Image-signal clamping circuit for electronic endoscope

• US 5,708,482 A
• Filed: 09/08/1995
• Issued: 01/13/1998
• Est. Priority Date: 09/08/1994
• Status: Expired due to Term

• Current Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Original Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Inventors: Iketani, Kohei, Takahashi, Akihiro
• Primary Examiner(s): Burgess, Glenton B.
• Application Number:
  US08/525,136
• Time in Patent Office: 858 Days
• Field of Search: 348/65, 348/71, 348/689, 348/695, 348/696, 348/677, 348/257
• US Class Current: 348/695
• CPC Class Codes: H04N 25/78 Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
• CPC Class Codes: H04N 5/18 by means of "clamp" circuit operated by switching circuit

Abstract

An image-signal clamping circuit processes image signals obtained from a solid state image sensor provided at a distal end of an electronic endoscope which do not have a direct-current component to restore a direct-current component thereof. The clamping circuit is arranged such that the restoration of a direct-current component of an image signal can be properly and stably carried out. The clamping circuit includes a sample-and-hold circuit to temporarily store an image signal, an analog-to-digital converter to output digital image signals, a device for digitally correcting the digital image data, and a digital-to-analog converter to output corrected analog image signals. The pedestal level of the corrected output analog image signal approximates a reference pedestal level.

Claims

1. An image-signal clamping circuit for processing image signals obtained from a solid state image sensor provided at a distal end of an electronic endoscope, comprising:

fixing device for fixing a pedestal level of an image signal obtained from said solid state image sensor;

first conversion device for converting said image signal into digital image data;

preparation device for preparing digital correcting data on the basis of pedestal level data of said digital image data in accordance with a look-up table; and

second conversion device for converting said digital correcting data into analog correcting data,

wherein said fixing of the pedestal level of said image signal is carried out in accordance with said analog correcting data, such that the pedestal level of said image signal approximates an ideal pedestal level, said fixing device comprising a sample-and-hold circuit that temporarily holds said image signal, a capacitor connected to an output of said sample-and-hold circuit, a switch provided between said capacitor and said second conversion device, a clamping-pulse generation circuit that outputs a clamping pulse to said switch such that said switch is turned ON for a period of time corresponding to a width of said clamping pulse.

2. An image-signal clamping circuit as set forth in claim 1, wherein said digital correcting data output by said look-up table is based on the pedestal level data of said digital image data inputted to said look-up table.

3. An image-signal clamping circuit for processing image signals obtained from a solid state image sensor provided at a distal end of an electronic endoscope, comprising:

fixing device for fixing a pedestal level of an image signal obtained from said solid state image sensor;

first conversion device for converting said image signal into digital image data;

preparation device for preparing digital correcting data on the basis of pedestal level data of said digital image data in accordance with a look-up table; and

second conversion device for converting said digital correcting data into analog correcting data,

wherein said fixing of the pedestal level of said image signal is carried out in accordance with said analog correcting data, such that the pedestal level of said image signal approximates an ideal pedestal level, said look-up table providing for a gamma-correction for said digital image data, said preparation mean further comprising a subtractor that calculates a difference between a reference data and a pedestal level data of digital image data subjected to a gamma-correction by said gamma-correction look-up table.

4. An image-signal clamping circuit as set forth in claim 3, wherein said first conversion device comprises an analog-digital converter connected to a capacitor, said second conversion device comprises a digital-analog converter connected to a switch, and said subtractor is provided between said gamma-correction look-up table and said digital-analog converter.

5. An image-signal clamping circuit for processing image signals obtained from a solid state image sensor provided at a distal end of an electronic endoscope, comprising:

fixing device for fixing a pedestal level of an image signal obtained from the solid state image sensor;

first conversion device for converting said image signal into digital image data;

gamma-correction device for subjecting said digital image data to a gamma-correction, said gamma-correction device amplifying said pedestal level data of said digital image data;

preparation device for preparing digital correcting data based on said amplified pedestal level data of said digital image data; and

second conversion device for converting said digital correcting data into analog correcting data,

wherein said fixing of said pedestal level of said image signal is carried out in accordance with said analog correcting data, such that said pedestal level of said image signal approximates an ideal pedestal level.

