ASX340AT_16 Datasheet, PDF (31/54 Pages) ON Semiconductor – 1/4‐inch Color CMOS NTSC/PAL Digital Image SOC

ASX340AT
External Memory Speed Requirement
For a 2 KB block of overlay to be transferred within a
frame time to achieve maximum update rate, the SPI NVM
must operate at a certain minimum speed.
TABLE 25. TRANSFER TIME ESTIMATE
Value
33.3ms
Type
4.5 MHz
Description
1ms
OVERLAY ADJUSTMENT
To ensure a correct position of the overlay to compensate
for assembly deviation, the overlay can be adjusted with
assistance from the overlay statistics engine:
• The overlay statistics engine supports a windowed
8-bin luma histogram, either row-wise (vertical) or
column-wise (horizontal).
• The calibration statistics can be used to perform an
automatic successive-approximation search of a
cross-hair target within the scene.
• On the first frame, the firmware performs a coarse
horizontal search, followed by a coarse vertical search
in the second frame.
• In subsequent frames, the firmware reduces the
region-of-interest of the search to the histogram bins
containing the greatest accumulator values, thereby
refining the search.
• The resultant row and column location of the cross-hair
target can be used to assign a calibration value to offset
selected overlay graphic image positions within the
output image.
• The calibration statistics patch also supports a manual
mode, which allows the host to access the raw
accumulator values directly.
Figure 30. Overlay Calibration
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