[Openexr-devel] Re: [Openexr] KeyKode offsets

[Thomas Kumlehn]

Dear Ken,
dear Dan,

in fact handling film footnumbers digitally often needs two perforation
offset values:

One is the number of perforations since the last valid barcode. This is
added to the perfOffset mentioned in the KeyKode manual.
A KeyKode reader would continiously count perforation holes and sometimes a
valid barcode comes by and resets it with its 16 digits. 
For uncut film this would happen twice per foot. For mixed footage, gaps
between valid codes can be bigger, because you are allowed to cut every
2/3/4 frames (depending on the film format).
After the reset to a barcode value the perforation holes are incremented
again giving values that are repeatable but you cannot be sure the values
belong to the right roll if rolls are mixed.

For every film roll (every part of a scan) we also need a second offset
that tells us on what perforation the camera frame is positioned.
When you load a film camera you cannot see foot print numbers. They are
latent and exposed by the manufacturer and only show up after neg
development. So given the 3 or 4 holes per frame a variety of offset
combinations can occur. This is important for interpreting EDL entries
automatically

What really matters as a scan reference IMHO is the first one updating the
KeyKode for frame based scanners and the second is needed internally by
continious scanners like the Spirit and for negative cutters. They use it
to decide whether to slice before or after a frame that lies on a border.

Just my 2 Euro-cents :-)

=====
Thomas Kumlehn
PIXEL PARTNER (R)
mobil +49 177 6990990


        

        
                
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