UNITED STATES
POSTAL SERVICE ™

MAILING EVALUATION, READABILITY AND LOOK-UP INSTRUMENT
(MERLIN)

BARCODE ERROR REFERENCE GUIDE

	Software Release Version 2.02
	Prepared by:  Hernan A. Borja
	June 20, 2002

TABLE OF CONTENTS

INTRODUCTION
METHODOLOGY
MERLIN POSTNET BARCODE EVALUATION THRESHOLDS
REPORT ERROR IDENTIFICATION
REPORTING ERRORS
Bar is Too Short
Bar is Too Wide
Bar is Too Narrow
Barcode Position Problem
Extraneous Ink Present
Baseline Shift Problem
Bar Tilt Problem
Pattern Skew Problem
Bar Pitch is Too Close
Bar Pitch is Too Far Apart
Background Reflectance is Low
Print Reflectance difference is low
Barcode Clearance Problem
Connected Bars
Barcode Will Not Decode
Invalid Delivery Point Barcode
Bar space is too close
Bar space is too far apart
UNRECOGNIZED BARCODE
RECOGNIZED BUT NOT ANALYZED BARCODE
REPORT IMAGE CAN’T BE DISPLAYED

INTRODUCTION

This document describes the various POSTNET barcode evaluation error codes reported in the MELRIN Barcode Readability Report.  MERLIN is capable of evaluating post cards, letters and flat mail.  Even though the mail physical requirement characteristics are different from post card, letter and flats, the majority of the parameters of the barcode evaluation are the same.  In fact the differences are related to barcode position on the mail piece.  The barcode printing requirements are the same for all types of mail.  In addition, this document provides a description of the standards for barcode printing per the Domestic Mail Manual (DMM.)

The document explains the differences of the requirements between letter and flats when it is appropriate.  When no references are made, the printing requirements are the same for all types of mail.

METHODOLOGY

There are three distinctive processes that help with the mail evaluation process in a MERLIN machine.  The first one is the singularizing process which is achieved at the feeder section of the machine.  The mail is singularized by the suction cups and mechanically advanced to the input rollers delivering it to the scale module.  The second process is the settling of the mail and is performed within the scale module.  At this module section, the weight of the mail piece is determined as the mail piece settles continuing to the imaging module station.  The third process is the image lifting process and it is performed as the mail moves along within the imaging module station to the stacker.  The imaging camera acquires a line-scan image that is used in the image recognizing process.  Lastly, the mail is stacked in the order it is presented at the feeder section.

It is during the transport of the mail piece through the imaging module section that the POSTNET barcode is recognized.  The image is analyzed within the Imaging PC (IPC) defining the best barcode recognition areas and selecting the area with highest barcode composition probability.  The barcode characteristic are determined and communicated to the Control PC (CPC) storing the results into the evaluation run database.

MERLIN utilizes two recognition engines for barcode analysis.  One engine does the reading of the code (ZIPCODE) from the barcode symbols and the results are utilized in the sortation analysis.  The second engine performs the barcode quality analysis comparing the recognized printing characteristics of the barcode within the specified MERLIN tolerances.  It is the results of the second engine that are reported in the MERLIN Barcode Quality Report.

The MERLIN Barcode Quality Report displays the barcode evaluation results using a set of error codes that are displayed with the POSTNET barcode image and summarized at the bottom of the report.

MERLIN POSTNET BARCODE EVALUATION THRESHOLDS

The following table identifies the threshold levels for the POSTNET barcode acceptance process.

