Film - A Practical Guide to Video and Audio Compression - page 70

computer, much of this becomes quite easy to do. The process is sometimes arduous and
time consuming, but a painstaking approach could yield a true gem of a movie from some-
thing that was simply unwatchable as projected film. Figure 4-27 shows a couple of exam-
ples. Both happen to be near the edge of the frame.
Being very gentle in the handling and scanning of film is of prime importance, and
reducing the number of times the film is despooled and passed through a film transport

Table 4-3 Repairing the Damage

Item Solution

1 Minor scratch to the film base substrate material on the side away from the

emulsion. This will cause some light scattering and depending on whether the
film is lit from the back or front, that will cause a spread of the illumination
when the film is scanned. Lit from the back, a larger area of emulsion will be
illuminated. Lit from the front, a few pixels will be scattered over a wider area
due to the refractive effect. The result is a slight blurring over a localized area.
De-blurring algorithms can usually correct this problem. Localizing them is
somewhat tricky.

2 This is a minor scratch to the protective layer over the emulsion. Similar

refractive problems occur. Because this scratch is nearer the emulsion, the
blurring effect will be less. Use the same fix as for Item 1.

3 This is a very deep scratch through the protective layer and in this example,

it has actually removed the yellow emulsion layer and partly damaged the
magenta layer. Added to the refractive effects are actual color changes and loss
of information. Blurring effects don't lose information, they just move it
around, but this has effectively obliterated part of the picture. The only kind of
repair you can do for this is reconstruction of the missing area.

4 This is a large piece of dust that prevents the light from getting through. Dust

on the intermediate negative prints will show up as white spots.
Reconstructing the missing pixels is the solution.

5 Fingerprints show as a distinctive pattern of light and shade. The oil in the

fingerprint causes a refractive effect, but removing it is hard because the edges
are complex and there is a large and odd-shaped area to correct. Blurring the
edges might hide the effects, but you should make sure there isn't a noticeable
difference between the frame with the fingerprint and the ones on either side.
A temporal interpolation may fix this.

6 Films or smears of oily material or the results of getting the emulsion wet may

show up as an area that is slightly discolored. You may only have to deal with
the edges if the deposit has no color-changing effects. Temporal interpolation
or manual rotoscoping the area to correct might be necessary.