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Add multi-eci decoding for PDF417 #1507

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merged 3 commits into from Mar 9, 2022

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AlexGeller1
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Also fixed issue that some multi-eci encoded PDF417 codes were missing ECIs
The unit test now also decodes the multi-eci encoding tests and verifies that the result is identical with the input.

- Fixed issue that some multi-eci encoded PDF417 codes were missing ECIs
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Minor comments.
Seems OK if this strictly increases the number of symbols that can be decoded

@AlexGeller1
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AlexGeller1 commented Mar 8, 2022

Seems OK if this strictly increases the number of symbols that can be decoded

Great. Yes, it does just that and it also fixes a bug in the encoding. Regarding the risks of this PR, I have the following thoughts:

  • Regarding the encoding bug fix. The fix is in the function PDF417HighLevelEncoder.encodeMultiECIBinary(). This function is only called if the encoding hint PDF417_AUTO_ECI is set so that the default behavior is not affected.
  • DecodedBitStreamParser line 105 .. 113: The removed code was newly introduced in the previous PR (Add support for multi-eci encoding for PDF417 #1506) to fix the issue that the decoder was failing to decode a single ECI code with no leading latch. The fix is no longer needed since the method textCompaction now handles ECIs. In other words, the change reverts the code to the previous state.
  • Changes to DecodedBitStreamParser.textCompaction(): The function now handles ECI_CHARSET in the switch case. There is no other behavior change. Before the change the ECI was ignored. As long as the new treatment doesn't crash, it may in the worse case replaces one buggy behavior with another.
  • Changes to DecodedBitStreamParser.decodeTextCompaction(): There is no behavioral change. The method can now be instructed to start in a particular state. In the default case (no ECI) it starts with the original state Mode.ALPHA (see line 286). The method now returns the last state that it latched to.

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Please don't merge it yet. The spec says that ECIs may occur in the middle of 901 data (less than 6 bytes) and at the boundaries of 924 blocks (every 5 codewords) without requiring a new latch. The encoder never creates that but I am making sure that the decoder can handle it.

…ocations in binary encoded data as specified in section 5.5.3.2 of the spec

- Added verifying unit test
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AlexGeller1 commented Mar 8, 2022

I condensed the code of the function DecodedBitStreamParser.byteCompaction() so that it is about half as long as before.
I think that it is pretty straightforward now. The previous code didn't lend itself well to add the extension.

@srowen srowen merged commit ce1a1a5 into zxing:master Mar 9, 2022
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