The Look of Film

by Eric Solstein

[Please note: This entire article may be downloaded as a PDF file.]

This article first appeared in two successive issues of Video Systems in 1998

Part 1 – Film vs. Video

Film is beautiful. It is an actual physical object that can be held between ones' fingers. It can be viewed directly, cut into pieces and reassembled with mylar tape, or even scratched, drawn on and baked in an oven to distort its delicate emulsion.
Basically three layers of light sensitive silver based chemicals suspended in an organic emulsion and uniformly spread over a long perforated strip of acetate, it is the stuff dreams are made of. The "dreamy" look of film is largely based on its physical characteristics and those of the cameras and lenses that are generally employed to actually expose it, as well as the range of practices and techniques that a film crew will bring to a production.

While video is unquestionably an electronic process (that current technology permits us to store on a wide variety of media such as video cassettes, hard drives, etc.), film is a precious object. Film is many other things that bear on this discussion: a mature mechanical technology, a chemical process, an aesthetic and even a culture.

We will begin our comparison of the two media by examining the different technologies, essential in understanding how video might be made to look like film. Motion picture film has been with us for a long time; it was the invention that bridged the gap between magic lanterns, which could project still images from slides, and kinetoscopes, which were moving "peep shows" in a box.

Today's perforated strip of plastic has to be manufactured to very high tolerances from very stable materials in order to move consistently through the gate (the channel that guides the film past the shutter and optical system) of a camera, projector or telecine, and these in turn must have an effective, well maintained registration system.
A worn gate or inadequate registration can cause weave, the continuous movement of the film from side to side, and jitter, the intermittent stuttering of the film, up, down and sideways. Old or poorly stored film can shrink, discolor, stain, exhibit dirt and scratches, and even grow mold.

When a film is projected, dirt and hair can accumulate and jitter about the gate aperture. Film can suffer a multitude of indignities when shown with an unsympathetic projector: it can lose its loop, causing frames to appear to be sliding up or down; it can break, tear, stop and possibly catch fire.

These various imperfections may not define the look of film, but they certainly evoke many filmic associations and they have recently become very popular graphic devices. No real equivalent artifacts exist for video, though our senior editor assures me that in the future, drop-outs, JPEG mosquitoes, SC/H phase errors and 60 cycle hum will all become sentimental favorites, perhaps as popular as video hash.
The subtle properties of grain, tonal range and colorimetry, and the temporal characteristics of film do not draw attention to themselves, yet they are responsible for a film's look. The "look" of a film can speak volumes and it says something clearly different than "video."

Unexposed color film begins its life as a series of layers incorporating silver halide grains that have been sensitized to different wavelengths of light that once exposed and processed will be replaced by dyes which will sum up to the colors we expect to see.

Though the grains are washed away, they leave a "footprint" of their original shape and size, that will vary according to the particular stock and manner in which it was processed. The grains are spread uniformly over the surface of the film but with a totally random pattern. Depending on the effectiveness of the pressure plate that holds the film flat against the gate, and the quality of the lens' color correction, one grain layer may be in sharper focus than another, or an entire frame, series of frames or portion of a frame may actually be out of focus.

In modern video cameras, a three CCD imaging block takes the place of film. The picture elements (or pixels) of each CCD are in a uniform array with very precise spatial alignment. A properly functioning camera and lens should always yield a consistently sharp image.

Resolution of the camera system will generally be greater than the tape format to which it records; this is important because the pixels in the grid are usually larger than film grains and have difficulty smoothly rendering diagonal lines, which will often appear to have a stair-step or aliased quality.

The apparent resolution of a film image will be dependent on the choice of film format, stock, optics and shutter angle. Video which is also dependent on tape format as well as camera and optical quality, generally has lower resolution than 16mm film but uses certain techniques that may actually allow it to appear sharper.

Though every video camera manufacturer has a different approach to image processing, they all use a variation on aperture correction, also referred to as detail enhancement. This technique of exaggerating the difference between thresholds of light and dark gives the illusion of sharpness. Unfortunately, when set too high it makes people look like outlined cartoon characters with very bad complexions. (Modern digital cameras have recently added the ability to decrease detail in an area localized by hue so that a subject's facial difficulties can significantly diminished).

Temporal resolution is different from spatial resolution and one area where video's specs exceed those of film. Film operates in frames, commonly 24 per second, while each of video's 30 frames per second (fps) is made up of two interlaced fields. (Each video field occupies either the odd or even set of lines that compose the full 525 lines of the NTSC video image. Though one field actually follows another at intervals of about 1/60th of a second; as the TV scans, they appear to be "woven" together in each individual frame).

When film is projected, a multi-bladed shutter rotating between the projector lamp and optics serves to increase the rate of flicker from 24 fps to 72 fps; this is to achieve a rate above the threshold of human perception. NTSC video, consistent with the power mains in the United States, operates at roughly 60 cycles (or fields, or flickers) per second. The higher the temporal resolution, the more realistic the movement of an image.

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Film vs. Video continued
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