Code 128

File:9494-RI476394652CH.jpg

A Swiss postal barcode encoding "RI 476 394 652 CH" in Code 128-B

Code 128 is a very high-density barcode symbology. It is used for alphanumeric or numeric-only barcodes. It can encode all 128 characters of ASCII and, by use of an extension character (FNC4), the Latin-1 characters defined in ISO/IEC 8859-1.

GS1-128 (formerly known as UCC/EAN-128) is a subset of Code 128 and is used extensively world wide in shipping and packaging industries as a product identification code for the container and pallet levels in the supply chain. The symbology was formerly defined as ISO/IEC 15417:2007.

Specification

File:Barcode diagram.svg

Code 128 (GS1-128) sections. 1: Quiet zone, 2: Start/stop character, 3: [FNC1]+Encoded data, 4: Check character

A Code 128 barcode will have six sections:

1. Quiet Zone
2. Start Character
3. Encoded Data
4. Check Character
5. Stop Character
6. Quiet Zone

The check character is calculated from a weighted sum (modulo 103) of all the characters.

Subtypes

Code 128 includes 108 symbols: 103 data symbols, 3 start symbols, and 2 stop symbols. The symbols consist of three black bars and three white spaces. The stop pattern is composed of two overlapped symbols and has four bars. The stop pattern permits bidirectional scanning. When the stop pattern is read left-to-right (the usual case), the stop symbol is recognized. When the stop pattern is read right-to-left, the reverse stop symbol is recognized. A scanner seeing the reverse stop symbol then knows it must read the symbol in reverse. To represent all 128 ASCII values, there are three code sets (A, B, C), which can be mixed within a single barcode (by using codes 98 and 99 in code sets A and B, 100 in code sets A and C and 101 in code sets B and C to switch between them):

• 128A (Code Set A) - ASCII characters 00 to 95 (0-9, A-Z and control codes), special characters, and FNC 1-4
• 128B (Code Set B) - ASCII characters 32 to 127 (0-9, A-Z, a-z), special characters, and FNC 1-4
• 128C (Code Set C) - 00-99 (encodes each two digits with one code) and FNC1

Quiet zone

The minimum width of the Quiet Zone to the left and right of the 128 Bar Code is 10x, where x is the minimum width of a module. It is mandatory at the left and right side of the barcode. The quiet zone must not be less than 4 mm-1.65 mm depending on the type of bar code. Source: Figure 5.2.1.4.4 – 1 of GS1 General Specifications

Start/stop and encoded data

Each character in the barcode symbol is composed of three bars and three spaces. (The stop adds an additional extra bar of length 2.) Each bar or space is 1, 2, 3 or 4 units wide, the sum of the widths of bars must be even, the sum of the widths of the spaces must be odd, and total 11 units per character. For instance, encoding the ASCII value 0 can be viewed as 10011101100, where a 1 (one) is a bar and a 0 is a space. A single 1 would be the thinnest line in the bar code. Three 1 (111) in sequence indicates a bar three times as thick as a single 1 bar.

The code uses 107 of the 108 possible patterns that fulfill the required criteria, with the pattern 211133 deliberately remaining unused. This is done to enhance omnidirectional scanning and help prevent misreads (if 211133 represented a legitimate symbol it could be mistaken for the stop code 2331112 when scanned backwards).

Check digit calculation

The check digit is a weighted modulo-103 checksum. It is calculated by summing the start code 'value' to the products of each character's 'value' multiplied by its position in the barcode string. The start character and first encoded value are in position 1. The sum of the products is then reduced modulo 103. The remainder is then converted back to one of the 103 non-delimiter characters (following the instructions given below) and appended to the barcode, immediately before the stop character.

For example, in the following table, the code 128 variant A checksum value is calculated for the alphanumeric string PJJ123C

Code	Value	Position	Value × Position
Start Code A	103	1	103
P	48	1	48
J	42	2	84
J	42	3	126
1	17	4	68
2	18	5	90
3	19	6	114
C	35	7	245
	Sum		878
	Remainder mod 103		54

Calculating check digit with multiple variants

As Code 128 allows multiple variants, as well as switching between variants within a single barcode, the absolute Code 128 value of a character is completely independent of its value within a given variant. For instance the Variant C value "33" and the Variant B value "A" are both considered to be a Code 128 value of 33, and the check digit would be computed based on the value of 33 times the character's position within the barcode.

