Film - A Practical Guide to Video and Audio Compression - page 48

Film stocks all exhibit different grain sizes, and the processing of the stock to force expo-
sures will also affect grain size because it's a chemical reaction based on crystals. One way
this could happen would be if the chemical reaction were caused to happen more slowly
by use of a more diluted solution. Some care is necessary with the formulation of chemi-
cals for film processing, because you only get one chance at it. It is best left to a competent
laboratory.

4.5.1 Real-World Scanning Resolutions

Examining some manufacturer literature provided by FilmLight Ltd. reveals some recom-
mended scanning resolutions for different film sizes on their Northlight scanner. Bear in
mind that film stock, age, and desired output resolution all affect the final choice of scan-
ning resolution. Table 4-2 summarizes some alternatives.
The quoted resolutions are approximate and based on nominal film sizes divided
into the maximum scanning resolution. This assumes the entire camera gate area is being
imaged and that may not necessarily be the case.
Scanning times are quoted as 4.7 seconds per frame when scanning 4 perf 35mm film
at 4K resolution. This needs to be taken into account when calculating how long a job will
take to complete. A roll of film that is 2000 feet long might contain 28,000 frames, and this
could take a couple of days to scan completely at the higher resolutions. Scanning is much
slower than simply projecting the film by a factor of more than 100:1. A similar roll of
16mm film might take even longer, although the scanning time per frame would be shorter
so the duration might be compensated accordingly.
Cintel uses flying spot CRT technology that seems to offer a slight increase in scan-
ning speed, but the output quality may be somewhat compromised in return.

Table 4-2 Northlight Scanner Resolutions Versus Film Sizes

Imaging size

Stock Width Height Resolution

16 mm 3.0k 1.5k 290 dpmm

4 perf 35mm 6.0k 4.5k 280 dpmm

Super 16mm 3.0k 1.5k 240 dpmm

4 perf 35mm (4.7 seconds per frame scan) 4.0k 3.0k 190 dpmm

16 mm 2.0k 1.0k 180 dpmm

Super 16mm 2.0k 1.0k 140 dpmm

4 perf 35mm 3.0k 2.0k 140 dpmm

4 perf 35mm (2.6 seconds per frame scan) 2.0k 5.0k 96 dpmm

Filmlight Ltd.: http://www.filmlight.ltd.uk/
Cintel International Ltd.: http://www.cintel.co.uk/