MERLIN Barcode Threshold Values	
 	Parameter	DMM	MERLIN Software	
 	 	Specification	Warning	Error	
1	Minimum Tall Bar Height	0.1150	< 0.0936	< 0.0860	
2	Minimum Short Bar Height	0.0400	< 0.0390	< 0.0234	
3	Minimum Tall Bar Width	0.0150	< 0.0078	< 0.0039	
4	Minimum Short Bar Width	0.0150	< 0.0078	< 0.0039	
5	Maximum Tall Bar Height	0.1350	> 0.1716	> 0.1872	
6	Maximum Short Bar Height	0.0600	> 0.0702	> 0.0780	
7	Maximum Tall Bar Width	0.0250	> 0.0351	> 0.0429	
8	Maximum Short Bar Width	0.0250	> 0.0351	> 0.0429	
9	Maximum Void Spacing	0.0050	> 0.0156	> 0.0234	
10	Maximum Baseline Shift	0.0150	> 0.0156	> 0.0234	
11	Overink Size	 	> 0.0156	> 0.0234	
12	Minimum Bars Per Inch	20.0000	< 20.0000	< 19.5000	
13	Maximum Bars Per Inch	24.0000	> 24.0000	> 24.5000	
14	Minimum Bar Pitch	0.0416	< 0.0351	< 0.0273	
15	Maximum Bar Pitch	0.0500	> 0.0546	> 0.0624	
16	Minimum PRD	30.0000	< 30.0000	< 15.0000	
17	Minimum Reflectance	GR45 – RD 50	< 50.0000	< 35.0000	
18	Barcode Clearance Top	0.0400	< 0.0390	< 0.0390	
19	Barcode Clearance Bottom	0.0400	< 0.039	< 0.0390	
20	Barcode Clearance Left	0.1250	< 0.1250	< 0.1250	
21	Barcode Clearance Right	0.1250	< 0.1250	< 0.1250	
22	Minimum Bar Space	0.0120	< 0.0078	< 0.0039	
23	Maximum Bar Space	0.0400	> 0.0429	> 0.0468	
 	FLATS	 		 	
24	Maximum Bar Rotation - Flats	10.0000	> 10.000 	N/A	
25	Maximum Pattern Skew - Flats	 	N/A	N/A	
26	Address Block Top - Flats	0.1250	> H - 0.125	> H - 0.125	
27	Address Block Bottom - Flats	0.1250	< 0.125	< 0.1250	
28	Address Block Left - Flats	0.1250	> L - 0.125	> L - 0.125	
29	Address Block Right - Flats	0.1250	< 0.125	< 0.1250	
 	LETTERS	 	 	 	
30	Maximum Bar Rotation - Letters	5.0000	> 5.0000	> 7.0000	
31	Maximum Pattern Skew - Letters	5.0000	> 5.0000	> 5.5000	
32	Address Block Top - Letters	4.0000	> 4.0000	> 4.0000	
33	Address Block Bottom - Letters	0.6250	< 0.6250	< 0.6250	
34	Address Block Left - Letters	10.5000	> 10.5000	> 10.5000	
35	Address Block Right - Letters	0.5000	< 0.5000	< 0.5000	
36	Address Block Left Edge Clearance - Letters	0.5000	> L - 0.5000	> L - 0.5000	
37	Barcode Read Area Top - Letters	0.6250	> 0.6250	> 0.6250	
38	Barcode Read Area Bottom - Letters	0.0000	> 0.0000	> 0.0000	
39	Barcode Read Area Left - Letters	4.7500	> 4.5000	> 4.5000	
40	Barcode Read Area Clear Zone (Right) First Bar - Letters	3.5000	> 3.5000	> 3.5000	
41	Barcode Clear Zone Top LRH - Letters	0.4375	> 0.4375	> 0.4375	
42	Barcode Clear Zone Bottom LRH - Letters	0.1875	< 0.1875	< 0.1875	
43	Barcode Clear Zone Left first bar - Letters	4.2500	> 4.2500	> 4.2500	
44	Barcode Clear Zone Right LRH - Letters	0.3000	< 0.3000	< 0.3000	

REPORT ERROR IDENTIFICATION

MERLIN software reports the POSTNET and PLANET barcode evaluation results based in a percentage level.  The reports were designed keeping the same information and format as the ABE POSTNET barcode evaluation process reports.  Since the sample size for the two machines is different, MERLIN utilizes an averaging approach in reporting the individual error categories at the bottom of the report (see Figure 1 – POSTNET BARCODE READABILITY REPORT)

FIGURE 1 – POSTNET BARCODE READABILITY REPORT

Upper and lower case alpha characters are displayed below the barcode’s bars when errors/warnings are identified.  Upper case characters represent hard errors.  One upper case character (hard error) will fail a barcode.  Lower case characters represent warnings.  More than 10 same lower case letters (warning) will fail a barcode. 

