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Spelt / ZXing.Delphi

ZXing Barcode Scanning object Pascal Library for Delphi VCL and Delphi Firemonkey
Apache License 2.0
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QR code detector susceptible to noise in scanned images #110

Closed sboydlns closed 3 years ago

sboydlns commented 3 years ago

I have found that the crossCheck* routines in FinderPatternFinder.pas are VERY sensitive to noise in the scanned image. I am talking about B&W TIFF images on Windows systems. Each of these methods only scan a single line of bits in order to cross check the validity vertically, horizontally or diagonally. A single white pixel in an otherwise black field (or vice versa) will cause any of these methods to fail.

To get around this, I have modified the code to scan 3 lines, centered on the requested line. If any of these lines are valid I assume that the QR code is valid. This seems to work for me.

Any suggestions or concerns with what I have done?

BTW I am using version 3.5

Steve Boyd

Spelt commented 3 years ago

Sounds very nice. Do you have a link to the code and a failing test case?

Op do 24 sep. 2020 om 21:46 schreef sboydlns notifications@github.com:

I have found that the crossCheck* routines in FinderPatternFinder.pas are VERY sensitive to noise in the scanned image. I am talking about B&W TIFF images on Windows systems. Each of these methods only scan a single line of bits in order to cross check the validity vertically, horizontally or diagonally. A single white pixel in an otherwise black field (or vice versa) will cause any of these methods to fail.

To get around this, I have modified the code to scan 3 lines, centered on the requested line. If any of these lines are valid I assume that the QR code is valid. This seems to work for me.

Any suggestions or concerns with what I have done?

BTW I am using version 3.5

Steve Boyd

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sboydlns commented 3 years ago

This archive contains the modified source and a sample image that fails using the original V3.5 source. I hope I attached the file properly.

zxing.zip

Spelt commented 3 years ago

Sorry for the delay, been busy.

Unfortunately there is a problem with your code, it breaks the unit tests. It will not scan some of the QR test images.

I hope you can find the time to fix it.

I also tested your tiff file and I can scan it without problems. Sometimes it depends also on the scan resolution. I do think your theory is sound and therefore I hope you can fix your patch.

Sincerely, Edward