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From: | Daniel Fort |
Subject: | Re: [Openexr-devel] Re: [Openexr] KeyKode offsets |
Date: | Fri, 1 Oct 2004 06:55:11 -0700 |
Ken McGaugh said: ....Your description is excellent and I think I'm starting to understand this. But I think there is conflicting terminology going on and I'm trying to get it straight..... It looks like I got it all wrong. Apparently the perf offset is alwayscounting from the perf identified as the zero perf in Kodak's key code. On 35mm this would count from 0 to 63 on 16mm it would count from 0 to 19 andon 65mm it counts from 0 to 119.
It looks like I'm still wrong. All I did was to elaborate on Kodak's key code documentation, not perf offset.
I have never worked with a system that counted in these perf offests--in editorial we count in frames, not perfs. The only time we refer to perfs is when talking about which perf number the "zero perf" falls on a frame.In the case of 35mm 3-perf the entire foot that follows that zero perf frame has the same perf offset number.
Thanks to Ken for clearing this up and posting a formula to convert between perfOffset and frame numbers: ------------------------------------------------------------------------ -------------------------------- As for the perfOffset, we will interpret it as the number of perforations
between the reference mark the *last* perf in the frame. Using integer math, we can compute the frame and alignment as follows: frameOffset = perfOffset / perfsPerFrame frameAlignment = perfsPerFrame - (perfOffset % perfsPerFrame) where frameOffset is the "+ 00" bit in the human readable keycode, and frameAlignment is the "p1" at the end.------------------------------------------------------------------------ --------------------------------
It seems that where I got it all wrong was that perf numbers we use in editorial and telecine count from the first perf of the frame and here we need to reference the last perf in the frame.
Hopefully this clears things up to others that may be in the same boat. Does anyone have a paddle?
--Dan
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