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

tel-00912566, version 1 - 2 Dec 2013
Figure 2.3: Two documents in our corpus that exhibit variability of font sizes in
newspaper style documents.
lines are adaptable for detecting printed text lines.
Here are some challenges that arise in text line detection:
• Variability of font size is a challenge in some documents (e.g. newspaper
style). Most methods assume that the distribution of font sizes in
one page is Gaussian. As a result, they tune the parameters for the average
font size. This often leads to overlook large characters in the title or
errors when there are sudden changes in font sizes. Figure 2.3 illustrates
this problem clearly.
• Slanted text lines are straight text lines that are not aligned with the
x-axis. Most algorithms prefer to start with a skew correction for the
whole page and then proceed to detect text lines. However, this is still
a challenge when text lines with different slant angles are present on the
same page.
• Touching text lines frequently occur in text regions, especially in handwritten
manuscripts where text lines are located close to one another.
This situation is a challenge for most methods. Connected componentbased
methods that work their way by aligning and grouping connected
components together, fail because in the case of touching text lines, two
characters from two lines that have touched are registered as one large connected
components that is not in alignment with either of the text lines.
If not dealt with properly, this will lead to either under-segmentation of
two lines into one line, or over-segmentation of two different text lines into
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