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

fixed range. When the elongation approaches one, it represents a square.
Most of characters have an elongation of about 0.57. However when the
value approaches to zero, it usually represents a rule line. Figure 3.4 shows
histograms of 1/elongation and log(1/elongation) for text components on
the whole corpus.
elongation
σ √ 2π
(ln x−µ)2
−
exp 2σ 2
where x is 1/elongation and µ and σ are the mean and standard deviation
of 1/elongation’s natural logarithm for all connected components on the
page.
tel-00912566, version 1 - 2 Dec 2013
• Log-normal distribution of height 3 . For pages that are written with
a single font size, heights are roughly equal. Even for handwriting with
connected scripts the width of CCs may be different but height values are
still the same. This feature is looking for outliers such as large graphical
elements and tables that have a considerably larger height compare to
other CCs on the page. Figure 3.5 displays histograms of height of text
components and its logarithm for components on the whole corpus.
1
(height)σ √ 2π
(ln x−µ)2
exp− 2σ 2
where x is the height of a component and µ and σ are the mean and
standard deviation of height’s natural logarithm for all components of the
page.
• Normalized X 4 and Y 5 coordinates of the component’s center.
These two features have a range between 0 and 1. They are simply the X
and Y parts of a component’s center, divided by the width and height of
the document image respectively. The reason behind using this feature is
that most of the time noisy components, borders and frames are situated
near the boundaries of a document. By themselves they do not provide a
direct solution for locating non-textual elements but a classifier can utilize
this information along side of other features to form boundaries in a feature
space that can better discriminate text and non-textual components.
• Logarithm of normalized height 6 and width 7 . These two features
are computed as follows:
3 LogNormalDist(height)
4 center.x/src.cols
5 center.y/src.rows
6 log(src.rows/height)
7 log(src.cols/width)
log
page’s height
component’s height
41