AV Police Squad

Throwing The DISCAS Out There!

“Move away from the screen! You’ll go cross-eyed!” How many times has this been yelled to kids by parents from kitchens around the world? If only we were equipped with the response, “Mother, I am taking part in an Analytical Decision Making task where I must discern information on a pixel by pixel basis, and based on human acuity factors, 12 inches is an appropriate distance to a furthest viewer. Duh!” If only.

It’s here, people! The InfoComm V202.01:2015 DS1 Display Image Size for 2D Content in Audiovisual Systems, or DISCAS for short. (I pronounce it /’diskƏs/, you know, like the heavy, thick-centered disk thrown by an athlete in ancient Greek games or in modern field events, because I’m cool like that.) For years, when someone asked how large an image should be, our best guess was based on SMPTE studies from the 1950s that didn’t really take into account what type of content was going to be shown on the display. We had the 4/6/8 Rule for a general guess. If you were going to read anything, the furthest viewer should be less than 6x the image height away. If you were going to look at medical images or plans, the furthest viewer should be less than 4x the image height away. It kind of worked, honestly, but it was a rule of thumb. And I prefer science to rules of thumb.

Welcome DISCAS!

The DISCAS standards committee based their standard on science, or ANSI/HFES 100-2007, to be exact. That is the Human Factors and Ergonomics Society (HFES) 100 which deals with the “ergonomic design of computer workstations for the seated operator.” Extrapolating from that study a bit, we arrive at an AV design criteria for image height based on peer-reviewed human factors, like visual acuity, rather than rules of thumb. It is very exciting.

The most exciting thing about the standard is the shift away from a “generic image height factor” to Percent Element Height (%EH) as the basis for how large an image should be, or how close a person should be to the image to view it easily and comfortably. I love this. Instead of guessing, or generalizing, we can now ask our clients for their “worst case image.” This might include drawings, or busy text documents, or spreadsheets…but ask for their most intricate drawings, their busiest documents, or the most crowded spreadsheets: the worst case. Then, pick the element (could be a pixel for a drawing or a lower-case letter for documents), measure its height, and normalize it to the size of the screen it’s currently being viewed on. That normalized height (element height/test image height) is the %EH. This is the smallest thing on the screen that people will have to look at and interpret. For clients without worst case content, using 2% or 3% can be a placeholder, but this can be tailored to each client’s preference. There is nothing wrong with using 2.85% for %EH for Client A. Basing image height and/or furthest viewer on the smallest thing people will have to look at is EXACTLY how images should be sized. That’s why this is so sexy.

The standard goes into more details about the type of task at hand, and different acuity factors for the task at hand (200 for Basic Decision Making and 3438 for Analytical Decision Making). This is based on the science in the HFES standards, similar to the 150 Rule. However, the 150 Rule dealt with the size of capital letters of text. The new standard and acuity factors are instead based on the size of the finest details or lower-case letters. It sounds simple because it makes so much sense.

The acuity factors relate to those with 20/20 vision, which is interesting. On one hand, that is typical human eyesight. However, the 150 Rule and 4/6/8 studies always claimed that older adults with deteriorating vision were taken into account for those rules of thumb. It will be interesting to see if the industry requires these factors to be skewed for those with worse than 20/20 vision (20/40 or 20/50?). Or, designers can just use a larger %EH for clients with older users. It will also be interesting to see if any type of time aspect will ever come into play. I can certainly squint and read a page from a book on a presentation slide for a few minutes…but if I had to do that for an hour, that would no longer be comfortable. It would be interesting to see if the standard evolves to include “reading” as part of Analytical Decision Making and “viewing slides” as Basic Decision Making. Only time will tell.

I encourage you to check out the new standard. The text can be found online, and InfoComm is going to start rolling out this content at the show. I really think this is a smart, easy-to-implement standard. It’s also easy to try yourself. Take your phone, put the most amount of text on it that you are comfortable with (worst case), and turn that example into a %EH. See if the rules for furthest viewer (i.e. – how far you hold your phone away from your face) jives with the standard. I did. It does. I just wish I had known about this standard when I was a kid. I would have left nose prints on the TV!

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