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OPERATION
Model 5550 Universal Film Data Decoder Manual
3.5.1.3.
Matrix Length
Not only does the matrix width vary in size, but so does the length. On
16mm film there is not much variation because the size variation is limited
by sprocket hole spacing. However, on 35mm film the length can vary from
between two to more than three perforations in length. This does not pose
any problem for the 5550 decoder because it measures the actual size of
the rows.
The length of the matrix will, however, affect the maximum rate at which
code can be recovered. Code consisting of long, stretched matrices can be
read at a much faster shuttle speed than code with short matrices. Short
16mm matrices may only be read as fast as two times play speed, while
long 35mm code may be read at the full shuttle speed of the telecine.
The MATRIX LEN extended display shows the relative length of the matrix
at a given speed.
approximately 12. As the film speed increases, this number will get lower.
When the number approaches 2 or 3 that indicates that the maximum
theoretical recovery speed has been reached.
decreases the number will get larger.
3.5.1.4.
Matrix Contrast
Low contrast code (light green in color on negative stock) is inherently
harder to recover than higher contrast code (dark green or purple in color).
The film edges, dirt and scratches create optical noise, that when added to
a low contrast signal makes the recovery of the data harder to perform. The
5550 auto light level routines are designed to maximize the signal to noise
ratio for the given code contrast. These auto intensity routines, however,
require biphase information to know how much film has gone by when it is
not reading so that it can adjust the light level.
In extreme cases of low contrast code, the sprocket holes, on 35mm film,
and KeyKode edges, on 16mm film, can start to look like matrix dots,
affecting decoding performance. The 5550 'MATRIX START' menu item
allows the user to block the decoder's algorithm from detecting these
edges.
See section 3.3.8 for information on setting the Matrix Start
position.
The TC MIN/MAX extended debug display gives an indication of the
contrast of the matrix.
3.5.1.5.
Distortion
If the exposure was not set correctly in the matrix writer of the camera or in
the edge lighting during printing, the 'on' dots vs. the 'off' dots will be a
different size and the edges between them will become wider. The 5550
decoder will account for this distortion while decoding, but as the distortion
The nominal matrix length value at 24 FPS is
As the film speed
Page 3-17
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