HBStR 75-743

Preparation of Slefereoee lata

Sats for Character Recognition Pjssarch

M. Leighton Greenough & Robert M. McCabe

\

Optical Systems Section

Product Engineering Division

stilute for Applied Technology

June 30, 1975

Final

Technical Report to U. S. Postal Service

Office cf Posta! Technology Research

Pattern Recognition and Communications Branch

Letter Agreement 74-02935, Task No. 3
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Table of Contents

Page

Introduction . 1

PART 1, MULTILEVEL CHARACTER IMAGES

1. Objective . 2 1.1 Summary of activity , 2

2. Selection of material for inclusion in the reference data set ... 3 2.1 Selection of cnaracters 3 2.1.1 Preparation of address tapes ... 4 2.1.2 Selection program 4

3. Data encoding. 4 3.1 Mailpiece data . ........... 4 3.2 Readability data

.....

5 3.2.1 Mailpiece runs on Postal address readers ........ 5 3.2.2 Analysis and encoding of readability 6

4. Preparation of microfilm editions of input test deck 7 4.1 Envelope films ..... ... 8 4.2 Address films 9 4.2.1 Film selection . 10

4.2.2 Camera arrangement .......... 11

4.2.3 Density and contrast control measures. . . 12

4.2.4 Resolution control 12

4.2.5 Spectral characteristic 12

4.2.6 Positive copy film . . 14

5. Scanning 14

5.1 Description of processing equipment, FOSDIC .... . 14

5.2 Scanner program ....... 15

5.2.1 Size calibration 16

5.2.2 Gray scale calibration 16

5.2.3 Raster scan for location 16

5.2.4 Raster scan for recording. 16

5.2.5 Teletype data entry 17

5.2.6 Magnetic tape recording. ........... 17

5.3 Scanner operation 17

6. Computer processing. .. .......

6.1 Linearization and digitization to 32 levels L8 6.2 Merge with mailpiece data 21

6.3 Reduction to 16-level output tapes

.

,21

6.4 Generation of separate Setup and Test tapes . 21

6.5 Brief description of data set

.

22

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Page

7. Conclusion and recommenda t ions 22

7.1 Factors affecting the fidelity of input/oodput

relationship for reflectance of lines 23

7.1.1 Flare and halation 23

7.1.2 Uniformity of measurement ovec scanned address area. 25

7.2 Thickening or thinning of lines 26

7.3 Typographic accuracy 26

7. A Intrusion removal 27

7.5 Feasibility of conversion to other spectral regions .... 27

PART 2, OCR CHARACTKR RECOGNITION RESULTS

8. Objective 29

8.1 Summary of activity ....... 29

9. Selection of material ....29

10. Readability evaluation . ....30

10.1 Ceneration of printout work sheet 30

10.2 Analysis of the AOCR printout 30

10.3 Transcription to machine language 32

11. Computer processing and formatting 34

12. Acknowledgments 35

13. References ..35

APPENDIX

A. Notes on microfilming and processing of Envelope films .... 36

B. Calibrated values of test reflectance chips. ..........37

C. Computation of spectral response .38

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List of Illustrations

Figure No . Titl e_

1 Enlargement of typical section of address films

2 Portion of computer-generated work sheet, showing

designation of selected characters

3 Work holder for microfilming mailpiece cards

4 Spectral characteristic of data set

5 Scanner in operation

6 Scanner output vs. test chip reflectance

7 Observed relation between measured and scannerindicated reflectance on lines in characters

8 Portion of computer-generated work sheet

9 Sample section of AOCR printout showing details of

character recognition

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Introduction

This report covers the development of two reference data sets

contained on magnetic tapes. These sets were derived from a common source

of input, a test deck of mailpieces simulated on cards. This test deck,

which was furnished by the U S Postal Service (USPS), had been developed

from photographs of samples of live mail. Most of the mail was originally

type-written, however a range of deliberate, controlled degradation had

been introduced during preparation of the test deck.

Part 1 of the report describes the development of a reference set of

character images. These Multilevel Character Image tapes were prepared for

the US Postal Service to use in Optical Character Recognition (OCR)

research principally for pre-processing investigation. The tapes consist

primarily of digitized video signals recorded during scanning with a small

grid raster placed over approximately 32 000 individual characters selected

from the total of 110 000 characters on the mailpieces.

Part 2 describes the development of a tape containing the OCR

recognition experience of all of the approximately 110 000 individual

characters when the mailpiece cards were read by one OCR machine of

advanced design. This tape was prepared in order to furnish a realistic

body of information on actual substitution and rejection incidents. It was designed for usefulness in context and in other post-recognition research.

Part 1 Multilevel Character Images

1. Objective

The objective was to develop a reference data set of characters on magnetic tape for the USPS to use in research in OCR. The recorded

information is a representation of the video signals generated during

scanning with a grid raster placed over individual characters printed

oh simulated envelope mailpieces.

These tapes contain data on approximately 32 000 characters. For each

character, data are recorded for a 2A x 24 point grid located on 0.006

inch (0.15mm) centers, encoded into 16 levels of equivalent

reflectance t

1 4 i Summary oJL_ac t lv i t

y

The development of the character image data set

involved the following major steps:

it Selection of material for inclusion

2t Preparation of address tapes

3» testing of source material for OCR readability

4» Preparation of microfilm editions:

-whole envelope faces for future address

location research

-address images only, for scanning and

inclusion in the data set

5w Scanning of address films

(5> Computer processing, including linearization and

tape merge

7% Evaluation of output

f'hes'e topics and others are covered in appropriate sections of

this report* In the concluding section the results are given on a

ferief study of the fidelity obtained in certain critical phases of

ttae •operation-. Finally an Appendix is included to document

details o? the spectral response calculations and of the special

Jphd tographic arrangements

.

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The data set itself, the result of the developmental effort,

Is described in detail in a separate report, ref (1). This

specification accompanied delivery of the data set tapes to the

sponsor.

Selection of material for inclusion in the reference data set

One of the USPS-f urnished materials for the project was an input

test deck consisting of approximately 6000 mailpieces simulated on cards. Printed addresses had been applied to the cards along with

individual plate (mailpiece card) numbers. It is our understanding

that the address contents had been obtained by microfilming of live

mail, with later substitution of artificial recipients' names. Degrees

of degradation of type or print quality had been introduced in the deck

by systematic voids in the strokes and by overstrikes. In some cases

the addresses were printed on labels which were then attached to the

cards. In addition, window coverings of glassine, as well as multicolor paper and print, were employed. Oversize characters were also

fairly common in the deck as supplied. An enlargement of a typical

mailpiece address is shown in Figure 1,

The specific description of mailpieces, such as color of printing

ink, paper, label if used, and window type were supplied NBS by the

USPS with the test deck in a contractor's report, ref (2).

In the test deck of approximately 6000 simulated addresses, many

were found to be replicated in quantity. When duplicates were removed,

2100 addresses remained, containing about 110 000 characters. From

this lot, it was desired to obtain approximately 32 000 representative

characters.

2.1 Selection of characters

The overall selection process resulted in extracting about

one-third of the envelopes from which one-third of the characters

were designated, based on rules which are given below. The

product of the selection activity described in this section was a computer-generated printout of those address mailpieces containing

one or more characters selected for representation on the data

sset* The initial step was to convert the addresses containing the

110 000 characters to magnetic tape.

2.1.1 Preparation of address tapes

This magnetic tape of addresses was generated by an operator

who copied the 2300 address mailpieces at a computer-connected

terminal. This tape has had two uses, namely as a source of input

for automated character selection and for providing context

. information accompanying each character represented in the data

base.

2.1.2 Selection program

The address tapes generated by the techniques of 2.1.1 were processed in a separate computer operation to obtain frequency

counts of the 62 characters chosen for the data set. These

characters are all 52 upper and lower case letters and the ten

numerals. Then the computer was instructed to select every "nth"

character of each type so as to yield 500 samples of each of the

62 characters. This produced the desired results for the most

part. However it left a deficiency of infrequently-encountered

characters, only 26 samples of lower case j for example, even

though all examples were r.aken. These totals were brought up to

at least 100 for each character through the addition of material

from typewriter font exhibits. After minor readjustment of the

chosen popular characters, a list was developed of over 32 000

selected characters to be included in the data base, with

individual frequencies ranging from 100 to 500, of 62 letters and

numbers

.

