US2286930A - Method of projecting color pictures - Google Patents

Description

June 16, 1942. c T 2,286,930

METHOD OF PROJECTING COLOR PIQTURES Filed July 2, 1940 jive 715E02 czZcZmc el 1,44 715.5 QEgZy,

Patented June 16, 1942' Gerald F. Backett, Los Angelea, Calif., minor to Technicolor Motion Picture Corporation, Hollywood, Calif., a corporation of Maine Application July 2, 1940, Serial No. 843,806

3 Claims. (01. 88-164) In the art of projecting motion pictures in natural colors one of the major problems is to obtain proper balance between the three complemental colors used to produce the various hues throughout the pictures. While the color balance can be controlled in the process of producing the color film, of course the film cannot be changed after it is finished. If the projection equipment were the same in all theaters in which the pictures are to be projected the color balance could be adjusted to suit the equipment. However, the equipment in different theaters varies widely, particularly in respect to the color of the projection light, and this variation affects the color balance. For example, projectors having arc lamps produce a bluish light while projectors equipped with incandescent lamps produce a yellowish light, and even projectors of the same type produce light of diflerent colors, respectively, depending upon the voltage and other factors affecting the temperature of the light source. If the color balance in the film is adjusted (in the manufacture of the film) to projection light of .one color temperature, the balance will be'wrong for projection light of another color temperature.

Objects of the present invention are to produce proper color balance in the pictures reflected from the screen notwithstanding the hue of the projection light does not correspond to the color balance of the film pictures, to compensate for the tendency of off-color projection light to destroy the color balance, to cause each film to produce the same visual effect in different theaters notwithstanding differences in the color temperatures of the projection lights in the different theaters respectively, and to accomplish the foregoing with maximum efllciency and minimum expense.

According to the present invention the tendency of the projection light to destroy the color absorb the ofl-color components of the projectio'n light; Thus, in each theater, the color of the- 1 screen is correlated with the color of the projec tion light in accordance with the color balance of the film pictures to be projected, whereby the screen pictures in different theaters have substantially the same color balance notwithstanding the aforesaid vdiflerences in color of the projecting light in the different projectors.

The preferred method of determining the proper relationship between the colors of. the screen and projection light, respectively, is to project light from the projector upon an area of the screen, simultaneously projecting light from a standard source upon an adjacent area, and varying the tone value of the light from the standard source and/or the spectral absorbing qualities of said adjacent area until the two areas approximately match in tone value.

For the purpose of illustration a typical method of tone determination is shown in the accombalance of the film pictures is counteracted by absorbing from the projectio'n light .the color components which tend to make the color balance of the screen pictures differ from the color balance of the film pictures. This absorption of the off-color components is preferably efiected at the screen, as by painting the screen the proper shade. For example, if the projection light is l more bluish than the light for which the color balance of the film pictures are adjusted, the

screen is colored the proper shade of yellow to panying drawing in which,

Fig.1 is a perspective view; and

Fig. 2 is a sectional view through the aforesaid juxtaposed screen areas.

The particular method chosen for the purpose of illustration involves a projection screen I, a v

projector 2, an auxiliary screen I, an auxiliary projector 4 and a mask 5 for shielding the auxiliary screen 3 from the light of the projector 2.

"The screen I and the projector 2 comprise re lar equipment in the theater where the test is being made, the other apparatus being portable for convenient removal from theater to theater. The auxiliary screen 3 may be supported in juxtaposition to the screen I in any suitable manner as by means of the tripod 6. v 1

The auxiliary projector 4 is preferably moun ed on a cabinet 1 containing means for regulating the voltage and current of the projector, together with metersfor indicating values of potential and current. The mask 5 may be mounted in any suitable way as by means of an adjust-' able post 8 extending upwardly from the cabinet I. Mounted on an extension 9 of the casing of the projector 4 is a filter holder l0 into which.

may be dropped one or more filters of diflerent thicknesses and colors.

To determine the proper color of the screen I for use with the particular color of light emitted by the projector 2, the screen i is illuminated by the projector 2, with the projector operating at the voltage. supplied to the projector 4 and/or varying the filters in the holder Ill and/or replacing screen 3 with a screen of different color, the tone value of the auxiliary screen can be made substantially to match the tone .value of the screen I. Having previously determined the screen color corresponding to each combination of filters and/or voltage in the auxiliary projector and/or color of auxiliary screen, the aforesaid test indicates the hue which the screen I must be colored to compensate for the off-color of the light from projector 2, thereby to produce in the pictures reflected from the screen I a color balance corresponding to th: aforesaid color balance of the dim pictures notwithstanding the improper color value of the light from" projector 2. When projecting pictures upon the two screens the pictures should 'be the same or at least similar in color.

