Imaging apparatus and method of optical-black clamping

1. An imaging apparatus comprising:

a solid-state image sensing device having an imaging area divided into at least two sub-imaging areas in a horizontal direction in the imaging area, a first optical-black area and a second optical-black area being provided at both edges of the imaging area in the horizontal direction;

an extractor to extract first video signals from a plurality of monitoring areas provided in the sub-imaging areas in the vicinity of the border between the sub-imaging areas; and

an optical-black clamp processor to apply optical-black clamp processing to second video signals output from the sub-imaging areas by subtracting a first optical-black signal indicating an optical black level in the first optical-black area from the second video signal output from one of the sub-imaging areas and subtracting a second optical-black signal indicating an optical black level in the second optical-black area from the second video signal output from the other of the sub-imaging areas, the optical-black clamp processor including:

a detector to detect a level difference between the extracted first video signals;

a calculator to calculate an adjusting value per row of pixels, that provides the smallest level difference per row of pixels in a vertical direction in the imaging area based on the detected level difference;

a plurality of optical-black clampers each subtracting the first optical-black signal from the second video signal output from one of the sub-imaging areas and subtracting the second optical-black signal from the second video signal output from the other of the sub-imaging areas, thus outputting an optical-black-clamped video signal; and

an adjuster to perform adjustments to video-signal levels by multiplying the optical-black-clamped video signal by the adjusting value.

2. An imaging apparatus comprising:

a solid-state image sensing device having an imaging area divided into at least a first sub-imaging area and a second sub-imaging area in a horizontal direction in the imaging area, a first optical-black area and a second optical-black area being provided at both edges of the imaging area in the horizontal direction; and

an optical-black clamp processor to apply optical-black clamp processing to first video signals output from the sub-imaging areas by subtracting a first optical-black signal indicating an optical black level in the first optical-black area from the first video signal output from one of the sub-imaging areas and subtracting a second optical-black signal indicating an optical black level in the second optical-black area from the first video signal output from the other of the sub-imaging areas, the optical-black clamp processor including:

a first optical-black adjusting-level calculator to calculate a first optical-black adjusting level per row of pixels in a vertical direction in the first optical-black area;

a second optical-black adjusting-level calculator to calculate a second optical-black adjusting level per row of pixels in the second optical-black area;

a first adjuster to subtract the first optical-black adjusting level per row of pixels from a second video signal per row of pixels in the first sub-imaging area close to the first optical-black area; and

a second adjuster to subtract the second optical-black adjusting level per row of pixels from a third video signal per row of pixels in the second sub-imaging area close to the second optical-black area.

3. The imaging apparatus according to claim 2 , wherein:

the first optical-black adjusting-level calculator calculates an average optical-black level in each of a plurality of first blocks each including a plurality of pixels in the vertical and the horizontal directions in the first optical-black area, and calculates first optical-black adjusting levels on the rows of pixels based on a plurality of average optical-black levels in the first blocks; and

the second optical-black adjusting-level calculator calculates an average optical-black level in each of a plurality of second blocks each including a plurality of pixels in the vertical and the horizontal directions in the first optical-black area, and calculates second optical-black adjusting levels on the rows of pixels based on a plurality of average optical-black levels in the second blocks.

4. The imaging apparatus according to claim 3 further comprising a controller to shift locations of the first and the second blocks within the first and the second optical-black areas, respectively.

5. A method of optical-black clamping for an imaging apparatus having a solid-state image sensing device having an imaging area divided into at least two sub-imaging areas in a horizontal direction in the imaging area, a first optical-black area and a second optical-black area being provided at both edges of the imaging area in the horizontal direction, the method comprising the steps of:

extracting first video signals from a plurality of monitoring areas provided in the sub-imaging areas in the vicinity of the border between the sub-imaging areas; and

applying optical-black clamp processing to second video signals output from the sub-imaging areas by subtracting a first optical-black signal indicating an optical black level in the first optical-black area from the second video signal output from one of the sub-imaging areas and subtracting a second optical-black signal indicating an optical black level in the second optical-black area from the second video signal output from the other of the sub-imaging areas, the applying step including:

detecting a level difference between the extracted first video signals;

calculating an adjusting value per row of pixels, that provides the smallest level difference per row of pixels in a vertical direction in the imaging area based on the detected level difference;

subtracting the first optical-black signal from the second video signal output from one of the sum-imaging areas and subtracting the second optical-black signal from the second video signal output from the other of the sum-imaging areas, thus outputting an optical-black-clamped video signal; and

performing adjustments to video-signal levels by multiplying the optical-black-clamped video signal by the adjusting value.

6. A method of optical-black clamping for an imaging apparatus having a solid-state image sensing device having an imaging area divided into at least a first sub-imaging area and a second sub-imaging area in a horizontal direction in the imaging area, a first optical-black area and a second optical-black area being provided at both edges of the imaging area in the horizontal direction, the method comprising the steps of:

applying optical-black clamp processing to first video signals output from the sub-imaging areas by subtracting a first optical-black signal indicating an optical black level in the first optical-black area from the first video signal output from one of the sub-imaging areas and subtracting a second optical-black signal indicating an optical black level in the second optical-black area from the first video signal output from the other of the sub-imaging areas, the applying step including:

calculating a first optical-black adjusting level per row of pixels in a vertical direction in the first optical-black area;

calculating a second optical-black adjusting level per row of pixels in the second optical-black area;

subtracting the first optical-black adjusting level per row of pixels from a second video signal per row of pixels in the first sub-imaging area close to the first optical-black area; and

subtracting the second optical-black adjusting level per row of pixels from a third video signal per row of pixels in the second sub-imaging area close to the second optical-black area.

7. The method of optical-black clamping according to claim 6 , wherein:

the first optical-black adjusting-level calculating step includes the steps of calculating an average optical-black level in each of a plurality of first blocks each including a plurality of pixels in the vertical and the horizontal directions in the first optical-black area, and calculating first optical-black adjusting levels on the rows of pixels based on a plurality of average optical-black levels in the first blocks; and

the second optical-black adjusting-level calculating step includes the steps of calculating an average optical-black level in each of a plurality of second blocks each including a plurality of pixels in the vertical and the horizontal directions in the first optical-black area, and calculating second optical-black adjusting levels on the rows of pixels based on a plurality of average optical-black levels in the second blocks.

8. The method of optical-black clamping according to claim 6 further comprising the step of shifting locations of the first and the second blocks within the first and the second optical-black areas, respectively.