The list of selected characters was printed out from the

computer in the form of a worksheet having horizontally triplespaced characters for each line of the 2100 addresses. The

selected, characters were shown by computer-printed underlines.-

Below the address lines in the printout, three more lines were

printed, blank except for underlines at the selected characters.

A section of a typical printout is shown in Figure 2. The

resultant printout thus became a suitable worksheet for entering

notes in the underlined spaces, as described under Section 3.<2-.2. Two addresses were listed on a page, with the plate (mail-piece

card) number appearing at the top of an address.

3« Data encoding

3«1 Mailpiece data

In the interest of future addition of information to the data

set, it was deemed advisable to include all known pertinent data ss part of each, character record. These mailpiece data were

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contained in a report from the developer of the original test

deck, ref (2).

The desired information related principally to paper and ink

colors, presence and type of window and the general nature of the

type face. The latter had to be determined visually by the coding

clerks, since it was not listed in the background report. Working

from the report, an operator keypunched the indicated codes into

machine tabulation cards. The format and code set of these cards

were chosen to match those of the original data. Plate numbers

for the mailpiece cards were also punched.

The next step was to merge these cards into the master

listing represented by the address tape, using plate numbers as

the common element. At this stage the master file then contained

all the necessary mailpiece data. The data for any given host

mailpiece was invariant for all characters derived from it.

3, 2 Readability data

A separate technique was used in order to enter an indicator

of readability which of course was specific for each character on

a mailpiece. The general approach was to determine the

readability of the selected characters and insert this information

as one of the items for manual data entry during the scanning

operation. The first task was that of determining the machine

readability of individual characters.

3.2.1 Mailpiece runs on Postal address readers

To determine character readability, the 2100 mailpieces and

200 supplementary materials were run through three postal machines

whose designs incorporated advanced forms of optical character

recognition. These runs were performed at Post Offices in Boston

and New York. Witnessing observers were present from NBS and the

USPS. During these runs, computer printouts were generated

showing summary details of reading experience for the 110 000

characters contained on the mailpieces. Although in most cases a tape was also generated as part of the printout cycle, it was believed that decoding of the tapes would have been more difficult

than visual data extraction from the OCR printouts. Hence the

product of the OCR runs was in the form of computer printouts

showing whether a character was correctly read, rejected,

improperly recognized (substituted) or disqualified for some reason (washout) . On the printouts this information was shown for

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1 mm.^m^^mw^^iH^ i

the 110 000 characters fed through the postal OCR machines. There were three such printouts, with greatly different formats.

During the runs there was a degree of wear on the mailpieces,

chiefly in the form of smudging of print caused by rollers in

holding bins of the machinery. This was introduced noticeably in

the course of the first run. Since these runs were repeated with

less subsequent deterioration, and then filmed after all runs were

completed, it is felt that the condition recorded on film for

scanning was a reasonably good representation of that during most

of the recorded OCR runs.

3.2.2 Analysis, and_encodlng of readability

The analysis of readability began with the task of simply

labelling the 2300 OCR printout sections with the plate numbers of

the originating mailpieces. All three printouts were so labelled.

This turned out to be surprisingly laborious but was necessitated

by loss of the initial numeric order during some of the reading

operations

.

For the analysis, the master file was considered to be the

address list worksheet as described in Section 2.1.2 - Selection

program. The analyst was required to work in sequential order on the master file, hence it was sometimes necessary to search

through the OCR printout to find the applicable mailpiece section.

Then she was expected to determine, through examination of the OCR

printout, the output character corresponding to the selected

(underlined) input character. Finally she was expected to note

whether correct reading, rejection, substitution or disqualification had occurred. To minimize confusion, an analyst

worked exclusively with the printout from one OCR machine at a time. The analyst's responsibility was to write in an appropriate

readability code in the underline boxes. The following codes were

used

:

C correct ("A also used synonymously)

R * rejection

E » error-, substitution

W - washout^ disqualification

Review of an analyst's work was on a spot-check basis, with

reduced frequency after confidence had been established.

Altogether three clerks were trained and employed in this phase of

the operation.

Thus at this stage, input material had been designated for

inclusion in the data set, a machine-language file had been

created of applicable group characteristics such as background and

print colors, and a worksheet had been prepared with the

designated characters marked. This worksheet carried the

information on character identification and readability, and was

in effect the instruction sheet to the scanner operators.

Preparation of microfilm editions of input test deck

Since the NBS FOSDIC was to be employed for producing the

character image data base, it was first necessary to prepare a film

replica of the input test deck. Two separate versions were generated,

one showing images of the entire faces of the mailpiece cards (Envelope

Films) and the other containing magnified images of the address

sections only (Address Films) . Only the Address Films were planned for

FOSDIC scanning. Both versions were produced with 16mm positive print

film copies as the final product. Altogether there were:

- 11 rolls of camera negatives, Envelope Films

- 11 rolls of positive print copies, Envelope Films

- 27 rolls of camera negative, Address Films

- 27 rolls of positive print copies, Address Films

Initially it was hoped that the same type of film could be used

for both applications, hence considerable effort was devoted to methods

for extending the gray-scale response of microfilms. Unfortunately no one film was found suitable for both the Envelope and the Address

films. As will be seen, the former required high resolution and fine

grain. The latter demanded high speed and long scale rendition, which

is usually accompanied by larger grain size. Thus these requirements

were basically incompatible. Advice was sought from film

manufacturers, and many experiments were conducted in an attempt to cover the full span from 5 to 90 per cent reflectance. Within the time

available we were not able to encompass the entire range with a microfilm, finding at best a condition of saturation below 10 to 15 per

cent reflectance and substantial flatteninp above about 80 per cent.

Close control of the exposure and developme steps was necessa: for even these limits.

4.1 Envelope films

The Envelope Films were generated to provide input material

for potential future applications such as research on OCR address

location, line finding and character segmentation. To this end,

the mailpiece cards were filmed, insofar as possible, under

controlled conditions. These are black and white films at 12:1

reduction, made with a spectral response extending from

approximately 400 to 660 nanometres. The image content includes

the mailpiece card which was placed against a bordering guide,

span markers for scaling, resolution charts and a gray-scale step

wedge for calibration of the overall rendition of reflectance.

Process controls were applied for uniformity of illumination and

contrast in order to preserve as much as possible of the usable

region of gray scale rendition.

The microfilming of envelopes was conducted at the Bureau of

the Census, using a standard planetary (table top) camera. Mailpiece cards were placed against an L-shaped corner angle so as to minimize variations in position. Portions of the images

included control elements such as size graduations, gray-scale

Chips and resolution charts.

The primary technical considerations on these films were:

1) Image to include whole envelope (mailpiece card)

2) high resolution

3) Low graininess

Factors of somewhat lesser importance were:

A) Gray-scale rendition

5) Spectral characteristic

The Chosen negative film for the process was a high-speed

type designed for rotary cameras, with which considerable

experience had been gained during the 1970 Census in connection

With FOSDIC processing. Other films were tried, but their slower

Speeds proved inadequate; when brought to low gamma by

underdevelopment, excessive light was required for exposure. The

Selected film was used in rolls frf -215 feet (65.5m) of 16mm width,

packaged in the normal 100-foot size box. This film has a 2.5-mil

(0%06mm) polyester base which is nearly transparent and has an antihalation coating on the back. Its spectral response extends

fc©m approximately 400 to 660 nanometres.

Details of the microfilming operation for envelope images are given in the description which follows.

For microfilming of whole envelopes (entire mailpiece cards,

4.5 x 8.5 inches) the reduction ratio was 12:1, producing an image

size of .375 x .707 inch (9.5 x 18mm). When the gray scale along

the top of the mailpiece card and the resolution chart samples are taken into account, the useful image area is approximately 0.5 x 0.75 inch (12 x 19mm) on the films. For the convenience of users who may wish to perform size determination or correction, two fine

scratch marks were located precisely 6 inches (15.25mm) apart

along the top edge of the card images. This corresponds to 0.50

inch (12.7mm) on the film.

As a check on resolution, two sections, of N'BS Microcopy

Resolution Charts were also included in every image. It was found

possible to resolve on the negative approximately 10 line pairs

per millimetre as referred to the mailpiece size. On the

resultant positive copies the resolution is 6 line pairs per

millimetre.

