Video camera with a function to correct defective pixels of solid state image pickup device and method of correcting defective pixels of solid state image pickup device

• US 5,796,430 A
• Filed: 01/27/1997
• Issued: 08/18/1998
• Est. Priority Date: 06/02/1993
• Status: Expired due to Term

• Current Assignee: Hitachi Consumer Electronics Company Limited (Hitachi, Ltd.)
• Original Assignee: Hitachi, Ltd.
• Inventors: Itoh, Kenji, Katoh, Minoru, Ohtsubo, Hiroyasu
• Primary Examiner(s): Faile, Andrew I.
• Assistant Examiner(s): CHRISTENSEN, ANDREW BRUCE
• Application Number:
  US08/786,733
• Time in Patent Office: 568 Days
• Field of Search: 348/241, 348/242, 348/243, 348/245, 348/246, 348/247, 348/363
• US Class Current: 348/246
• CPC Class Codes: H04N 25/674 based on the scene itself, e.g. defocusing
• CPC Class Codes: H04N 25/68 applied to defects
• CPC Class Codes: H04N 25/71 Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors

Abstract

When defective pixels of a solid state image pickup device of a video camera are corrected by signal processes, a white spot noise is detected by closing an iris and by comparing the signal level and a level of only a dark current. Further, in this case, a gain of an AGC circuit for controlling a gain of a video signal is raised and a precise detection is executed. By executing such a detecting operation at the time of turn-on or turn-off of a power source, the user is not annoying. In the ordinary photographing, a reference level in detection of a white spot noise is set to an optimum value in accordance with a temperature of the solid state image pickup device or its peripheral temperature or the gain of the AGC circuit so that the white spot noise detection is not influenced by the temperature of the solid state image pickup device or the operating state of the AGC circuit.

Claims

1. An electric camera comprising:

a lens system for forming an image from an incident light;

a solid state image pickup device for converting the image of an object formed by said lens system into an electric signal corresponding to a plurality of pixels;

a light shielding means for shielding the incident light to said solid state image pickup device;

a detecting means for comparing an output signal of each pixel of the solid state image pickup device and a predetermined level, thereby detecting defective pixels of the solid state image pickup device;

a means for controlling said light shielding means so as to shield the incident light to said solid state image pickup device when said detecting means detects defective pixels;

an automatic gain control circuit amplifying an output of said solid state image pickup device with an object imaging gain within an object imaging gain range for keeping a brightness of the image constant during times when the image of said object is formed, and with a defective pixel detecting gain during times when said detecting means detects said defective pixels, wherein said defective pixel detecting gain has a relative high gain level in said object imaging gain range;

a means for raising a gain of said automatic gain control circuit to said defective pixel detecting gain during times when said detecting means detects said defective pixels;

a memory for storing position information on said defective pixels detected by said detecting means; and

a replacing means for replacing a signal of a defective pixel of said defective pixels, which is specified by said position information in said memory by a signal formed based on a signal of a peripheral pixel of said defective pixel,

wherein said detecting means detects said defective pixel in a state in which the incident light is shielded by said light shielding means.

2. An electric camera according to claim 1, wherein the signal formed based on the signal of the peripheral pixel of said defective pixel is a signal of a pixel adjacent to said defective pixel.

3. An electric camera according to claim 1, wherein the peripheral pixel of said defective pixel is a pixel existing at a nearest position from among pixels having color filters of a same color as that of a color filter of said defective pixel.

4. An electric camera according to claim 1, wherein the detection of said defective pixels by said detecting means and the light shielding of the incident light by said light shielding means are automatically executed after a power source is turned on.

5. An electric camera according to claim 1, wherein the detection of said defective pixels by said detecting means and the light shielding of the incident light by said light shielding means are automatically executed when an operation to shut off a power source is performed.

6. A method of correcting a defect of a signal which is output for a plurality of pixels from a solid state image pickup device, comprising the steps of:

shielding an incident light to said solid state image pickup device by a light shielding means;

using an automatic gain control circuit to amplify an output of said solid state image pickup device with an object imaging gain within an object imaging gain range for keeping a brightness of the image constant during times when the image of said object is formed, and with a defective pixel detecting gain during times when defective pixels are detected, wherein said defective pixel detecting gain has a relative high gain level in said object imaging gain range;

detecting said defective pixels of the solid state image pickup device while said automatic gain control circuit amplifies said output with said defective pixel detecting gain by comparing an output signal of each pixel of said solid state image pickup device and a predetermined level;

storing position information on said defective pixels detected by said detecting step;

opening said light shielding means; and

replacing a signal of the defective pixel which is specified by said position information stored by a signal formed based on a signal of a peripheral pixel of said defective pixel.

7. A method according to claim 6, wherein the signal formed based on the signal of the peripheral pixel of said defective pixel is a signal of a pixel adjacent to said defective pixel.

8. A method according to claim 6, wherein the peripheral pixel of said defective pixel is a pixel existing at a nearest position from among pixels having color filters of a same color as that of a color filter of said defective pixel.

9. A method according to claim 6, wherein the light shielding of said incident light is automatically executed after a power source is turned on.

10. A method according to claim 6, wherein the light shielding of said incident light is automatically executed when an operation to shut off a power source is performed, and the opening of said light shielding means is automatically executed after the power source is turned on.