Using FNC4 to encode high (128-255) characters

Function 4 (FNC4) can be used to encode all the LATIN-1 (ISO-8859-1) characters in a Code 128 barcode. The feature is not widely supported and is not used in GS128. When a single FNC4 is present in a string, the following character will be converted to ASCII as usual (character sets A and B) and then have 128 added to the ASCII value. (If the following symbol is a shift, then a second symbol will be used to obtain the character.) If two FNC4s are used consecutively then all following characters will be treated as such, up to the end of the string or another pair of FNC4s. Between the double FNC4s, a single FNC4 will be used to denote that the following character will be standard ASCII.

Bar code widths

Code128 specifies a combination of 6 bars and spaces for each character except the Stop character, which uses 7. Thus, each character begins with a bar and ends with a space (with the exception of the stop character, which ends in a bar). The following tables detail the widths associated with each bar and space for each character. The width of each bar or space can be 1, 2, 3 or 4 units. Using the example above, an 'A' would be depicted with the pattern 10100011000, or as 111323 in the tables below.

Code 128

Value	128A	128B	128C	ASCII Code (Common/Barcodesoft)	Character (Common/Barcodesoft)	Bar/Space Pattern	Bar/Space Weights
0	space	space	00	0032 or 0212 / 252	Space or Ô / ü	11011001100	212222
1	!	!	01	33	!	11001101100	222122
2	"	"	02	34	"	11001100110	222221
3	#	#	03	35	#	10010011000	121223
4	$	$	04	36	$	10010001100	121322
5	%	%	05	37	%	10001001100	131222
6	&	&	06	38	&	10011001000	122213
7	'	'	07	39	'	10011000100	122312
8	(	(	08	40	(	10001100100	132212
9	)	)	09	41	)	11001001000	221213
10	*	*	10	42	*	11001000100	221312
11	+	+	11	43	+	11000100100	231212
12	,	,	12	44	,	10110011100	112232
13	-	-	13	45	-	10011011100	122132
14	.	.	14	46	.	10011001110	122231
15	/	/	15	47	/	10111001100	113222
16	0	0	16	48	0	10011101100	123122
17	1	1	17	49	1	10011100110	123221
18	2	2	18	50	2	11001110010	223211
19	3	3	19	51	3	11001011100	221132
20	4	4	20	52	4	11001001110	221231
21	5	5	21	53	5	11011100100	213212
22	6	6	22	54	6	11001110100	223112
23	7	7	23	55	7	11101101110	312131
24	8	8	24	56	8	11101001100	311222
25	9	9	25	57	9	11100101100	321122
26	:	:	26	58	:	11100100110	321221
27	;	;	27	59	;	11101100100	312212
28	<	<	28	60	<	11100110100	322112
29	=	=	29	61	=	11100110010	322211
30	>	>	30	62	>	11011011000	212123
31	?	?	31	63	?	11011000110	212321
32	@	@	32	64	@	11000110110	232121
33	A	A	33	65	A	10100011000	111323
34	B	B	34	66	B	10001011000	131123
35	C	C	35	67	C	10001000110	131321
36	D	D	36	68	D	10110001000	112313
37	E	E	37	69	E	10001101000	132113
38	F	F	38	70	F	10001100010	132311
39	G	G	39	71	G	11010001000	211313
40	H	H	40	72	H	11000101000	231113
41	I	I	41	73	I	11000100010	231311
42	J	J	42	74	J	10110111000	112133
43	K	K	43	75	K	10110001110	112331
44	L	L	44	76	L	10001101110	132131