Positive film copies were made of the camera negatives by a commercial laboratory. There are a total of eleven rolls of

positive films, containing the whole-envelope photographs of the

6000 mailpiece cards in the test deck. With their controlled

density and indicators for size, gray-scale and resolution, these

films should be found satisfactory for future purposes such as address and line finding experimentation.

Other details of the microf ilm-ing and processing procedures

are given in Appendix A.

4.2 Address films

These are the films containing the characters which were actually scanned. A typical image with its address content is

shown in Figure 1. All 6000 mailpiece cards in the input test

deck were microfilmed, producing 27 rolls of negatives. These were copied, producing the same number of positive copy films.

Thus the entire test deck was transferred to microfilm. The

characters selected for scanning, by the method described in

Section 2.1, involved 11 of these 27 rolls.

• The primary considerations on these films were:

1) Image of address portion only

2) Good gray-scale rendition

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3) Spectral characteristic

Factors of somewhat less importance were considered

to be :

4) High resolution

5) Low graininess

4.2.1 Film selection

From the earlier experimentation with microfilms it was recognized that these were not likely to be suitable. The

spectral requirement, introduced in order to simulate practical

OCR devices, necessitated limiting the spectral response to a rather narrow band. This of course resulted in considerable loss

of light energy reaching the film, by a factor of approximately

5;1. As a result it was necessary to use a higher-speed film of

the motion picture type. An additional reason for the selection

was to reproduce the low and high reflectance regions, a problem

•with microfilms as described in Section 4. The material selected

was one with medium speed, panchromatic spectral response, long

gray-scale rendition and moderate grain. These conditions were met with a readily available film, however it was again necessary

to use high illumination levels. The latter was considered

preferable to employing a still higher speed but grainier film.

In order to obtain the necessary image width without sprocket

hole intrusion, it was required to use negative film 35mm wide.

The positive copy films of both the scanned and unscanned

addresses were trimmed from 35 to 16 mm width.

4.2.2 Camera arrangement

The microfilm camera was of the standard commercial type,

modified for a reduction factor of 2X by the installation of a longer focal length enlarging lens (80 mm f/5.6 stopped down to

f/8). It was necessary to fabricate a new lens mount to fit the

lens platform of the camera. This mount was equipped with an ind exing scale for reproducible adjustment of focus.

A special work stage was constructed to hold the mailpiece

flat and to furnish alignment guides to the operator. A

photograph of the work stage is shown in Figure 3. Since the

address locations varied considerably from card to card, the work

Stage featured a window into which the operator was expected to

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place the address by moving the card. In those cases where the

address lines were skewed with respect to the edges of the card,

this skew was required to be shown in the photographed iinage.

Consequently parallel guidelines were included in the stage to

facilitate edge alignment. The window itself was 7/8 inch high

and 3-1/2 inch wide (22 x 90 mm).

Ip a band across the top of the window were located 14 grayscale reflectance chips, one resolution chart and three span

marker lines. The reflectance chips covered the range from 3.7 to

85 percent, as measured with respect to barium sulfate on the 45/0

ref lec tome ter regularly used in the paper industry, with filter

#13 having a spectral centroid of 536nm. Specific values are given in Appendix B.

Illumination of the material to be photographed was provided

by two reflector floodlamps operated on about 60 percent (70V) of

rated voltage 300w, 120V. The adopted illumination level of 225

footcandles (2420 lux) was monitored at least hourly with a small

photometer

.

In photographing the test deck, each address image was preceded by an image of the plate number of the host mailpiece

card. This allowed a visual check of the identification of

address images.

.2.3 Density and contrast control measures

Control of the overall input/output characteristic was effected through scanning the portion of the image containing the

reflectance chips, recording the density signals for the 14 chips

in the same block of data as the signals from the selected

characters in the mailpiece image. This provided the basic data

from which image information was calibrated in quantitative terms

of reflectance. The technique for this purpose is described in

Section 6.1 - Linearization and digitization. The process

compensated at the same time for the non-linear, quasi-logarithmic

response common with FOSDIC and other density-measuring devices.

In correcting the overall input/output characteristic to a linear function, the tacit assumption is made that at any position

over a character, the area weighted proportion of reflecting

material under the spot can be equated to an overall gray of

proper level. In a direct document scanner the equality is

inherent. However to produce the same results with photographic

films, which usually show approximately logarithmic response,

requires at least a reasonable match between the characteristics

of the negative and positive films. If the natch is not good

enough, there will be some thickening or thinning of printed lines

in the subject material. Without control measures, the effect can amount to perhaps one third of the spot diameter.

The controls imposed on density and contrast took the form of

upper limits on the densities of both negative and positive films.

Processing was in a commercial motion picture laboratory. It was necessary to specify "pushed" development, as had been learned

from test strips run previously. The group mean and range of

density were determined for the processed negatives. Reference

was then made to the characteristics of the copy printing

equipment, previously-measured (through test strips), yielding an exposure value which was specified for the copy printer.

For the control procedure, the density on the negative was measured for the whitest chip, 85.5 per cent reflectance. It was measured on the first one or two frames on each full length roll

of negative film. The density was found to range from 1.0 to

1.25, safely within the upper design limit of 1.33.

Because the microfilming took place over a period of several

weeks, the exposed rolls of film were stored in a refrigerator at

about 40 F (5°C). This step was taken to minimize fade of the

latent image, which would cause a larger density spread in the

negatives.

4,2.4 Resolution control

To verify that the necessary resolution was preserved through

the photographic steps, a portion of an NBS Microscopy Resolution

Chart was incorporated in the image area. This portion included

the finest lines on the chart, 18 line pairs per millimetre,

equivalent to 1.1-mil lines alternating with spaces of the same dimension. A visual check was maintained on these lines, which

were readily resolvable on the negative. On the positive copy,

the finest target, 18 line pairs per millimetre, could just be

resolved. Resolution of this order is necessary to avoid

degradation of the results derived from a beam width of 3 mils

(0.075mra) .

4.2»5 Spectral characteristic

The spectral characteristic is important in determining the

response to the color of the scanned input material. The colors

of both the background envelope or label, and the printing ink,

affect the magnitude of signal change as the scanning beam moves

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over the address. If the spectral response is "neutral", i.e.

non-selective, the response to all colors except black will be

weak. However most practical scanning devices exhibit a selective

function, exaggerating the response to certain colors and

their designations are as follows;

1) "OCR-1" 505 to 575 nn with max. at 530 nn

2) "Visible" 575 to 750 " " 675

3) "Infrared" 755 to 990 " " 850

The 0CR-1 characteristic was selected as being the only one suitable for use with the available films and lenses.

The spectral characteristic prevailing during the microfilming step established the spectral response function which

ultimately was assigned to the data set. Insofar as possible we attempted to natch the 0CR-1 characteristic, primarily through the

selection of a suitable filter during the microfilming of the

address test deck. For this purpose a yellow-green filter was placed in front of the camera lens. Once past the initial

photographic step, the spectral characteristics of the copy film

and the scanner are unimportant.

The spectral characteristic applicable to the data set was calculated from the following.

1) Measured transmission of the filter, a Wratten No. 5 8

2) Spectral sensitivity of the film, as supplied by the manufacturer

3) Color temperature of the illuminating lamps,

(2200 K) determined from the manufacturer's

data for color temperature at the actual

operating voltage.

The primary influence was the filter, with a slight shift toward

the longer wavelength introduced by the rapid dropoff of the

illumination toward shorter wavelengths. Details of the

computation are given in Appendix C.

Figure 4 shows the overall spectral characteristic as obtained by this process. It can be seen that there is a broad

peak which reaches its maximum at 550 nm , with 50% points at

approximately 515 and 58(1 nm. This can he compared with OCR-1

response, which calls for a maximum at 53C nm and 50% points at

505 and 575 nm. The degree of this match indicates that there

should be only a minor departure from design center response,

slightly evident with blue and yellow Inks and paper.

There is a possibility that under some conditions the data

obtained from scanning with one spectral response can be converted

to that of another. The apparent feasibility of this approach is

covered in Section 7.5 - Feasibility of conversion to other

spectral regions. Its promise was one of the major reasons for

•matching the spectral response represented in the data set to one

of the established characteristics.

