A CRT film recorder consists of a small cathode ray tube (see the next chapter), a color wheel with red, green, and blue filters and a camera. An image from the computer is sent to the monochrome CRT, which is photographed once through each of the color filters resulting in a full color image on film.

In CRT recorders mainly camera negative film is used for the recording because the CRT image is not bright enough to expose low speed intermediate film. If the recorded program originates from film, however, it will already contain grain from the camera negative that was used in shooting. The recording will add additional grain since the images are transferred to camera negative again. An additional problem is that it is not possible to produce the maximum density encoded in a DPX file, which is 2.046 log D.

A laser film recorder uses red, green, and blue lasers and a rotating mirror deflecting the light beam back and forth across the film frame. The lasers can output more energy than a CRT, which enables recording on intermediate film in the same speed a CRT recorder can expose the image on camera negative.

Intermediate film has a much finer grain than camera negative, as was already shown in Figure 2.3. Therefore, one can produce a sharper image on intermediate film and avoids building up additional grain.

Shooting on intermediate stock also allows the use of polyester-based film, which is incredibly tough and difficult to tear. As a result, release prints can be made directly from the original polyester based digital negative, providing first-generation quality. Rather than creating an IP and IN for release printing, many productions just make an IP for protection. This delivers significant cost savings when producing a limited release movie.

The most common image format used in DI is the Cineon/DPX format. As explained in the previous chapter, the DPX file is a linear encoding of negative densities. Therefore, it is only logical that the recorder transfers the DPX code values linearly into densities. Scanning from film and recording back to film should not alter the tonal characteristic of a scene.

To achieve this result both types of film recorders need to be calibrated regularly. This is usually done by recording a series of gray patches that vary from black to white onto negative film. The patch densities are read from the negative with a densitometer and the data is used to modify the intensity of the film recorder’s light source to achieve the target gray scale density. The aim for the recorder calibration is displayed in Figure 4.1.