 Research
 Open access
 Published:
Benchmark for anonymous video analytics
EURASIP Journal on Image and Video Processing volumeÂ 2021, ArticleÂ number:Â 32 (2021)
Abstract
Outofhome audience measurement aims to count and characterize the people exposed to advertising content in the physical world. While audience measurement solutions based on computer vision are of increasing interest, no commonly accepted benchmark exists to evaluate and compare their performance. In this paper, we propose the first benchmark for digital outofhome audience measurement that evaluates the visionbased tasks of audience localization and counting, and audience demographics. The benchmark is composed of a novel, dataset captured at multiple locations and a set of performance measures. Using the benchmark, we present an indepth comparison of eight opensource algorithms on four hardware platforms with GPU and CPUoptimized inferences and of two commercial offtheshelf solutions for localization, count, age, and gender estimation. This benchmark and related opensource codes are available at http://ava.eecs.qmul.ac.uk.
1 Introduction
Digital outofhome advertisement is rapidly growing thanks to the availability of affordable, internetconnected smart screens. Anonymous video analytics (AVA) aims to enable realtime understanding of audiences exposed to advertisements in order to estimate the reach and effectiveness of each advertisement. AVA ensures the preservation of the privacy of audience members by performing inferences and aggregating them directly on edge systems, without recording or streaming raw data (Fig.Â 1).
AVA relies on person detectors or trackers to localize people and to enable the estimation of audience attributes, such as their demographics. AVA should produce accurate results, be robust to environmental variations and varying illumination. While wellestablished performance measures exist to evaluate generic computer vision algorithms [1,2,3,4], these measures do not take into account the desirable features of AVA for outofhome advertisement, such as the opportunity for a person to see the advertisement. In fact, multiple datasets exist to benchmark detection [5, 6], tracking [7,8,9,10,11] and reidentification algorithms [12]. Further datasets include KITTI [5], which focuses on autonomous driving, and Common Objects in Context (COCO) [6], which covers object detection, segmentation, and captioning. Moreover, the robust vision challenge [13] evaluates scene reconstruction, optical flow, semantic and instance segmentation, and depth prediction tasks, the visual object tracking benchmark [10, 11] compares singleobject tracking algorithms and the multipleobject tracking benchmark [7,8,9] compares multipleobject trackers. These benchmarks and datasets are designed for scenarios that differ from those for digital outofhome advertisement and their annotations lack relevant information, such as demographics and attention of the audience, for assessing AVA algorithms.
Because of the growing importance of digital outofhome advertisement and the lack of a standard evaluation protocol, in this paper we present the benchmark for anonymous video analytics^{Footnote 1}. This work is the first publicly available benchmark specifically designed to evaluate AVA solutions. The benchmark includes a set of performance measures specifically designed for audience measurement, an online evaluation tool, a novel fully annotated dataset for digital outofhome AVA, and opensource baseline algorithms and evaluation codes. The dataset annotations include over a million localization bounding boxes, and age, gender, attention, pose, and occlusion information. We also benchmark eight baseline algorithms: two face detectors, two person trackers, two age estimators, two gender estimators; and two commercial offtheshelf solutions.
The paper is structured as follows. SectionÂ 1.1 introduces the main definitions of the work and describes the proposed analytics for AVA; Sect.Â 1.2 presents the performance measures used for benchmarking; Sect.Â 2 describes the detection, tracking, age, and gender estimation algorithms; Sect.Â 3 introduces the proposed dataset and its annotation; Sect.Â 4 presents the benchmarking results; and Sect.Â 5 summarizes the findings of the work.
1.1 Analytics
Let a digital signage be equipped with a system and a camera. The system is a computer that manages the advertisement playback and processes the video of the surroundings of the signage captured by the camera. Let the video \({\mathcal {V}} = \{ I_{t}\}_{t=1}^{T}\) be composed of T frames \(I_{t}\), each with frame index t. We consider the following attributes about the people in the video: count, age, and gender (see Fig.Â 2). To enable the estimation of the above attributes, we also consider the localization of people in \({\mathcal {V}}\), namely their position and dimensions in \(I_{t}\). We consider a person in \(I_{t}\) to have opportunity to see (OTS) the signage when their face is visible from its left profile to its right profile, and the person is not heading opposite to the location of the camera, as shown in Fig.Â 3. We consider only the attributes of people with OTS.