4,2.. 6 Positive copy film

Positive film copies were made by a commercial laboratory

using conventional print film for motion pictures. Density was controlled through adjustment of the printing lamp, as determined

from test strips which duplicated the measured range of density on the camera. These films have slightly less overall contrast range

than the original "mailpiece "materials (1.1 density range on the

positive compared to 1.26 on the source mailpieces) . As mentioned

in Section 4,2.1, the copying was carried out using 35 mm film,

followed by slicing to 16 tie width. Twenty seven rolls were produced from the entire deck of 6000 mailpieces. Of these 27, 11

contained the material required for scanning,

5, 0 Sca nning

This section covers principally the generation of video data

obtained by scanning the filmed character images. In the same operation, the readability data described in Section 3.2 above was entered manually via keyboard typing.

r

5,1 Description of processing equipment, FOSBIC

FOSDIC, an acronym for Film Optical Sensing Device for Input

to Computers, is a computer-actuated film scanner. In the mode of

Operation for this data set, the scanner was used simply as a programmable microdensitometer , optically reduced so that the spot

size was 0.0015 inch (0,04 mm). At this reduction the maximum

attainable scanning area is 0.5 by 0.75 inch (12.7 x 18 mm) on 16 mm film. In the densitometer mode, spot positioning is

programmable in increments as small as 0.0004 inch (0.01 mm or lO^m)

.

At each point the image density. can be measured and recorded

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in one of 256 levels up to a maximum density of 1.6 (2.5%

transmission). The general characteristic of the output is such

that the digitized level is approximately proportional to the

logarithm of the film transmittance.

An internal projection arrangement displays an enlarged film

image on a page-size (15x) viewing screen in front of the

operator. Separate observation of the scanning cathode ray tube

face through windows makes it also possible to see the scanning

pattern in exact registry with a AX reproduction of the film

image. These provisions for operator observation greatly

facilitate the location of desired portions of the image.

The complete FOSDIC system includes, besides the scanner and

the minicomputer with 4K memory, a magnetic tape unit and a lowspeed paper tape and keyboard unit. For preparation of the data

set, a video display device was attached, and external X and Y

positional controls were added.

Other data processing equipment used at other steps in the

production of the data set included a CRT/keyboard terminal and

the NBS 1108 central computing system.

5.2 Scanner program

The program for actuation of the scanner and related

peripheral devices included the following major routines:

a) Size calibration, wherein the amplitude of the

scanning raster was ajusted to cover a square of

48 x 0.003 = 0.144 inch (3.66 mm) on a side,

referred to address dimensions.

b) Gray scale calibration, which provided a quantitative

basis for assigning equivalent reflectance values

and which permitted linearization of overall response

c) Raster scan for location, used for positioning

each character inside the raster pattern

d) Raster scan for recording, during which the scanning

resulted in stored values (48 x 48 = 2304) in the

computer memory.

e) Keyboard data entry, used for manual insertion of

mailpiece plate number and data on character

identification, readability and intrusions.

-15-

f) Magnetic tape recording, involving the transfer

of video and keyboard-entered data from storage to

output magnetic tape.

Each of the above items is described in more detail in

the appropriately numbered paragraphs which follow.

5.2.1 Size calibration

The size of the scanning raster increment was set to 0.003

inch (0.075 mm) through the use of a special target frame photographed at the beginning of each roll of film. This target

contained a ruled square of 0.72 inch (18.3 mm) on a side,

corresponding to a total area of 5 x 5 or 25 rasters. The size

calibration program produced visible bars which were placed at the

sides of the square through manual adjustment of the horizontal

and vertical-axis scale factors of the respective deflection

amplifiers. It is estimated that scale factors were held to

within one per cent by this technique.

5.2.2 Gray-scale calibration

This was the portion of the program which measured the

densities of the individual gray-scale chips located along the top

of each image. Sixteen reading points were taken on each chip so as to form a group average over the center quarter of the chip

area. To take care of possible dust particles on the film,

readings showing excessively great film density (apparent low

reflectance of the chip) were effectively discarded. Typical

readings for the darkest chip of 3.7 per cent reflectance were 10

to 15 on an overall scale of approximately 220.

5.2.3 Raster scan for location

A repetitive raster was generated to permit centering of the scan raster over the character to be read out. This locating

raster had the same structure and position (48 x A8 points) as the

final recording pattern. The ten-per-second repetition rate,

combined with a long persistence display CRT, allowed the operator

to see the exact placement of each character in the grid. Before

going to the next step of recording, each character was centered

by the operator in the grid, through the external XY position

controls.

-16-

5.2.4 Raster scan for recording

Activation of the recording raster produced a one-time 48 x 48 grid, with memory storage of the resultant video data with 8

bits precision representing 256 gray levels. The time for the one complete raster was approximately one-fourth second.

5.2.5 Keyboard data entry

The entry of all supplemental data regarding character

identification, location in the address, readability, and

intrusions of adjacent characters into the scanning zone was accomplished via a keyboard while the locating raster scan was activated. Program interlocks were provided to prevent the

operator from calling for the recording raster, item (4) above,

until the data entry was complete.

The data entry portion of the program required the operator

to type from the coding sheet, entering the desired information in

a conversational mode. That is, the keyboard printer was programmed to supply the name of the next response expected of the

operator, to minimize the chance of confusion. Data for the final

entry, on intrusions, were obtained from observation of the video

display, rather than from the coding sheet. When the intrusions

field had been completed, the typing of a "@" caused the program

to initiate item (4), the recording raster, followed by an automatic initiation of the data transfer to magnetic tape.

5.2.6 Magnetic tape recording

During the time of recording, no other program action was performed. Upon completion of the record, the word "MAG" was typed out, and the locating raster scan was resumed.

5 . 3 Scanner operation

Because of the multiple sources of input data during the

keyboard data entry, it was found desirable to employ two persons

in the operation. A photograph of the system in operation is

shown in Figure 5. The typist controlled the sequence based on

the coding sheet containing the character identification, location

and readability. She conveyed verbal instructions to the TOSDIC

operator, who then placed the locating raster over the desired

letter, using the XY controls. When the operator had completed

centering the character, she called out the intrusion codes

(right, left, top, bottom), which wore then entered by the typist..

-17-

After this, with the concurrence of the operator, the typist

entered the "@", initiating the aforementioned data recording

sequence terminating in resumption of the locating raster (3)

.

The throughput rate for experienced teams performing the

ahove sequence was found to reach 200 characters per hour.

Additional time was of course devoted to quality control,

verification and correction re-runs.

0 Computer processing

The FOSDIC scanner tapes, containing the video data together with

the manually-entered information on character identification,

readability and intrusion were first put through a linearization

process and then reduced to a 32-level representation of reflectance.

The next step was to merge the video data with the mailpiece

information from the original address tapes. From the resulting set of

master high resolution tapes, the final tapes constituting the data set were prepared. This involved the reduction to a coarser grid and

digitization to larger intervals, to meet the overall requirements of

the data set. These various stages of computer processing are described below.

6.1 Linearization and digitization to 32 levels

The purpose of the linearization process was to produce an overall characteristic wherein the output indication was proportional to the input reflectance, i.e. the light reflected

at each position of the scanning spot. Then the output becomes

representative of a document scanner, making the data set suitable

for generalized applications. The overall control provided by the

linearization method was designed to make the system independent

of the internal characteristics of its elements, so that the

introduction of the intermediate photographic step would have

negligible influence on the overall input/output relationship.

Lacking this there might otherwise be an undesirable flattening of

the response at very low and very high reflectances.

Linearization was accomplished as follows. Fourteen small

chips having calibrated reflectances ranging from 3.7 to 85

percent were mounted to form a reflectance step wedge along the

top of every address image. The arrangement of these chips is

described in Section 4,2.2. The output data as recorded by the scanner included coverage of the wedge chips in the same image

from which character data was generated. Thus variations in

exposure due to camera shutter ir regulari.ties had no effect on the

final result.
1I
The scanner output is digital in 8 bits, allowing 256 levels,

in which the region from approximately 10 to 220 was used by the

3.7% to 85% calibrated reflectance chips. In general the same

range applied to the character scan signals as the beam traversed

the character strokes. Tapes with these recorded signals,

together with a list showing the calibrated reflectances of the

chips, formed the input to the linearization program.

