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IEEE SIGNAL PROCESSING MAGAZINE [44] JANUARY 2005 1053-5888/05/$20.002005IEEE igital cameras have become popular, and many people are choosing to take their pic-
 

Summary: IEEE SIGNAL PROCESSING MAGAZINE [44] JANUARY 2005 1053-5888/05/$20.002005IEEE
D
igital cameras have become popular, and many people are choosing to take their pic-
tures with digital cameras instead of film cameras. When a digital image is recorded,
the camera needs to perform a significant amount of processing to provide the user
with a viewable image. This processing includes correction for sensor nonlinearities
and nonuniformities, white balance adjustment, compression, and more. An important
part of this image processing chain is color filter array (CFA) interpolation or demosaicking.
A color image requires at least three color samples at each pixel location. Computer images often
use red (R), green (G), and blue (B). A camera would need three separate sensors to completely meas-
ure the image. In a three-chip color camera, the light entering the camera is split and projected onto
each spectral sensor. Each sensor requires its proper driving electronics, and the sensors have to be
registered precisely. These additional requirements add a large expense to the system. Thus, many
cameras use a single sensor covered with a CFA. The CFA allows only one color to be measured at
each pixel. This means that the camera must estimate the missing two color values at each pixel. This
estimation process is known as demosaicking.
Several patterns exist for the filter array. The most common array is the Bayer CFA, shown in
Figure 1. The Bayer array measures the G image on a quincunx grid and the R and B images on rec-
tangular grids. The G image is measured at a higher sampling rate because the peak sensitivity of the
human visual system lies in the medium wavelengths, corresponding to the G portion of the spec-

  

Source: Altunbasak, Yucel - School of Electrical and Computer Engineering, Georgia Institute of Technology

 

Collections: Engineering