45	M	M	45	77	M	10111011000	113123
46	N	N	46	78	N	10111000110	113321
47	O	O	47	79	O	10001110110	133121
48	P	P	48	80	P	11101110110	313121
49	Q	Q	49	81	Q	11010001110	211331
50	R	R	50	82	R	11000101110	231131
51	S	S	51	83	S	11011101000	213113
52	T	T	52	84	T	11011100010	213311
53	U	U	53	85	U	11011101110	213131
54	V	V	54	86	V	11101011000	311123
55	W	W	55	87	W	11101000110	311321
56	X	X	56	88	X	11100010110	331121
57	Y	Y	57	89	Y	11101101000	312113
58	Z	Z	58	90	Z	11101100010	312311
59	[	[	59	91	[	11100011010	332111
60	\	\	60	92	\	11101111010	314111
61	]	]	61	93	]	11001000010	221411
62	^	^	62	94	^	11110001010	431111
63	_	_	63	95	_	10100110000	111224
64	NUL	`	64	96	`	10100001100	111422
65	SOH	a	65	97	a	10010110000	121124
66	STX	b	66	98	b	10010000110	121421
67	ETX	c	67	99	c	10000101100	141122
68	EOT	d	68	100	d	10000100110	141221
69	ENQ	e	69	101	e	10110010000	112214
70	ACK	f	70	102	f	10110000100	112412
71	BEL	g	71	103	g	10011010000	122114
72	BS	h	72	104	h	10011000010	122411
73	HT	i	73	105	i	10000110100	142112
74	LF	j	74	106	j	10000110010	142211
75	VT	k	75	107	k	11000010010	241211
76	FF	l	76	108	l	11001010000	221114
77	CR	m	77	109	m	11110111010	413111
78	SO	n	78	110	n	11000010100	241112
79	SI	o	79	111	o	10001111010	134111
80	DLE	p	80	112	p	10100111100	111242
81	DC1	q	81	113	q	10010111100	121142
82	DC2	r	82	114	r	10010011110	121241
83	DC3	s	83	115	s	10111100100	114212
84	DC4	t	84	116	t	10011110100	124112
85	NAK	u	85	117	u	10011110010	124211
86	SYN	v	86	118	v	11110100100	411212
87	ETB	w	87	119	w	11110010100	421112
88	CAN	x	88	120	x	11110010010	421211
89	EM	y	89	121	y	11011011110	212141
90	SUB	z	90	122	z	11011110110	214121
91	ESC	{	91	123	{	11110110110	412121
92	FS	|	92	124	|	10101111000	111143
93	GS	}	93	125	}	10100011110	111341
94	RS	~	94	126	~	10001011110	131141
95	US	DEL	95	200 / 240	È / ð	10111101000	114113
96	FNC 3	FNC 3	96	201 / 241	É / ñ	10111100010	114311
97	FNC 2	FNC 2	97	202 / 242	Ê / ò	11110101000	411113
98	Shift B	Shift A	98	203 / 243	Ë / ó	11110100010	411311
99	Code C	Code C	99	204 / 244	Ì / ô	10111011110	113141
100	Code B	FNC 4	Code B	205 / 245	Í / õ	10111101110	114131
101	FNC 4	Code A	Code A	206 / 246	Î / ö	11101011110	311141
102	FNC 1	FNC 1	FNC 1	207 / 247	Ï / ÷	11110101110	411131
103	Start Code A			208 / 248	Ð / ø	11010000100	211412
104	Start Code B			209 / 249	Ñ / ù	11010010000	211214
105	Start Code C			210 / 250	Ò / ú	11010011100	211232
106	Stop (7 bars/spaces)			211 / 251	Ó / û	1100011101011	2331112
—	Reverse Stop used to detect reading right to left			—	—	11010111000	211133

The "Code A", "Code B" and "Code C" symbols cause all future symbols to be interpreted according to the corresponding subcode. The "Shift" symbol switches a single following symbol's interpretation between subcodes A and B.

The encoded ASCII char depends on the actual used barcode-font. Especially the ASCII char of value 0 and of value 95 and above can be defined differently in the font that is installed.

