Concepts in Digital Imaging Technology

Concepts in Digital Imaging Technology

Anatomy of a Charge-Coupled Device

Digital image sensor technology is centered around the semiconductor charge-coupled device, which is fabricated in a manner similar to that used in the production of integrated circuits.

Pixel Binning

Pixel binning is a clocking scheme used to combine the charge collected by several adjacent CCD pixels, and is designed to reduce noise and improve the signal-to-noise ratio and frame rate of digital cameras.

CCD Blooming

Under specific conditions where a CCD is exposed to very high intensity illumination, it is possible to exhaust the storage capacity of the CCD wells, a condition known asblooming.

Dynamic Range

In aCCDorCMOSimage sensor, dynamic range is typically specified as the maximum achievable signal divided by the camera noise, where the signal strength is determined by the capacity, and noise is the sum of dark and read noises.

Quantum Efficiency

The quantum efficiency of a charge-coupled device (CCD) is a property of the photovoltaic response defined as the number of electron-hole pairs created and successfully readout by the device for each incoming photon.

CCD Noise Sources & Signal-to-Noise Ratio

For any electronic measuring system, thesignal-to-noise ratio(SNR) characterizes the quality of a measurement and determines the ultimate performance of the system as discussed in this section.

Charge-Coupled Device (CCD) Linearity

An important characteristic of a scientific imaging system is thelinearityin response to incident light, particularly when applied for quantitative photometric analysis as explained in this section.

Electronic Shutters

Electronic shutters are employed in charge-coupled devices (CCDs) to control integration time (exposure) of the photodiode array and reduce smear when capturing moving objects in the microscope.

Charge Transfer Clocking Schemes:Two Phase CCD Clocking

A two phase charge transfer CCD clocking scheme employs four gates for each pixel, with adjacent gates connected together as pairs.

Charge Transfer Clocking Schemes:Three Phase CCD Clocking

Three phase CCD clocking improves spatial resolution over that obtained in four phase devices, yet requires only three gates per pixel.

Charge Transfer Clocking Schemes:Four Phase CCD Clocking

A four phase CCD has four polysilicon gate electrodes in each pixel cell, each of which requires a separate input clock signal to transport accumulated charge.

CCD Scanning Formats

CCDdigital imaging sensors are capable of acquiring images in one of three formats: point scanning, line scanning, and area scanning. Each of these formats has specific applications in digital photography.

Full-Frame CCD Architecture

Full-frame charge-coupled devices feature high-density pixel arrays capable of producing digital images with the highest resolution currently available and has been widely adopted due to the reliability and ease of fabrication.

Frame-Transfer CCD Architecture

Frame-Transfer charged coupled image sensors have architecture similar to full-frame CCDs. These devices have a parallel register that is divided into two separate identical areas, termed theImageandStoragearrays.

Interline Transfer CCD Architecture

Interline CCD architecture is designed to compensate for the shortcomings of frame-transfer CCDs. These devices are composed of a separate photodiode and an associated CCD storage region into each pixel element.

Microlens Arrays

Microlens arrays (also referred to as microlenticular arrays or lenslet arrays) are used to increase the optical fill factor in CCDs, such as interline devices, that suffer from reduced aperture due to metal shielding.

Metal Oxide Semiconductor (MOS) Capacitor

At the heart of all CCDs is a light-sensitive metal oxide semiconductor (MOS) capacitor, which has three components consisting of a metal electrode (or gate), an insulating film of silicon dioxide, and a silicon substrate.

Avalanche Photodiodes

Avalanche photodiodes provide gain by the generation of electron-hole pairs from an energetic electron that creates an "avalanche" of electrons in the substrate as explained in this article.

Photomultiplier Tubes

A photomultiplier tube is a photoemissive device in which the absorption of a photon results in the emission of an electron, and is useful for light detection of very weak signals.

Proximity-Focused Image Intensifiers

Learn more about image intensifiers in this section as they were developed to enhance our night vision and are often referred to aswafer tubesorproximity-focused intensifiers.

Electron-Bombarded CCDs

TheEBCCDis a hybrid of the image intensifier and the CCD camera, which has just been recently introduced. In this device, photons are detected by a photocathode similar to that in an image intensifier.

Electron Multiplying CCDs

The topic discussed in this section is primarily about an innovative method of amplifying low-light-level signals above the CCD read noise is employed inelectron multiplyingCCD technology.

Sequential Color CCD Sytems

Three-pass sequential color CCD imaging systems employ a rotating color wheel to capture three successive exposures in order to obtain the desired RGB (red, green, and blue) color characteristics of a digital image.

Digital Imaging Java and Flash Tutorials

These tutorials are intended to allow visitors to adjust a variety of parameters and observe the effects of these changes, while providing technical information about the phenomena under study.