AW00089317000 Chunk Features
Basler ace GigE 323
11.7 CRC Checksum
The CRC (Cyclic Redundancy Check) checksum feature adds a chunk to each acquired image
containing a CRC checksum calculated using the X-modem method. As shown in Figure 124, the
checksum is calculated using all of the image data and all of the appended chunks except for the
checksum itself. The CRC chunk is always the last chunk appended to the image data.
1. Use the Chunk Selector to select the CRC chunk.
2. Use the Chunk Enable parameter to set the value of the chunk to true.
Once the CRC chunk is enabled, the camera will add a CRC chunk to each acquired image.
To retrieve CRC information from a chunk appended to an image that has been received by your
PC, you must first run the image and its appended chunks through the chunk parser included in the
pylon API. Once the chunk parser has been used, you can retrieve the CRC information. Note that
the CRC 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 will indicate that the image data is OK. If the two do not match, the result
will indicate 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 time
stamp chunk, run the parser, and retrieve the frame counter chunk data:
// Make chunk mode active and enable CRC chunk
Camera.ChunkModeActive.SetValue( true );
Camera.ChunkSelector.SetValue( ChunkSelector_PayloadCRC16 );
The chunk mode must be active before you can enable the CRC feature or any of
the other chunk feature. Making the chunk mode inactive disables all chunk
features.
To enable the CRC checksum chunk:
Image Data
(including any required padding)
Chunk X
Data
Chunk Y
Data
Chunk
CRC
CRC checksum is calculated on this data
Fig. 124: CRC Checksum
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