Color Filter (Bayer Filter) - IDS uEye series User Manual

6.2.3

Color Filter (Bayer Filter)

For technical reasons, digital image sensors can only detect brightness information, but no color
information. To produce color sensors, a color filter is applied to each photocell (pixel). The
arrangement of the color filters is illustrated in the following figure. Two out of every four pixels have a
green filter, one pixel has a red filter and one has a blue filter. This color distribution corresponds to
the color sensitivity of the human eye, and is called the Bayer filter pattern. With the help of the
Bayer pattern the correct brightness and color information can be calculated for each pixel. Full
sensor resolution is retained.
Bayer conversion
A Bayer conversion, also referred to as de-Bayering, is carried out to determine the color information
from the raw sensor data (raw Bayer). By default all uEye cameras transmit the image data to the
PC in raw Bayer format. The PC then uses the functions of the uEye API to convert the image data
to the color format you need for displaying or further processing the data.
GigE uEye cameras additionally allow de-Bayering in the camera. In this case, the color images are
already finished when they are transmitted to the PC. This reduces the load on the computer's CPU
and increases the transmission bandwidth required by the camera.
To convert the colors, a filter mask moves over the image and calculates a color value for each pixel
from the surrounding pixels. The uEye API provides two filter masks that differ in image quality and
CPU load:
· 3x3 filter:
A filter mask of 3x3 pixels is used for conversion. This algorithm has a low load on the CPU. The
filter's averaging function may cause a slight blur. Noise is reduced. This filter is recommended for
image processing tasks.
· 5x5 filter:
A filter mask of 5x5 pixels is used for conversion. This algorithm offers very accurate color
positioning and an increased level of detail. The CPU load is higher than with the 3x3 filter. This
filter is recommended for visualization applications.
© 2009 IDS Imaging Development Systems GmbH
Some CMOS sensors have micro lenses offset to the sensor edge. They compensate
for shadows created by obliquely incident light. The use of parallel light causes slight
color variations. These may occur if telecentric stops or lenses with large apertures
whose last optical element is located at a great distance are used. The following
uEye models are equipped with CMOS sensors with offset micro lenses:
· 164x-C and 564x-C
· 155x-C and 555x-C
· 148x-M/C and 548x-M/C
Figure 28: Bayer filter and micro lenses
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