US1410884A - Differential development of color cinematographic films - Google Patents

Description

P. D. BREWSTER.

DIFFERENTIAL DEVELOPMENT OF COLOR CINEMATOGRAPHIC FILMS.

APPLICATION FILED JAN. 27, 1917. RENEWED JULY 30, 1921.

1A1 0,88% Pat nted Mar- 28, 1922.

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P. D. BREWSTER.

DIFFERENTIAL DEVELOPMENT OF COLOR CINEMATOGRAPHIC FILMS.

APPLICATION FILED JAN. 27, I917. RENEWED JULY 30, 1921.

Patented Mar. 28, 1922.

3 SHEETS-SHEET 2.

anvew foz mawm P. D. BREWSTER.

DIFFERENTIAL DEVELOPMENT OF COLOR CIN EMATOGRAPHIC FILMS. APPLICATION FILED JAN. 27, I917- RENEWED JULY 30I 1921.

1 A1 0,884 a Patented Mar. 28, 1922.

3 SHEETS-SHEET 3- PATENT OFFICE.

PERCY D. BREWSTER, OF EAST ORANGE, NEW JERSEY, A SSTGNOR, BY MESNE ASSIGN- MENTS, T BREWSTER PATENTS CORPORATION, OF NEW? YORK, N. Y., A CORPORA- TION OF NEW YORK.

DIFFERENTIAL DEVELOPMENT OF COLOR CINEMATOGRAPHIO, FILMS.

Specification of Letters latent.

Patented -Mar. 28, 1922.

Application filed January 27, 1917,-Seria1-No. 144,841. Renewed July 30, 1921. Serial No. 488,680.

T 0 all whom it may concern:

Be it known that I, PERCY D. BREWSTER,

' a citizen of the United States, residing at East Orange, Essex County, New Jersey, have invented new and useful Im rovements in Differential Development of olor Omematographic Films, of which the-following is a specification.

My present invention relates to the development of color cinematograplc films, in methods of color cinematography in whlch two series of negative images taken through separate color filters are printed on the same positive film and the resulting positlve 1mages colored in monochrome so that the blending of the monochrome'images in projection will reproduce the colors of the scene protographed.

My mventlon provides means for controlling the relative amount of development of the series 'of color value images taken. through one filter, say orange-red, in relation to the development of the other color value image series, taken through the other filter, say blue-green.

t is a well established fact that if a scene be photographed by redlight and by green light and developed the same length of time in the same developer, the red negative taken through the red filter, will be far more contrasty or have a higher'gammathan the deposit representing the deep shadows in the object photographed, if the relative exposure was correct, would be about equal in the red and green negatives while the high lights would be far denser on the red nega-J having thin shadows andheavyhigh lights,

so that when the picture was projected the general tendency would be toward greenish. shadows and reddish high lights.

For example, the tendency is to make a persons complexion (a high light) red, and the dark clothes or hair (relatively a shadow) green, a tendency which is always characteristic of two color work.

If the development of the red negative be materially reduced in relation to the green, the scale of contrasts of gammas will be more nearly correct and the resultlng prints will reproduce the scene photographed with materially lessened color distortion due to varying contrasts.

At present the usual practice is to rather underexpose the red negative and to overdevelop it while the green negative is given practically correct exposure and develo ment, thereby rendering correctly the middle tones in the finished picture and hava moderate excess of red in the high 1n ligits and green on the shadows, the rela-- tive exposure of the red and green negatives being judged from the most plea-singfinal color blend rather than the actually correct exposure.

According to my invention I prefer to give I the red a longer exposure and shorter development than ordinarily used in the prevailmg ractice.

I pre er to determine the speed of the film through the orange-red and blue-green filtersto be used in the camera by the well known Hurter and Drifiield system (photo-.

made in accordance with the scale. green negative. In other words the silver The development of the two negatives is so proportioned that the whites or greys of the object photographed are rendered in similar densities in the two negatives or, in other words, the two gamma or contrast lines are arallel. The determination of these relatlve times is readily effected by developing a series of red images for different lengths of time, for. instance the first for a time definitely known but somewhat less than what is judged (from experience) to be the proper, the second for a known longer time, etc. A series of green images is de veloped 1n like manner, and the two series are then compared (by the Hurter and Driffield method referred to above) and the images having equal gammas are found. The development times for these images are then noted. For example, it may be found that the third red development time, which was, say, two minutes, and the fifth green development time, which was, say,'three and a half minutes, have equalgammas. Ac-

between the film and the rails.

cordingly the red images will be developed two minutes and the green images three and a half minutes.

