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Noise analysis of CCD camera
Noise is an undesired signal component in an electronic image system. As an image sensor, CCD is a line array or an area array structure, which is mixed with various noises, thus greatly affecting the application of CCD in the field of high precision measurement. The noise processing of the CCD signal is to eliminate these high-level interferences as much as possible without losing the image details, and accurately extract the signal components in each pixel.
There are two sources of CCD noise, one is the noise inherent in the CCD gradually, such as dark current noise, charge transfer noise, etc., in one is the various noise interference in CCD operation, such as KTC noise. The output signal of the CCD image sensor is a spatially sampled discrete analog signal. The purpose of the CCD signal processing is to eliminate noise and interference as much as possible without loss of image detail, so as to improve the signal-to-noise ratio and obtain high-quality images.
There are several main noises in the CCD:
(1) Photon noise: This kind of noise is determined by the nature of photons, which is usually more serious in low-light imaging.
(2) Shot noise: Shot noise is frequency-independent and has a uniform power distribution over all frequency ranges. Under low illumination and low contrast conditions, when other noise is suppressed by various methods, shot noise will become the main noise of the CCD and determine the limit noise level of the device. The US QSI camera can suppress this noise.
(3) Transfer noise: The charge in the CCD is not fully transferred, and a part of the charge remains inside, which later becomes the noise interference of the charge. The root causes of transfer noise are transfer loss, interface state trapping, and posture trapping.
(4) Dark current noise: Dark current is divided into diffused dark current and surface dark current. The diffused dark current is generated in the conductive channel region of the CCD. The shorter the diffusion length is, the larger the dark current is. The dark current on the surface refers to an electron that can jump from the interface state to the conduction band under thermal excitation, and then forms free electrons. The potential well acts as a dark spot and collects to form a current. This current exists even in the absence of light.
Scientific, thermoelectric refrigeration CCD cameras manufactured by Quantum Scientific Imaging of the United States are widely used in astronomy, medical and industrial imaging. QSI cameras offer superior performance, wide dynamic range, good linearity, low noise and innovative design. In the past two decades, the company has developed high-quality CCD cameras that can be used under extremely difficult conditions. QSI cameras are currently developing a new generation of scientific digital cameras based on their experience to meet market demand.