Clamping device and clamping method

• US 6,700,609 B1
• Filed: 07/17/2000
• Issued: 03/02/2004
• Est. Priority Date: 11/19/1998
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Abe, Miki
• Primary Examiner(s): Christensen, Andrew
• Assistant Examiner(s): Tran, Nhan T
• Application Number:
  US09/600,456
• Time in Patent Office: 1,324 Days
• Field of Search: 348/243, 348/241, 348/222.1, 358/448, 358/461, 358/463
• US Class Current: 348/243
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/633 by using optical black pixels
• CPC Class Codes: H04N 5/185 for the black level

Abstract

An optical black portion in an output of a CCD image pickup device is extracted and a clamp level of each line is obtained by an integrating and averaging circuit. A difference value of the clamp levels between the front and rear lines and an absolute value of the difference are calculated by a comparing circuit. Either the clamp level of each line or the clamp level updated every (+1) or (−1) is selected by a selector in accordance with whether the absolute value of the difference of the clamp levels between the front and rear lines lies within a predetermined range or not. The clamp level which is outputted from the selector is subtracted from the output of the CCD image pickup device.

Claims

1. A clamping apparatus comprising:

means for masking a part of a solid state image pickup device and photoelectrically converting a signal of a dark current component which is outputted from said solid state image pickup device and corresponds to a masking portion and a photosignal which is outputted from said solid state image pickup device and corresponds to a non-masking portion;

integrating means for sampling and integrating said dark current component signal corresponding to said masking portion every line;

averaging means for averaging an integration value which is obtained by said integrating means;

comparing means for comparing an average value of each line averaged by said averaging means, thereby detecting a change state of said average value;

clamp level control means for holding the average value when a comparison result of said comparing means lies within a predetermined range and changing the average value so as to have a predetermined gradation when said comparison result of said comparing means is out of said predetermined range; and

subtracting means for subtracting said average value derived from said clamp level control means from an output of said photoelectric converting means,

wherein the signal is clamped on the basis of the signal of the dark current component that is outputted from said solid state image pickup device.

2. An apparatus according to claim 1, further comprising setting means which can arbitrarily set said predetermined gradation at a time when said average value is changed by said clamp level control means.

3. A clamping method comprising the steps of:

masking a part of a solid state image pickup device and photoelectrically converting a signal of a dark current component which is outputted from said solid state image pickup device and corresponds to a masking portion and a photosignal which is outputted from said solid state image pickup device and corresponds to a non-masking portion;

sampling and integrating said dark current component signal corresponding to said masking portion every line;

averaging an integration value;

comparing an average value of each line, thereby detecting a change state of said average value;

holding the average value when a comparison result lies within a predetermined range and changing the average value so as to have a predetermined gradation when said comparison result is out of said predetermined range; and

subtracting said average value changed so as to have said predetermined gradation from said photoelectrically converted output,

wherein the signal is clamped on the basis of the signal of the dark current component that is outputted from said solid state image pickup device.