ASX340AT Datasheet, PDF (21/75 Pages) ON Semiconductor – Color CMOS NTSC/PAL Digital Image

ASX340CS: 1/4-Inch Color CMOS NTSC/PAL Digital Image Sensor
Sensor Pixel Array
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 parameters can be adjusted through
register settings.
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.
ASX340AT/D Rev. H, 8/15 EN
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