Image-signal clamping circuit for electronic endoscope

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.

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.

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.

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.

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.