Angles Of View
Steven J. Orfield is President of Orfield Associates, a consulting and multi-disciplinary research laboratory in Minneapolis, MN which specializes particularly in the evaluation of perception. A frequent contributor to trade and technical journals on subjects ranging from acoustics to visual presentation, Mr. Orfield is interviewed here on the subject of
Visual Intelligibility - What Are We Looking At?Da-Lite: How do you distinguish between perception and presentation?
Orfield: The classic little metaphor that works to describe all perception is
SourceÞ PathÞ Receiver.
Presentation emphasizes the first two, perception ivolves the third. A good portion of my business comes from perception. We do a lot of work characterizing not what can be measured from a product but how people respond to a product and what they associate with their response.
So, when people look at a visual display I want to know not just if they think it’s bright, I want to know if they think it’s high quality. If they do think it’s high quality, then I’d like to be able to correlate that with how bright it is (or how even it is, or how good is its resolution). This is why we’re not so interested in the absolute value of the measurement as we are in the associative characterizations of the viewer.
Da-Lite: From this perspective, what are some of things you’ve learned about quality in visual displays?
Orfield: We have done a study (with Da-Lite’s help, I might add) on this question and the number one conclusion that it reached was that the only way to evaluate the quality of a visual image is to evaluate the amount of information that one can gain from it in a given time.
Da-Lite: And how do you go about measuring that?
Orfield: Well, with video the analysis is generally given by a set of statistics related to its transfer function: How well does a particular video display system accomplish the transfer from Source to Receiver? The answer has generally relied on the notion of accuracy. How closely does what I’m trying to do replicate an ideal solution?
Notice that the underlying assumption here is that if your projected video was exactly the same as the image it captured then you’d have perfection.
Da-Lite: -Is that unreasonable?
Orfield: Not at all. You just have to be careful about your measuring assumptions. An accurate transfer function in one circumstance may be wholly inadequate in another. Yet one of the big problems you see in video is the assumption that you either have a good system or you don’t. And if you do have a good” system, no matter what you put on it, it’s OK.
Da-Lite: Is your point that even the acquisition and assembly of top quality components may not produce an effective display?
Orfield: Exactly. If some members of the audience can’t make out what they’re supposed to from the screen, it may well be that upping the character size of the text could alter the perception of the screen and its quality more dramatically than changing the screen itself.
I believe one of the greatest services the video industry could do for its clients is to define in fact what constitutes appropriate displays. Developing a useful model for visibility of visual displays will have to include some sort of conclusion about what is the minimum amount of detail a person needs to see. And then that standard will have to be indexed against the age demographic of the viewer.
Da-Lite: The age question seems inarguable. Older viewers are statistically less likely to enjoy the same visual acuity as younger members of the audience. But a standard suggesting what constitutes minimum detail seems much more problematic. Isn’t looking at slides of the Grand Canyon (for example) a visual task hugely different from analyzing a complicated spreadsheet?
Orfield: Of course; but what’s the currency of the issue? In other words, some visual tasks have what’s called "Failure" as a possible outcome. Other visual tasks don’t. If you see less detail in a scenic image, it may well constitute less quality, but its generally not semantically considered failure.
So there are two types of visual tasks: those that embody the potential for failure and those which entail only quality issues.
Da-Lite: Could another way of labeling these two groups be Seeing vs. Reading?
Orfield: Sure. That’s distinguishing between a screen full of visual information and a screen full of cognitive information. In the latter case things can often get a lot more complicated than just reading.
Da-Lite: What do you mean?
Orfield: Reading is linear information gathering. Confronted by a projected page of text, everybody knows to start in the upper left hand corner of the screen and scan along the rows of characters, picking up pieces of data.
Images like maps or schematics, however, are what I call complex visuals. The process of looking at them is not linear. It’s generally not clear where you’re supposed to start looking. It’s a search task; it’s a detection task; it’s a sort task. Complex visuals are, therefore, much more demanding and unpredictable than pages of ordinary text.
Da-Lite: Given, then, this tremendous range of possible content, however is the A/V industry going to establish standards for reliably intelligible displays?
Orfield: I think that as you look at a dealer and a designer and their problems with video systems, there are two very important questions which sometimes don’t get asked. What are you going to display? And, Who’s going to view it?
These are the biggest issues that can cause a system to fail. It’s useful, for instance, to tell a client that if his display falls below this sort of characterization, it’s going to be too hard to see. Let’s don’t design this way. Don’t display below this size for information.
Also of course it’s very useful to consider who’s viewing. The problem here is that a lot of data which would be pertinent simply isn’t available. There’s very good reason, for instance, to have a body of research done that would characterize what happens with people’s viewing of different kinds of visual systems with age.
We do know that as we look at depreciation in vision and hearing that it’s bad for women and it’s worse for men. But if I want to consult a study of what an optimal display is and how it changes as you move from 20 to 70 years old, I won’t find it. It’s not in the literature. So these sorts of demographic issues simply have to be databased. But that work hasn’t been done yet.
Da-Lite: Do you think there’s been enough work done on the quality of the display itself?
Orfield: Probably not. I think we ought to find a way to throw out all the current evaluation procedures for visual displays and come back in with the viewer. I think we ought to apply standardized tasks to various viewing juries and determine what really happens, what really is the quality of a visual system.
It may well be, for instance, that quality has other, more important characterizations than luminance. There’s a whole matrix of preference issues which needs defining and many of our intuitive assumptions regarding the value of, say, contrast or color saturation may not fit in that matrix in predictable ways. We just don’t know; but we ought to find out.
Da-Lite: Do you think that changes in the projection screen can improve display quality?
Orfield: Of course. But I think that the information your company in particular is providing about the suitable use of your screens in terms of what is being displayed on them and who’s viewing them is dramatically more important and useful than any incremental improvements you may make in the products themselves.
Da-Lite: Do you think that new developments in projector and computer technology will ensure more intelligible displays?
Orfield: No. If you have a good, objective standard for the perceptibility of displays, the display technology becomes unimportant. And I doubt that new technologies will change that communication. And so once we have some standard displays and once we have some standard methods, and once we have some standardized viewers and once we have some correlation between all of those and measurement, then we’ll begin to understand what the question is. The screen and the projector will become part of a potential answer.
Da-Lite: Why do you think our industry hasn’t created these standards already?
Orfield: Because once you can be benchmarked, you can fail. And if you can’t be benchmarked, you don’t fail. So I think there’s an incentive not to have standards within the industry and within the design community too. Because if there are no standards, you don’t make mistakes. You may produce better or worse things, but it can’t be said that you simply screwed up.
Da-Lite: So if we did (somehow) have a display that fully met the standards of intelligibility, what would it look like?
Orfield: That’s an easy question. If a display represents a visual task - the assimilation of some quantity of information over some period of time - the technology producing that display should in no way mask the task. The final standard would be that the viewer could concentrate on the information alone and ignore the process of its delivery. In this way the achievement of the intelligibility standard would be its invisibility.