The Resolution Revolution
Larger video display pixel counts mean smaller text on the screen. This trend could make our old design rules obsolete ? and put more responsibility on the end-user.
CONSULTANTS, INTEGRATORS, and architects have always had to size an image for the audience in a space. Whether it's projection or direct-view, image size is a key parameter of AV design. The choice is based on the tasks and applications at hand, and will determine exactly how far the farthest viewer should be in the seating layout. This used to be a relatively straightforward task, but it's now becoming less so.
Once computers became more commonly displayed for larger audiences in the 1980s, image detail, display resolution, and text became more important in determining display size. Using traditional optometric criteria we were able to determine how far the farthest viewer should be from the screen to still view levels of detail and read text, but based on what text size?
At first, computer-generated text was fixed in size, and became larger only by making the image larger. But it didn't take long for spreadsheets and presentation software to enable text formatting onscreen. Even though the pixel counts of displays have been increasing, we've found some persistent rules of thumb that have served us well as a starting point. The most common one: The distance to the farthest viewer from the display should be no more than six times the height of the image — sometimes called the 6H rule. If more detail or smaller text will be displayed, use 4H. And if less detail will be viewed, go with 8H — at least for common displays on the market today.
Is the pixel the point?
AV providers put up the display, but presenters had to play along to make it work. Because guidelines for presentations were established based on the assumption that the screen would be of some unnamed minimum size appropriate to the audience area, a minimum 28-point font size is often recommended for onscreen presentations. But what does that really mean beyond a value in the computer's text box?
Typographical points are traditionally 1/72-inch high, so 28 points on a printed page should be just less than 0.4 inches high. But what about the onscreen size? As the VGA standard for displays evolved, the computer software industry soon assumed that the desktop display resolution in front of the user was either 72 dpi or 96 dpi, which may have been correct at one time, but various screen sizes and resolutions quickly changed that. This would mean that 28 points could be displayed at somewhere between 0.3 inches high (on an actual 96 dpi screen with software assuming a 72 dpi display) and 0.5 inches high (on an actual 72 dpi screen with software assuming a 96 dpi screen). Add to that larger and smaller screens with the same pixel count, and you get even more variations.
As we translate that scenario to larger displays, we end up with the same effect. Luckily, the 28-point rule combined with the common 6H rule has typically worked when both rules are followed, even with the increases in display resolutions over the past 20 years.
We can't be all thumbs
Yet we're quickly approaching the point where those rules are no longer valid. We've seen this coming for some time. Once the Web became popular and software training became commonplace, users didn't necessarily have the same control over font size that they had in spreadsheets and presentation software. Important text may only be 11 or 12 points on the display. We can deal with small text if the resolution of the display is somewhere near XGA vertically, which is where mainstream projectors and direct view displays have been for a while. We just make the display larger or place the farthest viewer closer.
But with more native 1080-pixel-high displays on the market, text on the screen is shrinking, and our rules of thumb may no longer apply. We may not be able to make the image large enough for a given application and room size using the legacy guidelines.
The quantum leap
We're approaching a time where the responsibility for readable text in presentations may be more on the users than AV designers. Displays beyond 1080 native pixels high exist, and more are coming. The quantum leap will occur when “digital ink” displays come into production for larger size displays at 200 dpi and higher. Yes, we can get more beautiful detail on a big screen, but the viewer in the back of the room may need binoculars to read any text on it. Unless, of course, the presenter understands that the software zoom level will need to be increased when switching from displaying an HD movie to a web page or word processing document.
With significantly higher pixel counts, the computer software industry may need to expand the use of Display PostScript and related technologies that can scale onscreen text independent of display resolution. This will benefit both AV providers and end-users if it makes 28-point fonts the same height on any display of a given physical size regardless of its pixel dimensions.
As we move into this higher-resolution world, we're forced to think more about the difference between high-definition entertainment and text-rich presentation in AV design. It means that end-users will probably need to be more computer-savvy than ever as they take on responsibility for their own text size. And our old rules of thumb may not be “close enough” for design without more closely considering the technology we're using to build the system and how presenters will use it.
Since the CGA video display standard was introduced in 1981 at 320 pixels high, display resolutions have steadily increased to HDTV, QXGA, and beyond at more than 1,000 pixels high. At 100 percent zoom on a 48-inch-high display, 12-point text display has decreased from more than 2.5 inches at CGA to less than 3/4 inch at XGA and less than 1/2 inch for higher resolutions.
Tim Cape is a contributing editor for Pro AV, the principal consultant for Atlanta-based technology consulting firm Technitect LLC, and co-author of “AV Best Practices,” published by InfoComm International. He's the current chairman of InfoComm's ICAT consultant's council, and an instructor and presenter in AV technology design and management. Contact him at firstname.lastname@example.org.