The first step in the program was, in effect, the

construction of a curve of reflectance vs. scanner output,

obtained by linear interpolation between the 14 chip signals.

This relationship was computed in its entirety for each mailpiece

image, then used for all computations involving the same image. A

typical relationship is plotted in smoothed form in Figure 6. It can be seen that the low and high reflectance ends show some

flattening, where there is less change in 256-level output for

incremental changes in input reflectance. Insofar as possible,

the selection of the 14 calibrating chips was made to enhance

accuracy of linearization in these regions.

From the computed response function of the type shown in

Figure 6, a value of reflectance was determined for the scanner

signal at each point in the character scanning raster. Following

this, the reflectance was looked up in a conversion table,

yielding the proper one of 32 possible output levels to express

the digitized reflectance. For example, reflectances greater than

6.0% but less than 9.0% were digitized to value "2". At 9.0%,

transition to the value "3" took place. By this means an input

range from just over 6% to just over 90% was encoded to output

values from 2 to 30. While it is believed that no samples

exceeded this range, there was no specific prohibition of output

values below 2 or above 30.

The uncertainty in the linearization and digitization was not

measured, but is estimated at about 1% plus or minus one (3%) step

in output, over the desired input range of 6 to 90% reflectance.

The major portion of conversion error is likely to be in the

regions where straight-line interpolation departs from the smooth

curve which might be drawn through the 14 calibration points.

The encoding of the digitized output indication is shown in

Table 1 which follows.

-19-

TABLE 1

Encoding of digitized output into 32 levels

When input reflectance is:

d L J U <: i r"> L « but less than: Output record

0 3 0

3 6 1 6 9 2

9 12 3

1 2 15 A

15 18 5

18 21 6

21 24 7 24 27 8

27 30 9

30 33 A

33 36 B

36 39 C

39 42 D

A2 45 E

45 48 F

48 51 G

51 54 H

54 57 I 60 jw

60 63 K

63 66 L

66 69 M

69 72 N

, 1

1

75 78 P 78 81 Q

81 84 R 84 87 S

87 90 T

90 93 U

93 96 V

(Note: Value uncertai:

below calibration

limit of 6%)

(Note: Value uncertain

above calibration

limit of 90%)

As the linearization and digitization proceeded,

video records were accumulated in computer mass storage.

These were filed according to mailpiece plate number,

for retrieval and merging with the address tape data.

-20-

6.2 Merge with mailpiece data

Mailpiece data contained on the address tapes

served for recalling the stored video records. New

tapes were created with longer records combining the

address and mailpiece data together with the video

data. These became the eight master tapes for subsequent processing into the data set output tapes.

6 . 3 Reduction to 16-level output tapes

The desired detail to be represented on the data set called

for reflectance digitized to 16 levels on a 24 x 24 grid. Spot

size and incremental positions were both to be 0.006 inch (0.15

mm). The goal of the reduction program was to generate the final

data tapes from the master tapes having 32-level data on a 48 x 48

grid, with spot size and incremental positions of 0.003 inch

(0.075 mm)

.

Data reduction was accomplished through taking the average

reflectance from clusters of four adjacent grid locations, then

rounding off to 16 levels of digitized output. New magnetic tapes were created with this reduced form of data representation. With

the coarser grid, the new records were 1044 bytes long rather than

the previous 2772.

Other minor changes were introduced in the same processing

step, such as to revise the heading data for indicated record

length from 2772 to 1044 bytes, and to modify the readability

encoding. The purpose of the latter was two-fold, to provide a single figure indicating readability for each character and to

prohibit traceability to specific OCR machines. The encoding plan

is given in Appendix D of the specifications covering the data

set, showing the relationship between the input (four categories

for each of three machines) and the final representation in one of

four categories.

6.4 Generation of separate Setup and Test Tapes

The final processing step resulted in the extraction of a ten-percent sample of the data base characters. This operation

was designed to provide an across-the-board sample of the data set

characters, to be useful for system checkout. Thus the Setup tape

contains approximately 3000 characters, selected as mostly

readable, however some non-readable characters are also present.

The remaining approximately 29 000 characters were recorded

as the four Test tapes in the data base.

-21-

6.5 Brief description of data set

The data set provides video information derived from scanning

individual character images on a 24 x 24 grid. A total of

approximately 32 000 characters are included, with an effective

spot size of 0.006 inch (0.15 mm). Output recordings are digitized into 16 levels.

The tapes are IBM-compatible, 9-track, 800 bpi, odd parity,

8-bit EBCDIC characters. All of the information pertinent to a single character is contained in a record of 1044 bytes. Each

record has two major sections of fixed length, covering its

originating mailpiece and other overall information in the address

data section of 316 bytes, and the specific character

identification and video information in the character data section

of 728 bytes. Because the address data section is included as part of each record, a compact printout of all known data

regarding any desired character is facilitated.

Detailed format and other information is given in a separate

publication, ref. (1).

7. Conclusions and recommendations

During the course of the work on the character image data set and

subsequently in the related project (covered in Part 2) which also

involved the same input material, it became possible to conduct a limited evaluation of the produced data base. Advantage was taken of

the opportunity to investigate the following topics:

1) The overall input/output fidelity, that is, the

relationship between true and indicated reflectance,

2) Whether the thickness of lines in characters

was altered by the scanning process, as evidenced

from an input/output comparison,

3) Typographic accuracy, both in the address contents

and perhaps more importantly, in the identification

of scanned characters.

While an exhaustive investigation was not possible, some conclusions

from the above subjects are given in Section 7.1 below.

Finally to conclude Part 1 of the report, recommendations are made

regarding 1) the removal of intrusions and 2) the possibility under

some conditions of converting the data set so as to be representative

of scanning with other spectral characteristics.

-22-

7.1 Factors affecting fidelity of input/output relationship

for reflectance of lines

7.1.1 Flare and halation

Practical scanning devices often differ from their laboratory

counterparts in the rendition of reflectance (gray level) of thin

lines forming the character shapes. The usual evidence is that as

the thickness of a dark line is reduced, it appears lighter, i.e.

loses contrast. While this is readily understandable when the

line is smaller than the nominal beam width, the effect may not

disappear completely even though the line thickness may be many

times the spot size. The problem is that the scanning spot is

rarely as well concentrated as would be desired.

The closest to ideal should be a laboratory ref 1 ectometer

having a well-defined aperture and carefully cleaned optical

elements. The latter is most essential, for dust on lenses can result in a condition of light scattering which allows

contributions from directions outside of those desired. Thus the

measured reflectance over some given aperture area can be

influenced by the "busy-ness" of the surrounding material. The

result is that the reflectance of the background paper appears to

drop as printed material is approached. Similarly when over a solid black zone, the reflectance will appear to rise near the

edges.

Scanning devices which use rows of photocells or which employ

moving apertures can be susceptible to the same problem. Lens

flare and dust on lenses and mirrors are likely to be problems

with mail processing OCR equipment, especially dust.

Scanners using a cathode ray tube have the additional problem

known as halation. It results from the fact that some of the

light emitted by the spot is reflected by the front glass-air

interface back onto the phosphor coating. This produces a weaklyglowing disc of light surrounding the beam. It is generally about

three-eighths of an inch (approximately one cm) in diameter and is

fairly uniform in intensity, but with a brighter ring at its outer

boundary. The total light in this disc ranges from 10 to 20

percent of the main spot. No practical method appears to

eliminate this halation in cathode ray tubes. Fiber optic face

plates, while effective, are prohibitively expensive.

Because the FOSDIC scanner used in the preparation of the

data base involves a cathode ray tube, it was deemed desirable to

evaluate the magnitude of the flare and halation effect present in

the data base. Such an evaluation consisted in comparing the

-2 3-

laboratory ref lectometer measurements with the output data for

exactly the same position on specific characters. From the video

printouts used for quality control, it was readily possible to

identify sufficient material to give a reasonable estimate of the

overall input/output fidelity. Since the ref lectometer had an aperture of 0.005 x 0.035 inch (0.12 x 0.9 mm), it was necessary

to derive an average reflectance from 24 output data points at

0.003 inch spacing. Because the most precise readings of data

were available at the scanner's output in 256 levels, these data were used for comparison. Readings were averaged, converted to

reflectance according to the procedure in Section 6.1 using

readings on the gray scale step wedge, and then compared with the

ref lectome ter measurements for the same area. Because the

information sought was for purely geometric factors, comparisons

were made primarily on black and gray lines spanning a wide range

of reflectance. Portions of characters were selected for a range

of line thickness and a minimum of nearby printed material.

