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

detection and we conclude that the text line detection algorithm by Vassilio Papavassilious
[75] is the most effective among the others. The original method
overlooks line detection in side notes, but being the best among the many and
the fact that we have already separated problematic areas such as side notes,
we adopt this method for the benefit of our own. Detailed explanation of this
method is chapter 5.
The final stage of the system is to group text lines into paragraphs. In
chapter 6 we propose a method based on a trainable binary tree model that
maximize the probability of preserving groups of lines using a goodness criterion
for paragraphs.
A brief outline of these processes is given here.
tel-00912566, version 1 - 2 Dec 2013
• Image binarization is the process that converts a given input gray-scale
image into a bi-level representation. In our case, pixels that belong to text
characters are assigned a value of 0 and pixels of non textual components
and background have a value of 1.
• Connected components analysis is the process of extracting and labeling
connected components from an image. In our case, all pixels of
text and non-text elements that are connected and have the same value
are extracted and assigned to a separate component.
• Noise removal tries to detect and remove noise pixels from the document
image. At this stage we only remove components that contain less than
a predefined number of pixels. The exact number of pixels can only be
determined through trial and error. A large number may remove points,
diacritics and punctuation marks. On the other hand, a small number
may not remove some dust and speckles from the scene.
• Text/Graphics separation is the process that classifies each component
into being part of text or graphics.
• Text region detection is the process that separates homogeneous regions
of text that belong to separate columns. It is also responsible for
separation of side notes from the main text region.
• Text line detection is the process that finds text lines inside every text
region. It is also responsible for breaking characters that are touched from
two adjacent lines and have formed a single component incorrectly.
• Paragraph detection is the process that groups text lines into paragraphs
based on their indentations and geometry.
1.4 Contribution of this dissertation
The main contributions that are presented in this dissertation are:
1. A new hybrid method for text/graphics separation. Figure 1.2 shows the
ability of our text/graphics separation method in segmenting a document
5