21-08-2014, 03:27 PM
There is a trend to replace thin film by Electronic Solid State image sensors in many application due to their outstanding performance and abilities in new fields of image capture applications such as digital still photography, video communications, as video conferencing cameras, and video phone. In addition to digital radiography, as medical radiography in which x- ray films are replaced. The results were superior. There is no need for film processing. It gives better resolution and the image can be restored digitally. The imaging system includes some essential and common elements, as an imaging lens, an image sensor, and a light source. The invention of two electronic solid state image sensing technology, namely the CCD’s and CMOS marks a new era in field of photography.For the foreseeable future, there will be a significant role for both types of sensor in imaging. The most successful users of advanced image capture technology will be those who consider not only the base technology, but also the sustainability, adaptability and support. They will perform the best long term in a dynamic technology environment that the battle between CCD’s and CMOS promises to deliver. Both image sensors are pixilated metal oxide semiconductors. They accumulate signal charge in each pixel proportional to the local illumination intensity, serving a spatial sampling function.When exposure is complete, a CCD transfers each pixel’s charge packet sequentially to a common output structure, which converts the charge to a voltage, buffers it and sends it off-chip. In a CMOS imager, the charge-to-voltage conversion takes place in each pixel. This difference in readout techniques has significant implications for sensor architecture, capabilities and limitations. The scope of this paper is to concentrate on these two main types of the image sensor elements, namely the CCD's and the CMOS