Why is HDTV's aspect ratio 16:9?

[Machine_Elf]

One of the defining features of the HDTV format is an aspect ratio of 16:9 (expressed alternatively as 1.78:1). And yet, when I watch movies from Blu-Ray discs, I’m still seeing letterboxing. In other words, the movies were made in an even higher aspect ratio than HDTV. Supposedly the two most common aspect ratios for cinema are 1.85:1 and 2.39:1.

So why did they make the HDTV format “boxier” than the most common aspect ratios used in cinema? Instead of letterboxing cinematic movies to present them on boxy HDTV screens, why didn’t they define the HDTV format match one of those aspect ratios (1.85 or 2.39 to 1), and then have all HDTV television programming produced to match that aspect ratio?

[Kimstu]

Some photographer bloke named Ken Rockwell sez:

Both 720p and 1080i use wider images, called 16:9 or 1.78:1.

Where did this come from, since it has nothing to do with movies or TV? Movies have been wider than HDTV since the 1950s.

Back in the 1980s, engineers working in their own vacuum decided amongst themselves that the most efficient shape for a screen, which had to display 4:3 TV and 1.85:1 and 2.40:1 movies, was 16:9 (1.78:1).

Why? Because TV picture tubes cost about the same based on their diagonal measurement, regardless of the shape of the rectangle or square inches of picture area. A 16:9 tube wasted the least space with black bars when you averaged all the wasted black space when showing the various formats, none of which fits a 16:9 tube.

When the artists who actually make movies heard about this dopey new arbitrary “sort of best fit” 16:9 aspect ratio, Hollywood’s by-invitation-only American Society of Cinematographers went crazy. They rightfully pointed out that TV finally had the chance to display movies properly, but botched it by coming up with a new, corny and completely unrelated to anything 16:9 aspect ratio.

Oh well, this is what we have today, and sadly very few people are fortunate enough to be able to watch on tubes, for which 16:9 was chosen.

Worse, as the ASC foretold, we now have four different aspect ratios, only one of which works properly on any given screen.

[Earl_Snake-Hips_Tucker]

Earlier threads:

Why 16:9?

How did 16:9 get chosen for HDTV

[ZenBeam]

From MrFloppy’s link, in the first thread Earl Snake-Hips Tucker linked to (I’ll repeat the part he quoted):

As the story goes, using a pencil and a piece of paper, Powers drew the rectangles of all the popular film aspect ratios (each normalized for equal area) and dropped them on top of each other. When he finished, he discovered an amazing thing. Not only did all the rectangles fall within a 1.77 shape, the edges of all the rectangles also fell outside an inner rectangle which also had a 1.77 shape. Powers realized that he had the makings of a “Shoot and Protect” scheme that with the proper masks would permit motion pictures to be released in any aspect ratio. In 1984, this concept was unanimously accepted by the SMPTE working group and soon became the standard for HDTV production worldwide.

These inner and outer rectangles are determined by the largest and smallest ratios, 1.33 and 2.35, the intermediate ones don’t matter. But they only turned out equal because 1.33^3 = 2.35, so you get 1.33^2 = 2.35/1.33 = 1.77 = 16/9.

(Equations accurate to about 1% or better)

[BigT]

You know, cinematographers could also start making things to fit the TV screens. Masking on a projected screen is much less noticeable.

As it is now, a lot of things are released in with some weird stretching that I always unstretch for screenshots.