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Author
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Topic: Why are Interpositive elements pink?
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Michael Barry
Jedi Master Film Handler
Posts: 584
From: Sydney, NSW, Australia
Registered: Nov 1999
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posted 06-20-2002 01:13 PM
I spent some time gaining work experience in DVD quality control, and one of the things I learned is that one of the signs that a transfer has been derived from an IP is that everything looks a bit reddish - the whites are a bit on the pink side and the reds are a bit too hot (although this depends, as some telecines can handle IPs better than others).Recently, I visited a lab where they were screening an IP, and indeed the film is pink - very pink! Why is this? Is this done for the same reasons that colour negative film is orange in colour? (Called a mask, if memory serves correctly.) The second question is: why would someone want to project an IP? What would this tell you that screening a one-light workprint or timed print would not? Thanks!
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Steve Kraus
Film God
Posts: 4094
From: Chicago, IL, USA
Registered: May 2000
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posted 06-20-2002 10:01 PM
Orange MaskingAs you know the image is formed of magenta (minus green), cyan (minus red) and yellow (minus blue) dyes. No dye is perfect in terms of what colors it passes and what are absorbed. Furthermore, the choice of what compounds to use as dyes is limited to what can be formed by the complex photographic chemistry. Thus, in the real world the dyes forming the image are absorbing some colors of light that they ought not to. This leads to errors as the image is printed. This isn't something you can correct for with the printing light because it varies across the image with the image itself. The solution to this problem is the colored color coupler. The color coupler is the molecule which will form the color dye during development IF it's been activated by the appropriate color light. (OK, technically it's usually a reaction with the oxidation product of the developer after reaction with the silver compound but let's not go there.) A colored color coupler is exactly like it sounds: It has a color to it before processing. The color, in this case, is designed to be very close to the UNWANTED light absorption of the dye molecule, if one is formed. Consider the old adage, "if you can't beat'em, join'em". With colored color couplers this unwanted absorption is the same everywhere. At one point it's because dye has been formed and the dye has the erroneous absorption as well as the desired one. At another point no dye has been formed and the colored color coupler left behind creates the same unwanted absorption. Now the unwanted absorption is the same everywhere and it can be compensated for with the color of the printing light but also more especially by the sensitivity designed into the material being printed on to. The combination of these unwanted absorptions appears as orange. On the unexposed parts of the film like the edges what you are seeing is entirely the colored color couplers. Within the image you are seeing a combination of them and spectrally deficient dyes. The same techniques is used on IP and IN stocks for the same reason it's used on camera negative. That's why these film stocks are orange. But not why you are observing different looks on DVD transfers.
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 06-21-2002 05:55 AM
Gee Steve, good explanation of colored couplers. Did you ever work for Kodak?Kodak invented colored couplers during the 1940's. The technology greatly improved the color reproduction of the negative-positive color system. Over 50 years later, every manufacturer of color film still uses this Kodak innovation in their color negative films. A complete discussion of colored couplers and how they work is in the book "Principles of Color Photography" by Ralph M. Evans, Wesley T. Hanson and W. Lyle Brewer (the Kodak inventors), published by John Wylie and Sons, Inc., 1953. LOC Catalog 53-6722. And some links:
http://www.kodak.com/country/US/en/motion/support/processing/sequence1.shtml
http://www.spinics.net/lists/scan/msg02606.html
http://frontiernet.net/~rlmsmw/photo/c41.htm
http://www.kodak.com/US/en/motion/support/h1/
Colored couplers are only one of the many sophisticated technologies that Kodak has developed to improve the color and sharpness, and reduce the graininess of film. More improvements are on the way!
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 06-21-2002 10:38 AM
For optimum quality, telecine transfers today are almost always made from a color-masked pre-print element, rather than a print. If a print must be used, Kodak makes a special low contrast print film for better telecine transfers:
http://www.kodak.com/US/en/motion/products/lab/h12395t.shtml There should be no contrast mismatch or color "bias" in a telecine transfer, regardless of the film type used. With modern telecines, even films faded by improper storage can usually be transferred with high quality results. ------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 06-21-2002 04:57 PM
Question to john,As I understand it, there is just one type of intermediate stock, but it may be necessary to make an interneg from many various types of positive material, e.g. an interpos, or a 16mm Kodachrome original. These will obviously have vastly different contrast, how can they both be printed onto the same stock, to produce internegs of suitable contrast for standard prints to be made? It may even be necessary to intercut material from different sources, so they would have to be quite closly matched. I wouldn't have thought it would be possible to vary the standard ECN-2 process enough to produce the required contrast without creating other problems.
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