A CCD is a type of imaging chip. The letters stand
for Charge Coupled Device.
A short introduction to the CCD
CCD chips are frequently used in digital cameras,
video cameras (also the analogue type), security
cameras (Such as CCTV) and a range of other imaging appliances. The original
CCD technology was developed in the 1970s, but has been constantly refined
A CCD chip is really range of light sensors (or
photosites / photodiodes), with anything from a few hundred to several million
sensors placed on a little chip. These sensors do not measure color, just
light strenghth. To have a CCD sensor produce a color image, a grid of color
filters is placed over all the little sensors. Usually the shape of this grid
(R means Red, G means Green, and B means Blue) Because of how
the human eye works, to be able to cover the whole color spectrum, there
have to be twice as many green sensors as red ones.
How a CCD chip works
Next to every photodiode, there is a small "Image holder"
(charge holding region). When a picture is taken, the light that hits the photodiodes
is turned into an electrical charge, which is stored in the image
holder. After all the charges are stored in the image holders (of which there
are as many as there are photodiodes. This means that a 3 mpx chip has 3 million
image holders). This information is then scanned line-by line, and the information
Unfortunately, this technology uses a lot more resources (electricity)
then a CMOS chip - currently it's biggest competitor.
Then, what is four megapixel image?
As you might have figured out, a 4megapixel CCD chip has about
4million pixels. For the sake of simplicity, let us assume that there are
exactly 4,000,000 sensors on our chip. of these, 2M would be green, 1M would
be red, and 1M would be blue.
However, the final image doesn't have lots and lots of blue, red
and green dots next to each other - in the final picture, every pixel has
a specified value of red, green and blue. To achieve this, the data from the
CCD chip is interpolated, so that the color of every pixel is
one particular color.
The essence of interpolating the image, therefore, is changing
2 million greens, 1 million reds and 1 million blues into 4 million pixels that
make up the final image.