evertz 4025 Instruction Manual page 17

1. OVERVIEW
OVERVIEW
The Model 4025 Film Footage Encoder is designed specifically to aid in the
encoding of film footage and time code during the film to tape transfer process.
The Model 4025 is a generator/reader for SMPTE/EBU Linear Time Code (LTC)
and Vertical Interval Time Code (VITC), and contains a high resolution video
character generator (VCG). The VCG is also used as an on screen programming
aid to the many operational modes of the Model 4025. The Model 4025 uses the
latest state of the art technology, combined with our extra intelligent firmware, to
offer you the ultimate in performance, reliability, and adaptability.
The 4025 Film Footage Encoder is capable of working with both 35 mm and 16
mm film. Telecine transfer speeds of 24 or 30 frames per second in NTSC
systems, or 25 frames per second in PAL are automatically sensed by the 4025.
Film is typically viewed at 24 frames per second (fps) while NTSC video is viewed
at 30 fps. To compensate for this difference in the frame rates, telecines use a 2/3
pulldown. Since each video frame is comprised of two video fields, video is
viewed at 60 fields per second. Telecines can transfer 24 film frames to 60 video
fields (30 video frames). The resulting ratio is 24:60 or 2:5, which means 2 film
frames every 5 video fields.
transferred to 2 video fields, the following film frame is transferred to 3 video fields,
and so on.
A video frame is always comprised of a field 1/field 2 sequence, and is defined by
a unique time code number. The film frames will not always be in phase with the
video frames. With the 2/3 pulldown, the film frames alternate between being 2
video fields long and 3 video fields long.
The 4025 Film Footage Encoder uses the telecine's bi-phase quadrature tach
pulse to keep track of the film motion. In addition, a field sequence pulse from the
telecine identifies which field of the 2/3 pulldown is in the current video field, thus
enabling the 4025 Film Footage Encoder to identify the precise film frame that is
contained in each video field.
Latent edge numbers have been present on motion picture negative film stocks for
many years in human readable form.
specific to various manufacturers and film stock types, some having 4, 5, 6 or 7
digits with varying numbers of alpha-numeric roll numbers, or prefix numbers to
the footage. Using normal BCD encoding, there is only room to encode a
maximum of 6 digits of film feet plus 2 digits of frames into the user bits. By using
a compressed binary format, up to 7 digits of feet plus frames can be encoded,
however, special decoding routines in the time code readers are required to
recover this information and display it as decimal digits. The 4025 Film Footage
Encoder allows the user to select which encoding style he prefers. In addition, the
maximum count of the footage can be preset, permitting a fixed numeric prefix to
be encoded in the unused footage digits.
In 1988, Eastman Kodak, in conjunction with the Society of Motion Picture and
Television Engineers devised a new edge print that not only standardizes the
numbering format, but is also printed as a machine readable barcode. Kodak calls
this numbering system KeyKode. Other film manufacturers have adopted this
numbering standard and have each given their version a proprietary name. For
the sake of clarity we shall refer to all of these implementations as KeyKode.
Model 4025 Film Footage Encoder Manual
The 2/3 implies that one of the film frames is
The edge numbering format has been
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