Digital Signal Processing Reference
In-Depth Information
8
SENSOR PROCESSING
FOR IMAGE SENSORS
CHAPTER OUTLINE
8.1 CMOS Sensor Basics 54
8.2 A Simplistic HW Implementation of Bayer Demosaicing 56
8.3 Sensor Processing in Military Electro-optical Infrared Systems
56
8.4 Conclusion
58
There are two primary types of sensors that are used to
capture video data
d
CCD sensors and CMOS sensors.
A significant difference between these two technologies is how
the video data is read out. For CCD sensors the charge is shifted
out whereas for CMOS sensors the charge or voltage flows
through column and row decoders, very much like a digital
memory architecture.
CMOS sensors are becoming prevalent for a variety of
reasons
e
not least because of their proliferation within
consumer devices. This not only drives up the quality but also
drives down the price. The latest iPhone has an 8 MP CMOS
sensor
e
the kind that was found only in the most expensive
digital SLR cameras just five years ago.
CMOS sensors are rapidly becoming the
de facto
standard
when it comes to digital image capture. The output of an image
sensor is not in a standard video format that can be processed: it
cannot be resized (scaled), deinterlaced, or composited for
example.
The sensor image must first go through a processing pipe-
line that may include a range of functions such as pixel
correction, noise reduction, Bayer-to-RGB conversion, color
correction, gamma correction, and other functions, as shown in
Figure 8.1
.
Given the wide variety of image sensors used, and the range of
application requirements, each processing pipeline will be
unique. In many cases hardware customization is required to
produce an optimum quality image.
