Frederic Eugene Ives - Halftone Process

Halftone Process

Halftone processes allow photographs, complete with their "half-tone" intermediate shades of gray or color, to be reproduced in ink on paper by means of a printing press, like text. Prior to such processes, images were printed in books and periodicals by means of hand-engraved metal plates or wood blocks, or from drawings made on lithographic stones. Half-tone effects were obtained by engraving closely spaced parallel or hatched lines, by stippling, or by exploiting the granular texture inherent in the stone lithography process.

Ives is sometimes referred to as "the" inventor of "the" halftone process, but this is incorrect and Ives never made such a claim for himself. There was not one halftone process, but a considerable number of them, the earliest dating nearly as far back as the introduction of practical photography in 1839. They varied widely in their degree of practicality and the quality of their results. The first attempts involved directly etching the unique images formed on metallic Daguerreotype plates. Although pleasing results were obtained, etching the plates required great skill and care, the images could not be printed along with ordinary type, and the delicate plates wore out after a very small number of impressions, making such processes useless for publishing on a commercial scale. More practical processes started appearing in the 1860s, but high cost, special printing requirements or low image quality variously kept these early processes from coming into widespread use.

Ives turned his attention to halftone processes in the late 1870s. The objectives were to more or less automatically convert the intermediate tones of a photographic image into small lines or dots of stark black and white; to do this better, or at least more efficiently, than was possible with existing processes; and to create a printing block that could be combined with blocks of text in an ordinary printing press. The lines or dots, of varying widths or sizes respectively, had to be small enough to adequately blend together in the eye at a normal viewing distance, producing the illusion of various shades of gray, yet the printing plates had to be durable enough to last through a typical press run without excessive degradation. Above all, the process had to be economical enough to make its widespread commercial use practical.

Ives patented his first "Ives' process" in 1881. This early process required the creation of a photographic relief image, made by a variety of the carbon process, from which a plaster cast was made. The highest areas on the surface of the plaster corresponded with the darkest areas of the original photograph. The cast was pressed into contact with an inked rubber grid consisting of an array of tiny pyramidal elements, which caused a regular array of ink dots to be deposited on the plaster, their sizes varying according to the heights of the surface. The dot pattern was then photographed onto a metal plate coated with photoresist, which was developed and chemically etched, a process known as photoengraving and already in use for making printing plates from line drawings, handwriting and other purely black and white subject matter. Although complex, this process was simpler and more efficient than other processes then in some limited use, and in 1884 Ives asserted that it was "the first patented or published process which was introduced into truly successful commercial operation."

A few years later, Ives replaced this process with the much simpler one usually associated with his name. In the new process, an ordinary photograph was rephotographed directly onto the sensitized metal plate. A crossline screen, consisting of two glass plates finely ruled with opaque lines and sandwiched together with their lines crossing at right angles, was positioned near the surface of the metal, and a specially shaped diaphragm was used with the camera lens. Combined with the inherently stark black-and-white nature of the photoengraving process, these devices served to break up the image into a regular pattern of dots of various sizes with optimized shapes. During the 1890s, photographs reproduced by this second "Ives process" largely replaced the use of hand-engraved wood block and steel plate illustrations, and it remained the standard process for photographically illustrating books, magazines and newspapers during the next eighty years. Although much more technologically sophisticated methods eventually came into use for creating the printing plates, the structure of most printed halftone images has remained virtually unchanged.