The Visual Computer https://doi.org/10.1007/s00371-019-01758-8 ORIGINAL ARTICLE Gestural flick input-based non-touch interface for character input Md. Abdur Rahim 1 · Jungpil Shin 1 · Md. Rashedul Islam 1 © Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract A non-touch character input is a modern system for communication between humans and computers that can help the user to interact with a computer, a machine, or a robot in unavoidable circumstances or industrial life. There have been many studies in the field of touch and non-touch character input systems (i.e., hand gesture languages), such as aerial handwriting, sign languages, and the finger alphabet. However, many previously developed systems require substantial effort in terms of learning and overhead processing for character recognition. To address this issue, this paper proposes a gesture flick input system that offers a quick and easy input method using a hygienic and safe non-touch character input system. In the proposed model, the position and state of the hands (i.e., open or closed) are recognized to enable flick input and to relocate and resize the on-screen virtual keyboard for the user. In addition, this system recognizes hand gestures that perform certain motion functions, such as delete, add a space, insert a new line, and select language, an approach which reduces the need for recognition of a large number of overhead gestures for the characters. To reduce the image-processing overhead and eliminate the surrounding noise and light effects, body index skeleton information from the Kinect sensor is used. The proposed system is evaluated based on the following factors: (a) character selection, recognition and speed of character input (in Japanese hiragana, English, and numerals); and (b) accuracy of gestures for the motion functions. The system is then compared to state-of-the-art algorithms. A questionnaire survey was also conducted to measure the user acceptance and usability of this system. The experimental results show that the average recognition rates for characters and motion functions were 98.61% and 97.5%, respectively, thus demonstrating the superiority of the proposed model compared to the state-of-the-art algorithms. Keywords Human–computer interaction · Hand gestures · Non-touch input · Gesture recognition · Kinect sensor 1 Introduction Humans communicate with computers in many ways, and the interface between humans and computers is an important fac- tor in the convenience of this interaction. Most of the research in this field therefore aims to improve the usability of the com- puter interface and to enhance human–computer interactions [1]. In the last few decades, the keyboard and mouse have played important roles in human–computer interactions. At present, the user is expected to use both touch and non-touch interfaces to interact with the machine, and various differ- B Jungpil Shin jpshin@u-aizu.ac.jp Md. Abdur Rahim rahim_bds@yahoo.com Md. Rashedul Islam rashed.cse@gmail.com 1 School of Computer Science and Engineering, The University of Aizu, Fukushima 965-8580, Japan ent devices are used in daily life, such as computers, tablet PCs, and smartphones. A keyboard is typically used to input characters on computers, and software keyboards to input characters on smartphones or tablet PCs. The user needs to touch the keyboard to input characters, even on smartphones or tablet PCs. There is also a large demand in industry to provide a hygienic and safe environment, and rugged and reliable computing and automation devices may be needed to increase production. These tough environments and tight regulations require special equipment to keep the environ- ment sterile and safe. In order to meet the highest hygiene and safety requirements, to ensure the traceability of all pro- cessing steps and to ensure the implementation of existing standards, many industrial applications have used advanced human–machine interface (HMI) technology [2]. There are many industrial computer production companies (e.g., JLT mobile computers, Noax Technology, Teguar Computer, and others) that offer fully sealed, waterproof, industrial touch- screen automation computers for production applications to 123