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Full-Spec HD and the Cinematic Experience

January 2, 2007

This is all about recreating the cinematic experience in your home. And that doesn't mean you have to own a huge TV. All it takes is finding the right balance of screen size, display resolution, and viewing distance.

By "cinematic experience" I mean the picture completely dominates your focus. In the theater, this happens because the screen is big and everything around it is dark.

When you're trying to recreate this at home, the purists want completely dark, but that's not necessary. A low ambient light level will suffice. But light level is not what I want to talk about; it's the other factors, starting with screen size.

As it turns out, the absolute screen size is actually not as important as the included angle (or arc) defined by your eye and the left and right sides of the screen. In other words, does the screen fill up your central field of view?

I had read in a couple of places that 30 degrees is the (more or less) separation point (notably at dvdfile.com) for "TV" versus theater experience. But I hadn't paid much attention to that, until I conducted a little experiment.

It seems to have a lot to do with the concentration of light receptors on your retina (those little cones and rods that your learned about in biology class). Those receptors are densely packed in the center of your retina and become more widely spaced further out (your peripheral vision). It would seem that the area of densely packed receptors roughly corresponds to a 30 degree field of view.

Anything within a 30 degree included angle will get the full attention of your brain. Objects outside will be there, but just peripherally.

So back to my experiment:

I'm planning to buy a mid-size TV for a viewing area in my less-than-spacious apartment. Looking at screen sizes at a large store does not give a good idea of how imposing (or not) the TV will be once you get it home. In my case, the width would be constrained by my left and right tower speakers, allowing for a 46" TV max. 37" was just too small for my purposes.

At first I thought a 42" TV would be right. So to get a better idea of how a 42" set would look, I got a box from a local bicycle store (bicycle boxes are heavy, about the right size and have a "widescreen" shape) and cut out a cardboard 42" screen and propped it up in place. It looked good, a nice size TV.

Since a friend is thinking about buying a 46" set, I used the other half of the box to cut out a 46" cardboard screen. I then propped that up and sat back at my six foot viewing distance and was shocked.

While the 46" set is only about three inches wider and two inches higher than the 42" set (with 20 percent more area), it had a dominating presence that the 42" screen simply lacked.

I remembered the 30 degree magic angle and drew the geometry to scale and measured with my protractor. The angle for the 46" screen was 32 degrees.

So there it was. With the 42" screen, I was seeing a TV and part of the surrounding room. With the 46" screen, I was seeing the TV; everything else was peripheral.

That would be the first part of the equation. For a cinematic experience, sit close enough to the screen so that the viewing angle is at least 30 degrees.

The other part of the equation works in the opposite direction: screen resolution. You want to sit far enough away so that you can't make out the pixel structure, and that of course depends on whether you're looking at a full-spec HD display (1920 x 1080) or a 720p display (1280 x 720).

For this part of the calculation, I used figures I had written down from one source. Other people may calculate the acuity of the human eye differently; you can substitute your own numbers if you have a preference. In any case, the calculations give you a viewing distance as a function of screen size and screen resolution.

Table

In this table, the first three columns show dimensions for six TV sizes. The fourth column lists the viewing distance in feet that gives you a 30 degree viewing angle. The fifth and sixth columns list the approximate threshold viewing distance for discrimination of pixel structure. If you sit that distance away, you can see all the picture detail present in the display and yet you cannot distinguish pixel structure (scan lines).

Of course everybody's eyes are different; this is an exercise.

These are the numbers people use when they tell you that 1080p won't do you any good if you sit ten feet away from your 52" TV. Your eyes won't be able to see the detail that a full-spec HDTV can display. However, if you move to nine feet away, then you'll see the pixels in your 720p TV.

On the other hand, if you sit that far away, you'll be looking at a box with moving pictures that is sitting in your living room. If you're looking at a movie, you will be in your living room, and not in the movie.

For the cinematic experience, you want to be totally involved. You don't want to be looking at one side of your living room, but neither do you want to be looking at individual pixels.

So look at this chart:

Chart

The purple line represents the 30 degree field of view line. The blue line is if you have a full-spec 1920 x 1080 HDTV. The green line is for 720p displays. Viewing distance is marked along the left/vertical axis, in feet. Screen size is indicated along the bottom of the chart.

For the cinematic experience, you want to be below the purple line, and above either the blue or green lines. Clearly, if you're below the purple line (field of view greater than 30 degrees), you cannot be above the green line. You can, however, be above the blue (1080) line.

For my situation, with my six foot viewing distance, it means my decision has been made. I will be buying a 46" 1080p television. That combination gives me a cinematic presence and just about the maximum benefit of all of the detail that full-spec HD has to offer.

A disclaimer: everyone's priorities are different as are their own personal situations (and their eyesight). My analysis is meant to give you something to think about. Whatever answer you end up with is the right one for you.

Good luck and may your new year be a great one!