A digital clamping circuit and a digital clamping method are provided which can effectively use the dynamic range of an output signal in black-level correction. When subtracting a black level serving as a reference value from an output signal of an analog front end circuit, a digital clamp circuit permits the production of a negative value, amplifies the dynamic range including the-negative value to increase the dynamic range, adds a predetermined value to the resulting signal, and performs clipping. As a result, the dynamic range of the digital clamp circuit is increased, so that the dynamic range of an output signal can be effectively utilized. Thus, processing that makes good use of a wider dynamic range can be performed in image processing at a subsequent stage, so that image quality can be improved.

An image processing system includes a charge-coupled device sensor having a wide input dynamic range, and an analog front end circuit coupled to the charge-coupled device sensor. The front end circuit includes an analog-to-digital converter module to receive an input analog signal from the charge-coupled device sensor, the analog-to-digital converter module having a signal to noise ratio corresponding to a predetermined number of bits and a higher resolution than the predetermined number of bits. The front end circuit further includes a digital multiplier module coupled to the analog-to-digital converter module, the analog-to-digital converter module and the digital multiplier module to adjust a full scale input range at the analog-to-digital converter module over the wide range without loss in analog-to-digital conversion resolution.

Disclosed herein is a semiconductor integrated circuit device such as a for-camera preprocessing LSI suitable for a semiconductor integrated circuit and having improved responsiveness. In a D/A converter circuit for generating a feedback signal for compensating for black level variation in a for-camera preprocessing LSI, first-conductivity-type MOSFETs as first current sources produce currents corresponding to digital signals. The digital signals are supplied to first-conductivity-type first differential MOSFETs and second-conductivity-type second differential MOSFETs, with the gates and drains of the first differential MOSFETs and the gates and drains of the second differential MOSFETs being connected together respectively. There is provided a differential amplifier circuit in which a bias voltage is supplied to a noninverting input terminal thereof and an inverting input terminal thereof is connected to an analog current output node which is the drains connected together of one sides of the first differential MOSFETs, and a resistive element is provided between the inverting input terminal and an output terminal thereof. A converted analog output voltage is generated at the output terminal, and a voltage equal to the bias voltage is supplied to drains of the other sides of the first differential MOSFETs.

A method and apparatus are described that detect and correct for over-saturation lighting conditions in a CMOS Image Sensor.

An automatic gain control device for an electronic endoscope is provided and comprises a controllable gain amplifier, an A/D converter, a histogram circuit, and a CPU. The controllable gain amplifier amplifies image signals from an imaging device. Amplified image signals from the controllable gain amplifier are input to the A/D converter. A histogram of the amplified image signals from the controllable gain amplifier is produced by the histogram circuit when an image taken in a white-balance test accessory is taken. By using the CPU, the gain of the controllable gain amplifier is adjusted in accordance with the determination of whether a saturated pixel exists for signals in the tolerance range of the A/D converter, so that a linear region of the image signals from the controllable gain amplifier substantially coincides with the tolerance range.