ASX340AT Datasheet, PDF (22/75 Pages) ON Semiconductor – Color CMOS NTSC/PAL Digital Image

ASX340CS: 1/4-Inch Color CMOS NTSC/PAL Digital Image Sensor
Sensor Pixel Array
Gamma Correction
The ASX340AT includes a block for gamma correction that can adjust its shape based on
brightness to enhance the performance under certain lighting conditions. Two custom
gamma correction tables may be uploaded corresponding to a brighter lighting condi-
tion and a darker lighting condition. At power-up, the IFP loads the two tables with
default values. The final gamma correction table used depends on the brightness of the
scene and takes the form of an interpolated version of the two tables.
The gamma correction curve (as shown in Figure 11) is implemented as a piecewise
linear function with 19 knee points, taking 12-bit arguments and mapping them to 8-bit
output. The abscissas of the knee points are fixed at 0, 64, 128, 256, 512, 768, 1024, 1280,
1536, 1792, 2048, 2304, 2560, 2816, 3072, 3328, 3584, 3840, and 4096. The 8-bit ordinates
are programmable through registers.
Figure 11: Gamma Correction Curve
RGB to YUV Conversion
For further processing, the data is converted from RGB color space to YUV color space.
Color Kill
To remove high-or low-light color artifacts, a color kill circuit is included. It affects only
pixels whose luminance exceeds a certain preprogrammed threshold. The U and V
values of those pixels are attenuated proportionally to the difference between their lumi-
nance and the threshold.
YUV Color Filter
As an optional processing step, noise suppression by one-dimensional low-pass filtering
of Y and/or UV signals is possible. A 3- or 5-tap filter can be selected for each signal.
ASX340AT/D Rev. H, 8/15 EN
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