Advanced Imaging


Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

High-Capacity CMOS Sensors: New Approaches to Document Scanning



X-ray Technology Bets on the Blue Chips

by Harvey Spencer

February 2003

Kodak sensors
Two sensors for the Kodak Professional DCS Pro 14n, CMOS (left) and CCD (right). (Photo: Kodak)

An overhead planetary camera, where the operator places each piece of paper on a plate before exposing it to the film, was traditionally the preferred low-cost and effective way to capture images of paper onto microfilm. For many years, this was used by service bureaus to microfilm most small documents (up to 11"x17" or A3), magazines and books on site for archival storage.

These planetary cameras typically cost $4,000 to $5,000, but with the advent of digital imaging and the corresponding reduction in microfilming, such cameras have largely become obsolete. Presently there is only one being manufactured, which costs around $7,000, from Alos.

Planetary scanners such as the Bookeye from ImageAccess can deal with awkward papers, books or magazines, but up to now they have been slow (around 3-4 seconds per page) and, therefore, only used for specialized jobs. The new 35 mm high-performance CMOS sensors developed by Eastman Kodak and Canon for their recently released professional level digital cameras have the potential to change that.

Canon's 11.1 megapixel sensor gives an area resolution of 4,064 x 2,074 pixels and Kodak's slightly larger 13.89 megapixel sensor gives a resolution of 4,560 x 3,048 pixels. Each has the ability to provide up to 200 dpi images from an 11" x 17" (A3) paper in one quick snapshot, although the Canon needs a little interpolation or edge removal. Each is capable of capturing multiple images per second (Canon's burst mode is 3 frames per second, Kodak's burst mode is 1.7 frames/second)-more than enough for an operator to achieve production speeds. Both CMOS sensors capture 12-bit depth, so images should be more than adequate if output with an 8-bit grayscale. Color is possible with 24-bit color depth, but it seems that this may compromise the sharpness needed for line art or text in typical document management applications.

Planetary operation is more efficient than flatbed because a flatbed requires that the paper be placed face-down and the lid be shut before pressing the "Enter" key or "Scan" button. Planetaries keep the page face-up on the platen using a foot-pedal or convenient button to expose the film or capture the image, keeping both hands free to place, hold and remove the paper quickly. Bookeye have touch button areas around the platen area, which can be pressed while the book or magazine is held on the platen-software then automatically removes the outline of the fingers or thumbs from the edges of the page. The process of picking up the paper and placing it on the platen eliminates the need for the separate data preparation task that has to be performed to use an automatic feeder. Staples do not have to be removed, tears do not need to be repaired, books do not need the spine to be cut off and selection of one or two sides can be made while picking up and moving the paper.

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