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MT9T111_DG - Rev. B 9/10 EN
110
©2007 Aptina Imaging Corporation. All rights reserved.
MT9T111: Developer Guide
Gamma
Preliminary
Gamma
The MT9T111 includes a block for gamma correction that can adjust its shape based on
brightness to enhance the performance under certain lighting conditions.
Gamma correction takes place in the RGB color space after color correction. The pixel
data is mapped to a gamma curve programmed by the user or a curve computed based
on the brightness level. The gamma curve is approximated by connecting 18 lines
segments. The ends of the line segments are called knee points and are at X coordinates
of 0, 64, 128, 256, 512, 768, 1024, 1280, 1536, 1792, 2048, 2304, 2560, 2816, 3072, 3328,
3584, 3840, and 4095.
Three gamma correction curves may be uploaded: one corresponding to a brighter
lighting condition that will enhance contrast VAR(0x0F, 0x0020–0x0032), another corre-
sponding to a normal lighting condition VAR(0x0F, 0x0033–0x0045), and one corre-
sponding to a darker lighting condition that will suppress noise
VAR(0x0F, 0x0046–0x0058). From these three curves, the MT9T111 will compute a
gamma curve that is appropriate for the current brightness level. At power-up the
MT9T111 loads these three tables with default values.
Programming the gamma selection variable VAR(0x0F, 0x0008) to a value of 0x00, auto-
matically calculates a gamma curve from the programmed three curves. Values of
0x01–0x03 select from one of the three programmed curves.
The automatic gamma correction curve is calculated by linearly interpolating each of
the 18 knee points in the curve. The linear interpolation is based on the current scene
brightness, and three programmed brightness levels corresponding to the three gamma
correction curves: VAR(0x12, 0x0169–0x016D). These brightness levels are independent
for each sensor, and can be separately set on page 0x13 for the secondary sensor. The
computed curve is a linear interpolation of the 18 knee points depending on the current
scene brightness.