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Sensor is the heart of
digital imaging devices - digital cameras and camcorders. Generally,
our digital image capture devices are equipped with CCD or CMOS
sensor that helps convert light into electrical signals that
represents the image and can be digitally stored. The captured image
quality is vary by the CCD size and also the CCD system. Currently
the are two most widely used systems are Single CCD and 3-CCD
system. Since most devices use CCD rather than CMOS, we'll focus on
CCD technology in this article. |
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Single CCD system
This system is commonly used in
consumer level camcorders and has been widely in used on digital
cameras.
Because CCD can only sense the luminance, therefore it has to rely
on a Color Filter Array (CFA) to mask out all other colors except
the specific color for each pixel to be passed-thru. There are two
main type of filter structure: stripe and mosaic. In general, mosaic
filter provide better horizontal resolution. There are two methods
for reproducing color with filter. One is primary color filter, and
the other is complementary color filter.
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Primary
color filter (RGB color filter)
Primary color filter is basically using Red, Green and Blue
color (SONY introduces the 4 color filter which is using the
Red, Green, Blue and Emerald color). This kind of color filter
is better in color reproduction. However, each RGB color has
less light transmittance compared to complementary filter hence,
30% less sensitive. It is widely used for digital camera and
certain DV camcorders (eg: SONY PC300K).
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| General primary color filter array |
SONY's 4 colors filter array |
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Complementary color filter
Complementary color filter can be some combination of colors and
two popular types are CY, G, YE, MG and YE, G, CY. It has better
low-light sensitivity and provides higher signal-to-noise ratio.
This is why complementary color filter is very popular in
consumer level camcorders.
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Complementary color filter array
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3-CCD
System
3-CCD system uses a beam splitting prism to separate light passing
through the lens into 3 individual components and each is sent to
its own CCD. This technology reproduces color in great fidelity and
high accuracy but slightly reduced light sensitivity.
Normally 3-CCD system is used in professional and prosumer range
products but now you can find even it on some consumer level DV
camcorders eg: Panasonic MX500, and GS70K. |
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Conclusion
Single CCD system uses color approximation method to reproduce color
but 3-CCD captures full RGB information for each pixel. The
difference is significant in poor lighting environment where 3-CCD
system usually sense color more accurately. If producing good
quality videos with the highest color fidelity is your goal, try
getting yourself a 3-CCD system. |
