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3.1 What mode and error_  level I can use?
3.2 qr-read can deal on all kinds of the code images?

3 FAQ

3.1 What mode and error_level I can use?

qr-code select Byte Mode as it’s default mode, The highest error-correct level "H".

All the iso8859-1(latin-1) code include in this mode.

If you want to use Alphanumeric Mode or Numeric Mode, you can use #:mode "A" or #:mode "N" keyword.

If you want to use other error-correct level, use #:error_level to specify a new one("L" "M" "Q" "H").

3.2 qr-read can deal on all kinds of the code images?

No, sorry, I tried, till now, qr-read only read some very "good" QR-Code, and must use Byte Mode and no error correction.