Image Processing Reference
the light sensor. Optical components collimate (or make parallel) the light transmitted
through the film, and the analog waveform is recorded. This design works well because
it mimics exactly the way a TV picture is produced but in reverse. Figure 4-16 shows
how this works.
The resolution of the output of a flying spot scanner is fixed at 2K or 4K or whatever
the manufacturer provides. The film is positioned and optical components introduced so
that the scanning area completely covers the frame. Resolution is inferred from the fixed
2K/4K sizes and the physical size of the film substrate.
Flatbed scanners that have backlight hoods for scanning film have a fixed resolution
and yield a varying-sized pixel image according to the area of the film being scanned.
A flying spot telecine always yields the same-sized image. This is another subtle point that
you need to understand to ensure you get what you want out of the scanner.
Modern scanners are more precise and have a CCD device lit by a projected image
of the film, and the electronics are very similar to those of a digital camera. This design is
technically superior since the imaging component creates a much better-quality result. The
recorded image is crisper and less prone to analog noise artifacts. This arrangement is
shown in figure 4-17.
The downside of the flying spot scanner is that the beam intensity is not 100% stable
all the time. The linearity and convergence of the telecine must be carefully adjusted and
Illumination created by a
scanning beam on a CRT.
Filtered light converted
to an electrical signal by
Figure 4-16 Flying spot scanner.