In a PDF417 barcode where number of columns are fixed, how would I calculate the number of rows required for some text?

Question

I need to generate a PDF417 barcode from some text. I have an API (that I didn\'t create) that generates a PDF417 barcode given the data, number of rows and number of column

Answer 1

I've made a Python port of Markus Jarderot's answer. The calculation remains the same.

import string

SUBMODE_ALPHA = string.ascii_uppercase + ' '
SUBMODE_LOWER = string.ascii_lowercase + ' '
SUBMODE_MIXED = "\t\r #$%&*+,-./0123456789:=^"
SUBMODE_PUNCTUATION = "\t\n\r!\"$'()*,-./:;<>?@[\\]_`{|}~"


def calculateNumberOfRows(sourceCodeWords, errorCorrectionCodeWords, columns):
    rows = ((sourceCodeWords + 1 + errorCorrectionCodeWords) / columns) + 1
    if columns * rows >= sourceCodeWords + 1 + errorCorrectionCodeWords + columns:
        rows -= 1
    return rows

def getErrorCorrectionCodewordCount(errorCorrectionLevel):
    if 0 > errorCorrectionLevel > 8:
        raise ValueError("Error correction level must be between 0 and 8!")
    return 1 << (errorCorrectionLevel + 1)


def calculateSourceCodeWords(msg):
    length = 0;
    submode = SUBMODE_ALPHA
    msgLength = len(msg)
    idx = 0
    while(idx < msgLength):
        ch = msg[idx]
        length += 1

        if not ch in submode:
            old_submode = submode
            if submode == SUBMODE_ALPHA:
                for mode in (SUBMODE_LOWER, SUBMODE_MIXED):
                    if ch in mode:
                        submode = mode

            elif submode == SUBMODE_LOWER:
                if ch in SUBMODE_MIXED:
                    submode = SUBMODE_MIXED

            elif submode == SUBMODE_MIXED:
                for mode in (SUBMODE_ALPHA, SUBMODE_LOWER):
                    if ch in mode:
                        submode = mode

                if idx + 1 < len(msg) and msg[idx + 1] in SUBMODE_PUNCTUATION:
                    submode = SUBMODE_PUNCTUATION


            elif submode == SUBMODE_PUNCTUATION:
                submode = SUBMODE_ALPHA

            if old_submode != submode:
                # submode changed
                continue

            length += 1

        idx += 1 # Don't increment if 'continue' was used.
    return (length + 1) / 2


def main():
    msg = "Hello, world!"
    columns = 7
    sourceCodeWords = calculateSourceCodeWords(msg)
    errorCorrectionCodeWords = getErrorCorrectionCodewordCount(0)
    rows = calculateNumberOfRows(sourceCodeWords, errorCorrectionCodeWords, columns)
    print("\"%s\" requires %d code-words, and %d error correction code-words. This becomes %d rows.\n"
           %( msg, sourceCodeWords, errorCorrectionCodeWords, rows))



if __name__ == '__main__':
    main()