Digital Intermediate FAQ

1.
Q. How many frames are there in a typical film?
A. A typical film is 100 minutes in length, and runs at a speed of 24 frames per second. 100x60x24= 144,000 frames. If you also consider the frames that don’t make it into the final cut, this can be 10 times higher (1.44 million frames).
2.
Q. How much disk space do I need for a typical film?
A. For a film mastered at 2k, each frame is approximately 12 MB, 100 minutes is 1.65 TB. At 4k, it’s around 48 MB per frame, or 6.59 TB for 100 minutes.
3.
Q. What’s the difference between 2k/4k?
A. 2k images have a resolution of approximately 2000 pixels horizontally (a typical frame size would be 2048×1556), whereas 4k images are approxmately 4000 pixels wide (typical frames size of 4096×3112).
4.
Q. But what’s the difference between 2k and 4k?
A. To you and me, the picture is much sharper and more detailed. To the average cinema audience, probably nothing, unless it’s on a really big screen, in which case the 2k images will probably exhibit more aliasing artefacts.
5.
Q. Why does dust-busting take so long/cost so much?
A. Because it has to be done a frame at a time (see also Q1).
6.
Q. How come digital graders can’t make film look as good as fashion photographers can?
A. Because it’s a different medium. It’s the same as trying to make a photograph look like oil on canvas, or a newspaper read like a work of Shakespeare. Graders can make a still image look like a fashion photograph, but unfortunately the movement spoils it.
7.
Q. Can I get arrested for using illegal colours?
A. No. But you might not get your show broadcast.
8.
Q. What’s the dfference between film I use in my camera for taking still photographs, and film used to make motion picture.
A. Almost nothing. There are a view differences in terms of the available stocks, and the response to light, but the stuff is the same- 35mm film. The key difference is that motion picture uses a lot more of it, and most productions (except those using the 8-perf “VistaVision” format) use half the area that a still camera does. Still cameras (and VistaVision film cameras) run the film horizontally, whereas most motion picture cameras run the film vertically.
9.
Q. What are video colour sampling ratios?
A. In video, bandwidth is a big issue affecting the cost of the system. In general, the lower the bandwidth requirements, the lower the cost. In order to reduce bandwidth, some systems use non-uniform colour sampling, which is almost analogous to digital image “lossy” compression. Say for instance you have a region of 4 pixels. Each of those pixels would be sampled for Luma (Y-component), but only two of them for chroma (I and Q components). In this case, the sampling ratio would be 4:2:2.
10.
Q. What does 4:4:4 mean?
A. It means that the image has colours sampled evenly. This then means that the images will appear more saturated, and also that the images will be more robust, less prone to banding than say 4:2:2 images.

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Posted: February 28th, 2005