from noticing distorted hues. There were so many other things happening, so many pressures on us to attend to content and to student response, that color problems went unnoticed, especially since the students didn't report this as a problem. None ever told us, "Hey professor, those colors on the screen are terrible." In addition, we had little incentive to go back and edit minor distortions in slides that we would not use for another year.

Next I went to the technical assistants who maintained the classroom projection systems. They were aware of the distortions. From them, I learned that every projector interacting with a different classroom environment produced different distortions. They said that there was no way to predict in advance how a hue would appear in a specific classroom, and that this also applied to portable digital projectors. They also noted that this was similar to the picture qualities of household TV sets, which are also subject to idiosyncratic distortions. I visited a large discount electronics store which had over a hundred TV sets on display, many tuned to the same station. I was amazed to see the variations in color, even on models from the same manufacturer.

The variability is idiosyncratic to individual display systems. It is not simply that all Brand-A projectors make scenes brownish and Brand-B projectors make them bluish, but that the projector in Room 126 Weldon Hall made things yellow while the same model projector in the adjacent classroom was subject to different color distortions. The technicians could help me standardize the hues in a specific classroom (provided we could visit the room together during a rare time of non-usage during a technician's working hours), but they could offer no assurance that the hues would be similar on a different display system. Because the basis of scientific research is reproducibility, this variability would be devastating for my research.

I saw no way of resolving this problem using digital technology. The only solution was to return to an older format. At a computer lab on campus, I used a film recorder to copy my PowerPoint images onto 35 mm slide film. Thankfully, color distortion in 35 mm projector technology was resolved decades earlier. The blue on the 35 mm slide also appeared blue on the classroom screen. There may have been minor discrepancies, but nothing like the major distortions I had experienced with digital projection.

Although it should have been obvious, I also found that dimming the lights greatly improved color saturation of PowerPoint images on the screen (although it did little correct distortions in hue). I also noticed, now that I was paying closer attention, that my PowerPoint images, even when shown in complete darkness, were less sharp than my 35 mm slide images. This was not a major concern for text and tables, but it made a huge difference in viewing landscape scenes and artwork.

Lessons Learned

When I began digitizing my paper slides, I thought that 35 mm slide projectors in the classroom were relics of the past, like the TV monitors hanging limply from wall brackets. Now that I have become aware of the color distortions in digital display systems, I no longer believe this. A TV technician told me that he would not recommend that an art history instructor, for example, adopt PowerPoint, and would suggest instead that the instructor continue using 35 mm slides.

I have since learned that Microsoft's sRGB standard, developed in collaboration with Mitsubishi, has attempted to address this problem. Mitsubishi has introduced a new line of projectors incorporating this technology, and Faroudja Laboratories claim to sell film-quality digital video processors. I have not had the opportunity to test one of these devices, but they may provide an effective way of bypassing the problems discussed above.

Lacking this option, one should use discretion when adopting PowerPoint slides for classroom projectors. When color matters, instructors will need to go to the actual room where their material will be shown, and then work with a technician to correct discrepancies. It may be necessary to make a new version of the presentation tailored for a specific projector and room. Guest lecturers should carry back up systems, such as overheads or 35 mm slides, in addition to digitized images.

I try not to critique color values in other instructors' presentations any more than I would complain about underexposed or overexposed images in a friend's home movie. There are politeness conventions to be respected. However, I think it is necessary to alert my colleagues to color distortions in digital projection before they discard their 35 mm slides (as I had planned to do) and also so that they can learn to override the color constancies that keep them from noticing distorted colors.

When making the transition to new media technologies, instructors often run the risk of rejecting previous forms that appear obsolete. Based on my experience, a more appropriate rule of thumb would be to always keep another set of options in reserve. Otherwise, even the most well-prepared instructor could end up singing the blues.

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