Gesture is a remarkable interaction way for Human Computer Interaction (HCI), which is a conventional non-verbal communication method. It is one type of pervasive body language that can be used for communication. However, with the development of the gaming interaction and wearable device, precise finger gesture have more advantages than body gesture, especially for control devices The finger movement is one of the micro-gestures that can accurately manipulate the device. Kinect and RBG-D camera are popular sensors for gaming in the Augmented Reality (AR) and Virtual Reality (VR) community with its low-cost been a major advantage, as well as its immersive user experience and usability . There displays support the 3D gesture systems and need free space to support flexible interaction .. However, these systems lack the ability to capture quality and accurate objects which could be seen as one of its major drawbacks. Recently, some new research from Leap Motion  and Google Soli Project  created new techniques for 3D detection that has huge potentials for success. Holoscopic 3D (H3D) imaging system is a novel potential technique which can satisfy the higher demand of user interactive experience. Detection of precision 3D micro-gesture can make use of the wide view coverage the of Holoscopic 3D camera to capture accurate finger movement .
This paper aims to use the H3D imaging system to create a unique 3D micro-gesture database, further to promote the gesture recognition. Even using H3D system is depart from precedents in capture and recognition of the gesture area, this technology was mature to use the 3DTV and display area. Meanwhile, the H3D system also supports the RGB high quality dynamic and static data, and it is renowned for high accuracy and true 3D to excellence than traditional 3D capture devices.
2 Related Work
HCI appeared early in 1983 , which use multiple modalities such as voice, gestures (e.g. body, hand, arm, finger, etc.). For example, Siri  is a very popular voice-based interface. However nature gesture is another way to interact with the computer. The trend of the HCI is user experience of intuitionistic and effective . Gesture is a touchless, non-intrusive method for HCI, and it is represented as the diverse type of the gestures . Manipulative type of gesture appears the most popular one from the preciously literatures. The aim is to control entity being manipulated through the actual movements of the gesturing hand and arm . Hand as a direct input device is more and more popular, as one of the outstanding interaction methods.
The Kinect and RGB-D camera are very popular in recent years due to the benefits of Kinect and RGB-D camera that have low cost and wide availability as a sensor  to capture gestures. However, RGB-D camera suffers from the underside artefacts such as the edge inaccuracies, low object remission and holes owning . The Kinect sensor offers the information of the depth measurement and create coordinates of the 3D objects. Although the abundant development toolkits can support the human body recognition, the weakness is its lacking ability to capture the flexible and robust mechanism to perform high-level gesture .
Leap Motion (LM)  is a device that can be used to detect the hand and finger dynamic movements through its API software. The API has the robust pre-processing function which can reduce the complexity of the user control. However, LM is a monocular video sensor which is a challenging for capturing the abundant dynamic hand gestures and finger micro movements .
Holoscopic 3D camera is a single aperture sensor not only to represent the real-time and represents a true volume spatial optical model of the object scene but also to record the viewing natural continuous parallax 3D objects within a wide viewing zone . It provides a new way to capture micro-gestures.
Isaac et al.  presents a review summary of 21 gesture datasets from previous research and publicly datasets, in which 7 databases are for hands. Most datasets are recorded using to the Kinect or RGB-D camera as the sensor.
In order to the support the diversification of the gesture recognition and encourage development of the human computer interaction, We propose a new 3D gesture database included the three ubiquitous micro gestures that are most the popular ones used in the Google Soli project. Those are intuitive and unobtrusive manipulative gesture. This database is not only include the continuous dynamic data, but also contained the abundant static data to support the 3D micro-gesture recognition.
3 Database Construction
There are many micro-gestures that can be used for control in AR and VR applications. In this research, three intuitive micro-gestures are selected refer to the Google Soli project  as shown in Fig.1. The three gestures are based on the human intuitiveness when they try to control display. For instance, the button gesture is the submission, dial gesture shows that user want to slight change the current situation, and the slider gesture is to express the slide up or down to adjust the volume and options. This three gesture belongs to the manipulative type of the gesture, which use to touch- less control the devices or simulation console.
