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2.2 Image Sensor
An image sensor plays a key role in converting lights through the lens into electrical signals. Based on the
manufacturing process, there are two types of sensors: CMOS (Complementary Metal Oxide Semiconductor) and
CCD (Charge-coupled Device).
2.2.1 Sensor Types
CMOS
CMOS is a standardized and constantly developing manufacturing process used in the semiconductors industry.
Each pixel on a CMOS sensor is accompanied by an amplifier based on p-n junction structure. The p-n junction
structure receives photons from the sensor and transmits them to an image signal processor.
CCD
CCD is a manufacturing process specially developed for digital imaging. A CCD is an analog shift register that
enables the transportation of analog signals (electric charges) through successive stages (capacitors), controlled
by a clock signal. The analog signals in each row of the capacitors are transmitted and converted to digital via an
analog-to-digital IC.
Table 2.1 Comparison of features and environments for CMOS and CCD
Features
Environment
2.2.2 Resolutions
Resolution refers to the number of pixels in a horizontal row and vertical column of an image. For example, a
resolution of 1280x1024 means the horizontal row consists of 1280 pixels and the vertical column includes 1024
lines. The resolution of the entire image is thus around 1.3 megapixel pixels. The higher the resolution, the more
information can be rendered, and thus the better image quality.
In traditional CCTV systems, the maximum resolution is 720x480 for NTSC (National Television System
Committee) and 720x576 for PAL (Phase Alternating Line).The most commonly used resolution is 704x480
NTSC/704x576 PAL.
NTSC
As the world's first color TV broadcast standard, NTSC was developed by National Television System Committee
in 1953. With an image size of 704x480 and up to 30 frames per second, NTSC is mainly adopted in the United
States, Canada and Japan that uses 60Hz AC electricity.
NTSC signals can be displayed on a black-and-white TV because they contain luminance signals and color
information. However, it has the disadvantages of phase distortion and unstable color.
PAL
1967 saw the development of a new color encoding standard for TV broadcasting in Germany, known as PAL,
which was exclusively developed for the 50Hz AC electricity used in Europe. PAL has an image size of 704x576,
with a full frame rate of 25 per second.
Since the phase of the color information in each line is reversed, PAL reduces color distortion problems.
CMOS
Smear, or blooming
Low power consumption
Low cost
Widely used in indoor
Chap.2 Lens and Image Sensor Technology
CCD
High light sensitivity
High color saturation
Low noise in low Lux
Widely used in outdoor
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