Let the estimated location and dimensions of person \(j \in {\mathbb {N}}\) with OTS in \(I_{t}\) be represented with a bounding box \({\hat{\mathbf {d}}}_t^j =[x,y,w,h]\), where \({\mathbb {N}}\) is the set of the natural numbers. The bounding box is defined by the horizontal, x, and vertical, y, image coordinates of its topleft corner, and by its width, w, and height, h. The location of person j, \({\hat{\mathbf {d}}}_t^j\), may be represented by their face or their body, and can be estimated with a detection or tracking algorithm. While with a detector, the index j may change over time (i.e.,Â the index j is not related to the identity of the person), trackers aim to maintain the index j consistent over time.
Localization algorithms enable the estimation of the number of people with OTS (counting) at time t, \(n_t \in {\mathbb {N}}\), and trackers enable the estimation of the number of unique^{Footnote 2} cumulative people with OTS within a time window between \(t_1\) and \(t_2\), \(n_{t_1:t_2} \in {\mathbb {N}}\).
If \({\mathcal {A}}\) is a set of age ranges, an age estimation algorithm is expected to determine the age, \(a_t^j \in {\mathcal {A}}\), of a person with OTS, \({\hat{\mathbf {d}}}_t^j\), with \({\mathcal {A}}\) defined as:
These age ranges have been selected as they are commonly used in audience analytics.
A gender estimation algorithm determines the gender, \(g_t^j \in {\mathcal {G}}\), of each detected person with OTS, \({\hat{\mathbf {d}}}_t^j\), where
is the set of possible classes.
In summary, for each person j with OTS, an AVA solution is expected to produce at each time t: j, the person index (for trackers, the tracking identity consistent throughout \({\mathcal {V}}\)); \({\hat{\mathbf {d}}}_t^j\), the estimated location of the face and/or body;
\({\hat{a}}_t^j \in {\mathcal {A}}\), the estimated age; and \({\hat{g}}_t^j \in {\mathcal {G}}\), the estimated gender.
1.2 Performance measures
We introduce a set of performance measures for assessing the accuracy of localization, counting, age and gender estimation. These measures, which are concise and easy to understand by a broad community, enable the evaluation and comparison of AVA algorithms.
Localization
We evaluate the localization performance based on precision (\(\textit {P}\)), recall (\(\textit {R}\)), and F1score (\(\textit {F}\)) [4], which are defined based on true positives (TP), false positives (FP), and false negatives (FN). Precision (\(\textit {P}\)) is the ratio between correct estimations and the total number of estimations. Recall (\(\textit {R}\)) is the ratio between correct estimations and the total number of actual occurrences. F1score (\(\textit {F}\)) is the harmonic mean of \(\textit {P}\) and \(\textit {R}\).
For localization, we define TP, FP, and FN based on the intersection over union (IOU) operator between estimations, \({\hat{\mathbf {d}}}^j_t\), and annotations, \(\mathbf{d} ^j_t\):
where \(\cap\) and \(\cup\) are the intersection and the union operators, and \(\text {IOU} \in [0,1]\). An example for face localization, with highlighted TP, FP and FN detections is given in Fig.Â 5.
We consider the variation of R for different personâ€“signage distances. Let \(A(\cdot )\) be a function that computes the area in pixels for bounding box \(\mathbf{d} _t^j\), and \(p_{\mathrm{dist}}^{a}\) be the ath percentile of all the bounding boxes in the video. We define two bands for the personâ€“signage distance, namely close when \(A(\mathbf{d} _t^j) \ge p_{\mathrm{dist}}^{50}\) and far when \(A(\mathbf{d} _t^j) < p_{\mathrm{dist}}^{50}\). We assume that people closer to the camera are annotated by a larger bounding box than for those who are farther.
We also consider the variation of R in presence of occlusions. Let \(o_t^j \in \{{\text{nonoccluded}}, {\text{partially occluded}}, {\text{heavily occluded}}\}\) be the annotated occlusion. The three occlusion bands are nonoccluded when the annotation is not occluded; partially occluded when the annotated area is occluded less than 50%; and heavily occluded when the annotated area is occluded more or equal than 50%.
Note that we only report R, and not P, for personâ€“signage distance and occlusion as false positives (necessary to compute P) cannot be unequivocally estimated when the annotations are divided in regions such as far/close (for distance) or nonoccluded/partially occluded/heavily occluded (for occlusion). For instance, a far/close estimation might not match with any far/close annotation but this does not necessarily imply to be a false positive as it might be matching with a close/far annotation.
Counting
We quantify the performance of the localization algorithms for the task of people counting with the following performance measures: mean opportunity error (MOE), cumulative opportunity error (COE), and temporal cumulative opportunity error (TCOE).
