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

is assigning a label to a region of the image, it tends to extract features based
on texture analysis or projection profiles.
The method we describe here is a hybrid approach for separating text from
graphics. It is designed to assign a label to one connected component but features
are gathered based on both the characteristics of the components and the
components in its neighborhood.
tel-00912566, version 1 - 2 Dec 2013
We consider 16 features as potential features for the purpose of separating
text and graphics components. Each feature may help to discriminate components
in a particular situation. The first three features are computed relative to
other components of a page. Using these three features, the aim is to estimate
how likely the current component is different from other components on the
same page in regard to its elongation, height or solidity. The rest of the features
are global features, extracted from all components of the pages from our training
dataset. Height and width of a component are equal to height and width
of the bounding box of the component. Elongation and solidity are defined as
follows:
and
solidity =
Considered features are:
elo =
min(height, width)
max(height, width)
Number of pixels of the component
height × width
• Log-normal distribution of 1/solidity 1 . For most of characters, the
number of black pixels divided by the area of their bounding box, namely
solidity, is located in a fixed range. This property does not hold on tables,
borders and many graphical drawings. Looking for outlier components
of the page regarding this criterion may help in classifying them as
non-textual components. Figure 3.3 shows histograms of 1/solidity and
log(1/Solidity) for text components on the whole corpus which visually
justify the use of Log-normal distribution.
solidity
σ √ 2π
(ln x−µ)2
exp− 2σ 2
where x is 1/solidity and µ and σ are the mean and standard deviation of
1/solidity’s natural logarithm for all connected components on the page.
• Log-normal distribution of 1/elongation 2 . Except for some characters
such as 1,l and I that resemble a very small rule line, the height
and width ratio of a character, namely elongation, is located roughly in a
1 LogNormalDist(1/solidity)
2 LogNormalDist(1/elo)
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