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DPRL CROHME 2014

Copyright (c) 2013-2014 Lei Hu, Kenny Davila, Francisco Alvaro, Richard Zanibbi

DPRL CROHME 2014 is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

DPRL CROHME 2014 is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with DPRL CROHME 2014. If not, see http://www.gnu.org/licenses/.

Contact:

• Lei Hu: [email protected]
• Kenny Davila: [email protected]
• Francisco Alvaro: [email protected]
• Richard Zanibbi: [email protected]

This document is about DPRL's submission for the CROHME 2014. CROHME is the abbreviation of Competition on Recognition of Online Handwritten Mathematical Expression

The handwritten mathematical expression is preprocessed and rendered to an image. Symbol segmentation considers strokes in time series, using a binary AdaBoost classifier to determine which stroke pairs to merge. Then for each stroke, we compute three kinds of shape context features (stroke pair, local neighborhood and global shape contexts) with different scales, 21 stroke pair geometric features and symbol classification scores for the current stroke and stroke pair. The stroke pair shape context features covers the current stroke and the following stroke in time series. The local neighborhood shape context features includes the current stroke and its three nearest neighbor strokes in distance while the global shape context features covers the expression. Principal component analysis (PCA) is used for dimensionality reduction. The details of the segmentation can be found in the paper Segmenting Handwritten Math Symbols Using AdaBoost and Multi-Scale Shape Context Features.

The symbol classifier uses a SVM with Gaussian Kernel trained for probabilistic classification for the symbol classification task. The feature vector used to describe each symbol contains a combination of general on-line features with some adaptations of off-line features. The on-line features used include the normalized length of the lines, number of traces, covariance matrix of the point coordinates, number of points with high variation in curvature and total angular variation used to draw each symbol. The off-line features include: normalized aspect ratio; the count, position of the first and position of the last times that traces intersect a set of lines at fixed horizontal and vertical positions (crossings); 2D fuzzy histograms of points and fuzzy histograms of orientations of the lines. All symbols are pre-processed in order to smooth the traces and reduce the amount of noise present on the symbol. More details about the symbol classifier can be found in the paper Using Off-line Features and Synthetic Data for On-line Handwritten Math Symbol Recognition.

The parser recursively: 1) groups vertical structures (e.g. fractions, summations and square roots), 2) extracts the dominant operator (e.g. fraction line) in each vertical group, and then 3) locates symbols on the main baseline, and on the main baselines in superscripted and subscripted regions by finding an MST defined over candidate symbol pairs with their associated classes and spatial relationship, and then 4) repeats the procedure in nested regions of vertical structures (e.g. fraction numerators and denominators).

The codes for the spatial relationship classifier are writeen in C++. All the other parts are written in Python. The version of Python we need is Python 2.7.3 or above.

The usage is: python DPRL.pyc DPRL_CROHME2014 <input_path> <output_path>

Both input_path and output_path are abosolute path. The input_path contains the xxx.inkml files need to be recognized and the output_path contains the recognition results xxx.lg without inherited relationships.

The input inkml file is in the format of CROHME and the description of the data file format can be found at CROHME data format. The output .lg file is label graph file and its format can be found at label graph file format. A Label Graph is a labeled adjacency matrix representation for a graph. More details about label graph and inherited relationships can be found in the paper Evaluating structural pattern recognition for handwritten math via primitive label graphs.

Library CROHMELib is needed to produce the .lg file. The details of CROHMElib can be found in CROHMELib document.