Crc Checksum Chunk - Basler acA2040-55 User Manual

Features

7.23.3.7 CRC Checksum Chunk

The CRC (Cyclic Redundancy Check) checksum chunk feature adds a chunk to each acquired
image containing a CRC checksum calculated using the X-modem method. As shown in
the checksum is calculated using all of the related image data and all of the appended chunks
except for the CRC chunk itself. If enabled, the CRC checksum chunk is always the last chunk
appended to the image data.
CRC checksum is calculated on this data
Chunk 1 (image data (payload) &
chunk ID & length)
Fig. 116: CRC Checksum
To enable the CRC checksum chunk:
1. Use the Chunk Selector to select the CRC checksum chunk.
2. Use the Chunk Enable parameter to set the value of the chunk to true.
Once the CRC checksum chunk is enabled and Chunk Mode Active (see Section 7.23.4 on
page 347) is enabled, the camera appends a CRC checksum chunk to each acquired image.
To retrieve CRC checksum information from a chunk appended to an image that has been received
by your computer, the image and its appended chunks must first be parsed. Once the chunk parser
has been used, you can retrieve the CRC checksum information.
For more information about retrieving chunk data, see Section 7.23.5 on
Note that the CRC checksum information provided by the chunk parser is not the CRC checksum
itself. Rather it is a true/false result. When the image and appended chunks pass through the parser,
the parser calculates a CRC checksum based on the received image and chunk information. It then
compares the calculated CRC checksum with the CRC checksum contained in the CRC checksum
chunk. If the two match, the result indicates that the image data is OK. If the two do not match, the
result indicates that the image is corrupted.
You can set the Chunk Selector and Chunk Enable parameter value from within your application
software by using the Basler pylon API. You can also run the parser and retrieve the chunk data.
The following code snippets illustrate using the API to activate the chunk mode, enable the CRC
checksum chunk, run the parser, and retrieve the CRC checksum chunk data:
// Make chunk mode active, select and enable CRC checksum chunk
camera.ChunkSelector.SetValue(ChunkSelector_PayloadCRC16);
camera.ChunkEnable.SetValue(true);
You can also use the Basler pylon Viewer application to easily set the parameters.
For more information about the pylon API and the pylon Viewer, see Section 3.1 on
346
Chunk 2 Chunk 3
Data Data
AW00123409000
Figure
...
Chunk N
CRC
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