US1954097A - Process for producing balanced half tones - Google Patents

Description

April 10, 1934.

F. T. POWERS 1,954,097

PROCESS FOR PRODUCING BALANCED HALF TONES Original Filed May 1, 1931 INVENTOR .Patented Apr. 10, 19 34 PATENT OFFICE PROCESS FOR PRODUCING BALANCED HALF TONES Frank T. Powers, Douglaston, N. Y.

Application May 1, 1931, Serial No. 534,343 Renewed October 12, 1933 4 Claims.

My invention relates to the photo mechanical reproductive arts and particularly to the making of tone balanced half tone plates and the copying of pictures in the graphic and photographic 5 arts.

The object of the invention is to provide a rapid and labour saving process for making a reproduction of a picture or drawing, which shall have the desired tone balance between high lights, middle tones and deep shadows, without the necessity of hand work or retouching by the artist.

In the art, as heretofore practised, it has been the custom, when copying or making a half tone reproduction of a picture, to make a negative or half tone plate of the picture, and by careful work by a skilled artist, to balance the high lights, middle tones and shadows to the desired degree to produce the best effects by the manipulation of various processes known to those skilled in this art.

Some of these processes, whereby such reproductions are improved by the artist, are intensification, re-etching, hand-tooling, printing withmasks and double printing. The suc- 26 cess or effectiveness of these processes depends in very large degree upon the skill, experience and artistic sense of the operator, and are slow and time-consuming, and since the operators are very highly paid, the processes are expensive.

By the application of my invention a picture which, in the original is poorly balanced, may be so reproduced that the high lights, middle tones and deep shadows will have such relative values as the artist desires to give them to produce the most artistic eflect, without the slow, tedious hand, chemical and tool processes now relied upon to produce these much desired results.

In the commercial reproduction of pictures it is more often true than not that the copy submitted to the reproduction process is lacking in what the photo-engraver calls balance. It may be what is called in the art on the high side or the low side of proper balance. The details may be weak or indistinct in the high lights, or

the shadows may be too deep.

By exposing in a camera a light sensitive plate to such a picture for a short time, a photograph may be obtained which contains all the details of the high lights, although the exposure has not been sufl'icient to bring out the middle tones or deep shadows with the desired distinctness or detail. If, on the other hand, the exposure is made sufiicient to get all the detail of the darker portions of the picture, then the lighter areas will be over exposed and the depth and detail therein lost.

If a compromise is made in thetime of exposure in an attempt to avoid both over exposure of the high lights and under exposure of the deep shadows, there results a reproduction which may be satisfactory in the middle tones or lighter shadows, but which still leaves much to be desired in both the high lights and the deep shadows.

To overcome this difiiculty, I have devised a as process which I carry out in the maner which I will now describe in such detail that one skilled in the art to which it pertains may practise it.

In this description and in the succeeding claims,

I use the word design to mean any design, picture, painting, photograph, drawing or graph of any sort, which may be copied by this process.

In describing the various steps of my new process, it is assumed that a design is being reproduced by the half tone process and that the design is unbalanced in that it has poorly defined detail in the shadows. My first step is to photograph the design on any suitable medium, which may be, for example, a dry plate, a wet plate, a cut film or a continuous film, or such film as is commonly 30 used in the moving picture industry.

In making the exposure of this first photograph of the design being reproduced, I intentionally under-expose it, with the result that I reproduce detail only in the high light portion 35 of the design. The fiddle tones and deep shadows are so underexposed as to fail to get detail therein.

My next step is to photograph the design in a manner exactly similar to the step described above, except that the exposure is somewhat nearer to normal exposure, with the result that somewhat greater detail will be secured in the darker tones.

I continue these steps of making photographs of the design and progressively increasing the exposure until I reach a point where the entire design is over-exposed, even in the darker shadows.

One convenient method of taking this series of pictures of varying exposures is to use a moving picture camera oi. suitable design and a moving picture film. By opening and closing an iris diaphragm in the lens of this camera, while a series of exposures of the design being copied is made, I produce a series of negatives, some of which are under-exposed and some of which are overexposed, whlle others are of more nearly normal exposure. Those exposures which are made when the diaphragm is wide open will be overexposed and those made when the opening in the diaphragm is small will be under-exposed, while the intermediate exposures will range between.

these two extremes.

