Wednesday, October 3, 2012

Digital Image Sensor

When the reflective light from the photographed subject passes through the lens and aperture, the image is captured by the digital image sensor. A digital image sensor is the computer chip inside the camera that consists of millions of individual elements capable of capturing light. The light-sensitive elements transform light energy to voltage values based on the intensity of the light.
The voltage values are then converted to digital data by an analog-to-digital converter (ADC) chip. This process is referred to as analog to digital conversion. The digital numbers corresponding to the voltage values for each element combine to create the tonal and color values of the image.
Each light-sensitive element on a digital image sensor is fitted with either a red, green, or blue filter, corresponding to a color channel in a pixel in the image that is captured. There are roughly twice as many green filters as blue and red to accommodate how the eye perceives color. This color arrangement is also known as the Bayer pattern color filter array. A process known as color interpolation is employed to ascertain the additional color values for each element.

Common Types of Digital Image Sensors
There are two types of digital image sensors typically used: a charge-coupled device (CCD) and a complementary metal oxide semiconductor (CMOS).

CCD : CCD sensors were originally developed for video cameras. CCD sensors record the image pixel by pixel and row by row. The voltage information from each element in the row is passed on prior to descending to the next row. Only one row is active at a time. The CCD does not convert the voltage information into digital data itself. Additional circuitry is added to the camera to digitize the voltage information prior to transferring the data to the storage device.

CMOS : CMOS sensors are capable of recording the entire image provided by the light-sensitive elements in parallel (essentially all at once), resulting in a higher rate of data transfer to the storage device. Additional circuitry is added to each individual element to convert the voltage information to digital data. A tiny colored microlens is fitted on each element to increase its ability to interpret the color of light. Advances have been made in recent years in the sensitivity and speed of CMOS sensors, making them the most common type of digital image sensor found in professional DSLRs.

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