Image signal processing apparatus and image signal processing method for controlling optical black level of image signal
View Patent ↗An image signal processing apparatus includes a clamp circuit that clamps an image signal having a horizontal synchronization signal, an optical black level period representing an optical black level, and an effective signal period representing an image signal for one horizontal line so as to clamp a value offset from the image signal on the basis of a first reference value during the optical black level period and to clamp the image signal on the basis of a second reference value different from the first reference value during the effective signal period, and a level computation circuit that determines the second reference value on the basis of a signal level clamped during the optical black level period.
1. An image signal processing apparatus that applies processing on an image signal having a synchronization period, an optical black level period representing an optical black level, and an effective signal period representing an image signal, comprising:
a clamp circuit that clamps a value offset from the image signal on the basis of a first reference value during the optical black level period, and clamps the image signal on the basis of a second reference value different from the first reference value during the effective signal period,
wherein the second reference value is found on the basis of a signal level clamped during the optical black level period; and
the second reference value is calculated on the basis of an average value of a signal clamped during the optical black level period.
2. The image signal processing apparatus according to claim 1 , further comprising:
an analog-to-digital converting circuit that converts a signal clamped in the clamp circuit from an analog form to a digital form,
wherein the first reference value is set in such a manner that a signal in the optical black level period is clamped almost at a center of a dynamic range of the analog-to-digital converting circuit in the clamp circuit.
3. The image signal processing apparatus according to claim 1 , further comprising:
a defect correction circuit that applies a defect correction to a signal output from the clamp circuit; and
a second clamp circuit that clamps the image signal in the optical black level period after processing in the defect correction circuit,
wherein the second reference value is found on the basis of a signal level clamped in the second clamp circuit.
4. An image signal processing apparatus that applies processing on an image signal having a synchronization period, an optical black level period representing an optical black level, and an effective signal period representing an image signal, comprising:
a clamp circuit that clamps a value offset from the image signal on the basis of a first reference value during the optical black level period, and clamps the image signal on the basis of a second reference value different from the first reference value during the effective signal period, and
an analog-to-digital converting circuit that converts a signal clamped in the clamp circuit from an analog form to a digital form,
wherein the second reference value is found on the basis of a signal level clamped during the optical black level period; and
wherein the first reference value is set in such a manner that a signal in the optical black level period is clamped almost at a center of a dynamic range of the analog-to-digital converting circuit in the clamp circuit.
5. An image signal processing apparatus that applies processing on an image signal having a synchronization period, an optical black level period representing an optical black level, and an effective signal period representing an image signal, comprising:
a clamp circuit that clamps a value offset from the image signal on the basis of a first reference value during the optical black level period, and clamps the image signal on the basis of a second reference value different from the first reference value during the effective signal period;
a defect correction circuit that applies a defect correction to a signal output from the clamp circuit; and
a second clamp circuit that clamps the image signal in the optical black level period after processing in the defect correction circuit,
wherein the second reference value is found on the basis of a signal level clamped during the optical black level period; and
wherein the second reference value is found on the basis of a signal level clamped in the second clamp circuit.
6. An image signal processing method for applying processing to an image signal having a synchronization period, an optical black level period representing an optical black level, and an effective signal period representing the image signal, comprising:
performing first clamp processing to clamp the image signal in the optical black level period by offsetting the image signal on the basis of a first reference value;
performing second clamp processing to clamp the image signal in the effective signal period on the basis of a second reference value different from the first reference value; and
performing reference value calculation processing to determine the second reference value on the basis of a signal level clamped by the first clamp processing;
the second reference value is calculated on the basis of an average value of the signal clamped during the optical black level period in the reference value calculation processing.
7. An image signal processing method for applying processing to an image signal having a synchronization period, an optical black level period representing an optical black level, and an effective signal period representing the image signal, comprising:
performing first clamp processing to clamp the image signal in the optical black level period by offsetting the image signal on the basis of a first reference value;
performing second clamp processing to clamp the image signal in the effective signal period on the basis of a second reference value different from the first reference value;
performing reference value calculation processing to determine the second reference value on the basis of a signal level clamped by the first clamp processing; and
performing analog-to-digital conversion processing to convert the signal clamped in the first clamp processing and the second clamp processing from an analog form to a digital form,
wherein the first reference value is set in such a manner that the signal clamped in the first clamp processing is clamped almost at a center of a dynamic range in the analog-to-digital converting processing.
8. An image signal processing method for applying processing to an image signal having a synchronization period, an optical black level period representing an optical black level, and an effective signal period representing the image signal, comprising:
performing first clamp processing to clamp the image signal in the optical black level period by offsetting the image signal on the basis of a first reference value;
performing second clamp processing to clamp the image signal in the effective signal period on the basis of a second reference value different from the first reference value;
performing reference value calculation processing to determine the second reference value on the basis of a signal level clamped by the first clamp processing;
performing defect correction processing to make a defect correction of the image signal having undergone the first clamp processing and the second clamp processing; and
performing third clamp processing to clamp the image signal in the optical black level period having undergone the defect correction processing,
wherein the second reference value is found on the basis of a signal level clamped by the third clamp processing.