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MT9T111_DG - Rev. B 9/10 EN
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MT9T111: Developer Guide
Auto White Balance (AWB)
Preliminary
Auto White Balance (AWB)
This section discusses the procedures to use when programming the color correction
matrix elements and manual white balance. To achieve good color rendition and color
saturation, interpolated colors of all pixels are subjected to color correction. The color
correction is a linear transformation of the image with a 3 x 3 color correction matrix.
The optimal values of the correction matrix elements depend on the spectrum of light
incident on the sensor. They can be either programmed by the user or automatically
selected by the AWB algorithm.
Color Correction Procedure
Color correction is done after the second black level block, and before the aperture
correction block. The interpolated RGB values are transformed by the color correction
matrix into color-corrected R', G', and B' values. The color correction matrix is uploaded
from the AWB driver into the corresponding registers in the color pipeline when AWB
has settled.
The color correction matrix consists of nine values, each of which represents a digital
gain factor on the corresponding color channel with the diagonal elements representing
the gain factors on each color channel, and the off diagonal terms representing the gain
factors to compensate for color crosstalk. The matrix is normalized so that the sum of
each row is “1.” All the color correction matrix values are stored in the AWB variable map.
Table 35:
Color Correction Matrix Structure
Gain R
Gain G
Gain B
Saturation red
ccmL[0]
ccmL[1]
ccmL[2]
Saturation green
ccmL[3]
ccmL[4]
ccmL[5]
Saturation blue
ccmL[6]
ccmL[7]
ccmL[8]