Rethinking pixel pitch

Like everyone working in A/V, we’re doing increasing numbers of video walls in our projects these days.  Most of our work is indoors, and we’re using LED walls where we might in the past have used projection or single large LCD panels.  After all, at 0.9mm pitch, a wall with UHD resolution is not quite 12’ wide, just the kind of size we often use for presentation applications.  Which presents us then with a question: should we be thinking of viewing distances in terms of video wall pixel pitch, or instead thinking of overall image dimensions?

These two approaches have very different origins.  The professional A/V community has grown out of teaching and presentation, where the ability to read lines of text was important.  We were excited when CGA computer graphics gave way to EGA, and we got 640×480 resolution.  An image was considered large enough if we could read 25 lines of text; of course we could see the discrete pixels on the screen.  Over the years the analysis has been refined; symbol heights and visual acuity for the rigorous, and rules of thumb for others, but the objective has remained.  Can we read what’s on the screen?

In contrast, direct-view LED products have descended from outdoor marketing, and the need to make still images visible over large distances.  Grainy images were unappealing and were to be avoided.  Stills have given way to motion video, and distances have shrunk, yet the aesthetic concerns remain.  And so our calculators tell us that we mustn’t be able to make out individual pixels in the display.  If we can, choose a finer pitch, or stand farther away.

As we come to employ LED walls indoors, what approach should we use?  My own is to use the best of both.  Overall image size continues to relate to content, and for information display walls, we want height to be some fraction of maximum viewing distance.  We can let content drive our choice of how many cabinets high and wide our wall will be.  But the pixel resolution within each cabinet should exceed what our eyes can resolve.  We still don’t like grainy images.

Cost of course remains a factor, and will for some time.  But it wasn’t that long ago that we had similar concerns about 4K monitors, and look at where we are now.  We’re early in the period where we can specify bright, high-performing displays in whatever size we like, and we’re still sorting through the design choices.