3. Deciding whether Optical Character Recognition is feasible
(PDF document) created for the Oxford University Digital
Library
www.odl.ox.ac.uk/papers/OCRFeasibility_final.pdf
Measuring Mass Text Digitization Quality and Usefulness:
Lessons Learned from Assessing the OCR Accuracy of the
British Library's 19th Century Online Newspaper Archive
www.dlib.org/dlib/july09/munoz/07munoz.html
www.impact-project.eu
6. Evaluating OCR accuracy is about more than just
character to character accuracy rates
Character accuracy rates are misleading
(more later…)
It is also about assessing the functionality enabled
through the OCR’s output
Search accuracy
Volume of hits returned
Ability to structure searches and results
Accuracy of result ranking
Amount of correction required to
achieve the required performance
7. Consider this scenario:
1,000 words with 5,000 characters
(an average of 5 per word) excluding spaces
90% character accuracy means:
4,500 characters correct
Possibly a maximum 900 words correct (90%)
Possibly a minimum 500 words correct (50%)
Reality is somewhere in between
Depending on the number of “significant
words” the search results could still
be almost 100% or near zero
8.
9. 100
90
80
70
60
50
1801
1810
1820
1830
1840
1850
1860
1870
1880
1890
1900
characters words
words with capital letter start significant words
Poly. (characters) Poly. (words)
Poly. (significant words) Poly. (words with capital letter start
10.
11.
12. OCR Results
% characters % words correct No. of corrections
OCR Engine correct
FineReader 91.1 70.9 110
PrimeOCR 93.95 79.1 79
Total number of characters = 2109
Total number of words = 379
I am petfood, God toil! uttedy-toverthroW, at feaft; $gy abafe
Men's affections tp; and seal for all Party-making Notions
amdngft CfiriftiansybefGieirie will raife his,Church to that prof-
perous, flourilhing State prophefied of, and prOmifed in the
Scrip* tures. There mult be more Love, and Charity, and
Unanimity amongft Chriftians,.
13.
14. OCR Results
% characters % words correct No. of corrections
OCR Engine correct
FineReader 73.7 57.5 31
PrimeOCR 75.9 62.37 28
Total number of characters = 411
Total number of words = 73
A THEATRE
erein be reprc-fented as wel the miferies &
calamities tijat foiioto tht too*
e^jr alfo the greate toyts and
plefures tobtcf) tbe fatrfc faltooenio^
An Argument both profitable and
dele&able, to all that finccrcly
loue the word of Codt'.
*Deuifedby S. hhnv&n~ derlS^oodt.
s 3^ Scene and allowed according to the order
appointed.
, ^ Imprinted at London by Henry Bynncman*
Anno Domini.
CVM PHIT