Datasheet

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MT9D111__7_REV5.fm - Rev. B 2/06 EN
143 ©2004 Micron Technology, Inc. All rights reserved.
MT9D111 - 1/3.2-Inch 2-Megapixel SOC Digital Image Sensor
Firmware
Micron Confidential and Proprietary
Firmware
Auto Exposure Driver
The AE driver works to achieve desirable exposure by adjusting sensor core’s integration
time, analog, and digital gains. The driver can be configured with respect to desired AE
speed, maximum and minimum frame rate, the range of gains, brightness, backlight
compensation, and so on.
AE driver typically runs in one of these modes. The modes are set in the sequencer driver
for each sequencer state.
• fast settling preview—reach target exposure as fast as possible
• continuous preview—a slow-changing mode good for video capture
• evaluative—evaluate current scene and adjust exposure for still capture
Some key variables affecting all modes:
•ae.Target—
controls target exposure for all modes. Increasing or decreasing this vari-
able makes the image brighter or darker
• ae.Gate—how accurate AE driver tracks the target exposure
• ae.weights—specify weights for central and peripheral backlight compensation in
preview modes
AE driver adjusts exposure by programming sensor gains, R43–46:0 and R65:0, sensor
integration time R9:0 and R12:0 and IFP digital gains R78:2 and R110:1.
Evaluative Auto Exposure
Evaluative AE (EAE) selects optimum exposure for scenes where conventional AE does
not give good results:
• scenes involving sun
• back light scenes
• strong contrast scenes and so on
EAE breaks down input image into a 4 x 4 grid of subwindows and analyzes their expo-
sure value (EV) readings. It evaluates brightness and contrast in the image, the scene and
adjusts exposure appropriately. Variables ae.mmEVZone1/2/3/4 keep programmable
thresholds defining brightness classes. Variable ae.mmShiftEV is used to calibrate EV
readings for particular module type.
Auto White Balance Driver
AWB detects the temperature of the light source in the scene and adjusts color correc-
tion to always produce image for sRGB display. In other words, it makes the gray areas in
the raw image look also gray in the output image. To detect the illuminant temperature,
the driver reads results generated by the statistics block in the color pipeline, R48–50:1.
Color correction is achieved via adjusting sensor analog RGB gains R43–46:0, IFP digital
RGB gains R106–109:1, and coefficients of the color correction matrix R96–102:1.
The adjustment is done in two ways:
The driver adjusts RGB gains to achieve a gray output. When gains are too large, the
driver also adjusts the CCM. During part calibration, two sets of CCM coefficients are
obtained, one for red-rich, incandescent illumination and one for blue-rich daylight illu-
mination. These two sets are specified in the AWB driver using awb.ccmL and
awb.ccmRL arrays of variables. Variable awb.ccmL corresponds to the red-rich set, also
called left. Variable awb.ccmRL is the delta between blue-rich—or right—and the left
sets. CCM programmed into the color pipeline is available in variables awb.ccm. The
current setting is calculated by interpolating between the left and right sets. The
awb.CCM position indicates the position, from 0–left, red-rich to 127–right, blue-rich.