Angles Of View
Much of this series has been devoted to explicating various and particular aspects of visual displays. Among the conclusions not yet presented, however, is a recommendation as to which of the many display criteria should receive priority over others. The present article seeks to offer in this regard
Some Summary JudgementsBefore declaring what are the most important attributes of an optimum visual display, it is useful to disclose a pair of fundamental assumptions. These are postulates regarding exactly what it is that a display is supposed to do and under what circumstances it generally will do it. Premise number one is: the primary goal of any display system is to deliver the maximum number of light rays from the projector into the eyes of the audience.
Premise number two characterizes the viewing environment and asserts: except for entertainment, the venues for all contemporary displays systems include ambient light. If these two presumptions are accepted, we can derive the conclusion: whenever the geometry permits it, rear projection is generally preferable to front projection. This is reasonable because only in rear projection can the projector be pointed directly into the eyes of the audience (premise one) and because only in rear projection can most ambient light be segregated from the projected light (premise two).
There is another set of observations to be professed which has to do with the way displays historically have been used. Ten years ago the only thing audiences had to do with video generated displays was to look at them. "Looking" was, as it were, the full extent of the visual task. Today, with the advent of data projection, the visual task has become very much more demanding and what audiences are now routinely required to do with displays is to read them.
Tomorrow, as the software creating the displayable content becomes ever more graphical, the visual task assigned to audiences will transcend reading and the requirement will be to inspect the displayed information.
When we look at something, the principle visual activity has to do mostly with recognition. If the "signal" is video, we find that we can tolerate quite a lot of "noise" within it and still have no difficulty recognizing the scene, identifying the actress, or following the action. We are, in effect, easily able to see "the picture" or, if you will, to watch "the movie."
If, however, we are required to read something, then suddenly our tolerance of seeing it in broad outline vanishes and being able to recognize that the image is, in fact, a page of text doesn't help us at all if we're not able to make out the individual words. Moreover, it definitely won't do if we can only discern some of the words, those that, for instance, happen to be printed in the middle of the page (and thus will be projected at the middle of the screen).
The strings of words which stretch along the outside edges of each line (or the numbers appearing within the peripheral cells of the spreadsheet) are just as important as their counterparts at screen center. And there are four times as many of them! (There are, after all, four corners to every screen; but there's only one center.)
And when we come to think about the inspection of graphical information, the visual task becomes harder still. When we see a screen that we're expected to read, we at least know to direct our attention to the upper left corner and to begin scanning right. If the content before us, however, is graphical - the schematic of our company's newest widget or even the plan for its new boardroom - we are bereft all such convenient visual cues and there is no special portion of the display which by virtue of its position alone deserves our attention. We know, therefore, neither where first to look nor what first to read.
Inspection, then, is a task which compels us to examine all areas of the display with equal acuity because there is no way to predict just where or in what manner our attention must be focused. That being said, one thing we do know is that we must be able to distinguish with equal facility every portion of the display.
And, while purely graphical displays, may today be an exception, they are certain soon to become the rule if only because the computer industry (of which, of course, the A/V business is a prominent, but decidedly collateral beneficiary) will never cease in its development of increasingly elaborate content. As the software encompassing that content and the hardware manipulating it both increase in power, capacity, and speed, the extent and kind of information which will be "presented" through projectors and onto screens is prospectively limitless.
Despite the vistas thus sketched by the prospects of Virtual Reality, 3D, and even, one day, holograms, there remains the stubborn reality that if the content being presented is informational, its audience is going to have to view it. (Conversely, if the purpose of the content is entertainment, the audience need only be able to see it.)
Here, then, are Da-Lite's five most important criteria for the viewing of visual displays:
Presumably, the case for uniformity has been adequately made above and can, therefore, be rested. It may serve only to add that no matter the absolute luminance emanating from any portion of a display, if some other portion of that display is more than two times brighter than the first, the human eye will perceive the first portion as being dim. Thus, if an image isn't adequately uniform, we shall not adequately be able to "read" it.
Resolution is second in importance because the drive to create more of it from the computer industry is inexorable. And, as the pixels become more numerous, they become smaller. And, as they become smaller, finer detail can be drawn with them. And, as the parts of an image become ever more detailed, the technology displaying the image has to become ever less obtrusive. Thus a screen must ideally be a surface that will always fail to degrade the resolution of the imagery cast upon it. (This is one of the reasons why diffusion screens are being returned to such a well deserved popularity.)
The third most important display attribute is contrast which is particularly vital to projected imagery as what is called its "black level" can never actually be black. This, of course, is because black (by definition "the absence of light") cannot (again by definition) be projected.
No matter how bright, nor how finely resolved, nor even how uniform a display may be if its content has too little contrast, if its darkest elements aren't a lot darker than its brightest, the human eye will have an extremely difficult time distinguishing among the data. As contrast is one display attribute which may not be limited exclusively by the projection source, careful screen selection can importantly enhance it.
The fourth attribute is size. How large we must make the display is directly proportional to the visual task expected by it. It's easy enough to recognize the general nature of an image that's too small. But if we are to read that image, we have to have it bigger. And if we are to inspect it, it will have to be bigger still.
Since reading and inspecting don't oblige visual interaction with the whole screen at once (but rather with only small portions of it at a time), sizing calculations should be made with reference to the back row and once useful formulae regarding front row geometry can usually be discarded.
And finally, but only finally, we come to gain. This series has always done its best to give gain a bad name, even when that slander has not always been fully deserved. But screen gain is all too often still assumed to be a panacea for any number of display problems. And it shouldn't be. Gain is just one of the criteria; it is not all five. This is why it should get considered last on the list, so that the other four can receive their fair and proper due.
Still, are there applications in which a high gain screen is clearly more effective than a low gain surface? Of course. And they are numerous. This is among the reasons why Da-Lite is committed to offering the widest and most diverse range of screens and surfaces in the industry.
There are data being displayed on screens today which are enormously complex and whose discernment is enormously demanding on their audiences. End users have come to expect that the quality of the image they see on their large screen display is at least the equal of what they see on their computer monitors. While that standard may not presently be entirely fair, it is unlikely to vanish. Almost certainly, in fact, it will be met.
Recommending the right standards for creating the best displays is Da-Lite's responsibility. Consistently providing our customers with products of only the very highest quality is our duty. Continuously striving to perfect and upgrade those products is our obligation. And ensuring that each and every customer find exactly the best screen and surface for each and every application will remain our mission