User Manual - twentynine
4.2
Color Imaging with Bayer Pattern
In an area image sensor pixels are arranged in a two dimensional array (see Figure 26). Each pixel
contains a light sensitive photo diode that converts the incoming light intensity into an electrical voltage.
The amount of light falling into a photo diode over a period of time, defined by the exposure or integration
time, determines the pixel voltage level. Based on the technology of a photo diode, each pixel is sensitive
for a wide range of wavelengths, covering on silicon based sensors the whole visible as well as near
infrared wavelengths. All incoming photons are accumulated to one intensity, a separation of the different
wavelengths and thus color information is therefore afterwards not possible.
To build up color images, an image sensor needs the ability to extract the color information already from
the incoming light. One common way for this purpose is to place a color filter array (CFA) on top of the
photosensitive cells, to catch significant wavelengths individually by filtering off all others and use them to
recalculate full color information for each pixel. The Bayer color filter array is the most widely used filter
array on image sensors, which uses the complementary colors red, green and blue. The main advantage
of this filter array is that only one image sensor is needed to separate color information of the light at one
time. In a Bayer filter array there are twice as many green as there are red or blue pixels, the reason behind
this is the higher sensitivity of the human eye for the color green.
Note
All color cameras of the twentynine family are equipped with area image sensors with
Bayer pattern.
Figure 26: Bayer Color Filter Array placed on top of an area image sensor
Figure 26 illustrates a Bayer color filter array placed on top of an area image sensor:
•
At a red color filter position, red light is fully transmitted, green and blue light are reflected or absorbed
by the filter
•
At a green color filter position, green light is fully transmitted, red and blue light are reflected or
absorbed by the filter
•
And at a blue color filter position, blue light is fully transmitted, red and green light are reflected or
absorbed by the filter
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SMARTEK Vision | User Manual - twentynine | Doc. v1.0.2
