Image pickup apparatus enlarging a dynamic range of an image pickup signal

• US 6,441,845 B1
• Filed: 02/22/1999
• Issued: 08/27/2002
• Est. Priority Date: 03/31/1998
• Status: Expired due to Term

• Current Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Original Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Inventors: Matsumoto, Kanichi
• Primary Examiner(s): Kelley, Chris
• Assistant Examiner(s): PHILIPPE, GIMS S
• Application Number:
  US09/255,550
• Time in Patent Office: 1,282 Days
• Field of Search: 348/65, 348/73, 348/76, 348/45, 348/46, 348/55, 348/68, 348/77, 348/72, 348/207, 348/229, 348/314, 348/255, 348/312, 348/311, 348/317, 348/221, 348/297, 600/109, 600/921
• US Class Current: 348/65
• 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 23/72 Combination of two or more compensation controls
• CPC Class Codes: H04N 23/73 by influencing the exposure time

Abstract

An endoscopic image pickup apparatus includes a camera head incorporating image pickup apparatus, a scope to which the camera head is connected detachably, and a light source apparatus supplying illumination light to the scope. A camera control unit (CCU) is provided as a processor body performing signal processing for the image pickup means provided in the camera head. A monitor displays a standard picture signal processed by the CCU. A detection circuit in the CCU detects the luminance of an image from an RGB digital signal outputted by a color separation circuit, and a detection output of the detection circuit is outputted to a CPU. The CPU judges whether the luminance of an image is equal to or more than a predetermined value, and controls a peripheral interface (I/F) on the basis of the luminance value of the image. The peripheral I/F outputs set signals and a control signal to an exposure control circuit and a CCD driver.

Claims

1. An image pickup apparatus comprising:

a charge storage type imaging device that converts subject images into electrical image signals, each image signal being characterized by a field period;

a drive circuit that determines an exposure time for an image by controlling the charge storage period of the imaging device;

a detection circuit operative to generate output signals according to luminance levels of fields of the image signals;

a picture signal generation circuit including a delay circuit that delays a signal from the imaging device by one field period, the picture signal generation circuit being responsive to an image signal for a first field period, and to an image signal for a second field period delayed by the delay circuit for one field period from that of the first field to generate a picture signal having a predetermined luminance;

a control circuit responsive to the output signals from the detection circuit to control the picture signal generation circuit and to provide control signals to the imaging device drive circuit that establish a long time exposure mode if the control circuit judges that the luminance detected by the detection circuit is lower than the predetermined luminance.

2. An image pickup apparatus according to claim 1, wherein:

the control circuit is operative during the long time exposure mode to control the picture signal generation circuit on the basis of luminance detected by the detection circuit;

the picture signal generation circuit comprises;

an addition circuit,

a first logic circuit responsive to a first control signal to couple an output of the delay circuit as an input to the addition circuit;

a second logic circuit responsive to a second control signal to couple an undelayed output of the imaging device as a first input to the addition circuit,

the first control signal is provided during the long time exposure mode, during a normal exposure mode in which the luminance detected by the detection circuit is not lower than the predetermined luminance, and during a transition period from the normal exposure mode to the long time exposure mode, but not during a transition period from the long time exposure mode to the normal exposure mode;

the second control signal is provided only during the long time exposure mode and during the transition period from the long time exposure mode to the normal exposure mode; and

the control circuit is operative to adjust the electric charge storage period of the imaging device for each field of the image signal during the long time exposure mode such that a signal outputted by the addition circuit does not exhibit an abrupt change in luminance when there is a transition between the normal exposure mode and the long time exposure mode.

3. An image pickup apparatus according to claim 1, wherein the one field period is {fraction (1/60)} sec.

4. An image pickup apparatus according to claim 1, wherein the picture signal generation circuit has a nonlinear processing circuit that performs a predetermined nonlinear processing to a field of the image signal.

5. An image pickup apparatus according to claim 4, wherein the nonlinear processing circuit is a lookup table ROM.

6. An image pickup apparatus according to claim 1, wherein:

the electrical image signals are comprised of a succession of frames defined by a field period;

the control circuit is operative during the long time exposure mode;

to control the picture signal generation circuit on the basis of luminance detected by the detection circuit; and

to provide control signals to the drive circuit which produce a succession of charge storage periods, which vary in duration from an initial short euration to progressively longer durations; and

the picture signal generation circuit further includes an addition circuit that is operative to add one field of an image signal delayed by the delay circuit that has a first charge storage period, and a corresponding field of an un-delayed image signal in a succeeding frame that has a second charge storage period that is the next charge storage period in the succession of charge storage periods.

7. An image pickup apparatus according to claim 6, wherein the duration for the initial charge storage period of the long time exposure mode is longer by a predetermined small amount than one-half the field period, and increases toward a charge storage period equal to the field period.

8. An image pickup apparatus according to claim 6, wherein the picture signal generation circuit includes a nonlinear processing circuit that performs a predetermined nonlinear processing to the output of the addition circuit, in the long time exposure mode.

