ASX340 datasheet(24/78 Pages) ETC2

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ASX340/MT9V139_DS Rev. C Pub. 3/11 EN

ASX340/MT9V139: 1/4-Inch Color CMOS NTSC/PAL Digital Image Sensor

Sensor Pixel Array

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Preliminary

Gamma Correction

The ASX340/MT9V139 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

condition 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.

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