The results of such a comparison are shown in Figure 7. The

dashed line at 45 dgreees is the calibration function, the

mathematically-forced agreement on the gray scale wedge. Points

have been plotted for a variety of printed lines ranging from

solid black to no black, i.e. the unprinted background of the

mailpiece card. The unbroken line in Figure 7 represents an approximate mean of the plotted points. It can be seen that the

indicated reflectance is slightly low (5 or 6 percent) at the high

end, with an opposite effect at the low end. Near zero "true"

reflectance, the output appears to be about 13 percent too high.

Both of these effects are to be expected, as was mentioned.

The slope of the unbroken line is less than unity, indicating

a loss in contrast in the overall process. This slope appears to

be in the order of .75 to .80. Thus the recorded scanner signals

in the data set show a light-to-dark excursion which is 75 to 80

percent of that which can be obtained from a laboratory re- flectometer. This loss can often be considerably higher for

practical scanning devices.

It may be worth noting that many of the points which are intermediate between the low and high extremes of reflectance were derived from mailpiece cards having glassine windows. Earlier

work on window materials had shown that the rise in low end

reflectance, and decrease in high end, was to be expected.

Measurements on window materials are covered in an NBS report of

1972, ref (3).

The source of the apparent thickening was believed to lie not

in the photographic resolution, but rather in a more complex

-24-

effect brought about by residual nonlinearity in the photographic

steps. Photographic resolution causes can be disqualified since

the loss in resolution was slight. As was mentioned in Section

4.2.4, the 1.1-mil lines and spaces (18 line pairs per mm) could

just be resolved, meaning that the thickening did not exceed 1.1

mil

.

The observed thickening of lines is instead believed

attributable to the residual non-linearity shown in Figure 6,

before application of the linearization process. In this process,

line reflectance responses were compared to those from the largearea step wedge responses. It is known that thickness changes can be introduced if the system uncorrected response (that shown in

Figure 6) departs from linearity. Such a condition can arise for

example when the uncorrected response for 50 percent reflectance

deviates from midway between that for 10 and 90 percent

reflectance. Then the scanning spot position for equal signal

will not be exactly at the half-on, half-off location at the edges

of the lines. Thus the apparent line width can depart slightly

from the true value.

7*1*2 Uniformity of measurement over scanned address area

An important characteristic in a scanning microdensitometer

is uniformity of optical efficiency over the total scanned area. For example if the system efficiency were found to show a 10-

percent reduction in sensitivity at the edges compared to the

center, measured reflectances would have the same degree of

uncertainty. Under this condition the indicated reflectance on a known uniform white card might be 90 percent at the center, but

only 81 percent at the edges of the scanned area. Such a variation therefore causes a position-dependent uncertainty in

indicated reflectance value.

In the arrangement employed for scanning to create the data

set, reflectance values for character signals were calibrated

through reference to those derived from the gray scale wedge along

the top of the scanning area. Because the characters were located

throughout the scanning area, a possible variability was introduced. Additionally, non-uniform lighting of the area viewed

by the microfilm camera could generate the same effect. For these

reasons the overall system uniformity was measured.

The test method consisted of microfilming a test card of 85

percent reflectance, then scanning at six sample positions over

the total scannable area. The variation was found to be

approximately +1,7 percent. It must be noted however that scanner

signals in the white and nearr-white region are effectively

^25-

expanded by the linearization procedure. Hence the above measure

sensitivity variation indicates that the output values in the dac.-. set nay have an uncertainty of as much as +2.2 percent due to

positional location in the address. The uncertainty in terms of

percentage reflectance is greatest in the representation of the

white paper stock and least for black ink.

7.2 Thickening or thinning of lines

The fidelity of rendition of line width was checked by

comparing measured line thicknesses with the scanned data. As wa^

the case with gray levels, the scanner output data furnished the

most precise indicator of system performance, since it resolved

256 levels of reflectance signal. Comparisons were carried out on lines of different widths and gray levels. Because of the work

entailed, these tests were conducted on only a limited basis.

Line thickness on input material was measured with a small

scaling magnifier, using the average of edge roughness as the

criterion to determine the thickness. At the output, line edges

were defined as those points having a threshold reflectance midway

between the smoothed lowest value over the printed line and

highest values on the paper away from the line. This 50-percent

criterion was chosen for its independence of the scanner spot

width. Using this criterion, line segments were analyzed in the

printouts of scanner data used for quality control.

The conclusion from these measurements showed a slight

tendency toward apparent thickening of lines. Very thin or gray

lines (9 to 10 thousandths of an inch (0.25 mm) 50^ reflectance)

were increased by about one thousandth. Thicker, blacker lines

(20 thousandths (0.5 mm) 20% reflectance) were found to show an apparent increase of 3 to U thousandths by the threshold

c riterion

.

7.3 Typographic accuracy

In each character record there is a reproduction of the source address on the mailpiece from which it was derived. This

material was added principally to provide context. While normal

care was used in the transcription of the address, a few examples

of typographic errors in the approximately 2200 mailpiece cards

have come to our attention. These errors should have no relation

to possible errors in character identification.

The accuracy of character identification, one of the critical

parameters in a data base, was promoted by verbal confirmation

between the operators during character scanning. Subsequent

-26-

verification was conducted on a sampled basis, by checking one character per mailpiece. While no errors have been discovered so far in this process, it cannot be guaranteed that errors of

character misidentif ication are completely absent.

7.4 Intrusion removal

In the preparation of the data set, no attempt was made to

eliminate intrusions from portions of adjacent characters when the

scanning raster of 0.144 inch square included such material.

However as an aid for researchers who wish to deal with isolated

character images, an intrusion code was included in the record for

each character. These codes were inserted by the machine operator

based upon visual observation of an enlarged video presentation.

Details of the coding are included in the accompanying

specification sheet, ref. (1). The actual implementation of

intrusion removal is left to the user.

7.5 Feasibility of conversion to other spectral regions

Conversion to other spectral responses should be feasible

under some conditions. The key would be the availability of

simultaneous reflectance measurements in two spectral regions, at

the same position on the address. It may be noted that spectral

conversion involves amplitude scaling but not positional shift.

For example it appears necessary to measure only two values near

the extreme conditions, such as with the scanning spot over

background paper for one and over solid inking for the other. The

reflectance values for the two spectral regions may then be

plotted on rectangular coordinates, such as "OCR-1 vs. Visible"

reflectance. Two points are thereby established. Since at other

positions over a character image, there is an area averaging of

paper and ink contributions under the measuring spot, a linear

relationship is reasonable to expect. Measurements bear out this

assumption to at least a first-order approximation. Thus it

should be possible to convert the signal value at each point in

the character image via a mathematical scaling during computer

processing. The result would be a data set representative of the

new spectral response.

As was mentioned, empirical readings of reflectance are required for the basic and converted spectral regions. The

feasibility examination was considerably assisted by the

availability of a prototype ref lec tometer developed commercially

under USPS sponsorship. Correlation between reflectances measured

over a full range of spot/ink coverage showed that the straightline interpolation resulted in agreement within about 5 percent

-27-

reflectance. Conversion was checked going from OCR-1 to Visible

and to Infrared.

While conversion thus appears possible when two colors, a paper and an ink, are involved, it cannot work when additional

colors are present. The basic assumption is made that the spot is

at any point receiving some proportionate sum of paper and ink in

the reflected light. The locus for converting values is

determined by the two sets of originally measured values. However

when an additional background color is introduced, as was the case occasionally in the test deck, there is no means for conveying the

necessary information about the relative proportions of the two

background colors. Hence, it should be recognized that the

proposed technique would be applicable only to simple combinations

of one background and one ink color.

-28-

Part 2 OCR Character Recognition Results

8. Ob] ect ive

The project objective was to generate a set of data on magnetic

tape, containing information on AOCK (Advanced Optical Character

Reader) recognition results on 110 000 characters from a 2100-piece

test deck of simulated mail. The desired data include whether 1) each

character was correctly read, 2) rejected as unreadable, 3) if

substituted, specific detail and 4) if expanded into multiple

characters, specific details. This classification by individual

recognition results was in contrast to the analysis performed in Part

1, where the interest was in whether or not the character was readable.

