Image Processing Reference
In-Depth Information
Fig. 3.4 A color image
consisting of three images;
red, green and blue
respectively; or alternatively:
SetPixel (image ,
4, R,
SetPixel (image ,
4, G,
SetPixel (image ,
4, B,
Typically each color value is represented by an 8-bit (one byte) value meaning
that 256 different shades of each color can be measured. Combining different values
of the three colors, each pixel can represent 256 3
16 , 777 , 216 different colors.
A cheaper alternative to having three sensors including mirrors and optical filters
is to only have one sensor. In this case, each cell in the sensor is made sensitive to
one of the three colors (ranges of wavelength). This can be done in a number of
different ways. One is using a Bayer pattern . Here 50% of the cells are sensitive
to green, while the remaining cells are divided equally between red and blue. The
reason being, as mentioned above, that the human eye is more sensitive to green.
The layout of the different cells is illustrated in Fig. 3.5 .
The figure shows the upper-left corner of the sensor, where the letters illustrate
which color a particular pixel is sensitive to. This means that each pixel only cap-
tures one color and that the two other colors of a particular pixel must be inferred
from the neighbors. Algorithms for finding the remaining colors of a pixel are known
as demosaicing and, generally speaking, the algorithms are characterized by the
required processing time (often directly proportional to the number of neighbors
included) and the quality of the output. The higher the processing time the better
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