Datasheet

PDF: 09005aef8202ec2e/Source: 09005aef8202ebf7 Micron Technology, Inc., reserves the right to change products or specifications without notice.
MT9D111__2_REV5.fm - Rev. B 2/06 EN
23 ©2004 Micron Technology, Inc. All rights reserved.
MT9D111 - 1/3.2-Inch 2-Megapixel SOC Digital Image Sensor
Architecture Overview
Micron Confidential and Proprietary
Preview
Context A is primarily intended for use in the preview mode. During preview, the sensor
usually outputs low resolution images at a relatively high frame rate, and its power con-
sumption is kept to a minimum. Context B can be configured for the still capture or
video mode, as required by the user. For still capture configuration, the user typically
specifies the desired output image size, if JPEG compression and flash should be
enabled, how many frames to capture, etc. For video, the user might select a different
image size and a fixed frame rate.
Snapshot and Flash
To take a snapshot, the user must send a command that changes the context from A to
context B. Typical sequence of events after this command is as follows. First, the camera
may turn on its LED flash, if it has one and is required to use it. With the flash on, the
camera exposure and white balance is automatically adjusted to the changed illumina-
tion of the scene. Next, the camera performs auto focusing. Once in focus, it enables
JPEG compression and capture one or more frames of desired size. A camera equipped
with a Xenon flash strobes it during the capture. Completing the sequence, the camera
automatically returns to context A and resume running preview.
Video
To start video capture, the user has to change relevant context B settings, such as capture
mode, image size and frame rate, and again send a context change command. Upon
receiving it, the MT9D111 switches to the modified context B settings, while continuing
to output YUV-encoded image data. Auto exposure and auto focus automatically
switches to smooth continuous operation. To exit the video capture mode, the user has
to send another context change command causing the sensor to switch back to context
A.
Auto Exposure
The auto exposure (AE) algorithm performs automatic adjustments of the image bright-
ness by controlling exposure time and analog gains of the sensor core as well as digital
gains applied to the image.
Two auto exposure algorithm modes are available:
1. preview
2. scene evaluative
Auto exposure is implemented by means of a firmware driver that analyzes image statis-
tics collected by exposure measurement engine, makes a decision and programs the
sensor core and color pipeline to achieve the desired exposure. The measurement
engine subdivides the image into 16 windows organized as a 4 x 4 grid.
Preview Mode
This exposure mode is activated during preview or video capture. It relies on the expo-
sure measurement engine that tracks speed and amplitude of the change of the overall
luminance in the selected windows of the image.
The backlight compensation is achieved by weighting the luminance in the center of the
image higher than the luminance on the periphery. Other algorithm features include the
rejection of fast fluctuations in illumination (time averaging), control of speed of
response, and control of the sensitivity to the small changes. While the default settings
are adequate in most situations, the user can program target brightness, measurement
window, and other parameters described above.