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MT9T111_DG - Rev. B 9/10 EN
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©2007 Aptina Imaging Corporation. All rights reserved.
MT9T111: Developer Guide
JPEG Encoder
Preliminary
Spoof Mode
For spoof mode, the LV signal is asserted and de-asserted in a pattern intended to
emulate the behavior of multiple horizontal video blanking intervals.
The software configures the spoof pattern by programming the total number of LV asser-
tion intervals, as well as the number of output clock periods both during and between LV
assertions. The user can configure a virtual JPEG output frame that is specifically
tailored to the expected JPEG file size. If this frame is larger than the total number of
JPEG bytes actually produced, the output buffer pads the remaining bytes of the last
JPEG data line with dummy patterns, then either de-asserts FV or continues to output
dummy patterns until end of frame. If the frame is too small, output buffer either
continues to output the excess JPEG bytes until whole JPEG frame is output or discards
the excess JPEG bytes and sets an error flag in a status register.
Note:
Although the number of bytes on each JPEG line will be same, the corresponding time
interval will vary due to instantaneous changes in the JPEG data rate.
For the parallel output interface, when the FIFO underflow happens during one line
transmit, the PCLK will be gated off and wait for more data. For the MIPI/CCP interface,
the output buffer will not start transmitting until one line of data is ready in the FIFO.
The JPEG output clock can be configured to be either gated off or continuous while LV is
de-asserted. The JPEG output clock can also be optionally gated off between frames to
save power.
The adaptive clock switching feature is supported for the parallel output interface. The
PCLK changes according to the output buffer FIFO fullness status.
The 2 bytes of JPEG status information and 3 bytes of JPEG length information can be
enclosed with SOSI/EOSI codes, and appended to be the last 9 bytes of the last line in the
frame.
When the thumbnail asserts a request and the FIFO is less than 5/8 full, the output
buffer services the thumbnail request immediately until the end of thumbnail line. Then
the output buffer switches back to JPEG data, if there is any. When the thumbnail asserts
a request and the FIFO is more than 5/8 full, JPEG data has higher priority. The output
buffer doesn't service the thumbnail request until the FIFO drops below 5/8 full.
Thumbnail Index Table
Some customers may use processors which are not efficient in pattern search opera-
tions, therefore their systems take more time to extract thumbnail data from the JPEG
stream by looking for thumbnail header and footer code set. The thumbnail index table
provides an alternative solution to speed up the thumbnail extraction.
The position (pointer) of the first thumbnail data for every thumbnail line is captured by
the sensor. These pointers are saved in the internal memory during transmission, and
can be appended at the end of the frame so that the user can decode these pointers and
locate the thumbnail data position directly.