Advanced Information
Preliminary
OV8610/OV8110
OV8610 SINGLE-CHIP CMOS VGA COLOR DIGITAL CAMERA
OV8110 SINGLE-CHIP CMOS VGA B&W DIGITAL CAMERA
OmniVision Technologies, Inc. 930 Thompson Place Sunnyvale, CA 94085 U.S.A.
Tel: (408) 733-3030 Fax: (408) 733-3061
e-mail: info@ovt.com
Website: http://www.ovt.com
Version 1.3, August 27, 2001
Page 8
Analog Processing Circuits
Overview
The image is captured by the 824 x 615 pixel image array and
routed to the analog processing section where the majority of
signal processing occurs. This block contains the circuitry that
performs color separation, color correction, automatic gain
control (AGC), gamma correction, color balance, black level
calibration, “knee” smoothing, aperture correction, controls for
picture luminance and chrominance, and hue control for color.
The analog video signals are based on the following formula:
Y = 0.59G + 0.31R + 0.11B
U = R – Y
V = B – Y
Where R,G,B are the equivalent color components in each
pixel.
YCrCb format is also supported, based on the formula below:
Y = 0.59G + 0.31R + 0.11B
Cr = 0.713 (R – Y)
Cb = 0.564 (B – Y)
The YcrCb or RGB data signal from the analog processing
section is fed to two on-chip 10-bit analog-to-digital (A/D)
converters: one for the Y/G channel and one shared by the
CrCb/BR channels. The converted data stream is further
conditioned in the digital formatter. The processed signal is
delivered to the digital video port through the video multiplexer
which routes the user-selected 8-, or 10-bit video data to the
correct output pins.
The on-chip 10-bit A/D operates at up to 20 MHz, and is fully
synchronous to the pixel rate. Actual conversion rate is related
to the frame rate. A/D black-level calibration circuitry ensures:
•
The black level of Y/RGB is normalized to a value of 16
•
The peak white level is limited to 240
•
CrCb black level is 128
•
CrCb Peak/bottom is 240/16
•
RGB raw data output range is 16/240
(Note: Values 0 and 255 are reserved for sync flag)
Image Processing
The algorithm used for the electronic exposure control is based
on the brightness of the full image. The exposure is optimized
for a “normal” scene that assumes the subject is well lit relative
to the background. In situations where the image is not well lit,
the automatic exposure control (AEC) white/black ratio may be
adjusted to suit the needs of the application.
Additional on-chip functions include:
•
AGC that provides a gain boost of up to 24dB
•
White balance control that enables setting of proper color
temperature and can be programmed for automatic or
manual operation.
•
Separate saturation, brightness, hue, and sharpness
adjustments allow for further fine-tuning of the picture
quality and characteristics.
The OV8610/OV8110 image sensor also provides control over
the White Balance ratio for increasing/decreasing the image
field Red/Blue component ratio. The sensor provides a default
setting that may be sufficient for many applications.
Windowing
The windowing feature of the OV8610/OV8110 image sensors
allows user-definable window sizing as required by the
application. Window size setting (in pixels) ranges from 2 x 2 to
800 x 600, and can be positioned anywhere inside the 824 x
615 boundary. Note that modifying window size and/or position
does not change frame or data rate. The OV8610 imager alters
the assertion of the HREF signal to be consistent with the
programmed horizontal and vertical region. The default output
window is 800 x 600.
column start
column end
Sensor Array
Bondary
HREF
column
Display
Window
Figure 4. Windowing
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