ASX340 datasheet(23/78 Pages) ETC2

23 / 78 page

PDF: 171981479/Source: 8304342517

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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

Color Interpolation

In the raw data stream fed by the sensor core to the IFP, each pixel is represented by a

10-bit integer number, which can be considered proportional to the pixel's response to a

one-color light stimulus, red, green, or blue, depending on the pixel's position under the

color filter array. Initial data processing steps, up to and including the defect correction,

preserve the one-color-per-pixel nature of the data stream, but after the defect correc-

tion it must be converted to a three-colors-per-pixel stream appropriate for standard

color processing. The conversion is done by an edge-sensitive color interpolation

module. The module pads the incomplete color information available for each pixel

with information extracted from an appropriate set of neighboring pixels. The algorithm

used to select this set and extract the information seeks the best compromise between

preserving edges and filtering out high frequency noise in flat field areas. The edge

threshold can be set through register settings.

Color Correction and Aperture Correction

To achieve good color fidelity of the IFP output, interpolated RGB values of all pixels are

subjected to color correction. The IFP multiplies each vector of three pixel colors by a

3 x 3 color correction matrix. The three components of the resulting color vector are all

sums of three 10-bit numbers. Since such sums can have up to 12 significant bits, the bit

width of the image data stream is widened to 12 bits per color (36 bits per pixel). The

color correction matrix can be either programmed by the user or automatically selected

by the auto white balance (AWB) algorithm implemented in the IFP. Color correction

should ideally produce output colors that are corrected for the spectral sensitivity and

color crosstalk characteristics of the image sensor. The optimal values of the color

correction matrix elements depend on those sensor characteristics and on the spectrum

of light incident on the sensor. The color correction variables can be adjusted through

To increase image sharpness, a programmable 2D aperture correction (sharpening filter)

is applied to color-corrected image data. The gain and threshold for 2D correction can

be defined through register settings.

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