Exposure control method for use with optical readers
First Claim
1. A method for controlling an exposure period of an optical reader, said reader having an image sensor including a pixel array comprising a plurality of pixels, said method comprising the steps of:
- generating an image sensor signal that varies in accordance with the intensity on light incident of said pixel array;
generating an illumination signal that varies in accordance with a time averaged value of said image sensor signal;
establishing an initial exposure control variable, said exposure control variable determining the duration of said exposure period;
detecting whether said illumination signal is inside or outside of an illumination window bounded by predetermined maximum and minimum illumination values;
increasing said exposure control variable if said illumination signal is below said predetermined minimum illumination value; and
decreasing said exposure control variable if said illumination signal is above said predetermined maximum illumination value.
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Accused Products
Abstract
An exposure control apparatus for use with optical readers, such as bar code readers, which utilize photosensitive image sensors. An illumination signal generating circuit generates an illumination signal having a magnitude that varies in accordance with the illumination level at the image sensor. A window detecting circuit samples the illumination signal during a predetermined part of each scan to determine whether the illumination signal is within the window, has exited the widow, or has re-entered the window. Exposure control circuitry uses the output of the window detecting circuit to control which of a plurality of the subdivisions of the exposure control range of the image sensor will be used. Changes in exposure time are made only between adjacent subdivisions of the exposure control range. Together with a predetermined hysteresis between the exit and re-entry thresholds of the window, the latter changes stabilize the operation of the reader by reducing exposure control “hunting”.
192 Citations
43 Claims
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1. A method for controlling an exposure period of an optical reader, said reader having an image sensor including a pixel array comprising a plurality of pixels, said method comprising the steps of:
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generating an image sensor signal that varies in accordance with the intensity on light incident of said pixel array;
generating an illumination signal that varies in accordance with a time averaged value of said image sensor signal;
establishing an initial exposure control variable, said exposure control variable determining the duration of said exposure period;
detecting whether said illumination signal is inside or outside of an illumination window bounded by predetermined maximum and minimum illumination values;
increasing said exposure control variable if said illumination signal is below said predetermined minimum illumination value; and
decreasing said exposure control variable if said illumination signal is above said predetermined maximum illumination value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An optical reader comprising:
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an image sensor comprising an array of pixels;
an optical assembly for focusing an image onto said image sensor;
a circuit for controlling an exposure period of said optical reader, said circuit being adapted to;
(A) generate an illumination signal based on an output of said image sensor;
(B) establish an initial exposure control variable, said exposure control variable determining a duration of said exposure period;
(C) detect whether said illumination signal is within a window bounded by minimum and maximum illumination signal values;
(D) increase said exposure control variable if said illumination signal is below said minimum illumination value; and
(E) decrease said exposure control variable if said illumination signal is above said maximum value. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for controlling an exposure period of an image sensor based optical reader, said method comprising the steps of:
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(A) generating an illumination signal based on an output of said image sensor;
(B) establishing an initial exposure control variable, said exposure control variable determining a duration of said exposure period;
(C) detecting whether said illumination signal is within a window bounded by minimum and maximum illumination signal values;
(D) increasing said exposure control variable if said illumination signal is below said minimum illumination value; and
(E) decreasing said exposure control variable if said illumination signal is above said maximum value. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. An optical reader comprising:
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an image sensor comprising an array of pixels;
an optical assembly for focusing an image onto said image sensor;
a circuit for controlling an exposure period of said optical reader, said circuit being configured to establish an exposure control variable of said reader to one exposure control variable value out of a step pattern of possible exposure control variable values, said circuit being adapted to;
(A) generate an illumination signal based on an output of said image sensor;
(B) establish an initial exposure control variable, said exposure control variable determining a duration of said exposure period;
(C) detect said illumination signal;
(D) increase said exposure control variable if said illumination signal is below a value indicative of said exposure control variable being at a desire value; and
(E) decrease said exposure control variable if said illumination signal is above a value indicative of said exposure control variable being at a desired value. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43)
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Specification