The Hobbit, frame rates explained!

Recently, Peter Jackson announced some camera and frame rate specifics regarding the highly anticipated film The Hobbit. He is currently shooting the film in 3D on the new and fabulous RED EPIC (a camera truly worthy of its name). This camera is capable of shooting in a native 5k resolution! 5k means 5120 x 2700 lines of pixel resolution-this is 6.6 x the resolution of an HD TV’s 1920×1080! Avatar, generally regarded as a visually fantastic looking film (though painfully lacking in other areas-yeesh) was shot in 1080p. So, one could only attempt to imagine the detail that will be captured with the EPIC (provided one could find a display that can well… display it. Currently, there are no consumer 5K displays available)

Jackson has also announced that he is filming and releasing The Hobbit in 48 progressive frames per second (fps). This is 2x the frame rate that movies have historicly been released in. Why is this important? Because frame rate is, in part, the reason movies look like movies. Frame rate basics go as follows:

The broadcast television standard has, until recently, been 60 interlace fps. This means that every other horizontal line is displayed 60x a second. This is the “TV look”. The new television standard being adopted is 30 progressive(p) fps. This means that the whole image is displayed 30x a second. This is similar to the “film look”.  Film is normally shot and displayed in 24 progressive fps. The difference to the viewer is largely the “feel” of what is being displayed. In laymen’s terms a lower frame rate like 24 fps makes “this movie seemed kinda jerky”. When viewing high frame rates, one might notice “this movie looks like a soap opera; it’s too real looking” or that “this looks too much like a video game”. The variance has sometimes been described as “video look” vs  ”film look”.

Another factor is shutter speed. Shutter speed refers to how long the shutter of the camera is open and capturing an image. Think of a still photograph camera. The longer the shutter is open, the longer light is reaching the sensor or film. This results in motion blur if the subject and/or the camera move while the shutter is open. Photographers often use the low shutter speed setting to capture and show the movement of their subject. If a photographer wants to freeze the motion, then they would select a high shutter speed. In film or video, a low shutter speed can smooth a low frame rate by allowing the blur of movement (camera or subject) from frame to frame. Transversely, high shutter speed setting causes a choppy or stuttery look. For example, the films Saving private Ryan and Gladiator utilized high shutter speed and 24P for a great saccato feel.

Shutter speed is largely up to the scene-to-scene discretion of the persons making the film, however, there is an industry rule of thumb for a shutter speed that offers the most natural results. This is referred to as the “180 degree rule”. Before digital cameras and sensors, the only cameras available were film cameras with physical shutters. These shutters were disks with portions cut out of them like pie graphs. As the disk would spin it would allow light to hit the film for a percentage of time. A 180 degree shutter was a disk that was cut in half, so as it would spin it would let light through exactly half the time. For something shot in 24p fps the shutter speed for a 180 degree shutter would be 1/48 second. So in short the rule of thumb for natural looking movement in progressive frames is a shutter speed 2x the frame rate.

Now back to The Hobbit.  Word has it that it is being shot at 48p fps with a shutter angle of 270 degrees. This is where things get a bit complicated. A 270 degree shutter is a like a pie with 75% missing, so as it spins it is letting in light for 75% of the time, it will also be spinning at 48 times a second because Jackson is shooting in 48p fps. So, we see that not only is the frame rate 2x higher than the standard 24p fps, the shutter angle will let in light a greater percentage of the time than our 180 degree rule. This will result in a VERY smooth look. It will also be very unlike any movie we are used to seeing. The reason for this decision, as I understand it, is that 3D has been deemed “fatiguing” to watch at lower frame rates. It also requires higher frame rates to look as realistic as possible.

However, most theaters are not equipped for 48p fps. This means a conversion to 24p for us to see it in a traditional projection screen theater. The conversion process is a simple one but it has profound implications. Every other frame is simply removed and each frame left is displayed for 1/24th of a second instead of 1/48th. But what does this do to the movie?

Lets think about this: a 270 degree shutter angle at 48p fps is the same as a 1/64 second shutter speed per frame. However when you remove every other frame to come up with 24p fps the shutter speed is still 1/64th of a second. Each frame will always stay at the speed you shot it. The motion blur you captured per frame is the motion blur you are stuck with and there is little you can do about it. So 24p fps at 1/64th of a second shutter speed means that the shutter is now only letting in light for 38% of the total time the camera is filming. It’s the same look you would get if you shot with a 136 degree shutter angle at 24p fps. This means that the look of the film is now more jerky than it would have been if it had just been shot using the normal 180 degree shutter rule. Its shutter speed is not 2x the frame rate where it would have looked natural, it is now higher.

So what does this all mean? Jackson explained the shutter angle, “… shooting at 48 fps with a 270 degree shutter angle. This gives the 48 fps a lovely silky look, and creates a very pleasing look at 24 fps as well. In fact, our DP, Andrew Lesnie, and I prefer the look of 24 fps when it comes from a 48 fps master.”

This is kind of a double talk in that what he is saying here is that he likes a super smooth 48p fps look but when it comes to 24p fps he prefers a slightly more stuttery look than the norm. My opinion is that he is simply compromising between a high frame rate for 3D and a normal looking shutter speed for 24p. If he was shooting for 3D ONLY he would likely shoot 60P 1/120 second shutter. That could never be converted to a normal looking 24p though. If he was shooting for NON 3D only he would shoot at 24p 1/48th of a second, the industry standard. I believe that is because we are in a transition from old to new technology and he is shooting with both in mind; it’s a compromise.

~Doug De Young    www.videocandycompany.com

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