3.2 H3D imaging technology
H3D imaging technology is success for use in the 3D cinema, 3D-capable televisions and broadcasters. The H3D camera used here is built from the 3D Vivant Project (3D Live Immerse Video-Audio Interactive Multimedia)  and the purpose is to capture high quality 3D images. The developed camera includes micro-lens array, relay lens and digital camera sensors. The principle of the holoscopic 3D imaging is shown in Fig.2. The 3D holoscopic image’s spatial sampling is determined by the number of lens. It shows that the captured 2D lenslet array views is slight different angle than its neighbor and reconstructed image in relay . The detailed parameters of the camera are shown in Fig.3.
Holoscopic 3D camera sensor has unique optical components which support the continuous parallax RGB image system, contain the depth information viewpoint images. The figure show the H3D imaging having the full color with full parallax. H3D imaging is comprised of the 2D array of micro images.
The H3D sensor is a crucial requirement for the capture of the objects. This database uses the H3D imaging system to support the dynamic and static RGB data. And it’s not only can record the continuous motion, but repetitive lens array can extract different angles viewpoint images. The uniqueness to encourage the innovation of gesture capture and recognition.
3.3 Recording Setup
The recording H3D gesture place, as in Fig.4. A green screen room is used for the recording where it can offer clear and professional recording background to reduce noise. Before the recording, the holoscopic 3D camera adapter and surface are set up in advance. Canon 5D camera is used and the film speed is ISO200, shutter 1/250. Holoscopic 3D camera adapter is calibrated and the lens are corrected.
Considering to the influence from distances, angles, and backgrounds, we prepared 4 positions for participants. Two positions are the close and far locations where the objective lens set to 45cm and 95cm. The other two positions are from left and right hand side for the convenience of the participants. In the close position, we set a hollow frame to help the participant to find the 3D micro-gesture capture zone. We remind the participants the gesture name while record their finger movements. The participants can perform their micro-gesture at their own speed. The recording are done during the time around 15 minutes for one participant.
We prepared two different colour backgrounds, two different distances of close and far from end of the camera lens to gesture area. The recorded imaging resolution is 1086x1902, and the micro lens is 28x28. Participants are successively stand each pre-established position to play three gestures around 3-5 seconds. The three gestures are involved button, dial and slider.
|Micro-gesture||Button (B), Dial (D), Slider (S)|
|Participants||Male (33), Female (17)|
|Hand||Right (R), Left (L)|
|Distance||Close ( 45cm), Far ( 95cm)|
|Background||Green (G), White (W)|
|Image resolution||1902 x 1086|
|Lens array||28 x 28|
|Recording length||Between 2 and 20 Sec.|
In total, 40 participants attended the recordings including 17 female participants and 33 male participants, who all read the participant information sheet guidance and sign the research ethics application forms before the recording. There is no any limited of age and race for the participants and We respect the participants’ will. Some participants wear married rings and watches during the recording on finger movements. These increase the data’s noise and bring more challenges. We recorded the participants’ double hands in order to increase the diversity of the data. The detailed information about the data acquisition is summarized in Table 1.
3.5 HoMG Database
For the data collection, the recordings from 40 participants are selected to make the HoMG database. The recordings were done under different conditions. One participants were recorded 24 videos. In total, 960 videos are included in the database.
For micro-gesture recognition, it can be done based on single image or can be done from a short video. So this database was divided into two subsets: image based and video based micro-gesture subsets.
3.5.1 Video subset
There are 40 subjects and each subject has 24 videos due to the different setting and three gestures. For each video, the frame rate is 25 frames per second and length of videos are from few seconds to 20 seconds and not equally. The whole dataset was divided into 3 parts. 20 subjects for training set, 10 subjects for development set and another 10 subjects for testing set. In this way, the micro-gesture recognition are person independent.
