REAL-TIME EXPOSURE CONTROL FOR AUTOMATIC LIGHT CONTROL

• US 20100073512A1
• Filed: 09/15/2009
• Published: 03/25/2010
• Est. Priority Date: 05/17/2004
• Status: Active Grant

• Current Assignee: Given Imaging Limited (Medtronic Plc), Micron Technology, Inc.
• Original Assignee: Given Imaging Limited (Medtronic Plc), Micron Technology, Inc.
• Inventors: Olsen, Espen A., Iversen, Steinar, Avni, Dov, Glukhovsky, Arkady, Olsen, Alf, Moholt, Jorgen
• Granted Patent: US 8,149,326 B2
• Time in Patent Office: Days
• US Class Current: 348/229.100
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means
• CPC Class Codes: H04N 23/76 by influencing the image signals

Abstract

An imager and a method for real-time, non-destructive monitoring of light incident on imager pixels during their exposure to light. Real-time or present pixel signals, which are indicative of present illumination on the pixels, are compared to a reference signal during the exposure. Adjustments, if necessary, are made to programmable parameters such as gain and/or exposure time to automatically control the imager'"'"'s exposure to the light. In a preferred exemplary embodiment, only a selected number of pixels are monitored for exposure control as opposed to monitoring the entire pixel array.

Claims

1-71. -71. (canceled)

72. An image sensor comprising:

an array of pixels;

means for starting an exposure period;

means for obtaining pixel signals from a set of pixels in said array;

means for comparing a value of each pixel signal to a reference level;

means for comparing a current exposure time to a maximum exposure time; and

means for adjusting at least one exposure control parameter based on results of the comparing means.

73. The sensor of claim 72, further comprising means for ending the exposure period if the current exposure time is greater than or equal to the maximum exposure time.

74. The sensor of claim 72, further comprising means for ending the exposure period if a predetermined number of pixels have a pixel signal value greater than the reference level.

75. The sensor of claim 72, wherein the at least one exposure control parameter is a gain value.

76. The sensor of claim 72, wherein the at least one exposure control parameter is the maximum exposure time.

77. The sensor of claim 72, wherein the at least one exposure control parameter is the reference level.

78. The sensor of claim 72, wherein said means for adjusting comprises:

means for determining if a predetermined number of pixels have a pixel signal value greater than the reference level;

means for determining a time interval for the current exposure time; and

means for setting the at least one exposure control parameter to a value based on results of said determining acts.

79. The sensor of claim 78, wherein said means for setting sets a readout gain to a minimum gain and sets the reference level to a full scale level if it is determined that a predetermined number of pixels have a pixel signal value greater than the reference level and the current exposure time is within a predetermined time interval.

80. The sensor of claim 79, wherein the predetermined time interval is based on a preferred exposure time and a maximum gain value.

81. The sensor of claim 78, wherein said means for setting sets a readout gain to a gain between a maximum gain and a minimum gain and sets the reference level to a full scale level divided by the gain between a maximum gain and a minimum gain if it is determined that a predetermined number of pixels have a pixel signal value greater than the reference level and the current exposure time is within a predetermined time interval.

82. The sensor of claim 81, wherein the predetermined time interval spans a first time based on a preferred exposure time and a maximum gain value and a second time based on the preferred exposure time and the gain between the maximum and minimum gains.

83. The sensor of claim 78, wherein said means for setting sets a readout gain to a maximum gain and said sensor further comprises means for ending the exposure period.

84. The sensor of claim 72, wherein said means for starting the exposure period comprises an illumination device.

85. The sensor of claim 72, wherein said means for obtaining comprises:

means for scanning rows of pixels in the array; and

means for inputting pixel signals from a set of columns of the array.

86. An image sensor comprising:

an array of pixels;

means for continuously monitoring, during an exposure period, pixel signals from a set of pixels in the array; and

means for adjusting at least one exposure control parameter based on said monitoring and a current exposure time.

87. An image sensor comprising:

an array of pixels comprising a plurality of rows and columns;

a plurality of comparison circuits, each comparison circuit receiving a reference signal and being coupled to a respective column, each comparison circuit comparing a pixel signal to the reference signal and having an output indicative of a result of the comparison;

a first circuit connected to and counting the results output from the comparison circuits, said first circuit having a first output; and

a logic circuit connected to the first output, wherein during an exposure period said logic circuit uses the first output and a current exposure time to perform automatic light control for the exposure period.

88. The image sensor of claim 87, wherein said logic circuit adjusts at least one exposure control parameter based on the first output and current exposure time.

89. The image sensor of claim 88, wherein the at least one exposure control parameter is a gain value.

90. The image sensor of claim 88, wherein the at least one exposure control parameter is the maximum exposure time.

91. The image sensor of claim 88, wherein the at least one exposure control parameter is the reference level.

92. The image sensor of claim 87, wherein said logic circuit ends the exposure period if the current exposure time is greater than or equal to a maximum exposure time.

93. The image sensor of claim 87, wherein said logic circuit ends the exposure period if a predetermined number of pixels have a pixel signal value greater than the reference signal.

94. The image sensor of claim 87, wherein said first circuit comprises:

a collection circuit connected to receive the outputs from all of the comparators; and

a counter connected to the collection circuit, said counter counting the results from the connection circuit and generating the first output.

95. The image sensor of claim 87, further comprising a reference generator for generating and outputting the reference signal to the comparators.

96. The image sensor of claim 95, wherein said reference generator generates the reference signal based on a mean reset value.

97. The image sensor of claim 95, further comprising:

a plurality of first switches, each first switch having a first state connecting a first input of a respective comparator to a pixel signal from a respective column, each switch having a second state connecting the first input of the respective comparator to the reference signal, each comparator having a first output for outputting a comparison result based on the first input;

a plurality of second switches, each second switch having a first state connecting a second input of a respective comparator to the reference signal, each switch having a second state connecting the second input of the respective comparator to a pixel signal from a respective column, each comparator having a second output for outputting a comparison result based on the second input; and

a plurality of third switches for outputting the first output from the comparators to the first circuit in a first state, and for outputting the second output from the comparators to the first circuit in a second state.