As an example of the foregoing the following procedure may be followed. First select a standard projection system with a screen and projection light of known color, preferably one approximating that of the average theater. Alongside this system set up one of the aforesaid auxiliary systems which has a Mazda lamp and precision means for adjusting the color temperature of the lamp to a predetermined value (say 3200 K.) or to some indicated departure from I that value. With thecolor temperature of the Mazda lamp at said predetermined value the color of the auxiliary screen is varied by application of difierent pigments until it appears to match the screen of said standard system. For

example, the pigments may comprise flat white, ultra marine blue and ultra marine green and the proportions required to produce the standard auxiliary screen may comprise:

Parts Flat white 90 Ultra marine blue 5 Ultra marine green 5 The aforesaid color temperature and auxiliary screen color are then adopted as the standard conditions for use in regulating the color balance of the picture in the process of manufacture; that is the pictures are produced so that, when projected with a Mazda lamp at said color temperature upon a screen having the same color as said auxiliary screen, the pictures present the desired color contrast.

For use in testing the projection conditions in the different theaters in which the pictures are to be projected, different proportions of said pigments are used to produce a series of auxiliary screens which differ in color from said standard auxiliary screen in regular steps, the series of screens covering the entire range of screen col- Screen No. Subtract 1 part ultra marine blue.

2 parts ultra marine blue. 3 parts ultra marine blue. 1 part ultra marine green. 2 parts ultra marine green.

3 parts ultra marine green. r

Thus, for example, the proportions for 113 and 3G would be as follows:

Flat white 90 4 Ultra marine blue 5 6 Ultra marine green 2 ner but without pictures, the standard auxiliary screen is inserted in the auxiliary screen holder and the auxiliary Mazda lamp is operated at the aforesaid predetermined color temperature. If the colors of the two screens appear identical then the theater system will display the aforesaid-pictures in proper color balance without altering the theater conditions. However if the two screens do not match the auxiliary screen is replaced by first one and then another of said series of auxiliary screens until the theater screen and auxiliary screen do match. For each auxiliary screen there is a tint which, when applied to the theater screen, will make it match the standard auxiliary screen and therefore display the aforesaid pictures with the desired color balance, the particular tintx'being determined empirically. For example the aforesaid screens may indicate the following tints.

Screen No. A volatile solvent containing- 1 part ultra marine blue. 2 parts ultra marine blue. 3 parts ultra marine blue. 1 part ultra marine green. 2 parts ultra marine green. 3 parts ultra marine green.

Thus if auxiliary screen No. 3B is required to match a theater screen the latter should be tinted lwlith a carrier containing 3 parts ultra marine Inasmuch as it is the color of the light reflected from the screens which is to be matched (rather than the color of the screens per se) and inasmuch as the color of the light reflected from a screen may be variedby changing the color of the light projected to the screen (as well as by changing the color of the screen) the light reflected from the screens may be matched by changing the color of the light projected upon either screen. Thus instead of interchanging auxiliary screens to match the theater screen only the aforesaid standard screen need be used, the matching then being effected by varying the voltage of the auxiliary projector or by inserting different filters in the auxiliary beam, each voltage and each filter indicating a certain tint to be applied to the theater screen as determined empirically.

In many cases the difliculty is not with the color of the theater screen but with the color of the projector light. Obviously the aforesaid method indicates the right screen color to display the pictures in desired color balance because the apparent color of the theater screen in matching it with an auxiliary screen, depends upon the color of the projection light as well as the color of the screen itself. Thus the method broadly involves any correlation of the color of the light reflected from the screen with the color of the projection light, by selectively absorbing 2,286,930- from the projection light, uniformly throughout the cross-sectional area of the projected beam of light, those predetermined color components which tend to make thecolor balance of the' screen pictures differ from the color balance of the film pictures. If the color of the light reflected from the two screens is matched by altering the color of light projected to the picture screen it is preferably done with pre-cali-brated transmission filters in preference to change in voltage of the projector lamp.

It should be understoodthat the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

This application is in part a continuation of Y my prior application Serial No. 221,557, filed July 27, 1938.

I claim:

l. The method of projecting natural color pictures on a picture screen, the color of the screen or the projection light being unknown, with a color balance substantially the same as that produced with a standard system having an auxiliary screen and auxiliary light of known colors, the method comprising projecting said projection light on said picture screen without color-picture film in the path of the light, projecting said auxiliary light on said auxiliary screen, producing a variation in the color of the light reflected from one of said screens until it matches the color of the light reflected from the other screen, said variation indicating the color components to be absorbed from the light in order to make the color of the light reflected from the picture screen match the color of the auxiliary light reflected from the auxiliary screen, and then projecting the color pictures on the picture screen with said projection light while absorbing the 40 said color components from the light uniformly throughout the entire cross-sectional areaof the light. p

2. In the art of projecting color pictures having a predetermined color balance, the method of determining the combination of colors of pro-' I jection light and picture screen respectively which will display said pictures with the desired combination of colors which is required to dis-.

play said pictures with the desired color balance.

3. The method of projecting natural color pictures on a picture screen, the color of the screen or the projection light being unknown, with a color balance substantially the same as that produced with a standard system having an auxiliary screen and auxiliary light of known colors, the method comprisingprojecting said projection light on saidpicture screen without color-picture fllm in the path of the light, measuring the color of the light reflected from the picture screen to determine the color components which make it differ in color from that of the auxiliary light reflected from the auxiliary screen, and then projecting the color pictures on the picture screen with said projection light while absorbing said color components from the light uniformly throughout the entire cross-sectional area oi! the light.

' a, F. aacxm'r.

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