Part 2 was instead concerned with supplying the raw data from which

confusion matrices may be developed.

Determination of the apparent causes of the misreadings observed

was not within the scope of the project.

8.1 Summary of activity

The development of the OCR character recognition data set

involved the following major steps:

1) Selection of material

2) Evaluation of recognition results

3) Conversion to machine language

A) Computer processing, formatting

5) Preparation of documentation including

specifications describing the resultant

data set, ref (4)

r9. Selection of material

Input material was selected from the same test deck of simulated

mailpieces supplied by the USPS and used for the character image data

set reported on in Part 1.

The source material was typewritten in the majority, but with an appreciable quantity of printed oversized characters. Prior to

reproduction, many of the typewritten addresses were systematically

degraded through half-tone line screens. Overstrikes, obtained by

typing two characters in the same location, were also introduced. The

intent of the test deck was to span the range from readily readable to

-29-

plainly unreadable characters. As mentioned, these steps in the

production of the test deck had been performed earlier by a commercial

supplier

.

10 . Readability evaluation

This initial step, common to both data sets, was designed to

obtain a realistic evaluation of each character's recognition

experience. For this purpose, the mailpiece cards were put through

three large mailsorting OCR machines. The results from one of these,

Advanced OCR, (AOCR) was used for the project described herein. As

each card was processed by the AOCR, information was stored regarding

the machine's recognition. Subsequent printout furnished a hard copy

version of the recognition experience of some 110 000 characters. The

complex nature of the printout, plus the human analysis required for

character segmentation, dictated that the desired information could

best be obtained through visual analysis of the AOCR printout.

10. 1 Generation of printout work sheet

A sample work sheet is shown in Figure 8. The work sheet was prepared by printing out the contents of the address tapes

described in Section 2.1.1 of Part 1. The tape dump program was formatted so that two addresses were printed on a page, the text was spread out horizontally and underlines were placed under each

character in the address. As can be seen, the analyst's notes on character recognition results were entered in the underlined

spaces. This technique was chosen to minimize the possibility of

misplaced notation. There were approximately 1100 work sheet

pages produced to contain the listed addresses.

10.2 Analysis of AOCR printout

This activity was the major phase of the project. It was recognized that the AOCR printout contained all that could be

learned about character readability. A guiding rule in the

analysis and transcription was to preserve and carry along to the

next step as much information as possible about each character.

This can best be explained by first considering certain details of

the AOCR machine operation.

In the AOCR system, recognition of an input character is

performed simultaneously in two modes, alphabetic and numeric.

The results of both are shown in the data set, that is, the

alphabetic and the numeric choices are both included. In many

cases recognition was not accomplished and the machine rejected

the character for alphabetic and/ or numeric recognition. In

-30-

other cases there were misrecogni t ions , which were regarded as errors by substitution. Finally there were also occasions when no output character was indicated, because the reader did not detect

the input character. This was called a washout. The most common washouts were caased by the loss of a whole line, brought about by

extraneous printed material near the genuine address. This

resulted in the absence of a basis for decision.

A sample section of the AOCR printout is shown in Figure 9.

There are two lines of principal interest, labelled ALPHA and

NUMERIC. These contain the reader's decision on the best choice

of character identification, from alphabetic and numeric

repertories respectively. Under the ALPHA and NUMERIC lines there

are two pairs of lines; these represent the internal machine

symbol for the printed ALPHA or NUMERIC entries. These lower

lines were useful when the ALPHA or NUMERIC lines contained an asterisk indicating rejection. While the equipmenc manufacturer

indicated that the internal codes could be of only limited use, it was felt worthwhile to preserve the detail contained in these

codes

.

Besides these lines of data on the AOCR printout there are several others containing information primarily on the number of

characters in each line. These latter lines were not needed in

the analysis.

In the analysis and its concomitant encoding, the work, sheet

formed the master list. That is, it was considered necessary to

report the treatment given every character on the work sheet, but

no more. Material not included in the address and, consequently,

not appearing in the typed copy of address files would frequently

be found by the AOCR reader; such characters were ignored in the

analysis. This rule was set up so that the final data set could

be generated directly from the original typed address files.

In the interest of preserving word separation in the data

base, spaces and punctuation as typed were retained in the set.

The analysis itself was straightforward when there were no discrepancies in character count, i.e. none missing or expanded.

The analyst was required to note on the work sheet, at the

appropriate AL or NU line and character, whether the character was correctly read or not, using a check mark for the former. In cases of substitutions, the replacement character was written in.

When an asterisk appeared in the ALPHA line, the analyst was directed to write the internal code, such as 12, 13, 14 or 15. In

the NUMERIC line, most of the printed entries were asterisks;

-31- •

these were left blank in the work sheets to save labor. Various

other labor saving techniques were introduced, such as special

marking to indicate that entire words were correct.

About one-third of the addresses contained expanded

characters, with two and three apparent characters being indicated on the AOCR printout for one genuine input. Almost invariably

these were caused by oversize figures on the nailpiece cards.

Such expanded characters were segmented by the analyst as appeared

appropriate, sometimes taking into account the indicated numeric

interpretation. All of these data were noted on the work sheet

with bounding lines as needed. It was found that segmentation of

(expanded characters was quite laborious, as was to be expected.

The availability of the original mailpiece cards was helpful at

this stage.

Ot her aberrations such as dropped characters (washout) were

noted on the work sheet by selected codes.

1.

0

* 3 Transcription to machine language

A .keyboard typing system was employed to convert the data

fyom the worksheet into machine language. Insofar as possible,

steps were taken to minimize the amount of typing. The total

£,hara£ter content was approximately 110 000 characters; thus

typing two characters for each input (ALPHA and NUMERIC) meant

typing 220 000 characters, or the equivalent of a manuscript of 44

000 words^ The adopted technique was to use a remote terminal

device attached to a small computer.

Thg remote terminal- included a keyboard and a cathode ray

t&ibe for display. As the initial step the address tape was fed

-into the computer,. Addresses were formatted so that each complete

address was displayed, with a pointer underlining one character.

The purpose of the pointer was to indicate to the typist the

particular input character for which she was expected to type in

the ALPHA and NUMERIC entries from the worksheet. After the

worksheet data had been typed for an input character, a Transmit

button caused the typed AL and N'U entries to be joined to the

specific input character in the address. Additionally the pointer

pjpyed on tP the next character.

in the interest ©f reducing entry time, the underlining

ppint.gr was programmed to jump over punctuation and spaces in the

priginal address contents. This eliminated the need for a response frpm the typist for the blank remainders of lines in

which fhp address contained less than the maximum of 38

characters.

-32-

Keying conventions were developed for all of the special

conditions to be reported. These are listed in Table 2 below.

TABLE 2

Typing Codes for Transcription of Recognition Results

Reported character

on AOCR Printout

ALPHA line

Alpha (correct)

Alpha (incorrect)

* (12,13, 14 or 15)

Written character

on Worksheet

Typed character

at CRT

. (Period)

Same alpha character Same as left

as on AOCR printout

12,13,14 or 15 " (See note

// below)

$

Space (40)

None

NUMERIC line

Numeral (correct)

Numeral (incorrect)

*(10)

Space (AO)

None

Note = The characters "

-40 A

S

Same numeric

character as on AOCR printout

Blank

40

A

Space

- (Minus)

. (Period)

Same as left

Space

Space

- (Minus)

//, $ and % were obtained by

typing Shift 2, Shift 3, Shift $ and Shift 5 according to the information on the AOCR Printout.

When multiple output characters appeared in the AOCR

printout for one input character, each ALPHA and NUMERIC

pair was typed according to the above table. Thus if two

output characters were generated for one input, two ALPHA

-33-

and NUMERIC pairs were typed before the message was transmitted. Three or even four pairs were permitted, however

in these cases the information beyond two pairs was truncated at a later stage.

