Everything Old is New Again: How Technology Moves Ahead While Staying the Same

12Dec11

Originally posted to www.hmml.org 4-17-11

Today’s digital cameras are prime examples of 21st century high technology. If one could transport any of today’s digicams back in time to perhaps 1930, it would be considered utterly miraculous. However, a 1930’s-era photo expert would immediately understand the basic principles of how the digital camera’s sensor works. That’s because the state-of-the-art color photography technology of that time worked in pretty much the same way! Here’s why.

Our history is often imagined in black and white; such are the vast majority of images that have survived to document the past. In truth, the quest to produce color images is almost as old as photography itself. In 1839, the Daguerreotype photographic process was announced, producing black and white images on polished silver plates. In the early 1850’s, a minister from upstate New York named Levi Hill claimed to have invented a way to create Daguerreotypes in color. He wrote a treatise on the process, which he called Heliochromy in 1851, but others weren’t able to reliably replicate the process and his work was discredited. In recent years, studies have shown that his Hillotypes indeed recorded certain colors in a crude fashion, with further hand-coloring often done after the fact to enhance the effect.

In 1855, the Scottish physicist James Clerk Maxwell suggested that the range of human color vision could be created using three primary color components; Red, Green and Blue (RGB). Experiments were made by photographing three separate monochrome images of a subject through red, green and blue colored filters; when the resulting black and white positive images were projected back through their respective colored filters, a color image was formed.

By the start of the twentieth century, the techniques for creating color images by making monochrome pictures using RGB filters matured. To accomplish this, a photographer could photograph the subject three times in rapid succession through the three color filters, as was done by the photographic pioneer Sergey Prokudin-Gorsky, who produced an impressive color record of Tsarist Russia. A more sophisticated solution was the tricolor camera, a large and complex apparatus that produced three negatives at once by splitting the incoming image into three components and exposing three plates simultaneously through the RGB filters. This could work quite well—indeed there were variants of this process in use until the 1950’s, but it was hardly the portable and simple solution for the average photographer using conventional equipment.

Instead of filtering for each primary color on a separate monochrome plate, what about putting the red, green and blue color filters on a single black and white plate? This was the concept behind the additive screen plate processes that emerged in the first decades of the century. There were a number of these, but they all worked the same way: some sort of pattern of very tiny red, green, and blue filters was applied to the black and white photographic plate. The image was exposed through this filter array, and each tiny portion of the monochrome emulsion recorded the light intensity based on the filter that was right above it. When the image was processed as a positive monochrome image and viewed through the color filter array, the scene would appear to be in full color, even though it was actually made up of thousands or millions of tiny red, green, and blue components.

The filter array could be created in a number of ways. The earliest process, the Lumière Autochrome, used dyed grains of potato starch (no kidding!) to create the filter layer. Germany’s Agfacolor system used tiny colored resin beads to create the filter array. Finlaycolor and Dufaycolor used a geometric array of RGB squares or stripes to create the tricolor pattern. Some of these processes lingered on into the 1950’s but were largely made obsolete by the introduction of Eastman Kodak’s Kodachrome in 1935. With Kodachrome, three separate layers of monochrome emulsion, called an integral tripack, were in the film, each sensitive to a different color primary. During processing, the appropriate color dye was added to each layer to create the full-color transparency.

screen-plate technologies

Fast forward now to the digital age. In most cases, the electronic sensors used in scanners and digital cameras are, like black and white film, capable of recording light intensity but not color. In most modern digital cameras, the solution is to put a Bayer-pattern filter array on top of the sensor elements to create an RGB “mosaic” image from the camera’s sensor. Each pixel in this image has only one color value, depending on which filter color the light passed through.

Bayer filter array

Look familiar? The Bayer-pattern system would be immediately recognizable to any 1930’s photographer working with Finlay or Dufay color plates. The way it works is identical. The modern twist is that, unlike the older screen-plate processes, the digital camera has a computer inside that can transform the RGB “mosaic” image into a full-color RGB array by estimating what the missing color values for each pixel would be by examining patterns in the image and the color values of neighboring pixels. This is the process, called demosaicing, by which the “RAW” image file (the mosaic image) is converted into a usable JPEG or TIFF image.

In a similar nod to the technology of the past, many high-end color video cameras work by splitting the incoming image into three parts and sending each to a separate sensor through red, green and blue filters, just like those old, clunky tricolor cameras. And if you want to see another high-tech example of this old concept, look at your computer monitor through a high-powered magnifying glass and see the red, green, and blue stripes that make up each pixel.

Some companies are working on the digital equivalent of the integral tripack introduced with Kodachrome in the 1930’s, but the market today continues to be dominated by imaging concepts that have 100-year-old roots. One can look at this in a number of ways. From a nostalgic viewpoint, it may seem comforting that things don’t really change as much as they seem. On the other hand, one can only wonder what the next revolution in digital imaging might look like.

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One Response to “Everything Old is New Again: How Technology Moves Ahead While Staying the Same”

  1. 1 Photos

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    in the same niche. Your blog provided us beneficial
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