[tig] Digital Intermediate from TDF

Rob Lingelbach rob
Thu Jun 12 03:24:37 BST 2003


The following messages were originally posted to the daVinci
forum and are reprinted here with permission from the
authors.  The messages are separated from each other by a
series of '+' characters.

the reprinting here is intended to encourage the discussion
and evolution of the process and knowledge of the Digital
Intermediate, which for our purposes is not intended to be the
middle finger of the human hand.

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From: "Kevin Shaw" <kevs at davsys.com>
Subject: Re: [TDF] Digital Intermediate (plain text)
Date: Mon, 9 Jun 2003 16:16:33 -0400

Dear all,

I am writing a document that introduces the concept and
workflows of Digital Intermediates, with solutions and
reference sites. The finished document will be available
from the da Vinci web site and other venues.

If you are interested in digital intermediate, what
questions do you have?  If you are involved in digital
intermediate, would you like to be included as a reference
site?

My own first question is how do we define "digital
intermediate" ?

Answers to the forum for discussion, or to me at
kevs at davsys.com directly are welcome

Thanks in advance
   Kevin Shaw
   Director of Training           kevs at davsys.com
   The da Vinci Academy        www.davsys.com
 Total Image Solutions

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From: "Emil" <emil at compt.com>
Subject: Digital Intermediate (plain text)
Date: Mon, 9 Jun 2003 15:03:32 -0400

Dear Kevin,

     If your Digital Intermediate document will include
technical aspects of the technology, I can mention some
issues and questions, that need to be addressed by
post-production houses nowadays. Those issues may have
different impact on different facilities, and they are
listed below not in order of importance:

    1) Calibration of Digital Intermediate ( DI ) system
from input to output

     2) Static and dynamic modulation transfer function (
MTF ) of Digital Intermediate, including parameters of
telecine and film recorder.  Resolution and aliasing
problems

     3) Entry image processing in DI - exposure latitude,
dynamic range, white balance, grain reduction, smear
correction, clip and knee function; Exit image processing in
DI - colour rendering, tone mapping, gamut mapping, luma
transforms, non-linear correction, saturation processing,
aperture correction, editing

     4) Colour grading and the question of optimal
one-light-transfer. Bit interpolation in Digital
Intermediate,  10-12-14-16 bits and bit rounding

     5) Film-to-data transfer and MTF of slow scan process.
Rotated frames and segmented frames of HDTV image files

     6) Varispeed film-to-video transfer and advanced
pulldown, or long frame motion

     7) Colour correction - colour triangle and colour cube
vector processing. Scene-to-scene correction and
layer-to-layer correction

     8) Colour space conversion:
           scene-referred colour encoding
           picture-referred colour encoding
           output-referred colour encoding

     9) Resolution "coexistence" in DI systems and HDTV
frame format conversions. Mastering format selection

    10) Lossless compression and lossy compression. VTR
compression

    11) Visual Effects and Computer Animation interfaces for
HDTV files.  File format conversions

    12) Network processing in Digital Intermediate. Local
and global standards.

Regards,
Emil Borissoff
Command Post and Transfer,
Toronto

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From: "Kevin Shaw" <kevs at davsys.com>
Subject: Re: [TDF] Digital Intermediate (plain text)
Date: Mon, 9 Jun 2003 16:16:33 -0400

Thanks Emil,

I would like to concentrate on the solutions available, and
possible methods of overcoming the most common problems,
many of which you list. I did not fully understand some of
your points, so perhaps you could expand on them. Others, I
am well aware of and would welcome your opinions, especially
if you have direct experience of them.

Going back to my opening question, "what is Digital
Intermediate?" - it could be argued that all digital color
correction is a digital intermediate. I am sure that most of
us reserve the term for film or at least D-Cinema finishing,
even if the process includes video masters along the way. If
we agree on this, your point 10) on compression is relevant.
By lossless compression are you referring to 10 bit log
transfers, and is that truly lossless? Is lossy compression
acceptable for DI?  D Cinema is delivered lossy compressed,
so how does that influence the workflow? Current VTR
compression can compromise color correction, so is that a
reason to rule it out of a valid DI workflow?

I am thinking that there is a difference in workflow between
video finishing that goes to film out, and DI with film
finishing that includes video mastering.  Would you agree?
Could you perhaps expand on points 5,6,10 and 11 with this
in mind ?

Thanks to all the others who have replied to me privately by
the way, especially Rob Lingelbach for offering the
considerable resources of the TIG in this project. And yes
the results will be made available on the TIG web site too.

Looking forward to your replies
Kevin

       Kevin Shaw
       Director of Training           kevs at davsys.com
       The da Vinci Academy        www.davsys.com
       Total Image Solutions

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From: "Emil" <emil at compt.com>
Subject: Digital Intermediate (2)
Date: Wed, 11 Jun 2003 16:15:28 -0400



Dear Kevin,

    I asked our Operation Department re some of your
questions of  workfow and I got a feeling that all
possible paths would be included in the broad understanding
of Digital Intermediate, while the nominal understanding 
is still film-in, followed by HDTV processing and film-out.

   Following our discussion, please take a look at the issues mentioned,
expanded from engineering point of view:

   LOSSLESS COMPRESSION:   One example of lossless
compression is Run Lenght Coding in video disk recorders. I
assume that the category of lossless or lossy compression
will be applied once film images are transfered to HDTV
signal. The question is whether the transfered pixel-frame
structure will be preserved  (lossless), or whether it will
later undergo spatial and temporal filtering (lossy).

   CURRENT VTR COMPRESSION: There are lossless-based VTRs,
which play a role in VFX. They might be considered part of a
DI system, in my opinion.

    FILM-TO-DATA TRANSFER: In the case of CRT- based
telecine and slow scanning, automatic afterglow correction
contributes to increasing the spacial resolution.  This
process supports 4K for DI.

    VARISPEED TRANSFER AND ADVANCED PULLDOWN: Pulldown with
the 2:3:3:2 cadence. Discussion can be found at www.24p.com.
The standard pulldown 2:3:2:3 gives a more consistance look
to the motion.

    VISUAL EFFECTS INTERFACES. FILE FORMAT CONVERSIONS:  As
an open source image file format, OpenEXR is an example for
digital representation of film with a dynamic range of over
30 f-stops, and an additional 10 f-stops at the low end.

Regards,
Emil Borissoff
Command Post and Transfer
Toronto

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the foregoing compiled by
Rob Lingelbach
TIG admin - colorist





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