3.5.2 Image subset
Video can capture the motion information of the micro-gesture and it is a good way for micro-gesture recognition. However, it needs more data and take long time. It is very interesting to see whether it is possible to recognise the micro-gesture from a single image with high accuracy.
From each video recording, different number of frames were selected as the still micro-gesture images. In total, there are 30635 images selected. The whole dataset were split into three partitions: a Training, Development, and Testing partition. There are 15237 images in the training subsets of 20 participants with 8364 in close distance and 6853 in far distance. There are 6956 images in the development subsets of 10 participants with 3077 in close distance and 3879 in far distance. There are 8442 images in the testing subsets of 10 participants with 3930 in close distance and 4512 in far distance.
4 Initial investigation on Micro-Gesture Recognition
The initial investigation are carried out independently for video and image based micro-gesture recognition study. We would like to see how high performance can be achieved from each way.
4.1 Video based micro-gesture recognition
are selected. These features can not only calculate the distribution of the local information of each frame, but also the distribution of finger movements along to the time. From each video, the frame size was reduced to 74x42 from 1920x1080 firstly, then a feature vector with dimension of 768 is extracted using LBPTOP and LPQTOP for the classification. For the classification, it is a three class classification problem. There are lots of classifiers available. Here, most popular ones such as k-NN, Support Vector Machines (SVM) and Naive Bayes classifiers are chosen for comparison purpose.
Table 2 shows the accuracy using three different classifiers under different distance on video based micro-gesture recognition. From this table, it can be seen that LPQTOP is better than LBPTOP for feature extraction. SVM is better than k-NN and Naive Bayes classifiers in most cases. The accuracy on close distance is better than far distance because the detailed information of the finger movement can be captured. For the testing set, both training and development sets were used for training. Overall, 66.7% accuracy can be achieved even use the feature extraction methods from all videos in the testing set.
4.2 Image based micro-gesture recognition
For each image, 2D texture features such LBP  and LPQ  were extracted to represent each image. These two features captured the edge and local information of the 2D image in different ways and form a histogram feature vector with dimension of 256. Popular classification methods such as k-NN, SVM and Naive Bayes classifiers were used for recognising the three different micro-gestures.
Table 3 should the experimental results on video based micro-gesture recognition by training on the training set and tested on development and testing subsets. From this table, it can be seen that for most of the classifications, around 50% accuracy can be achieved.
5 Conclusions and Future Works
This paper introduces a unique holoscopic 3D micro-gesture database (HoMG), which is recorded under different settings and conditions from 40 participants. The data recording uses the similar the H3D system of fly viewing to capture the participants’ precise finger movements. The H3D imaging system supports robust 3D depth micro lens array to capture dynamic and static information. The HoMG database has 3 unobtrusive manipulative gestures in two different backgrounds, two different distances, left and right hands. These micro-gestures can be used to control multifarious displays. This database would speed up the research in this area.
The database is further divided into video and image subsets. Initial investigation on micro-gesture recognition is conducted. For the comparison, video based method achieved better performance as it has dynamic finger movement information in the data. However, this method needs much more data and computing time. Image based method is convenient for the user and might have more applications, especially on the portable devices. Even with the standard 2D feature extraction methods and basic classification methods, 72.5% recognition accuracy can be achieved for micro-gesture videos and over 50% accuracy for micro-gesture images. This baseline methods and results will give a foundation for other researchers to explore their methods.
5.2 Future works
From the initial investigation, it can be seen that the recognition accuracy can reach around 66% even just using the 2D image processing methods. For 3D image processing methods, such as extracting the different viewing point images and extract 3D information of the micro-gesture, high accuracy will be achieved. This will be our future works.
We gratefully acknowledge the support of NVIDIA Corporation with the donation of the Tesla K40 GPU used for this research.
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