OV6620 Datasheet, PDF (5/31 Pages) List of Unclassifed Manufacturers – SINGLE-CHIP CMOS CIF COLOR DIGITAL CAMERA

OMNIVISION TECHNOLOGIES, Inc.
Advanced Information
Preliminary
OV6620/OV6120
SINGLE IC CMOS COLOR AND B/W DIGITAL CAMERAS
1.2 Analog Processor Circuits
1.2.1 Overview
The image is captured by the 356 x 592 pixel image ar-
ray and routed to the analog processing section where
the majority of signal processing occurs. This block con-
tains the circuitry which performs color separation, ma-
trixing, Automatic Gain Control (AGC), gamma
correction, color correction, color balance, black level
calibration, “knee” smoothing, aperture correction, and
controls for picture luminance, chrominance, and anti-
alias filtering. 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.
A YCrCb format is also supported, based on the formula
below:
Y = 0.59G + 0.31R + 0.11B
Cr = 0.713 x (R - Y)
Cb = 0.564 x (B - Y)
The YCrCb/RGB Raw Data signal from the analog pro-
cessing section is fed to two on-chip 8-bit Analog-to-
Digital (A-to-D) converters: one for the Y/RG channel
and one shared by the CrCb/BG channels. The A-to-D
converted data stream is further conditioned in the digi-
tal formatter. The processed signal is delivered to the
digital video port through the video multiplexer which
routes the user-selected 16-, 8-, or 4-bit video data the
correct output pins.
The on-chip 8-bit A-to-D converters operate at up to 9
MHz, fully synchronous to the pixel rate. Actual conver-
sion rate is set as a function of the frame rate. A-to-D
black-level calibration circuitry ensures the following:
– 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
– Peak/Bottom is 240/16
– RGB raw data output range is 16/240
(Note: Values 0 and 255 are reserved for sync flag)
1.2.2 Image Processing
The algorithm used for the electronic exposure control
is based on the brightness of the full image. The expo-
sure is optimized for a “normal” scene which assumes
the subject is well lit relative to the background. In situ-
ations where the image is not well lit, the Automatic Ex-
posure Control (AEC) White/Black ratio may be
adjusted to suit the needs of the application.
Additional on-chip functions include Automatic Gain
Control (AGC) which provides a gain boost of up to
24dB. White balance control enables setting of proper
color temperature and can be programmed for automat-
ic or manual operation. Separate saturation, brightness,
contrast, and sharpness adjustments allow for further
fine tuning of the picture quality and characteristics. The
OV6620 image sensor also provides control over the
White Balance ratio for increasing/decreasing the im-
age field Red/Blue component ratio. The sensor pro-
vides a default setting which may be sufficient for many
applications.
1.2.3 Windowing
The windowing feature of the OV6620/OV6120 image
sensors allows user-definable window sizing as re-
quired by the application. Window size setting (in pixels)
ranges from 2 x 2 to 356 x 292, and can be positioned
anywhere inside the 356 x 292 boundary. Note that
modifying window size and/or position does not change
frame or data rate. The OV6620/OV6120 imager alters
the assertion of the HREF signal to be consistent with
the programmed horizontal and vertical region. The de-
fault output window is 352 x 288.
1.2.4 Zoom Video Port (ZV)
The OV6620/OV6120 image sensor includes a Zoom
Video (ZV) function that supports standard ZV Port in-
terface timing. Signals available include VSYNC,
CHSYNC, PCLK and 16-bit data bus: Y[7:0] and
UV[7:0]. The rising edge of PCLK clocks data into the
ZV port. See Figure 2, Zoom Video Port Timing below.
14 May 1999
Version 1.11
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