US2011544A - Color photography - Google Patents

Description

Patented Aug. 13, 1935 ooLon PHOTOGRAPHY N e Isaac PLRodman, South Orange, N. J., assignor;

to Lektophone Corporation, Jersey City, N. J., a corporation of Delaware N Drawing. Application October 18, 1930, Serial N0. 489,709.. Renewed March 30, 1934 Claims. 01. 95 2) I In the past therehave been several processes for photographically reproducing objects in color which processes fall into two general classifications known as additive and subtractive. These processes are described in "Natural ColourPhoigggaphy, by Keonig and Wall, published May, All the heretofore known processes absorb light and are objectionable in that theftime of exposure is materially increased. In thoseprocesses in which semi-transparent filtersare used between the object and the sensitive surface,,it is necessary. to use deep colored filters to obtain a high quality, and the deeper the color of the filter, the less will be its light transmission and consequently, in practice, a compromise between the depth of color of the filter and quality is employed 7 to avoid the necessity of making very long exposures. 5

Length of exposure is not always objectionable from the photo-engravers'point of View, more particularlywhere the object is stationary. However, in the colored photography of animate objects where short exposures are essential none of theknown methods are satisfactory and none, of them render a scientifically accurate color reproduction. l v

It is an object of this invention to provide a method whereby a scientifically accurate reproduction of both moving and still objects can be photographically reproduced in natural colors with none of the objectionable features of the heretofore known processes.

It is a further object to provide an improvement in the method of making plates to'be used for photo-engraving or color printing purposes.

It is a furtherobject to provide an improvement in the method of making. photographs in color to red lights are applicable to the additive system.

For the subtractive system the lights may consist of (d) blue; (b) a combination of blue, green and yellow; (0) ,a combination of green, yellow and red.

First the camera is' focused on'the object being photographed, any suitable light being used for this purpose. Then allwhite or otherextraneous The blue light is'the'n shut off and-the object is 5 illuminated with a green light and an exposure is light is shut out of the enclosure or studio within" which the picture is being'taken. Next, the object is illuminated by a blue light and an exposure is made using a negative sensitive to blue light.

made on a new negativesurface sensitive to green light. The green light is then shut "ofi and the object illuminated with a red lightand an exposure made on a new surface sensitive to red light. 10 The negatives are'then developed and fixed by I ordinary and well known photographidmethods." Therehas now been produced "one'negative on which there is a record of all the blue light reflected by the object, one negative recording the green light and a' third recording thered light.

photo-engraving purpose,'and in the color'separation obtained they will be at least equal'in' value to those which are obtained by the present known standard practice, but my invention makes is possible to obtain a more perfect separation as will be clearly shown by the following example. i In actual practice, I have is desired to produce a plate to 'be printed'with red ink, it is desirable that thenegative from;

which the plate is to be produced should register all colors with the exception of red, namely, blue, yellow and green. This combination of colors can be obtained by the use of an unfiltered pure mercury vapor arc, the spectrum of which includes violet, blue green and yellow lines. I have found, iii-actual practice, that where a plate is to be produced to be printed in blue ink, a more perfect result is obtained by a negative which registers all colors with the exception of blue, I have produced such negatives by theuse of a neon gas arcjthe spectrum of which contains red, yellow.

and-green lines. It is impossible to obtain this. 40

result by the use of filters, with a white light source. In actual practice I havev also dispensed with all filters between the object and the light sensitivesurface. It will be seen from .the foregoing that no filters are used or are necessarybetween the object and the light sensitive surface.

It will be further seen that the intensity of the respective lights may be easily variedmaking it possibleto secure either equal intensity for each 50,

- of the lights or to secure the accentuation of one found that, when it 25 I illuminating source.

ly used a light sensitive surface known, as

depending upon ionization of necessary to compensate by some means for such inequality and it can readily be seen that compensation may be made by adjusting the in-" tensities of the illuminating sourcest Occasion might arise when it wouldprovelfde sirable to accentuate one or more colors. It can readily be seen that this also can be accomplished by adjusting the intensities of thejilluminating sources.

In colored photographic work there is frequentp chromatic which is sensitive to all colors. However, the sensitivity of the panchromatic surface is not equal for all colors and accordingly it is necessary that compensation be made with this typeof surface in order that all colors may be reproduced uniformly. This compensationmay also be made by adjusting the intensities of the The colored lights may be produced by filters between the object and a source of white light; or such colored lights may be produced by lights H gases. For example a red lightmay be produced by a clear glass, tube containing neon gas; a yellow light bya tube containing sodium vapor; a green light may be obtained by using a special glass tube (for example didymium glass) containing mercury vapor; and a blue may also be obtained by a special glass tube (for example cobalt glass) containing mercury vapor.

