[Tig] Film Timer Question
jean-c at moving-picture.com
Tue Dec 11 18:40:33 GMT 2012
Pete, it was quite limiting to have to have one single value for each scene, why a system allowing continuous changes during a scene was never invented?
Director of Colour Grading
127 Wardour Street, Soho, London, W1F 0NL
T +44 207 434 3100
Live Colour Grading availabile with Paris | Stockholm | Oslo | Hamburg | Milan
From: peter_swinson at compuserve.com [peter_swinson at compuserve.com]
Sent: 10 December 2012 18:06
To: tig at colorist.org
Subject: [Tig] Film Timer Question
Sohonet www.sohonet.co.uk sponsors the TIG.
Support from Digital Vision www.digitalvision.tv
The Film Timer
Filmer timers are the colorists of the film lab whogenerat the correct color and intensity values for film printers. (Film is copied from a negative onto anotherlength of film that produces a positive, the films are normally sandwichedtogether at the printer gate and light is shone through the negative to exposethe “print” material.)
Throughout the life of the film industry, shot to shotexposures have varied and would look like abrupt changes at scene cuts. Thefilm timer creates data to change the printers light values.
In early B/W days printing machines such as Bell & Howellmodel D & J had a crank that adjusted the amount of light as the printerwas running. A film timer would either asses the negative or look at a onelight (single exposure print), and decided where the crank should be set foreach shot, thus evening up the scene to scene density levels.
Then some bright individual created a band of 35mmcardboard, into which varying apertures could be punched. As each scene wentthrough the printer a new aperture was used by advancing the cardboard band. In both the above scenarios the light levelwas pre-selected, prior to the scene approaching the printer gate. A notch atthe edge of the film near the splice would cause the change to then happenquickly. This allowed the printer illumination to be changed in less than 1frame even when printing at speeds greater than 24 fps.
Then color film appeared and not only was density correctionrequired, but also color balance.
Until the 1960’s this was achieved often by stapling variouscyan, magenta and yellow filters of varying density over the apertures in thecardboard band. Each set of filters and the aperture corrected for overalldensity and color balance. Again in these days the film timer made theassessment visually, often by holding various density color filters over a one light print. A real skill was required and several printswere often needed before the result was acceptable. This entire process was knownas subtractive color printing, as the cyan, magenta and yellow filters removedlight from the printer light path.
Late in the 1960’s/ early 70’s Bell & Howell developedthe light valve. This ingenious device was electronically controlled, initiallyby relay driven electronics, then in the later 1970’s and beyond by computers.The light valve comprised of a variable width slit that could be changed inmilliseconds. A light box attached to the printer split the original printer light beam intoRed, Green & Blue, a light valve was inserted in each beam, then the beamswere recombined to form a slit at the film path. Therefore the three light valvescould control the color balance and illumination level.
The Bell & Howell model C printers and there currentsuccessors, the B&H modular printers all use this principle. It is known asadditive printing because the beams are added together.
Concurrent with this development Hazeltine Corporation (New York, Long Island) and Kodak (Rochester)designed devices called a Color Film Analyzers. Both were basically crudetelecines that turned a film negative image into a positive image on a TV display.Hazeltine used a color display an RGB beam splitter and RGB detectors, much like later Cinteltelecines, while Kodak used a B/W display and a single detector around whichspun a RGB color drum, providing a “sequential” RGB color image.Both used CRTs as the scanning light source.
The Film Timer now had a great new tool to define the lightlevels for printing film.
The analyzer is loaded with the film negative and eachscene is examined as a positive on the TV monitor. Three basic controls areavailable to the Film Timer, Red, Green and Blue. Each calibrated from 1 to 50,this being the same as the range of the Bell & Howell light valves. Theseare known as printer points, each is 0.25log E, whereby 12 printer pointsequates to a 2:1 change in light level. Unlike a telecine there is no separateLift Gamma & Gain, nor any secondary color correction. This because aboutthe only thing you can do when printing film is to change the exposure.(There are other setup adjustments but these are not varied when analyzing the film)
The resulting printer values were recorded on punch tape andthe printer would replay the tape making the desired light changes at the scenechange. These changes happened within ½ frame even when printing film at around1000 feet per minute. Quite some achievement for the early 1980’s.. I believe punched tape is used to this very day on these machines. The tape being stored with the negative in its own can. This I guess forms a very reliable, non electronic archive of the color values!
The trigger for where the changes occurr is still eithera notch in the edge of the negative or a small metallic cue tab that is stuckto the negative edge. Latterly many computerized systems rely on counting thefilm position much like time code, to determine the light change point .
So the Film Timer is to Film printing what the colorist isto Film to Video and Digital mastering.
Sorry to be so long winded, hope it helps.
More information about the Tig