REPORTING ERRORS

The following table lists all the error codes and their associated messages.  The last three error conditions do not have a letter associated with them, but the message replaces the barcode image of the identified piece.

Code	Description	Code	Description	Code	Description	
A/a	Bar is too tall	H/h	Base line shift problem	P/p	Barcode clearance problem	
B/b	Bar is too Short	J/j	Bar tilt problem	R/r	Connected bars	
C/c	Bar is too wide	K/k	Pattern skew problem	S/s	Barcode will not decode	
D/d	Bar is too narrow	L/l	Bar pitch too close	T/t	Invalid delivery point barcode	
E/e	Barcode position problem	M/m	Bar pitch too far apart	U/u	Bar space too close	
F/f	Void (Area without ink)	N/n	Background reflectance is low	V/v	Bar space too far apart	
G/g	Extraneous ink present	O/o	Print reflectance difference is low			
	Unrecognized barcode		Recognized but not analyzed barcode		Report image can’t be displayed	

The following addresses each error code providing a description of the problem and the DMM requirement:

Bar is too tall

DMM Section C840 4.0 a, b

A full bar must not be greater than 0.135” in height.
A half bar must not be greater than 0.060” in height.

Bar is Too Short

DMM Section C840 4.0 a b

A full bar must be no less than 0.115” in height.
A half bar must be no less than 0.040” in height.

Bar is Too Wide

DMM Section C840 4.0 c

No bar can be greater than 0.025” in width.

Bar is Too Narrow

DMM Section C840 4.0 c

No bar can be less than 0.015” in width.

Barcode Position Problem

See DMM Sections C840 2.3 - 2.5

For letters the barcode position follows the two areas described in the figure.  For flat mail, the barcode can be within the flats OCR area (Greater than 0.125 inches from each edge of the mail piece.)  Also, the barcode clearance zone requirements need to be observed within this category.

Void (Area Without Ink)

DMM Section C840 4.0

Extraneous ink or ink voids must not cause any bar to fail to meet the minimum or maximum bar dimension standards.

Extraneous Ink Present

DMM Section C840 4.0

Extraneous ink or ink voids must not cause any bar to fail to meet the minimum or maximum bar dimension standards.

Baseline Shift Problem

DMM Section C840 6.1

The individual bars of a barcode must not shift (be vertically offset) more than
0.015 inch from the average baseline of the barcode.

Bar Tilt Problem

DMM Section C840 6.1

The combined effects of positional skew (slant or tilt of the entire barcode baseline) and rotational skew (slant or tilt of the individual barcode bars) must be limited to a maximum rotation of the bars of ±5 degrees from a perpendicular to the bottom edge of the piece.

For flat mailings, the requirement is limited to a maximum of ±10 degrees.

Pattern Skew Problem

DMM Section C840 6.1 

The combined effects of positional skew (slant or tilt of the entire barcode baseline) and rotational skew (slant or tilt of the individual barcode bars) must be limited to a maximum rotation of the bars of ±5 degrees from a perpendicular to the bottom edge of the piece.

For a flat mailing, there are no requirements at this time.

Bar Pitch is Too Close

DMM Section C840 4.0 d

Measured over any 1/2 inch, horizontal spacing of the bars must be 22 ±2
bars per inch, and pitch (a bar and a space) must average at least 0.0416
inch but no more than 0.05 inch. The clear vertical space between bars must
not be less than 0.012 inch or more than 0.04 inch.

Bar Pitch is Too Far Apart

DMM Section C840 4.0 d

Measured over any 1/2 inch, horizontal spacing of the bars must be 22 ±2
bars per inch, and pitch (a bar and a space) must average at least 0.0416
inch but no more than 0.05 inch. The clear vertical space between bars must
not be less than 0.012 inch or more than 0.04 inch.

