Segmentation of heterogeneous document images : an ... - Tel

tel-00912566, version 1 - 2 Dec 2013
(a) 73.74% (b) 79.98%
Figure 3.6: Two documents that have obtained the lowest accuracy rate for
text/graphics separation. Black components are labelled correctly. Red components
should have been assigned a graphics label but they are incorrectly labelled as text.
Blue components on the other hand have text label in ground-truth, however they are
misclassified as graphics.
In the second part of the evaluation, we report the accuracy of text/graphics
separation per document. 78 documents from our own corpus are selected and
after applying text/graphics separation, each document obtains an accuracy rate
that indicates the percentage of components that are labelled correctly. The
average accuracy rate for 78 documents is 96.30% according to area weighted
match counting A criterion. Figure 3.6 displays two documents that have obtained
the lowest accuracy of 73.74% and 79.98%. In this figure all components
in black are labelled correctly. Red or blue components indicate that the label
was supposed to be graphics or text respectively, but they are labelled incorrectly.
The majority of errors are either due to misclassification of noise, punctuations
or part of drawings classified as text. The low graphics recall rates are
mostly due to broken drawings and the majority of them are corrected in postprocessing
stage. Figure 3.7 displays example of errors that occasionally happen
in documents.
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