MT9M114_16 Datasheet, PDF (26/62 Pages) ON Semiconductor – High-Definition (HD) System-On- A-Chip (SOC) Digital Image Sensor

MT9M114: 1/6-Inch 720p High-Definition (HD) System-On-A-Chip (SOC) Dig-
ital Image Sensor
Digital Gain
Image stream processing starts with multiplication of all pixel values by a programmable
digital gain. Independent color channel digital gain can be adjusted with registers.
Adaptive PGA (APGA)
Lenses tend to produce images whose brightness is significantly attenuated near the
edges. There are also other factors causing fixed pattern signal gradients in images
captured by image sensors. The cumulative result of all these factors is known as image
shading. The MT9M114 has an embedded shading correction module that can be
programmed to counter the shading effects on each individual R, Gb, Gr, and B color
signal.
In some cases, different illuminants can introduce different color shading response. The
APGA feature on the MT9M114 will compensate for the dependency of the lens shading
of the illuminant. The MT9M114 will allow for up to three different illuminants to be
compensated.
Color Interpolation and Edge Detection
In the raw data stream fed by the sensor core to the IFP, each pixel is represented by a
10-bit integer, 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 adds 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 variable 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 either be programmed by the user or automatically selected
by the AWB algorithm implemented in the IFP.
Traditionally this would have been based off two sets of CCM, one for Warm light like
Tungsten and the other for Daylight (the part would interpolate between the two
matrixes). This is not an optimal solution for cameras used in a Cool White Fluorescent
(CWF) environment, for example when using a webcam. A better solution is to provide
three CCMs, which would include a matrix for CWF (interpolation now between three
matrixes). The MT9M114 offers this feature which will give the user improved color
fidelity when under CWF type lighting.
MT9M114/D Rev. 11, 2/16 EN
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