11 . Computer processing and formatting

Processing of the typed data resulted in formatted records on magnetic tape, one record of 720 characters for each mailpiece card. The precise layout of these records is covered in

a separate specification which is included with the data set,

ref (4). In brief, each record contains a Heading followed

by a Recognition Results section. The latter is a series of sixcharacter groups for each input character contained in the

address tapes. The first character in the group is a re- production of the original input from the mailpiece, the

second through the fifth are the AOCR reading data, and the

final character is a status flag or code to report on errors,

rejects, joined characters etc. In each record there are 3 (lines) x 38 (input characters per line) x 6 (output characters

for one input), or 684 characters of data on recognition results. The

remaining, initial 36 characters, include the heading data.

In the computer processing the action was to generate the six

character groups, one from each input character contained on the

address tapes. The recognition results were inserted into the

second through fifth byte positions, substantially as typed. The

major exception was for the typed period, which was the abbreviation

for correct reading. In the processing the period was replaced with

the original alphabetic or numeric character. Finally the sixth

byte, the status code, was generated automatically by the program

based upon logical comparisons of the data in the first five

byte positions.

This status code was employed to facilitate rapid search through the

tape with minimum programming effort by users. Thus it is possible to

extract only those characters having substitution errors, for example, by

searching on the basis of an "E" in the last position. Other possibilities

of status code usage are indicated in the summary tape description,

reference (4 ) .

The total number of records is greater than 110 000 by more than a factor of two. In the interest of complete context preservation and

uniform file length, the data set also includes the residual space

-34-

characters following the address characters in each line. Thus the data

set contains approximately 240 000 actual records, of which 110 000 are the

useful address characters, including embedded spaces and punctuation

between words.

12 . Acknowledgment

The authors wish to acknowledge the contribution of Miss Harriet

A. Baker for her painstaking analysis of the character recognition

results which form the reference data set in Part 2. Mention is due

also of Mrs. Betsey Heacock's careful transcription of the data into

the computer.

13. References ;

(

1) "Summary tape description, multilevel character data tapes

for computer evaluation of optical character recognition

techniques," June 1974, prepared by NBS to accompany data

set tapes.

2) Optical Character Reader Test Decks, Final Report, Control

Data Corp Rockville, Md. March, 1972 for USPS, Washington, D C

Vol. 1 & Vol. 2 Contract RER 143-71.

3) "Laboratory evaluation of effects of envelope windows on bar-code reading" NBS Report No. 10823, March 15, 1972.

4) "Summary tape description, OCR character recognition results,

data tape for evaluation of context processing" June 1975,

prepared by NBS to accompany data set tape.

USCOMM-NBS-DC -35-

APPENDIX

A. Notes on nicrof ilming and processing of 1'nvelopc Films

A. 1 Illumination

The illunination during microfilming employed conventional incandescent

lighting which was checked for uniformity within a few percent. In

order to provide as much tolerance as possihle for the overexposureunderdevelopment technique for enhancing the gray scale range, the

illumination was raised by a factor of 5 to 7 over normal levels. At

this high Intensity, it was found desirable for the operators to wear

.-dark glasses. Operators were also changed frequently during the

approximately AO hours of filming to reduce fatigue.

-A.. 2 Density and contrast control

The techniques used for extending gray-scale rendition were the

.^standard ones, namely choice of one of the fastest microfilms, followed

:by .overexposure and matching underdevelopment. By .these means the

:gamma (contrast -slope) of the ifilm was reduced from its usual 4 to 1.5.

While almost identical speed and contrast characteristics were obtained

on :test strips wLth diluted -normal developer and with less active

ccmttlnuous- tone -solutions, we preferred the latter as less prone to

rrapld exhaustion.

The design center for development control called for a density on

:the -negative of 1.25 for ;the image of the 85 percent reflectance chip.

Under these conditions, rgrrod .rendition from white to near-black

:r.efJLectances was found. At the extreme black end, the transparency of

;the resultant negative made it difficult to see ichips whose reflectance

-.wa-s .less than 10 per cent.

The films were processed at the Bureau of the Census, with a -developer normally used for low contrast motion -picture film.

Processing :took place in a small laboratory unit designed for microfilm

work, with the -result that the development time was considerably less

rthan normal for the solution employed. No replenisher was used; rather

:the developer was discarded after two -rails had :baen processed.

.Exhaustion was checked with rpre-exposed test strips which showed

megllglble lade .as lull .rolls .were developed . To rprodnce :the -required -positive oopies, :the :rolls of negatives

wjerre -printed onto conventional -microcopy rfllm by a commercial

laboratory. Optimum exposure In the printer was worked out through

5Submisslon of .test strips, .after which .the entire batch was printed.

There .was :a :slight Increase In oontrast produced by .the characteristic

30r£ '.the -print .film. As a ^result, _i.t .can be noted on the :films :that .the

-136-

high reflectance chips, 80 percent and above, are difficult to

distinguish individually. However this was considered an inevitable

consequence for keeping the maximum density (1.2 nominal) within the

useful region for film scanning devices.

Approximate linearity exists for the reflectance range from 15 to 75

per cent, allowing the user a wide region for the application of

thresholding techniques.

B. Calibrated values of test reflectance chips

Envelope and Address films

Chip No .

Measured Reflectance at 536nm

(in percent compared to

barium sulfated

12

3

4

5

A.O

5.8

12.0

17.4

24.1

6

78

9 10

29.0

33.9

41 .9

48.7

56.0

11

12

13

14

68.0

74.1

81.8

85.5

-37-

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DL f'T . O' COMM.

PIIM IOCRAPHIC DATA

SHEET

1. PI II H A I ION OK K I. I'OK I f.O.

JIB S IR 75-746

2. <«i» ( Accession

N„.

1 1 | I.I. AND SUM I I I Li- Preparation of Reference Data Sets for

Character Recognition Research

7. All I ICR'S)

M . t.p-i gpfnn r.rpe nough £ Lfl_h_C It M . McCabe

j[7M Kl ()HMIN(i OrU.ANT/AITON NAMI AND ADDRESS

3 . K c c i p i c n l ' * At t i: ssiiin

5. Public .»( ion I ) ji i

6. Performing Oij;jni2.iiiun I

8. Performing Orgjn. Report N

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project 'Task/ tt'ork Uni 4460492

11. Contrjci/Gr.mt No. Letter Agreement

I 12. Sponsoring Organization Name an 'J ( omplete Address (Street, City, State, ZIP)

U. S. Postal Service

11711 Parklawn Drive

Rockville, Maryland 20852

13. Type of Report i: Period Covered

Final Report

- - — . 14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less Inrtual summary of most significant information. If document includes a signiticant

bibliography or literature survey, mention it here.)

A reference data set contained on magnetic tape has been generated for

research in optical character recognition and related fields. The data

set contains video data in 16 levels for each point in a 24 x 24 scanning

grid, applied to approximately 30 000 characters. The input material, on some 2200 simulated address mailpieces, includes a range of character

quality from excellent to poor.

The data set was prepared by first microfilming the address fields and

printing positive transparencies. Then preselected characters were

scanned in the NBS FCSDIC. Through the use of calibrated gray scales

which were filmed and scanned along with the addresses, corrections were

applied to assure linearity of overall response.

A second reference data set was also prepared from the same input materia]

of simulated mailpieces. Through analysis of the recognition results

printed out during runs on one address reader, details of identification

on both alphabetic and numeric recognition modes were noted. These were

encoded into s i x- cha r a c t er groups on the data tapes, formatted to provide

one such group for each input character in the original addresses.

Recognition results are shown for approximately 110 000 input characters.

17. Kh\ WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the fust key word unless a proper

name; separated by semicolons ) . . . Character recognition; context research; data bases; optical character

recognition; pattern recognition; reading machines

18. AVAII.AIIILITY [^| Unlimited

CI ? For Official Distribution. Do Not Release to NTIS

( ! "r.let From Sup. ol Doc, U.S. (..ivernmcnt Printing Office

11 i-hinpton. D.C. 20 10?. SP < .1 Nm. < 1 1 IX I'r.ln 1 inn National 'lccliiiic.il lnfi-im.ll inn Service (NTIS)

SpmiffjrM, Virginia iVIVI

1°. SECURITY CLASS , (THIS REPORT)

UNCI. AS.S1FIF.D

21. NO. OF PACL^j

52

20. SI < L'RI'I'Y CLASS

(THIS PACE)

UNCI.A.ssn il.D

22. Piice

$ 4.25

CISC Ouu.OC