The mean opportunity error (MOE) quantifies the ability of an algorithm to count people with OTS at a specific time t, \({\hat{n}}_t\), and it is calculated with respect to the actual number of people with OTS at t, \(n_t\):
\(\text {MOE} \ge 0\) (Fig.Â 4c) and its optimal value is \(\text {MOE}=0\). We analyze how MOE varies with the personâ€“signage distance, as in localization, and when the input video frame rate is reduced. We show a visual sample of MOE in Fig.Â 5.
The cumulative opportunity error (COE) quantifies the ability of an algorithm to count unique people with OTS and it is calculated with respect to the actual cumulative number of people with OTS for the whole video, \(n_{1:T}\):
where \(\text {max}(\cdot )\) is the max operation. \(\text {COE} \ge 0\) and its optimal value is \(\text {COE}=0\). This performance measure is normalized with respect to the actual cumulative number of people; therefore, COE indicates the ratio of error with respect to the actual cumulative number of people.
The temporal COE (TCOE) quantifies the ability of an algorithm to count unique people with OTS over temporal segments of generic duration (e.g.,Â 10s duration), and it is calculated with respect to the cumulative number of unique people with OTS:
where \({\mathcal {T}}_{D,T}=\{1,2,3,\dots ,TD\}\) is the set of the initial frame of each segment, \(D < T\) is the duration in frames of the segments, and \({\mathcal {T}}_{D,T}\) is the total number of segments. We consider values that correspond to the typical duration of digital outofhome advertisements \(D=\{10,20,30,60,90,120\} \, \gamma\), where \(\gamma\) is the video frame rate inÂ fps (i.e.,Â segments of 10, 20, 30, 60, 90, 120s durations). \(\text {TCOE}\) considers all possible Dframe segments within the video. We show an example for 10second segments in Fig.Â 6. \(\text {TCOE}_{D,{\mathcal {T}}} \ge 0\) and its optimal value is \(\text {TCOE}_{D,{\mathcal {T}}}=0\). Note that when \(D=T\), TCOE equals COE.
To quantify whether algorithms estimate all people in the field of view but fail to only estimate the ones with OTS, we define two accessory measures, mean people error (MPE) and cumulative person error (CPE). If \(p_t\) is the number of people at t and \(p_{1:T}\) is the number of people in the whole video, then
and
Attributes
We compute the perclass precision, recall, and F1score for age and gender estimation. We consider the variation of F for different personâ€“signage distances and for different occlusion levels.
We give now a few examples of the definitions of TP, FP, and FN for each attribute. For age estimation and the class [19,34], a TP is a correct age estimation. To relax the hardness of the age ranges, we consider overlapping age ranges with Â± 2 years, as shown in Fig.Â 7 (e.g., an estimation of a person of 17 years will be a true positive if the actual age of the person is in [0,18], or [19,34]); a FP is an incorrect age estimation for a person from another ageclass; and a FN is an incorrect estimation of the age of a person that belongs to the class. For gender estimation and the class female, a TP is a female estimated as female; a FP is a male estimated as female; and a FN is a female estimated as male.
For algorithms able to output unknown as a possible class, the corresponding estimations will contribute neither as TP, FP nor FN. We show an example of attribute evaluation in TableÂ 1.
2 Methods
Algorithms must be accurate and perform in realtime for being suitable to generate reliable and useful AVA. Therefore, we select algorithms for benchmarking that obtain close to stateoftheart results, that are causal (i.e., they only need past and present information), and that are able to perform close to realtime in the defined settings. We select algorithms that are compatible with GPU and OpenVINO^{Footnote 3} optimization for fast CPU computation.
We use RetinaFace [14] and Joint Face Detection and Alignment using Multitask Cascaded Convolutional Networks (MTCNN) [15] as detection algorithms; Simple Online Realtime Tracking with a Deep Association Metric (DeepSORT) [16], and Towards RealTime MultiObject Tracking (TRMOT) [17] as trackers; and FaceLib [18] and Deep EXpectation of apparent age from a single image (DEX) [19] as age and gender estimators. In addition to the above baseline algorithms, we benchmark two commercial solutions, Commercial1 (C1) and Commercial2 (C2), which we maintain anonymous. Localization, age, and gender estimation algorithms for AVA are described next and summarized in TableÂ 2.
AlgorithmÂ 1 (A1), RetinaFace [14], is a face detector with a singlestage pixelwise dense localization at multiple scales that uses joint extrasupervised and selfsupervised multitask learning. The algorithm predicts a face score, face box, five facial landmarks, and their relative 3D position, using input images resized to a resolution of \(640 \times 640\) pixels. The algorithm is trained on the WIDER FACE dataset [20].
AlgorithmÂ 2 (A2), MTCNN [15], is a face detector with a cascaded structure and three stages of deep convolutional networks that use the correlation between the face bounding box and the landmark localization to perform both tasks in a coarsetofine manner. The first stage is a shallow network that generates candidate windows. The second stage rejects false positive candidate windows. The third stage is a deeper network that outputs the locations and facial landmarks. The learning process uses an online hard sample mining strategy that unsupervisedly improves the performance. The algorithm is trained on the WIDER FACE dataset [20].
AlgorithmÂ 3 (A3), DeepSORT [16], is a multiobject tracker that combines the detector YOLOv3 [21] and the tracker SORT [22]. YOLOv3 detects the body of people with a single neural network that divides the image into regions and predicts bounding boxes and probabilities for each region. These bounding boxes are weighted by the predicted probabilities. The predictions are informed by the global context of the image. With respect to the tracking module, DeepSORT uses Kalman filter and the Hungarian algorithm for performing association of detections over time. In addition, DeepSORT employs a convolutional neural network, trained to discriminate people, that combines appearance and motion information.
AlgorithmÂ 4 (A4), TRMOT [17], is a multiobject tracker based on the Joint Detection and Embedding (JDE) framework. JDE is a singleshot shared deep neural network that simultaneously learns detection and appearance features of the predictions. The algorithm is based on Feature Pyramid Network [23] that makes predictions at multiple scales. Then, embedding features are upsampled and fused with the feature map from higher feature maps levels by using skip connections to improve the tracking accuracy for people far from the camera (i.e.,Â small bounding boxes). The JDE framework learns to generate predictions and features simultaneously.
AlgorithmÂ 5 (A5), FaceLib [18], is an opensource repository for face detection, facial expression recognition, and age and gender estimation. The age and gender estimation modules use as input the true positive detections generated by RetinaFace (A1), and they use a ShuffleNet V2 with 1.0x output channels [24] as architecture. FaceLib is trained on the UTKFace dataset [25].
AlgorithmÂ 6 (A6), DEX [19], estimates the apparent age and gender using as input the true positive detections generated by RetinaFace (A1). DEX uses an ensemble of 20 networks on the detected face and it does not require the use of facial landmarks. This work introduces and uses the IMDBWIKI, a large public dataset of face images with age and gender annotations.
Commercial offtheshelfÂ 1 (C1) is composed of a frontal face detector based on a cascade detector that uses a variety of grayscale local features, a tracker designed for frontal, eyelevel images; and a gender and age classifier based on regression trees.
Commercial offtheshelfÂ 2 (C2) uses a tracker based on a Kalman Filter for tracking people specifically designed to be robust to occlusions; and a gender and age classifier based on deep learning.
We employ A1â€“4 and C12 to estimate the instantaneous and cumulative number of people with OTS. The instantaneous number of people at t is estimated as the number of detections/tracks at the current time. The cumulative number of people between any two instants, \(t_1\) and \(t_2\), is estimated as the number of unique identities j during the considered time segment. Detectors (A1â€“2) simply assign a new identity to each detection without considering temporal relationships, thus producing an overcount. As trackers require detectors and a temporal association of detections mechanism to prevent multiple counts of the same person over time, in general trackers require more computational resources than detectors. Besides, trackers (A3â€“4) use person detectors (as opposed to face detectors), therefore trackers may not have skills to differentiate people with OTS from those who do not have OTS.
We make the codes and pretrained model weights of all baseline algorithms available at the project website. Without altering the core of the original algorithms, we integrate changes to ensure that every algorithm processes the videos and generates the outputs following the same procedure. The codes for all baseline algorithms have been modified to enable both GPU (NVIDIA inference) and CPU (OpenVINO^{Footnote 4} inference) computation in PyTorch (TableÂ 2).
3 Dataset
3.1 Videos
The dataset was collected in settings that mimic realworld signageâ€“camera setups used for AVA. The dataset is composed of 16 videos recorded at different locations such as airports, malls, subway stations, and pedestrian areas. Outdoor videos are recorded at different times of the day such as morning, afternoon, and evening. The dataset is recorded with Internet Protocol or USB fixed cameras with wide and narrow lenses to mimic realworld use cases. Videos are recorded at 1920 \(\times\) 1080 resolution and 30Â fps. The dataset includes videos of duration between 2 minutes and 30 seconds, and 6 minutes and 26 seconds, totaling over 78 minutes, with over 141,000 frames. The videos feature 34 professional actors with multiple ethnicities, with ages from 10 to 80, and including male and female genders. People have been recorded with varied emotions while looking at the signage. A sample frame of each location is shown in Fig.Â 8. We show sample frames with a reduced number of people for facilitating the visualization of the background. For the mall location, two videos are at different times: indoors (Mall1/2) and outdoors (Mall3/4).
3.2 Annotations
A professional team of annotators used the Intel Computer Vision Annotation Tool [26] from OpenVINO ecosystem to fully annotate all videos with the following attributes (Fig.Â 9): bounding boxes for face and body of the people, identity, age, gender, attention, pose, orientation, and occlusions. Annotations were generated for every keyframe. The keyframes were selected depending on the behavior and the location with respect to the camera of the person to be annotated. People closer to the camera (or moving faster) were annotated more often than people that are farther away (or moving slower). Interkeyframes annotations were generated using linear interpolation. The annotations were validated by expert annotators that checked the consistency of personface groups, person identity within a video and across videos, and an individual visual inspection of each of the annotated attributes. For preventing the analytics to focus on very small (far from signage) people, who are likely to not have OTS, and to simplify the annotation process, we define a region in some scenarios where people are omitted, and thus not annotated. We refer to these regions as ignore area, shown as a white shading in Fig.Â 8. Estimations within the ignore areas are also omitted. The annotations maintain the identity of each person throughout the same video, even if the person exits and reenters into the field of view, and even across videos. However, for the purpose of AVA benchmarking, when an actor exits and reenters into the field of view of a camera within the same video after more than 10 seconds, we consider the same actor to have a new identity. Each video includes a range between 11 and 158 unique people. The dataset annotation includes a total of 785 unique people, and over a million annotated bounding boxes. Most of the people present in the dataset have OTS and roughly 10% of them looked directly at the camera. The main characteristics of the dataset are summarized in TableÂ 3.
4 Benchmarkâ€”results and discussion
4.1 Experimental setup
We evaluate the performance of the algorithms on four systems that enable ontheedge AVA processing. The systemsâ€™ properties are summarized in TableÂ 4. The algorithms are executed in both GPU and CPU (one core), separately. GPU inference is used for systems with an integrated NVIDIA GPU. CPU inference is used for all systems, and it can be native (i.e.,Â without optimization) or optimized using OpenVINO. The use of OpenVINO optimization depends on the system and the algorithm. Systems must be equipped with an Intel processor, and algorithms must be compatible with the OpenVINO optimization. For the baseline algorithms (A1â€“6), all algorithms but A4 are OpenVINO compatible.
We define as realtime processing the capability of a systemalgorithm pair to complete the analytics for \(I_t\) before the new data frame \(I_{t+1}\) is available. When a systemâ€“algorithm pair does not achieve realtime processing (e.g.,Â input data are at 30Â fps and the processing speed is at 1Â fps), one can reduce the frame rate and/or resolution of the videos. We decide to maintain the resolution of the videos and intentionally reduce the frame rate (i.e.,Â drop frames) of the input videos to ensure that every systemalgorithm pair performs (near) real time. TableÂ 5 shows the input frame rate of the videos that we use for all experiments for every systemalgorithm pair. For System 1, all algorithms run with 30Â fps videos with both GPU and CPU inference. For System 2, all algorithms run with 30Â fps videos with GPU and 3Â fps videos with CPU, except for A4 with CPU that runs with 1Â fps videos. For Systems 3 and 4, all algorithms run with 3Â fps videos, except for A4 that runs with 1Â fps videos.
Most of the results shown next are represented by box plots. The horizontal line within the box shows the median; the lower and upper edges of the box are the 25percentile and 75percentile; and, the bottom and top edges show the minimum and maximum values.
We provide an online evaluation tool that allows one to effortlessly assess the performance of AVA algorithms in the proposed dataset. Further information regarding the requested data format and use of the evaluation tool is available at the project website.
4.2 Localization
FigureÂ 10 shows the evaluation results of A1â€“2 on face localization, and A3â€“4 on person localization. Regarding the detectors, A2 obtains a higher precision but lower recall than A1. This indicates that A1 generates a larger amount of false positives than A2. However, the median results for F1score show that A1 outperforms A2 by a small amount. Regarding the trackers, A3â€“4 obtain comparable results across the systems. For instance, in System 1 with GPU, A1 obtains a F1score 0.17 higher than A2, and A3 and A4 obtain a median F1score of 0.80 and 0.81, respectively. When considering the distance between peopleâ€“signage, results show that all algorithms are able to localize a larger amount of people (i.e.,Â higher recall) when people are closer to the camera. For instance in System 1 with GPU, A1 obtains a median recall of 0.94/0.68 for closer/farther faces; and A3â€“4 trackers obtain a median recall of 0.91 for closer people, and 0.55 and 0.63 for farther people, respectively. When analyzing the performance measures as a function of the occlusion levels, results indicate that the recall drops when faces/bodies are partially or heavily occluded. For instance in System 1 with GPU, while the median recall for nonoccluded people and algorithms A1, A3, and A4 is above 0.8; the median recall drops to values below 0.6 for partial occlusions and below 0.5 for heavy occlusions.
4.3 Counting
FigureÂ 11 shows the counting evaluation in terms of MOE, MPE, and COE. Regarding mean opportunity error (MOE), A1â€“2 (i.e.,Â detectors) have errors up to 10 people for some videos considering all systems. Detector obtains a large range of errors, indicating a nonuniform performance throughout different videos of the dataset. On the contrary, A3â€“4 (i.e.,Â trackers) have a smaller median error as well as a smaller range of errors, which are always under 4 people. As observed in localization, algorithms commit fewer errors with people who are closer to the camera/signage, than with people who are farther. Algorithms that consider the body of people, instead of their faces (i.e.,Â A3â€“4) obtain a lower mean people error (MPE). This is expected, as these tracking algorithms have no skill in determining the OTS of people; thus, when considering all people regardless of their OTS, a lower error is obtained. Face detection algorithms (A1â€“2) obtain median MPE above 2 people, whereas body person tracking algorithms (A3â€“4) obtain median MPE below 2 people. Similar performance is obtained across systems and inference units (i.e.,Â GPU vs CPU) except for A1, which has a smaller error range when executed in CPU.
When the task is to count the cumulative number of unique people with OTS, cumulative opportunity error (COE) indicates that tracking algorithms obtain more accurate count than detection algorithms. With System 1, while the tracking algorithm A3â€“4 obtains a median COE under 1.02 and 4.20, respectively; detection algorithms A1â€“2 obtain a median COE of at least two orders of magnitude higher. In this case, algorithms that are using the GPU for inferring obtain in general higher error than when using CPU. This is due to the fact that algorithms that process more frames (i.e.,Â GPU) are more prone to overcount the cumulative number of people than when processing fewer frames (i.e.,Â CPU). Algorithms using CPU inference use as input videos with lower frame rate than when using GPU inference (e.g.,Â System 2 uses 3Â fps videos with CPU inference and 30Â fps videos with GPU inference), thus the overcount is likely to be reduced as the number of processed frames is reduced. This effect can also be seen in the results with System 1, where CPU and GPU use the same video frame rate, therefore, obtain very similar results regardless of the inference type. When the task is to estimate the cumulative number of people over a specific segment of time, temporal cumulative opportunity error (TCOE) results show that the error increases monotonically when the duration of the segment (D) increases (Fig.Â 12). Also, it can be observed that detectors (A1â€“2) obtain several orders of magnitude higher TCOE than trackers (A3â€“4). With System 1 GPU, trackers obtain TCOE of 1.519 (A3) and 670 (A4). The most accurate algorithm for this task is A3, which can estimate the cumulative number of people with OTS for 10 (120)s segment video with a median TCOE of Â±2.20 (Â±18.81), with System 1 and GPU.
4.4 Error vs input frame rate
Results indicate that the input frame rate of the videos has an important effect on the performance of the algorithms. Thus, we analyze the tradeoff between the error obtained by the algorithms and the input frame rate of the videos. This analysis is divided into two experiments. In the first experiment, we intentionally modify the input frame rate of the videos to \(\gamma =\{0.25,0.5,1,2,6,7.5,10,15,30\}\)Â fps, and then, we compare the performance of the localization algorithms in terms of MOE, MPE, and COE. FigureÂ 13 shows the results. For MOE and MPE, in the first row, the errors are mostly flat. This indicates that those performance measures are not affected by the input frame rate of the videos. This is expected as these two measures are performed on a framebyframe basis. Therefore, when reducing the frame rate of the input videos, the number of frames that the algorithms compute is reduced but this reduction does not affect to the performance of the algorithms, as nonseen frames are used neither for inference nor evaluation. However, when computing cumulative counts across time, the performance of the algorithms can be affected. In fact, the second row of Fig.Â 13, we observe that COE varies for A3â€“4 when the input frame rate of the videos change. COE monotonically increases when the frame rate increases for detection algorithms (A1â€“2). The performance obtained by A3 does not change substantially for different input frame rate, and its minimum occurs around 6Â fps. Surprisingly, COE monotonically increases for A4 when the frame rate increases. However, when considering absolute values, the error is considerably lower than the one obtained by detection algorithms. This indicates that higher frame rates do not necessarily ensure higher counting performance. In the second experiment, we apply the same frame rate reduction than in the previous experiment, and we compute TCOE for different segment duration of \(D=\{10,20,30,60,90,120\} \, \gamma\) frames (i.e.,Â 10, 20, 30, 60, 90, 120Â seconds). The results are in Fig.Â 14. Results in the first two rows indicate that TCOE monotonically increases for detection algorithms (A1â€“2) when the frame rate increases, and also when the duration of the segment increases. As mentioned before, this occurs as detectors have no skill for counting the cumulative number of people. When the segment increases its duration, the overcount accumulates further, thus TCOE also increases. Unlike detectors, trackers (A3â€“4), shown in the last two rows of Fig.Â 14, obtain a more stable TCOE for any segment duration and frame rate. Segments with larger duration produce a slight increment in the TCOE. Note that as A4 cannot be optimized using OpenVINO for CPU computation, we limit the input frame rate of the videos up to 1Â fps as higher framerate videos make the algorithm very slow. In this experiment, A3 is the most accurate baseline algorithm under comparison. Visual and detailed pervideo results obtained by each algorithm are available at the project website.
4.5 Age and gender estimation
Age and gender estimation algorithms require as input a crop with the personâ€™s face. We employ the face detector that obtains the highest recall (A1) as detector. To fairly compare the age and gender estimation algorithms and disregard the localization performance, we compute the age for correctly detected (i.e.,Â true positive) faces only. The results with A5â€“6 for age estimation are shown in Fig.Â 15 (first three columns), and for gender estimation in Fig.Â 15 (last three columns).
Age estimation results indicate that this task is challenging as the highest median F1score obtained is below 0.7. While the highest results are obtained for classes [19,34] and [35,65] with median F1score between 0.3 and 0.7, even lower F1scores are obtained for [0,18] and [65+] classes where algorithms obtain median F1score under 0.1. This suggests that the baselines algorithms, A56, are not skilled in determining the age of younger and older people, where both algorithms obtain a very low recall for these classes. Similar results are obtained regardless of the system and inference type (i.e.,Â CPU and GPU).
Gender estimation results indicate that A56 algorithms obtain a similar F1score performance for both classes (male, female). For the male class, both algorithms obtain a precision between 0.4 and 0.8 with a recall between 0.6 and 1.0. The opposite behavior happens for the class female, obtaining higher precision than recall. For this task, results indicate that all systems and inference types behave similarly. Note that A6 is not able to run in System 4 due to memory limitations.
4.6 Commercial solutions
As we did not have access to the source codes, the commercial solutions (C12) are executed in two external systems equipped with an Intel i7 CPU. To preserve the integrity of the complete dataset, until submission time, we only shared a subset of the dataset with the creators of C12. Thus, for this comparison, we use a subset of the dataset that is composed of the following videos Airport1, Airport2, Mall3, Mall4, Pedestrian2, and Pedestrian3. As a reference, we show next the results obtained by the baseline algorithms (A1â€“6) with System 1 GPU in the same subset of videos.
The results of this experiment are reported in Fig.Â 16. For localization, A1â€“2 and C12 are evaluated for face localization, and A3â€“4 are evaluated for person localization. Results show that both commercial solutions (C12) perform similarly than A2 for all performance measures, while A1 outperforms other face detectors obtaining a recall higher than 0.4 and similar precision. Person detectors (A3â€“4) obtain higher detection performance than face detectors with F1score around 0.8 and precision over 0.85. Count results show that all baselines and the commercial solutions obtain very similar MOE with median errors around 1 and always under 2.5, except for A1 that obtains a median MOE of 3.5 with values up to 8. Commercial solutions obtain similar MPE errors than A2 with a median error of around 2 people. A3â€“4 obtain lower MPE indicating that these algorithms obtain a lower error (below 1 in its median) when counting instantaneous people regardless of their OTS. A1 obtains a higher error than other algorithms with median MPE around 4. Regarding COE, the commercial solution C1 obtains the lowest error with a median of only 0.20 and a small range of errors. This indicates that the algorithm can count the cumulative number of people in each complete video with an error below Â± 1 person. The authors of C2 have a different definition of OTS than the one described in this paper. C2 define OTS as any person within the field of view, regardless of their face visibility. Therefore, we also compute, for C2 only, the CPE, where all people visible on the field of view of the video are considered to have OTS. The results are on the last COE bar.
When we consider the ability of the algorithms for counting the cumulative number of people for different segment duration, algorithms obtain an average TCOE between 1 and 50 (Fig.Â 17). C1 is again the algorithm that obtains the lowest error for all segment duration, achieving TCOE between 2 and 4.
