The quest to capture the world in color through photography is a journey marked by innovation and scientific breakthroughs. Early color photography predominantly employed ‘additive’ methods, which, as the name suggests, relied on combining red, green, and blue light to create a spectrum of colors. However, a distinct and ultimately more practical approach emerged: ‘subtractive’ color synthesis. This method offered a different pathway to color photography, addressing some of the limitations of its additive counterpart.
The Limitations of Additive Color Processes
Additive color processes, while pioneering, came with significant drawbacks that hindered their widespread adoption and practicality:
- Light Blocking Filters: These processes inherently relied on filters to separate and recombine colors. Filters work by blocking out certain wavelengths of light, which meant a considerable reduction in the light reaching the photographic material.
- Long Exposure Times and Dense Transparencies: The light-blocking nature of filters necessitated longer exposure times to capture an image. This, in turn, resulted in transparencies that were very dense, requiring strong light sources for viewing.
- Viewing Restrictions: Color photographs produced through additive methods could only be viewed using transmitted light. This meant they were primarily limited to projection or viewing through specialized devices, making them less accessible for everyday use compared to prints on paper.
Subtractive Color: A More Efficient Approach
The theoretical groundwork for subtractive color reproduction was laid out by French physicist and inventor Louis Ducos du Hauron. In his seminal book, Les couleurs en photographie, solution du problème (1869), Du Hauron detailed the subtractive method. His proposal was ingenious: instead of adding colors of light, subtractive color would use color separation negatives to create three positive images. These positives would then be dyed in colors complementary to the primary colors: cyan (blue-green), magenta (blue-red), and yellow.
The term “subtractive” comes from how these complementary colors interact with light. Each dye absorbs, or subtracts, one of the primary colors from white light. For example, cyan dye absorbs red light, allowing blue and green light to be reflected, effectively mimicking the function of a red filter in additive processes. Similarly, magenta absorbs green light, and yellow absorbs blue light. By precisely layering these three complementary colors, a wide spectrum of colors can be reproduced. Unlike additive color, subtractive color achieves color through dyes or pigments, not colored filters.
Image alt text: Gandolfi bellows camera with repeating back, circa 1930, showcasing early photographic technology for color separation.
A key advantage of subtractive color is its efficiency with light. White in subtractive color is represented by clear areas or white paper, allowing light to be reflected directly, rather than requiring light to pass through multiple filters. This makes subtractive processes far less wasteful of light. Critically, subtractive color works with reflected light, paving the way for color photographs on paper, a major leap forward in accessibility and practicality.
The Evolution of Subtractive Color Processes
The development of subtractive color photography took two main paths. One focused on creating specialized cameras for capturing sets of color separation negatives. The other was dedicated to finding practical techniques for producing and layering three positive images in the complementary subtractive colors.
For stationary subjects, like still-life arrangements, a standard camera could be adapted for color separation negatives. The process involved simply changing the color filter for each exposure. To streamline this, inventors designed ‘repeating backs.’ These camera attachments were movable sections that allowed different colored filters to be shifted into position sequentially.
Various repeating back devices entered the market. The simplest versions were elongated plate holders equipped with three filters. Photographers would manually slide these holders along the camera back in three steps to make the exposures. More sophisticated models incorporated clockwork motors, enabling rapid succession exposures – as fast as two to three seconds for all three negatives.
However, even with automated repeating backs, capturing moving subjects like portraits posed a challenge. The exposure sequence, even when rapid, could still result in color fringing or misregistration due to subject movement between exposures. This necessitated the development of ‘one-shot’ cameras capable of exposing all three negatives simultaneously.
Over the years, numerous designs for these one-shot cameras were patented, and several were commercially produced. These cameras employed intricate systems of mirrors and prisms to split the incoming light into three separate beams. Each beam was directed to a plate holder fitted with a specific color filter. Among the more successful and recognized one-shot camera designs were models from Jos-Pe, Bermpohl, Klein, and Mirkut.
In conclusion, the invention of color photography was not a singular event but a gradual evolution. While additive processes marked the early stages, the subtractive color method, pioneered theoretically by Ducos du Hauron and practically developed through innovations in cameras and processes, ultimately paved the way for more practical and accessible color photography. Subtractive color’s efficiency with light and its ability to produce prints on paper were crucial steps in making color photography the pervasive medium we know today.