6. An image-signal clamping circuit as set forth in claim 5, wherein said fixing device comprises a sample-and-hold circuit for temporarily holding the image signal, a capacitor connected to an output of said sample-and-hold circuit, a switch provided between said capacitor and said second conversion means, and a clamping-pulse generation circuit for outputting a clamping pulse to said switch such that said switch is turned ON for a period of time corresponding to a width of said clamping pulse.

7. An image-signal clamping circuit as set forth in claim 6, wherein said first conversion device comprises an analog-digital converter connected to said capacitor, said second conversion device comprises a digital-analog converter connected to said switch, said gamma-correction means comprises a look-up table connected to an output of said analog-digital converter, and said preparation means comprises a subtractor between provided said look-up table and said digital-analog converter.

8. The image-signal clamping circuit of claim 5, wherein said preparation device includes a subtractor that determines a difference between said pedestal level data of said digital image data and a data reference.

9. The image-signal clamping circuit of claim 8, wherein said pedestal level data of said digital image data is subjected to a gamma-correction.

10. An image-signal clamping circuit for processing image signals obtained from a solid state image sensor provided at a distal end of an electronic endoscope, comprising:

fixing device for fixing a pedestal level of an image signal obtained from said solid state image sensor;

first conversion device for converting said image signal into digital image data;

preparation device for preparing digital correcting data on the basis of pedestal level data of said digital image data;

filter device for eliminating noise from said digital correcting data; and

second conversion device for converting the filtered digital correcting data into analog correcting data,

wherein said fixing of the pedestal level of said image signal is carried out based on said analog correcting data, such that the pedestal level of said image signal approximates an ideal pedestal level, said fixing device comprising a sample-and-hold circuit that temporarily holds said image signal, a capacitor being connected to an output of said sample-and-hold circuit, a switch being provided between said capacitor and said second conversion device, and a clamping-pulse generation circuit outputting a clamping pulse to said switch such that said switch is turned ON for a period of time corresponding to a width of said clamping pulse.

11. An image-signal clamping circuit as set forth in claim 10, wherein said first conversion device comprises an analog-digital converter connected to said capacitor, said second conversion device comprises a digital-analog converter connected to said switch, said preparation device is connected to an output of said analog-digital converter, and said filter is provided between said preparation device and said digital-analog converter.

12. An image-signal clamping circuit for processing image signals obtained from a solid state image sensor provided at a distal end of an electronic endoscope, comprising:

fixing device for fixing a pedestal level of an image signal obtained from said solid state image sensor;

first conversion device for converting said image signal into digital image data;

preparation device for preparing digital correcting data on the basis of pedestal level data of said digital image data;

second conversion device for converting said digital correction data into analog correcting data; and

filter device for eliminating noise from said analog correcting data,

wherein said fixing of the pedestal level of said image signal is carried out based on filtered analog correcting data, such that the pedestal level of said image signal approximates an ideal pedestal level, said fixing device comprising a sample-and-hold circuit that temporarily holds said image signal, a capacitor being connected to an output of said sample-and-hold circuit, a switch being provided between said capacitor and said second conversion means, and a clamping-pulse generation circuit outputting a clamping pulse to said switch such that said switch is turned ON for a period of time corresponding to a width of said clamping pulse.

13. An image-signal clamping circuit as set forth in claim 12, wherein said first conversion device comprises an analog-digital converter connected to said capacitor, said second conversion device comprises a digital-analog converter connected to said switch, said preparation device is provided between said analog-digital converter and said digital-analog converter, and said filter is provided between said switch and said digital-analog converter.

14. An image-signal clamping circuit for processing image signals obtained from a solid state image sensor provided at a distal end of an electronic endoscope, comprising:

conversion device for converting an image signal, obtained from said solid state image sensor, into digital image data;

first storage device for temporarily storing actual image data of said digital image data, said first storage device being formed as a line memory;

second storage device for temporarily storing pedestal level data of said digital image data;

calculation device for calculating a difference between said actual image data and said pedestal level data to digitally fix a pedestal level of an image signal; and

synchronization device for synchronously outputting said actual image data, from said first storage device, and said pedestal level data, from said second storage device, to said calculation means.