Background compensating bar code readers
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United States of America Patent
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-
Jan 8, 1991
Issued Date -
N/A
app pub date -
Aug 10, 1989
filing date -
Mar 1, 1989
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
Methods and apparatus for reading a luminescent and substantially transparent bar code 1 on a background surface 2 whose reflectance may vary over the coded area. Light 7 scans (70), and excites luminescence 8 in, the bar code 1. The light 7 also reflects (9) without luminescence from the background surface 2 of the bar code 1. A first electrical or optical signal 11 is provided (4) responsive to the reflected nonluminescent light 9, and a second electrical or optical signal 10 is provided (4) responsive to the luminescent 8. Typically the first signal 11 is processed (5) to provide a third signal 31 that varies with background reflectance substantially as does the second signal 10; and the second and third signals 10, 31 are combined (5) to provide a fourth signal 12 that is substantially independent of background reflectance in the coded area, and which is decoded (6) to provide the desired reading.
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