Background Reflectance is Low

DMM Section C840 5.1 

A background reflectance of at least 50% in the red portion and 45% in the green portion of the optical spectrum must be produced in the following locations when measured with a USPS or USPS-licensed envelope reflectance meter:
a.	The barcode clear zone of a card-size or a letter-size piece barcoded in the lower right corner.
b.	The area surrounding the barcode (within 1/8 inch of the leftmost and rightmost bars and 1/25 inch above and below the barcode) of a card-size, letter-size, or flat-size piece barcoded in the address block and of a flat-size piece barcoded elsewhere.
c.	The barcode clear zone on a non-barcoded card-size or letter-size piece in an upgradable mailing.
d.	

Print Reflectance difference is low

DMM Section C840 5.2

A print reflectance difference (PRD) of at least 30% in the red and green portions of the optical spectrum is required between the background material of the mailpiece and the barcode, when measured with a USPS or USPS-licensed envelope reflectance meter. (PRD equals the reflectance of the background minus the reflectance of the ink.)

Barcode Clearance Problem

DMM Section C840 2.4c
                      C840.2.5 c,d,e

When the insert showing through the window is moved to any of its limits inside the envelope, the entire barcode must remain within the barcode clear zone, and a clear space must be maintained that is at least 1/8 inch between the barcode and the left and right edges of the window, at least 1/25 inch between the barcode and the top edge of the window.

Connected Bars

DMM Section C840 4.0d 

The clear vertical space between bars must not be less than 0.012 inch or more than 0.04 inch.

Barcode Will Not Decode

DMM Section C840 1.0 

When separated into groups of five, these bars sequentially represent each of the digits of the ZIP Code (or ZIP+4 code or delivery point code) for the delivery address, plus an additional digit designated as the correction digit (check digit). The correction digit is derived from adding the numbers in the ZIP Code (or ZIP+4 or delivery point code) and determining which single-digit number must be added to that sum to make the total a multiple of 10. The first and last bars of the barcode are frame bars and they must always be full bars and be present.

Invalid Delivery Point Barcode

DMM Section C840 1.4

The correct DPBC must be derived as specified in Exhibit 1.4, which provides rules for common and unusual address formats.  This code may also appear in conditions in which a digit is printed incorrectly or the check digit is incorrect.

Bar space is too close

DMM Section C840 4.0 d. 

Measured over any 1/2 inch, horizontal spacing of the bars must be 22 ±2 bars per inch, and pitch (a bar and a space) must average at least 0.0416 inch but no more than 0.05 inch. The clear vertical space between bars must not be less than 0.012 inch or more than 0.04 inch.

Bar space is too far apart

DMM Section C840 4.0 d

Measured over any 1/2 inch, horizontal spacing of the bars must be 22 ±2 bars per inch, and pitch (a bar and a space) must average at least 0.0416 inch but no more than 0.05 inch. The clear vertical space between bars must not be less than 0.012 inch or more than 0.04 inch.

In addition to the error codes, there are other messages that the MERLIN barcode evaluation process reports and they are as follows:

UNRECOGNIZED BARCODE

This condition is present when neither the barcode analysis engine nor the barcode reader engine produces a favorable read.  The possible causes for this error condition are:
•	Erroneous check digit
•	Incorrect barcode symbology (incorrect POSTNET representation of tall and short bar combination)
•	More than 62 bars present
•	Frame bars not present
•	Improper bar height
•	Improper barcode clearance zone
•	Any barcode parameter that renders the barcode unrecognizable

The sample barcode image appears to be properly printed.  But, a careful analysis indicates that the image is of a barcode that has more than 62 bars.  This will produce an unrecognized barcode condition.

RECOGNIZED BUT NOT ANALYZED BARCODE

In this error condition, MERLIN knows that there is a barcode but the barcode analysis engine does not have an image available for performing the barcode analysis.  The reader engine was able to recognize it.  This error condition is associated with poor printing of a barcode for the analysis engine to recognize it and perform measurements. 

The sample barcode image has a barcode tilt problem.  The barcode reader engine may be able to decode it, but the barcode analysis engine may not be able to recognize it.  This error condition may produce a recognized but not analyzed barcode condition.

REPORT IMAGE CAN’T BE DISPLAYED

This error condition is reported if barcode readability failed, but due to internal MERLIN file transfer, an image was unable to be included in the report.  Readability errors are included in the legend.