Angles Of View

At Da-Lite Screen Company we try very hard to make screens for almost every purpose, in nearly every configuration, and in almost any size. We do that because we appreciate the enormous number of ways our customers and friends, rely on our products to help create displays of the highest possible quality. One thing we’d like you to help us consider, however, is how the definition of “quality” as it applies to visual displays is changing. With that in mind, let’s look carefully, then, at

Presenting Technology - It's Harder than it Looks

When we sit down before a projection screen and await the beginning of the “presentation,” what are we looking at? The answer, of course, is a rectangular surface which is from our perspective fairly large but is otherwise, well, blank.

When we prepare ourselves to receive most other sorts of formal visual information, this empty “blankness” is generally not in evidence. We do not, for instance, open a book to wait for the print to swim up out of the page before we can begin reading. The information we seek is already there, passively awaiting our regard.

Projection screens are just the opposite. The information to be written on them is not illuminated by light falling on their pages. It is contained in the light itself. Thus, although there is often text, there is never print. Although there is certainly white space,
there is never paper.

All of us who make up the display industry are right to be sensitive to these differences. They are one way of describing the core question we must be adept at answering: How do you make projected information maximally comprehensible to its audience?

The problem, of course, is that the “V” part of the A/V industry is continually evolving. This is in sharp contradistinction to the “A” part whose essential “content,” at least, hasn’t materially changed in decades. Technically, the properties and attributes of the human voice (and ear) are extremely well understood and there are wonderfully sophisticated computer programs to aid designers in laying out sound systems for virtually any venue. The same, regrettably, cannot be said for large screen display systems.

If we think for a moment about why that would be so, we soon come to see that the imitative quality of the two representations is really quite different. Sound coming out of a loudspeaker is an analog signal consisting of pressure waves and discernable by our ears. The nature of the signal is identical to the nature of the signal emitted by our vocal cords whenever we speak. The audio trick, if you will, is to deliver the same collection of wavelengths (the speech) to the ear at the same amplitude and with a minimum of extraneous noise (non-speech). Given typical ingenuity and skill, it is certainly possible to create an “artificial” audio signal that is really hard to distinguish from the original.

With visual information, the delivery of the signal is much more complicated because the signal itself is not an analog representation of the original. No one, for instance, ever mistakes figures cavorting on a movie screen for real people. But everyone accepts that the speeches the actors are uttering are real sound.

Technically speaking, this difference in signal can be quantitatively
expressed in terms of the bandwidth required to produce it. Audio, at least in terms of the human voice and ear, needs only modest bandwidth, about 20 kHz, to deliver a really convincing signal.

Another way of expressing why this is true is to note that an audio signal need be transmitted in only one dimension: time. The resolution of visual images, conversely, requires at least two dimensions (the horizontal and vertical) and often a third, time. An image displayed by any of the chip driven or CRT projectors will not only be cast at some, precise resolution, it will, even if its content is static, have to be refreshed a minimum number of times each second or, its audience will see it flicker. Just to make sure that an audience won’t be distracted by flicker requires a minimum refresh rate of 60Hz (and 72Hz is a lot safer). The total time bandwidth, of course, for a visual signal is hugely greater and is found by multiplying the refresh rate by the number of pixels in the display. Thus an SVGA image needs a bandwidth of something like 50 MHz, or more than 2,000 times larger than its audio component.

With respect to the spatial dimensions of a visual image, resolution is, of course, defined by the pixel density of the device projecting it. If that matrix is 1024 x 768, it's very clear that every single image you put up is going to be divided exactly into 786,432 symmetric and identical pieces. The absolute size of those picture elements will vary according to screen size, of course, but their absolute number will not.

Intuitively, more than three quarters of a million pixels seems like a lot, doesn't it? But let's see if it really is. If the image size is taken, typically, to be 120 inches in diagonal, then the absolute size of each pixel turns out to be .09375 inches square. More usefully we can say that there are about 114 of them for every square inch of our screen.

Now let's contrast this with what we've all been trained to read, a printed page. Its average resolution will be 600dpi (dots per inch) which translate to 360,000 dots per square inch. Even when we scale from a viewing distance of about 24 inches (two diagonals) from a printed page to 20 feet (two diagonals) from a 6 x 8 foot screen, the resolution of the printed information remains 300 times better than the projected data. Three hundred.

As an indication of just how enormous this difference is, let's choose as a random example the word Visibility. First, we'll allow our word processor to write it Large (36 points) and our laser printer to print it at 600dpi:




is what we get and few would quibble over its quality, much less its legibility. Now let's have a look at how it might appear were it to be projected onto a screen:




It seems almost superfluous and certainly rhetorical to pose the question, which would you rather read?

All of these remarks have been intended to illustrate and to emphasize the inherent difficulties in producing a high quality visual display. If the definition of quality is to include functionality (and it certainly must), then we, the display producers, must acknowledge and accept that the technology available to us currently is not nearly good enough to get the job done perfectly. Not yet, anyway.

Computers, of course, are sure to become more powerful. So will projectors. Both will deliver information at ever increasing resolution and density. Eventually the combination will become good enough that the differential between printed and projected media will shrink to less than one order of magnitude. That will be an important day.

Screens, interestingly enough, will not undergo nearly as many transformations. That isn't because people in the screen business aren't innovative (we like to think we are), but it is because many of our products are already completely developed and entirely suitable for the display of the future. It is extremely hard to imagine, for instance, any way in which a Matte White screen can or could be improved. It already really is "the perfect white diffuser."

On the other hand, making sure that your screen is the right shape and size, seeing that it gets positioned properly relative to its audience, and controlling the amount of ambient light affecting it are all of paramount importance to the creation of effective displays.

This series has been at pains to present other issues relating to the control and creation of the best possible visual displays. Not so very long ago, some of those would have been considered arcane and superfluous. Fonts? Character size? Cosines and arc minutes? Should we really have to worry about those sorts of things? Yes; we should. And, as the resolution of the information we're projecting continues ineffably to climb, we must.

One day these issues may in fact vanish. One day the imagery we'll all look at projected onto Da-Lite screens will look just perfect. There will be no more artifacts or anomalies to distract us. We will not be able to tell, looking at the image, what sort of projector is creating it. Nor will we be able to tell the difference between one portion of the picture and another. All that we will see is the only thing we're supposed to see: the information and only the information. Just as when we pick up a book, we do not need to look at either paper or ink, so should the goal of display technology also be: