The Hobbit Technical Thoughts


I'm not sure why my game dev blog has become a boring movie review site but I try to blog about what I'm thinking about and this year I've seen a lot of movies-- so there.

However I'm not really reviewing the movie here, I'm more just musing on the technology behind it. This does relate to game development, so I'm partly on-topic here (not that I really care.)

I went to see the fully-super'd out IMAX 3D HFR version, on a proper IMAX screen (not LieMAX.) Well at least I think that's what I saw.

Moving Pictures for Home and for Theatre

The big deal with this movie, if you don't know, is that it's "high frame rate". First a quick lesson on optics:

- Film (or video as in videogame) is just made up of a series of still images, played in sequence; each image is called a "frame"

- The number of images shown per second is called the frame rate, measured in "frames per second" or fps

- Videogames range from 15 frames per second to 60 or more frames per second, and in general are not constant; because a videogame normally will re-draw the entire scene each frame, the more it has to draw (and the less computer power to do it with) means that it will not be able to draw as many frames

- Computer monitors or HDTVs normally operate at 30 fps or 60 fps

- Some new computer monitors (or some old CRTs) operate at 120 fps

- Old television or DVDs are 30 fps

- Blu-ray can show 720p at 60 fps but 1080p at only 30 fps

So at the end of the day most "home entertainment" is 30 or 60 fps. But...

Movies traditionally (for at least 80 years) have always been 24 frames per second. Some people feel this is part of what makes movies magical-- the lower framerate. Word to Hollywood for this trick.

(Aside: I realize this is the first part of a terribly basic lesson in moving pictures, and I realize all this gets repeated ad nauseum with respect to The Hobbit.)

The Hobbit is a big deal because it is shown at 48 frames per second and it's really the first major movie ever to do so. No matter how you slice it, that is significant and daring and folks (especially the critics) ought to take a step back and think about just how big a thing Mr. Jackson is trying with this.

More Optics

That's not the whole thing, though.

In still photography, the amount of light hitting film (or a sensor) is a function of two things: the aperture, which is how big of a hole is letting light through the camera lens, and the duration of time the shutter is left open.

A wider aperture (lower f-stop number) lets in more light, so you can take the same brightness of picture in a shorter amount of time.

However, a larger aperture also lets in more "unfocused" light; this seems confusing but it's actually really simple to understand (I won't explain here.) Often portraits are taken where the background is lovely and blurry or has nice out of focus bright spots. This is a nice practical effect since it brings the subject into relief and gives an "automatic" conceptual background of abstract colors.

At any rate what matters is that a larger aperture means less of the picture is in focus, but the less light you need in order to take a bright enough photo.

Typically to take a photo you pick your shutter speed and aperture together, in order to produce a picture where enough of the light made an impression on the film so as to render the scene visible.

Why mention all this? Well if you stop to think about it, a movie camera can not really alter it's shutter speed. It turns out that traditional movie cameras are open for about 1/48th of a second for a 24 fps film.

Wait, 1/48th of a second?

Imagine a dot moves across the screen:

2012-12-19


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