To accomplish this result it is necessary to treat one series of images longer with the same developer or to use developer of different strengths on the two image series. The method of operating the first of these systems is illustrated in the accompanying drawings, in which-- Fig. 1 is a diagrammatical section and Fig. 2 is a plan of a developing machine adapted to treat film with one image series on one side and the other image series on the other side. Figs. 3 and 4, respectively, are similar views of a developing machine adapted to treat film with the images series side by sidet Fig. 5 is a section through the machine, about on line a-a of Fig. 4. Fig. 6 is a plan view of the type of film used in the machine illustrated in Figs. 3 and 4. Fig. 7 is a diagram of a machine where pressure is used in place of vacuum to hold film in place.

The tank 1 is constructed with a slot 3, preferably along its top formed bythe rails 2, 2 and having a width about equal to the distance between the perforations in the film to be used. The film 4 is mounted on spool 5 and passed over the slot 3 preferably guided by pins 6, 6 over rollers 8, 9, 10 and 11. The film is drawn constantly and continually through the machine by any desired means.

Negative film is preferably run across the slot 3 with the red images on top while if positive fiim (with the images on its opposite sides) is being developed the image series which is to be stained green is on top so that it will receive the shorter development.

The edge of the film are held in close contact with the rails by the slight vacuum maintained in the tank by the exhauster 13, through pipe 14 which also prevents the escape of any developer by mamtaining a current of air into the tank through any crevice It, is frequently desirable to first treat the film with absolutely fresh developer and then continue the development with partly used developer. Fresh developer is led into the machine through pipes 15, 15 and sprayed on the two sides of the film through sprays 16, 17 respectively so that both sides of thefilm areacted upon first by the fresh developer- The connection to the spray 17 is preferably through the flexible pipe 15 so that the relative duration of the development of the two sides of the film can be controlled by shifting. the spray back and forth along the rails. The front lip 18 and sides of the spray 17 are arranged to make a close contact with the film rails while the end19 toward roller 8 is left open so that the excess of developer, aided preferably by a slight incline, will 1,4.m,se.4

panse of film exposed in the slot requires a greater amount of developer which may be provided by the use of the pump 22, adapted to draw developer in from the tank through pipe 23, and to discharge it through pipe 24 and the. series of sprays against the underside of the film 4. Outlet 21 provides an overflow for any excess developer.

Figures 3, 4and 5 illustrate the machine adapted to treat film of the general type shown in Fig. 6 in which the red and green images extend side by side down the film on the same side. The film 26 is wound on spool 27 and led across the treating slots with the margin containing the perforations in contact with rails 37, 37. guided by the pins 38, 38,38. If the film has a space between the red and green images, preferably,

the partition 39 is arranged to maintain coninto the machine through pipe 34 and into spray pipes 35 and 40 so arranged that both of the image series are first acted upon by fresh developer. The relative positions of the sprays 35 and 40 determining the amount of differential developing by the time one image is acted upon .until the corresponding image in the other series is acted upon. To continue the action of the developer 0n the side having the longer development the machine is preferably equipped with an auxiliary spray through pipe 36 fed from pump 33 which withdraws'the developer in the tank and discharges it through the sprays. The exhauster 32 is adapted to maintain a slight vacuum under the film to hold it in contact with the slot.

Fig. 7 illustrates a machine of similar structure except that instead of maintain ing a slight vacuum in the-tank to hold the film in place, a cap 41 is constructed'over the slot and a slight pressure is maintained on the film by means of the fan 42, the out= let pipe 43 of which is connected to the ca 41.

n three'color cinematography with three images side by side, or two images side by side and the third image on the other side it is apparent it would be possible to give all three films different developing which a plurality of series of images of dif-- ferent color values, including red and green are produced, the improvement comprising develop ng thegreen series of imagesto a greater degree than the red whereby substantially equal densities are produced in the high-lights of the images of the red and green series.

3. In the art of color cinematography in which a series of color value images recording the action of light transmitted through a red filter and a series of color value images recording the actionof light transmitted through a green filter are produced, the improvement comprising developing to substantially the normal degree the series of images which are to be colored red, and de veloping the other series to less than the normal degree, whereby substantially equal densities are produced in the high-lights of the two series.

4. In the art of color cinematography in which a series of color value negative images recording the action of light transmitted through an orange-red filter and a series of color value negative images recording the action of light transmitted through a blue-green filter are produced, the improvement comprising developing the blue-green series to produce a desired degree of contrast, and developing the orange-red series to produce in the high-lights thereof substantially the same density as in the high-lights of the blue-green series.

In testimony whereof, I have signed my name to this specification in the presence of two subscribing Witnesses, this fifth day of January, 1917.

PERCY D. BREWSTER.

\Vitnesses THOMAS D. BERAU, E. M. THEISE.

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