Putting It All Together

Let’s now take all of the data from the other sections, to create an entire PDF417 label.

From the examples, we encoded the string PDF417. The following codewords were calculated:

Data codewords d4 ,..., d0:                                                                                                                                                5,453,178,121,239

Error Detection/Correction Codewords c3 ,..., c0:                                                                                                                                                     452,327,657,619

Now we need to decide what type of aspect ratio is used for our label. Clearly, this is a user’s decision; the printer simply follows what the user specifies.

Since we have 9 codewords, we can arrange the bar code to be 3 rows of 3 codewords, or 9 rows of 1 codeword. If we need some other arrangement, we would have to pad the data codewords with null codewords (unused shift or latch characters at the end of the data).

Let’s make it 3 rows of 3 codewords.

The bar code layout would be:  

Where L_r = Left Row Indicators and R_r = Right Row Indicators and
ECC = Error Correction Codewords

From all of the sample calculations above, take the data, row indicators, and error detection/correction codewords. Substitute into the above layout to get:  

Now the codewords must be converted to bar-space patterns (low-level encoding).

The entire set of codewords is divided into three mutually exclusive encodation sets, or clusters. Each cluster encodes the 929 available PDF417 codewords with distinct bar-space patterns so that one cluster cannot be confused with another. A codeword must be encoded according to the cluster used by that row.

Each row uses only one of the three clusters (0, 3, or 6) to encode data, with the same cluster repeating sequentially every third row. Row 0 codewords use cluster 0, row 1 uses cluster 3, and row 2 uses cluster 6, etc. In general, cluster number = ((row number) mod 3) *3.

Look up each value from the appropriate cluster tables, add the start pattern 81111113 to the left of the left row indicators, and add the stop pattern 711311121 to the right of the right row indicators.

The bar code bar space patterns would then be:

The resulting bar code itself is: