This work summarizes the results of the first Competition on Harvesting Raw Tables from Infographics (ICDAR 2019 CHART-Infographics). The complex process of automatic chart recognition is divided into multiple tasks for the purpose of this competition, including Chart Image Classification (Task 1), Text Detection and Recognition (Task 2), Text Role Classification (Task 3), Axis Analysis (Task 4), Legend Analysis (Task 5), Plot Element Detection and Classification (Task 6.a), Data Extraction (Task 6.b), and End-to-End Data Extraction (Task 7). We provided a large synthetic training set and evaluated submitted systems using newly proposed metrics on both synthetic charts and manually-annotated real charts taken from scientific literature. A total of 8 groups registered for the competition out of which 5 submitted results for tasks 1-5. The results show that some tasks can be performed highly accurately on synthetic data, but all systems did not perform as well on real world charts. The data, annotation tools, and evaluation scripts have been publicly released for academic use.

We present a model for recognizing typeset math formula images from connected components or symbols. In our approach, connected components are used to construct a line-of-sight (LOS) graph. The graph is used both to reduce the search space for formula structure interpretations, and to guide a classification attention model using separate channels for inputs and their local visual context. For classification, we used visual densities with Random Forests for initial development, and then converted this to a Convolutional Neural Network (CNN) with a second branch to capture context for each input image. Formula structure is extracted as a directed spanning tree from a weighted LOS graph using Edmonds' algorithm. We obtain strong results for formulas without grids or matrices in the InftyCDB-2 dataset (90.89% from components, 93.5% from symbols). Using tools from the CROHME handwritten formula recognition competitions, we were able to compile all symbol and structure recognition errors for analysis. Our data and source code are publicly available.

Online lecture videos are increasingly important e-learning materials for students. Automated content extraction from lecture videos facilitates information retrieval applications that improve access to the lecture material. A significant number of lecture videos include the speaker in the image. Speakers perform various semantically meaningful actions during the process of teaching. Among all the movements of the speaker, key actions such as writing or erasing potentially indicate important features directly related to the lecture content. In this paper, we present a methodology for lecture video content extraction using the speaker actions. Each lecture video is divided into small temporal units called action segments. Using a pose estimator, body and hands skeleton data are extracted and used to compute motion-based features describing each action segment. Then, the dominant speaker action of each of these segments is classified using Random forests and the motion-based features. With the temporal and spatial range of these actions, we implement an alternative way to draw key-frames of handwritten content from the video. In addition, for our fixed camera videos, we also use the skeleton data to compute a mask of the speaker writing locations for the subtraction of the background noise from the binarized key-frames. Our method has been tested on a publicly available lecture video dataset, and it shows reasonable recall and precision results, with a very good compression ratio which is better than previous methods based on content analysis.

Lecture videos are a valuable resource for students, and thanks to online sources they have become widely available. The ability to find videos based on their content could make them even more useful. Methods for automatic extraction of this content reduce the amount of manual effort required to make indexing and retrieval of such videos possible. We present a method that generates static image summaries of handwritten whiteboard content from lecture videos recorded with still cameras. We generate a spatio-temporal index for the handwritten content in the video, and we use it for temporal segmentation by detecting and removing conflicts between content regions. Resulting segments are used to produce key-frame based summaries. Our method has been tested on a video collection showing promising results for automatic lecture video summarization with good compression ratios and 96.28% recall of connected components in test videos.

Math-aware search engines need to support formulae in queries. Mathematical expressions are typically represented as trees defining their operational semantics or visual layout. We propose searching both formula representations using a three-layer model. The first layer selects candidates using spectral matching over tree node pairs. The second layer aligns a query with candidates and computes similarity scores based on structural matching. In the third layer, similarity scores are combined using linear regression. The two representations are combined using retrieval in parallel indices and regression over similarity scores. For NTCIR-12 Wikipedia Formula Browsing task relevance rankings, we see each layer increasing ranking quality and improved results when combining representations as measured by Bpref and nDCG scores.

Large data collections containing millions of math formulae in different formats are available on-line. Retrieving math expressions from these collections is challenging. Based on the notion that visually similar formulas are related, we propose a framework for appearance-based formula retrieval in two different modalities: symbolic for text documents and image-Based for videos.

When using a mathematical formula for search (query-by-expression), the suitability of retrieved formulae often depends more upon symbol identities and layout than deep mathematical semantics. Using a Symbol Layout Tree representation for formula appearance, we propose the Maximum Subtree Similarity (MSS) for ranking formulae based upon the subexpression whose symbols and layout best match a query formula. Because MSS is too expensive to apply against a complete collection, the Tangent-3 system first retrieves expressions using an inverted index over symbol pair relationships, ranking hits using the Dice coefficient; the top-k formulae are then re-ranked by MSS. Tangent-3 obtains state-of-the-art performance on the NTCIR-11 Wikipedia formula retrieval benchmark, and is efficient in terms of both space and time. Retrieval systems for other graphical forms, including chemical diagrams, flowcharts, figures, and tables, may benefit from adopting this approach.