I do not restrict myself to the aforesaid light sources but itshould be noted that the light sources should be so chosen that when their respective spectra are added together the result will cover the entire visible spectrum thereby producing a white light.

It may not always be practicable to adjust the intensities of the light sources to the desired values, in which cases an equivalent result can be obtained by the proper adjustment of the aperture and shutter timing.

It'is necessary to determine the proper intensities of the light sources, and for this purpose I employ a fiat surface divided into areas progressively graded from white through the greys to black. By examining the image of this surface on the ground glass of the camera, alternately using each of the light sources, an approximate adjustment of the intensities of the light sources is made. Subsequent trial exposures and readjustments make it possible to secure an accurate balance.

My method is especially adapted for photoengraving or color printing purposes. The usual method employed heretofore for producing color prints has been very expensive, complicated, inaccurate and slow.

In the making of a color'print by these well known methods it has been first necessary for an artist to make a picture in color of the object; this picture is then photographed through three color filters such as red, green and blue, and also black and white photographs are taken. From the four negatives thus obtained proofs are made and it is then necessary to retouch the negatives in order to compensate for inaccuracies therein.

The next step in the process is to make a conpractical to make such colorsensitizedtinuous tone positive which is also retouched. From this continuous tone positive which has been retouched, half-tone negatives are made,

which are also retouched, and then from the half-tone negatives, which have been retouched,

the plates for the press are made, which also have to be retouched.

. From the above it will be seen that the method isinaccurate and very slow as the retouching must be carefully done by an expert, and the time consumed in making the color reproduction is about four weeks.

In accordancewith my method, practically all of the steps enumerated above in the usual photoengraving method are eliminated. By using my method, the object is photographed directly in three color lights to produce three negatives, one of the negative records only red, yellow and green qualities of the object; a second negative records only the blue, yellow and green qualities of the object; and a third negative records only ,the blue qualities of the object.

A half tone screen is placed in the camera so I that the above mentioned negatives are half tone negatives. From the three half tone negatives thus produced, it is only necessary now to make from them the print plates for the press, and no retouching is necessary.

It will be seen that my method eliminates entirely the necessity of employing an artist to make a painting or color drawing of an article and also the various retouching operations are obviated. V

The foregoing disclosure is to be regarded as descriptive and illustrative only, and not as restrictive or limitative of the invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. The method of making color separation negatives in color photography, comprising adjusting a neon arc light to a desired color value for a red negative, adjusting a mercury are light to a desired color value for a. justing a mercury are light to a desired color value for a blue violet negative, then separately adjusting the intensity of each of said lights, successively illuminating an object with each of said lights, and photographing the object through a half-tone screen at each of said illuminations.

2. The method of making color separation negatives in color photography, comprising limitthe object and light sensitive surfaces, and wherev in the object to be photographed is directly and separately successively illuminated by a plurality of different colored light sources in'succession, with short exposures of the light sensitive surface, the method of making color separation negatives having predetermined characteristics, which comprises, adjusting the spectral emission of a source of red light to a desiredcolor value green negative, ad-

1 ing the emission of one set of vapor arc lights, a

for a red negative, adjusting the spectral emission' of a source of green light to a desired color value for a green negative, adjusting the spectral emission of a source of blue light to a desired color value for a blue negative, correlating said adjustments so as to obtain a desired proportionate color resolution relationship between the spectral emissions of the several light sources,

then separately adjusting the intensity of each.

of said light sources to balance the component exposures to the relative sensitivities of the light sensitive surface to secure substantially the same effective exposure for each light source, separately and successivelyilluminating the object tobe photographed with light from each of the said light sources, and photographing the object on 'a separate sensitive surface at each of said adjusted illuminations for relatively short exposures.

4. In color photography without filters between the object andlight sensitive surfaces, and wherein the object to be photographed is directly and separately successively illuminated by a plurality of difierent colored light sources in succession, with short exposures of the light sensitive surface, the method of making color separation negatives having predetermined characteristics,

which comprises, proportionately adjusting the spectral emission of each of a plurality of different colored light sources to each other, then separately adjusting the intensity of each of said light sources to balance the component exposures to the relative sensitivities of the light sensitive surfaceto secure substantially the same efiective exposure for each light source, separately and successively illuminating the object to be photographed with light from each of the said plurality of light sources, and photographing the object on a separate sensitive surface at each of said adjusted illuminations for relatively short