github.com/makiuchi-d/gozxing/qrcode/decoder fails on QR codes with black background

[johnnybubonic]

The QR code decoder fails if the QR code is on a black background/surrounded by black. It seems to make no difference whether I use a luminance histgram or not.

[makiuchi-d]

?

[webaddicto]

@makiuchi-d

I think the issue is that if the qrcode image has dark background color, it cannot decode it:

While if the qrcode image has white/light background it works perfectly:

Decoded as: SMSTO:+1234567890:Message Me

I could reproduce the issue:

If I use #000000 as background color and #ffffff as foreground color (like first image), it can't decode the text.

Hope that helps.

[makiuchi-d]

Inverted black-and-white QR codes are not defined in the QR Code specification, so they're not considered valid QR codes.
Since the original ZXing doesn’t support them, gozxing doesn’t either.
If you need to decode such images, please invert the colors before decoding.

[webaddicto]

Thanks for the information, didn't know they were not considered valid QR codes.

I tried your suggestion, to invert the colors in case the first decoding attempt fails, and it works perfectly.

[johnnybubonic]

Inverted black-and-white QR codes are not defined in the QR Code specification, so they're not considered valid QR codes.

This is false.

ISO/IEC 18004:2024, 4ed., figures 1.b. and 1.d. clearly demonstrate that these are supported formats:

The first example @webaddicto gives above:

is, in fact, a valid QR code yet it fails to decode. The surround black is the "quiet zone", which is why the finder pattern is in white.

[makiuchi-d]

Thank you very much for pointing that out.
It appears that the specification I was referring to was an older one (ISO/IEC 18004:2000).
However, since the original ZXing does not support inverted QR codes, gozxing also does not support them.