Thus I have a series of photographs of the design, which advance by small stages or increments of exposure from one which is greatly under-exposed to one which is greatly over-exposed. The number of pictures in this series varies with different subjects and also with the effects sought in the final reproduction. The number may be as few as three, or it may be as many as several score, as is the case when moving picture film is used in making the photographs, as is further described herein.

This series of negatives is next printed on another light sensitive plate or film to produce a series of positives. In making the positive prints the exposure of each picture is identical with each other exposure, so that the resulting positives form a series of pictures having characteristics ranging from under-exposure to over-exposure. Or if I desire a positive of the design on my final picture, I may omit this last described step.

I next project, one after another, images of these pictures in register with each other, upon a suitable screen by means of a suitable projector, and while so projected upon the screen I expose a light sensitive medium in a suitable camera to the image on the screen. In front of the light sensitive medium in the camera is interposed between it and the lens a half tone line plate of the type well known in the art, and commonly called a screen or line screen. It will be referred to in this description as a half tone line plate to avoid confusion with the word screen which is herein used to denote a screen upon which the pictures are projected. While making the exposure of the light sensitive medium to the image projected on the screen, I progressively throw upon the screen, one after another, images of the series of pictures which were exposed various lengths of time to the original design, some of which are under-exposed and some of which are over-exposed, and all intermediate degrees of exposure. In projecting these images upon the screen, care must be taken to insure that each successive image registers'in the exact position on the screen with the previous image. Unless these images all register exactly with each other on the screen, the resulting half tone composite negative of these images will be blurred or lack sharpness of detail.

In the accompanying drawing, I have shown diagrammatically the arrangement of projector screen and camera as they are set up to carry out my new process.

When I use moving picture film, as described above, I may splice the two ends of the filmtogether to form a continuous loop, which may be placed in a moving picture projector and the series of pictures thrown repeatedly upon the screen as many times as is desired. The result is that the light sensitive medium in the camera is exposed successively to images on the screen, which are of gradually increasing depth or density, and which impart the tones and details so much desired, but which in the past were only obtained with difilculty, if at all.

. By this process I capture on the photographic plate being exposed in the camera, a composite picture containing all the detail and balance possessed by any of the pictures in the series. For example, from the under-exposed imageson the screen I secure detail in the high lights, while from the over-exposed images I secure detail in the shadows. Thus, by manipulating the exposures and so subjecting the half tone plate to the various pictures of the series, I produce a well-balanced efiect with greatly improved detail, and do it without the usual resort or tedious methods referred to above.

Having described my invention, I now state what I claim to be new and novel and for which I pray that Letters Patent be granted.

I claim:

1. The process for producing tone balanced half tone negatives, which consists in preparing a series of negatives of the design to be reproduced, said series varying in successive, approximately equal steps, from under-exposure to over-exposure, preparing positives of said negatives, projecting images of. said positives successively in register on a screen and photographing through a half tone line plate on a single light sensitive medium the successive images to produce a composite half tone negative having balance between the high lights, shadows and half tones.

2. The process for producing tone balanced reproductions of a design which consists in preparing a progressive series of photographs of the design, some of said photographs being under-exposed, sorne normall exposed, and some over-exposed, projecting images of said photographs in register on a screen and simultaneously exposing a light sensitive medium in a camera to said images .to produce a reproduction having balance in the high lights, shadows and half tones.

3. The process for producing tone balanced reproductions of a design which consists in exposing successive portions of a continuous strip of light sensitive medium in a suitable camera to the design, with changing degrees of exposure, developing the pictures so produced, preparing positives of said pictures, projecting the images of said positive pictures successively in register on a screen and simultaneously exposing through a half tone line plate a light sensitive medium in a camera to said images to produce a tone balanced, composite half tone negative.

4. The process for producing tone balanced reproductions of a design which consists in exposing successive portions of a continuous strip of light sensitive medium in a suitable camera to the design with changing degrees of exposure, developing the pictures so produced, preparing positives of said pictures on a continuous strip of light sensitive medium, attaching the ends of the said strip of light sensitive medium to form an endless strip, projecting images of said positive pictures successively in register on a suitable screen, and simultaneously exposing through a half tone line plate a light sensitive medium in a camera to said images to produce a tone balanced composite, half tone negative.

FRANK T. POWERS.

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