9. An image pick up apparatus comprising:

an imaging device for imaging a subject to output an image pickup signal;

an imaging device drive circuit for outputting a drive signal which can drive said imaging device for a first electric charge storage period to output a first field of image pickup signal and also drive said imaging device for a second electric charge storage period to output a second field of image pickup signal which is continuous with said first field of image pickup signal;

a signal processing circuit for processing said image pickup signal;

a detection circuit for detecting a luminance signal from said image pickup signal outputted from said imaging device;

a comparison circuit for comparing said luminance signal detected by said detection circuit and a predetermined luminance value; and

a control circuit which sends out a control signal to said imaging device drive circuit based on the result of comparison in said comparison circuit to control the electric charge storage periods of said imaging device and also sends out a predetermined coefficient signal to said signal processing circuit to process said image pickup signal,

wherein said signal processing circuit comprises;

a field delay circuit which delays said first field of image pickup signal outputted from said imaging device by one field period;

a first multiplier circuit which multiplies said first field of image pickup signal delayed by said field delay circuit by a first coefficient signal set by said control circuit based on the result of comparison in said comparison circuit;

a second multiplier circuit which multiplies said second field of image pickup signal outputted from said imaging device by a second coefficient signal set by said control circuit based on the result of comparison in said comparison circuit; and

an adder circuit which adds an output signal of said first multiplier circuit and an output signal of said second multiplier circuit.

10. An image pickup apparatus comprising:

a charge storage type imaging device that converts subject images into electrical image signals, each image signal being characterized by a field period;

a drive circuit that determines an exposure time for an image by controlling the charge storage period of the imaging device;

a detection circuit operative to generate output signals according to luminance levels of fields of the image signals;

a picture signal generation circuit operative to generate a picture signal having a predetermined luminance; and

a control circuit responsive to the output signals from the detection circuit to control the picture signal generation circuit and to provide control signals to the imaging device drive circuit that establish a long time exposure mode if the control circuit judges that the luminance detected by the detection circuit is lower than the predetermined luminance;

wherein the picture signal generation circuit includes;

a delay circuit;

a nonlinear processing circuit that performs predetermined nonlinear processing to the image signal using a first nonlinear function in the long time exposure mode and a second nonlinear function during a normal exposure mode for which the control circuit judges that the luminance detected by the detection circuit is not lower than the predetermined luminance; and

an addition circuit that is operative during the long time exposure mode to add a first signal, which has been generated using a first charge storage time in one field period, processed through the nonlinear processing circuit, and delayed by the delay circuit, and a second signal, which has been generated using a second charge storage time in one field period in a next stage, and processed through the nonlinear processing circuit, but has not been delayed by the delay circuit.

11. An image pickup apparatus according to claim 10, wherein the first electric charge storage period and the second electric charge storage period are electric charge storage periods at the time of high-speed shutter.

12. An image pickup apparatus according to claim 10, wherein the nonlinear processing circuit is a lookup table ROM.

13. An image pickup apparatus according to claim 10, wherein, when the second nonlinear function to an input signal x is f(x), the first nonlinear function g(x) is:

14. An image pickup apparatus comprising:

a charge storage type imaging device that converts subject images into electrical image signals comprised of a succession of frames defined by a field period;

a drive circuit that determines an exposure time for an image by controlling the charge storage period of the imaging device;

a detection circuit operative to generate output signals according to luminance levels of fields of the image signals;

a picture signal generation circuit operative to generate a picture signal having a predetermined luminance; and

a control circuit responsive to the output signals from the detection circuit to control the picture signal generation circuit and to provide control signals that establish a long time exposure mode if the control circuit judges that luminance levels detected by the detection circuit are lower than a predetermined luminance, the control circuit being operative during the long time exposure mode;

to control the picture signal generation circuit on the basis of luminance detected by the detection circuit; and

to provide control signals to the drive circuit which produce a succession of charge storage periods;

wherein the picture signal generation circuit includes;

a delay circuit that delays a signal from the imaging device by one field period; and

an addition circuit, the addition circuit being operative to add

one field of an image signal delayed by the delay circuit that has a first charge storage period, and

a corresponding field of an un-delayed image signal in a succeeding frame that has a second charge storage period that is the next charge storage period in the sequence of charge storage periods; and

a nonlinear processing circuit comprised of a lookup table ROM that performs a predetermined nonlinear processing to an output of the addition circuit.

15. An image pickup apparatus comprising:

a photoelectric imaging device capable of producing an electrical signal output representative of an image characterized by a luminance;

an image exposure control circuit that controls exposure time of the imaging device;

an image processing circuit responsive to the electrical signal output of the imaging device to determine the luminance of the image;

a comparison circuit operative to generate a control signal if the luminance falls below a predetermined value;

the image exposure control circuit being operative in response to the control signal to gradually increase the exposure time for the image from a first value to a higher value in accordance with the luminance thereof.