1 ETISEO: Video Understanding Performance Evaluation Francois BREMOND, A.T. Nghiem, M. Thonnat, V. Valentin, R. Ma Orion project-team, INRIA Sophia Antipolis, FRANCE

2 Outline Introduction ETISEO Project Video Data ETISEO Results Metric Analysis ETISEO General Conclusion

3 Introduction There are many evaluation initiatives with different objectives Individual works projects: CAVIAR, ILids, VACE, CLEAR, CANTATA,… Workshops: PETS, VS, AVSS (CREDS),… Issues: Not standard annotation (ground truth) Lack of analysis of Video Data which specific video processing problems a sequence contains how difficult these problems are Lack of analysis of metrics Numbers, base-line algorithm

4 ETISEO Project 2 years duration, from January 2005 to December 2006 To evaluate vision techniques for video surveillance applications. Goals: Unbiased and transparent evaluation protocol (no funding) Large involvement (32 international teams) Meaningful evaluation provide the strengths and weaknesses of metrics to help developers to detect specific shortcomings depending on –scene type (apron, building entrance etc.) –video processing problem (shadows, illumination change etc.) –difficulty level (e.g. strong or weak shadows)

5 Approach: 3 critical evaluation concepts Ground truth definition Rich and up to the event level Give clear and precise instructions to the annotator E.g., annotate both visible and occluded part of objects Selection of test video sequences Follow a specified characterization of problems Study one problem at a time, several levels of difficulty Metric definition various metrics for each video processing task Performance indicators: sensitivity, precision and F-score. A flexible and automatic evaluation tool, a visualization tool. ETISEO Project

6 4 Companies: - Barco - Capvidia NV - VIGITEC SA/NV - Robert Bosch GmbH 12 Academics: - Lab. LASL University ULCO Calais - Nizhny Novgorod State University - Queen Mary, University of London - Queensland University of Technology - INRIA-ORION - University of Southern California - Université Paris Dauphine - University of Central Florida - University of Illinois at Urbana-Champaign - University of Maryland - University of Reading - University of Udine ETISEO Project : Large participation (16 active international teams)

7 ETISEO : Video Data Large annotated data set 85 video clips with GT, organized into scene types : apron, building entrance, corridor, road, metro station, video processing problems : noise, shadow, crowd, … sensor types : one\multi-views, visible\IR, compression…

8 : Airport Video Data : Airport Silogic Toulouse – France Apron Multi-view

9 INRETS-LEOST Villeneuve d’Ascq – France : INRETS Video Data : INRETS Building Entrance Car Park Light Changes

10 : CEA Video Data : CEA Street Corridor Video Type & Quality

11 : RATP Video Data : RATP Subway People Density

12 Detection of physical objects ETISEO : Results 16 Teams Detection rate Evaluation on 6 videos

13 Tracking of physical objects ETISEO : Results Detection rate Teams

14 ETISEO: Results Good performance comparison per video: automatic, reliable, consistent metrics: 16 participants: 8 teams achieved high quality results 9 teams performed event recognition 10 teams produced results on all priority sequences Best algorithms: combine moving regions and local descriptors A few limitations: Algorithm results depend on time processing (RT), manpower (parameter tuning), previous similar experiences, learning stage required or not…: questionnaire Lack of understanding of the evaluation rules (output XML, time-stamp, ground truth, number of processed videos, frame rate, start frame…) Video subjectivity: background, masks, GT (static, occluded, far, portable, contextual object, event) Many metrics and evaluation parameters Just evaluation numbers, no base-line algorithm Need of two other analyses: 1. Metric Analysis: define for each task: Main metrics: discriminate and meaningful Complementary metrics: provide additional information 2. Video Data Analysis: impact of videos on evaluation define a flexible evaluation tool to adapt GT wrt videos

15 Metric Analysis : Object detection task Main metric: Number of objects Evaluate the number of detected objects matching reference objects using bounding box Unbiased towards large, homogenous objects Difficult to evaluate object detection quality Complementary metric: Object area Evaluate the number of pixels in reference data that have been detected Evaluate the object detection quality Biased toward large, homogenous objects

16 Metric Analysis : Example (1) Sequence ETI-VS2-BE-19-C1 has one big object (car) and several small and weakly contrasted objects (people)‏ Algorithm 9 correctly detects more objects than algorithm 13 (metric: Number of objects)‏ F-Score Algorithm F-Score Algorithm Performance results using the metric “number of objects”

17 Metric Analysis : Example (2) Using metric Object area, biased toward big object (car): algorithm 13 cannot detect some small objects (people), algorithm 9 has detected difficult objects at low precision. Metric Object area is still useful: it differentiates algorithms 1 and 9: both are good at detecting objects but algorithm 1 is more precise F-Score Algorithm F-Score Algorithm Performance results using the metric “object area”

18 Metric Analysis : Advantages & Limitations Advantages : various metrics for every video processing task. analysis of the metric strengths and weaknesses and how to use them. insight into video analysis algorithms: for example, shadows, merge Still some limitations : Evaluation results are useful for developers but not for end-users. Ok, not a competition nor benchmarking But difficult to judge if one algorithm is good enough for a particular application, or type of videos.

19 ETISEO limitations: Generalization of evaluation results is subjective : comparing tested and new videos Selection of videos according to difficulty levels is subjective Videos have only qualitative scene description: eg. strong or weak shadow Two annotators may assign 2 different difficulty levels One video may contain several video processing problems at many difficulty levels The global difficulty level is not sufficient to identify algorithm's specific problems for improvement ETISEO : Video Data Analysis

20 Objectives of Video Data Analysis : Study dependencies between videos and video processing problems to Characterize videos with objective difficulty levels Determine algorithms capacity in solving one video processing problem. Approach: To treat each video processing problem separately Define a measure to compute difficulty levels of videos (or other input data) Select videos containing only the current problems at various difficulty levels For each algorithm, determine the highest difficulty level for which this algorithm still has acceptable performance. Approach validation : applied to two problems Detection of weakly contrasted objects Detection of objects mixed with shadows Video Data Analysis

21 Video Data Analysis : Detection of weakly contrasted objects Video processing problem definition : the lower the object contrast, the worse the object detection performance For one algorithm, determine the lowest object contrast for which this algorithm has an acceptable performance Issue: one blob may contain many regions at several contrast levels

22 Video Data Analysis : conclusion Achievements: An evaluation approach to generalise evaluation results. Implementation of this approach for 2 problems. Limitations: Need to validate this approach for more problems. Works well if the video contains only one problem. If not, detects the upper bound of algorithm capacity. The difference between the upper bound and the real performance may be significant if: The test video contains several video processing problems The same set of parameters is tuned differently to adapt to several dependent problems

23 General Conclusion Achievements: Good performance comparison per video: automatic, reliable, consistent metrics. Emphasis on gaining insight into video analysis algorithms (shadows, occlusion,..) A few limitations: Data and rule subjectivity: background, masks, ground truth,… Partial solutions for Metric and Video dependencies Future improvements: flexible evaluation tool Given a video processing problem: Selection of metrics Selection of reference videos Selection of Ground Truth : filters for reference data, sparse GT for long videos ETISEO’s video dataset and automatic evaluation tools are publicly available for research purposes:

24 At each contrast level, the algorithm performance is x/m x: number of blobs containing current contrast level detected by a given algorithm m: number of all blobs containing current contrast level Algorithm capacity: the lowest contrast level for which algorithm performance is bigger than a given threshold Video Data Analysis : Detection of weakly contrasted objects

25 Video Data Analysis : Detection of weakly contrasted objects Error rate threshold to determine algorithm capacity: 0.5