Automatic gain control device for electronic endoscope

• US 7,248,296 B2
• Filed: 05/29/2003
• Issued: 07/24/2007
• Est. Priority Date: 05/31/2002
• Status: Expired due to Fees

• Current Assignee: Hoya Corporation
• Original Assignee: Pentax Corporation (Hoya Corporation)
• Inventors: Iketani, Kohei
• Primary Examiner(s): Ometz; David
• Assistant Examiner(s): PRABHAKHER, PRITHAM DAVID
• Application Number:
  US10/446,849
• Publication Number:
  US 20030222997A1
• Time in Patent Office: 1,517 Days
• Field of Search: 348/45, 348/223.1, 348/222.1, 348/255.1, 348/229.1, 348/230.1, 348/255, 600/101, 358/522, 396/17
• US Class Current: 348/255
• CPC Class Codes: A61B 1/045 Control thereof
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 23/555 for picking-up images in sites, inaccessible due to their dimensions or hazardous conditions, e.g. endoscopes or borescopes
• CPC Class Codes: H04N 23/76 by influencing the image signals
• CPC Class Codes: H04N 5/20 Circuitry for controlling amplitude response
• CPC Class Codes: H04N 5/202 Gamma control circuits for controlling camera response irrespective of the scene brightness H04N23/82

Abstract

An automatic gain control device for an electronic endoscope is provided and comprises a controllable gain amplifier, an A/D converter, a histogram circuit, and a CPU. The controllable gain amplifier amplifies image signals from an imaging device. Amplified image signals from the controllable gain amplifier are input to the A/D converter. A histogram of the amplified image signals from the controllable gain amplifier is produced by the histogram circuit when an image taken in a white-balance test accessory is taken. By using the CPU, the gain of the controllable gain amplifier is adjusted in accordance with the determination of whether a saturated pixel exists for signals in the tolerance range of the A/D converter, so that a linear region of the image signals from the controllable gain amplifier substantially coincides with the tolerance range.

Claims

1. An automatic gain control device for an electronic endoscope, comprising:

a controllable gain amplifier that amplifies image signals output by an imaging device comprising a plurality of pixels;

an A/D converter that digitizes the amplified image signals;

a detector that detects a status of digitized amplified reference image signals output by the imaging device when the imaging device captures images of a white-balance test accessory; and

a gain control processor that, based on the detected status of the digitized amplified reference image signals, sets a gain of the controllable gain amplifier to a value such that a linear operating range of an amplified image signal corresponding to a pixel of the plurality of pixels, having a smallest linear operating range out of the plurality of pixels, is approximately equal to a tolerance range of the A/D converter.

2. A device according to claim 1, wherein the detector comprises a histogram generator that generates a histogram based on the digitized amplified reference image signals.

3. A device according to claim 2, wherein said histogram indicates, for at least one image signal output value, a number of pixels corresponding to each of the at least one image signal output value.

4. A device according to claim 3, further comprising a saturated pixel detecting processor that determines whether a saturated pixel exists by determining whether a pixel corresponds to an image signal output value other than a predetermined image signal output value.

5. A device according to claim 1, wherein said reference image signals are luminance signals.

6. A device according to claim 5, wherein the value which the gain of the controllable gain amplifier is set to is a minimum gain value at which all of the digitized amplified reference image signals exceed a maximum value of the tolerance range of the A/D converter.

7. A device according to claim 1, wherein said reference image signals are color difference signals.

8. A device according to claim 7, wherein the value which the gain of the controllable gain amplifier is set to is a minimum gain value at which all of the digitized amplified reference image signals have a value corresponding to one-half a maximum value of the tolerance range of the A/D converter.

9. A device according to claim 1, wherein said gain control processor decreases said gain by a predetermined amount in successive steps, a saturated pixel detecting processor determines at each step whether a saturated pixel exists, and, when the saturated pixel detecting processor determines at a step that a saturated pixel exists, the gain control processor sets the gain to the gain of a previous step.

10. A device according to claim 1, wherein said gain control processor increases said gain by a predetermined amount in successive steps, a saturated pixel detecting processor determines at each step whether a saturated pixel exists, and, when the saturated pixel detecting processor determines at a step that a saturated pixel does not exist, the gain control processor maintains the gain at its present level.

11. A device according to claim 1, further comprising a memory that stores said gain, adjusted by said gain control processor.

12. A device according to claim 11, wherein said gain is stored in said memory together with information that is used to identify at least one electronic endoscope.

13. A device according to claim 11, further comprising

a memory verification processor that determines whether said gain is stored in said memory;

and

a message indicating processor that indicates a message which prompts an execution of a gain control operation when said memory verification processor determines that said gain is not stored in said memory.

14. A device according to claim 1, wherein said gain control processor is driven when a white balance correction process is executed.

15. An electronic endoscope apparatus that comprises an automatic gain control device, the automatic gain control device comprising:

a controllable gain amplifier that amplifies image signals output by an imaging device comprising a plurality of pixels;

an A/D converter that digitizes the amplified image signals;

a detector that detects a status of digitized amplified reference image signals output by the imaging device when the imaging device captures images of a white-balance test accessory; and

a gain control processor that, based on the detected status of the digitized amplified reference image signals, sets a gain of the controllable gain amplifier to a value such that a linear operating range of an amplified image signal corresponding to a pixel of the plurality of pixels, having a smallest linear operating range out of the plurality of pixels, is approximately equal to a tolerance range of the A/D converter.

16. An apparatus according to claim 15, wherein a memory that stores information to identify an electronic endoscope is provided in said electronic endoscope apparatus.

17. An automatic gain control device for an electronic endoscope, comprising:

a controllable gain amplifier that amplifies image signals output by an imaging device comprising a plurality of pixels;

an image signal processor that processes the amplified image signals;

a detector that detects a status of processed amplified reference image signals output by the imaging device when the imaging device captures images of a white-balance test accessory; and

a gain control processor that, based on the detected status of the processed amplified reference image signals, sets a gain of the controllable gain amplifier to a value such that a linear operating range of an amplified image signal corresponding to a pixel of the plurality of pixels, having a smallest linear operating range out of the plurality of pixels, is approximately equal to a tolerance range of the image signal processor.