Kodak's Patent for the Digital Camera

We previously looked at Kodak's 1885 patent for its original, easy-to-use camera. We've also seen Bell Labs' 1950 patent for the transistor. Bell Labs' physicists continued to innovate and in the 1960s they developed the “charge-coupled device” (CCD), an integrated circuit made up of highly sensitive areas (known as pixels) that convert photons of light into an electronic charge. Kodak's engineers also continued to make advances and in 1977 filed for the attached U.S. Patent No. 4,131,919, which applies CCD technology to provide the first self-contained digital camera. This patent marked a pivotal moment, providing the blueprint for the digital imaging technology that would eventually transform how we capture, store, and share moments.

Overcoming Technical Hurdles: Tackling Dark Current in CCDs

Kodak's 1977 patent resulted from the work of Steven Sasson, a 24-year-old engineer tasked with finding a way to make a CCD image sensor for a camera. As described in the patent, Sasson had to overcome the issue of “dark current” in CCDs. Dark current is the unwanted thermal generation of charge in the CCD sensor when no light is present. This constant buildup of charge manifests as background noise that degrades the output signal and results in distorted images.

Sasson's solution, shown in the circuit diagram of Figure 2 in the patent (annotated below), involved rapidly (e.g., within 75 ms) digitizing the image data from the CCD sensor and transmitting it to a high-speed buffer memory. 

This rapid transfer reduced the time electrons generated by dark current could accumulate in the CCD sensor, thereby minimizing the noise. The patent describes this technique for transferring a 10,000 pixel (0.1 megapixel) image (for context, the current iPhone includes a 48 megapixel camera):

Each CCD pulse for the interval is digitized in real time to form a digital word, i.e., a total of 10,000 digital words for the aforementioned type CCD, and such words are advantageously stored in a high-speed buffer memory. 

Innovative Storage and Playback Solutions: No More Need for Film

The patent also describes Sasson's solution for permanently storing the image data and turning it into a picture you could actually see. The patent describes a completely digital system of storage and playback without the use of film, paper, or any consumables. Specifically, the patent describes transmitting the “scene information” from the buffer memory to an “inexpensive recording apparatus,” namely, a cassette tape (shown in Figure 1 below). The recorded data on the cassette tape is then read by a microcomputer, converted to analog form, and displayed on a television monitor. 

The patent explains the benefits that come with storing image data in non-volatile memory like a cassette tape (and foreshadows deleting all those pictures of your kids refusing to smile or caught with their eyes closed):

[T]he camera operator may first visually display each recorded scene, then decide whether to keep the picture. Unwanted scenes may be erased from the tape, and the tape may be reused without incurring additional cost.

A Single Prototype: A Lackluster Initial Response

Sasson designed and built a working prototype capable of displaying low-resolution, black-and-white images. Weighing in at a hefty eight pounds and having the form factor of a toaster, Sasson's prototype (shown here) was nothing like the sleek, pocket-sized digital cameras we are accustomed to today. And at the time, Kodak's executives “were convinced that no one would ever want to look at their pictures on a television set.” It took many years for digital cameras to completely disrupt the film photography industry. Ironically, Kodak failed to fully embrace digital photography until it was too late. 

Sasson's Legacy: Paving the Way to Sharing Pictures of Your Food 

Kodak kept Sasson's work secret for years, but his accomplishments were eventually recognized. His 1975 prototype is now maintained at the Smithsonian’s National Museum of American History. In 2009, Sasson was awarded the National Medal of Technology and Innovation at a White House ceremony.  Three years later, Kodak filed for bankruptcy.

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