In addition to showing the results using the proposed performance measures, we show the raw estimated and annotated counts for a set of selected videos in Fig.Â 18. We can observe that for instantaneous count most of the algorithms often estimate the number of people in the surrounding of the annotated value. An exception here is A1, which often generates multiple false positives, thus overestimating the actual number of people with OTS for a given instant. Regarding the cumulative count (second column of Fig. 18), and as done for COE, we show the estimated cumulative count of unique people with OTS from the initial frame. The charts indicate that the most accurate algorithms in this task are C1 and A3; and that the cumulative count is a challenging task and even stateoftheart trackers (i.e.,Â A4) and commercial solutions (i.e.,Â C2) might drift from the actual number of people.
The detailed pervideo results are available at the project website.
4.7 Execution speed
Figure 19 Â shows the statistics of the execution speed of the baseline algorithms in the four systems with both CPU and GPU, and of the commercial solutions. Considering the baseline algorithms (A1â€“6), the fastest algorithms are the age and gender estimation algorithms (A5â€“6), followed by the detection algorithms (A1â€“2). The tracking algorithms (A3â€“4) are the slowest ones. All six baseline algorithms run close to realtime (i.e.,Â 30Â fps), indicated in the charts by the black dashed line, when considering Systems 12 with GPU. In general, the chart confirms that GPU inference is the fastest, followed by CPU inference with OpenVINO optimization, and the slowest is nonoptimized CPU inference. For instance, A1 with OpenVINO optimization increases its average execution time by 3.6 times (from 0.10Â s per frame, in GPU, to 0.36Â s per frame, in CPU) in System 1. In the same system, A4 (without OpenVINO optimization) increases its average execution time by 19 times (from 0.08Â s per frame, in GPU, to 1.52Â s per frame, in CPU).
5 Conclusion
We proposed an opensource benchmark for the evaluation of anonymous video analytics (AVA) for audience measurement and released to the research community the first fully annotated dataset that enables the evaluation of AVA algorithms. Using this benchmark, we conducted a set of experiments with eight baseline algorithms and two commercial offtheshelf solutions for the tasks of localization, counting, age, and gender estimation. All the tasks are evaluated in four systems, with CPU and GPU. Results showed that trackers perform better than detectors in all scenarios, that localization algorithms should improve when objects are far/occluded (Figs.Â 10 and 11 ), and that the use of higher input frame rate videos do not ensure a better performance. Further efforts should be made towards the design of holistic tracking solutions that synergistically consider body and face to account for robustness and attention attributes. The performance of age estimation algorithms is limited and results suggest that the performance in estimating the age for younger, [0,18], and older people, [65+], is degraded. This might be due to an existing bias in the datasets used for training age estimation algorithms. Based on the outcomes of the benchmark, future work could explore the design of improved AVA algorithms for age estimation and cumulative count based on multipleobject tracking, as well as for attention to evaluate the audience responsiveness to an advertisement.
Availability of data and materials
The dataset, benchmark and related opensource codes are available at http://ava.eecs.qmul.ac.uk.
Notes
Benchmark websiteÂ http://ava.eecs.qmul.ac.uk.
Unique means that the algorithm does not repeatedly count the same person over time.
OpenVINO framework is available at https://docs.openvinotoolkit.org/.
At submission time, some operations required by A4 (i.e.,Â ScatterND) are not supported by OpenVINO framework; hence, no OpenVINO optimization is used with this algorithm.
Intel is committed to respecting human rights and avoiding complicity in human rights abuses. See Intelâ€™s Global Human Rights Principles. Intelâ€™s products and software are intended only to be used in applications that do not cause or contribute to a violation of an internationally recognized human right.
Abbreviations
 AVA:

Anonymous video analytics
 COCO:

Common objects in context
 COE:

Cumulative opportunity error
 CPE:

Cumulative person error
 CPU:

Central processing unit
 FN:

False negative
 FP:

False positive
 GPU:

Graphics processing unit
 IOU:

Intersection over union
 MOE:

Mean opportunity error
 MPE:

Mean people error
 OTS:

Opportunity to see
 TCOE:

Temporal cumulative opportunity error
 TP:

True positive
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Acknowledgements
We wish to thank Sangeeta Ghangam Manepalli for her feedback and Chau Yi Li for her help in developing the online evaluation tool.
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The research presented in this paper was supported by Intel Corporation.
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SanchezMatilla, R., Cavallaro, A. Benchmark for anonymous video analytics. J Image Video Proc. 2021, 32 (2021). https://doi.org/10.1186/s13640021005715
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DOI: https://doi.org/10.1186/s13640021005715