Marshall Brain's Blog

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The latest thing at the movie theater is digital movie delivery. Instead of shining light through film with a projector, theaters are now retooling with digital projectors. I cannot explain why this is so fascinating to me, but it is...

A digital movie projector gets the movie as a file from a satellite feed or over the Internet. A typical file for a feature length film (in Media9 format) has a size of 7 gigabytes or so. For comparison, a DVD movie uses MPEG-2 compression, has about 1/8th the resolution and can consume about 4 gigabytes.


A 2048 x 1024 pixel Digital Micromirror Device

The movie file plays on a DLP Projector, the most modern of which are using three mirror arrays with 2048 x 1080 pixels.


A DLP projector

Most studios that are filming digitally are using HD cameras with 1920 x 1080 pixels. They film at the standard movie frame rate of 24 frames per second (fps).


A professional HD camera - current cost about $100,000

The big advantage of digital projection is that it lowers the cost of distribution. A typical film print that is 100 minutes long comes on 6 or 8 reels that are expensive to produce, weigh up to 80 pounds and have to be spliced together by hand.

One interesting thing about all of this is the compression ratio. If you took a 100 minute long film and digitized it frame by frame, you would have 24 x 60 x 100 = 144,000 frames. Each frame has 1920 x 1080 = 2,073,600 pixels. If you use 3 bytes per pixel (one byte for red, green and blue color information), that is over 6 million bytes per frame or 895,795,200,000 bytes total for the film. Roughly a terabyte, in other words. To shrink that down to 7 gigabytes, you are compressing the film by a factor of about 125. Over a T1 line, it takes 10 hours to transfer the 7 gigabyte file. With a T3 line, it takes 14 minutes.

What's funny is that 5 years from now, it is possible to imagine the same files being available at home, displayed on big 1920 x 1080 plasma screens or OLED panels that have fallen in price down to $500.