The FNCx codes are used for special purposes. FNC1 at the beginning of a bar code indicates that it begins with a 2- 3- or 4-digit application identifier assigned by the Uniform Code Council, which explains the following digits. For example, application identifier 421 indicates that an ISO 3166-1 numeric country code and ship-to postal code follows. For example, the U.S. ZIP code for the White House would generally be printed as "(421) 840 20500", but would actually be coded as "[Start C] [FNC1] 42 18 40 20 50 [Code A] 0 [Check symbol 92] [Stop]"

Check Digit Calculation for above Zip Code Example

	Value	Weight	Weight x Value
Start C	105	1	105
FNC1	102	1	102
42	42	2	84
18	18	3	54
40	40	4	160
20	20	5	100
50	50	6	300
Code A	101	7	707
0	16	8	128
		Sum =	1740
1740	Mod 103 =	92

Availability

For the end user, Code 128 barcodes may be generated by either an outside application to create an image of the barcode, or by a font-based barcode solution. Either solution requires the use of an application or an application add in to calculate the check digit and create the barcode.

Barcode length optimization

Although code set C uses one code symbol to represent two digits, its usage does not necessarily make a more compact code compared to code sets A or B. While encoding "X00Y" with code set A or B results in 7 code symbols (e.g., [Start B] 56 16 16 57 [checksum] [Stop]), encoding the inner "00" with code set C will result in a code 8 symbols long due to the overhead in switching in and out of code set C. Although one symbol is saved on encoding "00" to code symbol C, two code set switching symbols are required: the first to switch into code set C and the second to switch back to code set A or B (e.g., [Start B] 56 [Code C] 00 [Code B] 57 [checksum] [Stop]).

Conversely, applying of code set C to a sequence of digits produces code with fewer symbols compared to code sets A or B only under these conditions:

Position of sequence of digits in data	Number of digits for switching to code set C
beginning of data	4+
end of data	4+
middle of data (surrounded by characters from code set A or B)	6+
entire data	either 2 or 4+

Example: For data "098x1234567y23", savings on barcode length using code set C are achieved only if it is applied to middle part of data and the transition to code set C is done when there are an even number of digits remaining to encode (so "234567"). For beginning and ending part of the code, switching to code set C is not effective. Code symbols: [Start B] 16 25 24 88 17 [Code C] 23 45 67 [Code B] 89 18 19 [checksum] [Stop].

Delaying the transition to code set C until there are an even number of digits remaining avoids an extra symbol. Consider the string "...01234": a delayed switch produces ... 0 [Code C] 12 34 [checksum] [Stop] but an early switch produces ... [Code C] 01 23 [Code A] 4 [checksum] [Stop].

Optimizing length of resulting barcode is important where barcode readers are used which require to detect the entire barcode image at once in order to read a barcode, such as laser scanners. The longer the barcode is, the greater distance of laser barcode reader from barcode image is needed, making reading difficult or impossible above some threshold lengths/distances.

External links

• GS1-128 Specification Detailed List of Application Identifiers
• Barcodesoft Font mapping of Barcodesoft, which differs from the common ascii mapping (see http://ascii-code.com/).
• The 128 code Learn the Code 128 encoding algorithm with a font-based barcode solution.
• Online barcode generator Free online Barcode generator for the various barcode types.

Sample code

• ZXing Multiplatform open source barcode scanner / generator with versions available in Java (core project) and ports to ActionScript, C++, C#, ObjectiveC and Ruby.
• Python Bar Code 128 This code appears to draw boxes 1 pixel wide. It appears it was modified from a short line long line bar code which would have drawn lines. The "Black boxes" should be the same size as the "White Boxes".
• GenCode128 Free C# source code implementation of Code128. Almost all features are implemented, but is not 100% complete.
• Barcode1DTools Ruby gem Ruby source code for many 1D barcode symbologies including Code 128.
• Perl barcode generation code Perl source code for many 1D barcode symbologies including Code 128.
• Barcode::Code128 Free Perl barcode generation module.
• GOCR Free OCR with Code 128 recognition.
• Barcode Code 128 Free JavaScript source code implementation of Code128.
• Barcode4J Free Java API with implementation of Code128 and other standard barcodes.
• JavaScript Code 128 Open source JavaScript implementation of Code128 and other linear barcodes.