Privacy-enhanced computer display

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Developed by Mitsubitshi Electric Research Laboratories,[1] a privacy-enhanced computer display allows information that must remain private to be viewed on computer displays located in public areas (i.e. banks, hospitals and pharmacies) by employing the use of both ferroelectric shutter glasses and a unique device driver.[1]



Privacy-enhanced computer display technology utilizes a public display image ( denoted Pij for the pixel value at location i,j in the public image), a secret display image (Sij, similarly denoted for pixel value at pixel location i,j ), a proprietary device driver, a CRT capable of rapid refresh rates (up to 120 Hz) and a set of synchronized ferroelectric shutter glasses. The device driver causes the computer monitor to alternately display the pixelwise difference (Pij – Sij) and the unaltered secret image (Sij).

When viewed directly without the shutter glasses, the human eye's persistence of vision blurs the two images into [(Pij – Sij + Sij) / 2], which reduces to (Pij / 2), which is the public image, effectively preventing an unintended recipient from viewing the secret image.

The intended recipient, wearing the synchronized glasses, will see only the (Sij) secret image.[1]

Advantages and disadvantages[edit]

The major advantage of the shutter glass system was that it allowed the same display to be used for multiple unrelated images, one of which was visible without any glasses at all. Unfortunately, the contrast ratio of the public image is only 1/2 the available contrast ratio of the CRT when driven with only a public image.

A secondary issue was that although the image was privacy-enhanced, it was not secure. The secret image appeared as a "ghost" if one moved one's head rapidly - or struck the viewer's head with a soft object, thereby offsetting the two image fields and revealing the edges of the difference image.

With the rapid growth of handheld phones with integrated digital cameras (and fast shutters) the phone's camera video will often reveal alternating frames of the public and secret images. This effectively breaks the privacy capability of the system.

A final issue is the decline of the CRT and the rise of the LCD in display technology, because nearly all LCDs are too slow to support the 120 Hz or faster refresh rate needed for this privacy enhancement to work. Meanwhile, lenticular Monitor_filter have diminished the need for the shutterglass technology.

Possible applications[edit]

  • Banks (bank balance information)
  • Hospitals (patient health information)
  • Pharmacies (prescription drug information)
  • Airline ticketing and airport gate agent stations (passenger and security information)


The patent was sold in 2010 to Intellectual Ventures, who obtained a reissue in 2012 (US patent RE43,362) with additional claims.


  1. ^ a b c "MERL – Privacy Enhanced Computer Display". 2001-08-02. Retrieved 2009-07-28. 

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