Adobe After Effects 7.0 Studio Techniques

Film, HDR, and 32 Bit Compositing

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That medium is film.

Cineon Log Space

A film negative gets its name because areas exposed to light ultimately become dark and opaque, and areas

unexposed are made transparent during developing. Light makes dark. Hence, negative.

Dark is a relative term here. A white piece of paper makes a nice dark splotch on the negative, but a lightbulb

darkens the film even more, and a photograph of the sun causes the negative to turn out darker still. By not com-

pletely exposing to even bright lights, the negative is able to capture the differences between bright highlights

and really bright highlights. Film, the original image capture medium, has always been high dynamic range.

If you were to graph the increase in film “density” as increasing amounts of light expose it, you’d get something

like Figure 11.7. In math, this is referred to as a logarithmic curve. I’ll get back to this in a moment.

Figure 11.7. Graphing the darkening of film as increasing amounts of light expose it

results in a logarithmic curve.

Digital Film

Because all the computer film work is essentially the processing of Cineon files and then sending a new set back

to the client to be printed on film, some further examination of the Cineon log color space and its properties

will serve you well.

I’ll tell you now that if a monitor’s maximum brightness is considered to be 1.0, the brightest value film can

represent is officially considered by Kodak to be 13.53 (although using the more efficient ICC color conversion,

outlined later in the chapter, reveals brightness values above 70). Note this only applies to a film negative that

is exposed by light in the world as opposed to a film positive, which is limited by the brightness of a projector

bulb and is therefore not really considered high dynamic range. A Telecine captures the entire range of each

frame and stores the frames as a sequence of 10-bit Cineon files. Those extra two bits mean that Cineon pixel

values can range from 0 to 1023 instead of the 0 to 255 in 8-bit files.

Having four times as many values to work with in a Cineon file helps, but considering you have 13.53 times

the range to record, care must be taken in encoding those values. The most obvious way to store all that light

would simply be to evenly squeeze 0.0 to 13.53 into the 0 to 1023 range. The problem with this solution is that

it would only leave 75 code values for the all-important 0.0 to 1.0 range, the same as allocated to the range

10.0 to 11.0, which you are far less interested in representing with much accuracy. Your eye can barely tell the

difference between two highlights that bright—it certainly doesn’t need 75 brightness variations between them.