History of Image Scanners

High-quality digital image scanners have become common and very inexpensive. The path from early analog transmission of images over telephone lines to the modern flatbed scanner and high-end drum scanners have taken us from low-quality, low-resolution image transmission to the ability to transmit a digital scan of a photograph that is indistinguishable from the original.

Early Analog Scanners

The first image scanner was developed by Walden Kirsh at the National Bureau of Standards. This early scanner was a drum scanner. Drum scanners capture images using photomultiplier tubes. The original to be scanned is mounted on a drum, which spins very quickly. The drum moved in front of an image sensor.

Early Digital Scanners

Early digital scanners built on this drum scanning technology. A single image sensor was used, making it easy to capture black-and-white images. As color photography progressed, filters were placed in front of the sensor to scan either red, green or blue, with the image being reassembled from the three passes at a later time.

Drum Scanners

At present, drum scanners are still the most accurate, highest-resolution scanners available. Modern drum scanners make use of improvements in technology and optics to capture images as high as 12,000 pixels per inch (PPI). Modern sensors often dispense with the color filters in favor of multiple sensors calibrated for the three primary colors: red, green and blue. The quality of a drum scan often comes at a very high purchase price. Drum scanners are much more expensive than flatbed scanners.

Flatbed Scanners

The high cost of drum scanners triggered research into a type of scanner where the original remains stationary and has the sensor move over the surface. Early flatbed scanners borrowed the filter concept from drum scanners. Color images were scanned in three passes, one each for red, green and blue. This three-pass process meant that it took three times as long to scan a color image as a black-and-white image. In the early 1990s, inexpensive three-color charge couple devices (CCDs), the imaging sensor on most scanners, were developed allowing single pass scans of both color and black-and-white images.

Hand-Held & Specialty Scanners

In the early 1990s, both drum scanners and flatbed scanners were too expensive for simple home use. A number of companies produced small hand-held scanners. As the scanner slid over an image, wheels in the scanner took a sequence of thin "slices" of the image that were reconstructed in a computer as a black-and-white image. In recent years, this concept has re-emerged with small, portable wands that can be used to scan photographs and books to an internal memory for later download into a computer.

References

• History of Image Scanners
• History of the Image Scanner
• History of the Scanner