An efficient, dense and long-range marker system for the guidance of the visually impaired
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ORIGINAL PAPER
An efficient, dense and long-range marker system for the guidance of the visually impaired Juan Manuel Sáez1 · Miguel Angel Lozano1
· Francisco Escolano1 · Javier Pita Lozano2
Received: 5 February 2019 / Revised: 20 December 2019 / Accepted: 24 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this paper, we address the problem of making a mobile/smartphone camera sensitive to distant fiducial markers. To this end, we carefully design a novel visual marker that is both dense and readable from large distances. The main novelty of the proposed marker is the combination of a quaternary color-based coding system with robust methods for reading the color patterns included in each frame once it is detected. These patterns include a CRC whose length grows linearly, whereas that of the message grows quadratically. Our experiments show that the proposed bundle marker-vision algorithm outperforms the alternatives in terms of distance and angle and also that it is very robust to changes in lighting conditions, thus making it a good intelligent system for guiding people with visual impairments in their day to day use of public transportation systems. Keywords Computer vision · Mobile vision · Visual markers · Visually impaired
1 Introduction An artificial visual marker is an element that is intentionally introduced in the scene and contains information related to the environment (e.g. a description of the scene, or signposting). Such information is intended to be captured and recognized by the digital camera integrated in a mobile device (e.g. a smartphone). Unlike other kind of markers such as barcodes, whose information is mainly displayed unidimensionally, visual markers display their information in a bidimensional layout. Attending to their design, there
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Miguel Angel Lozano [email protected] https://cvnet.cpd.ua.es/curriculum-breve/en/lozano-ortegamiguel-angel/1687 Juan Manuel Sáez [email protected] Francisco Escolano [email protected] Javier Pita Lozano [email protected]
1
Mobile Vision Research Laboratory, University of Alicante, Ctra. San Vicente s/n, 03690 San Vicente del Raspeig, Alicante, Spain
2
Nuevos Sistemas Tecnológicos S.L., Calle Central, 10, 30100 Espinardo, Murcia, Spain
are two families of visual markers: dense markers and longrange markers. Dense visual markers: Their layout usually consists of a large number of visual elements, to enable the potential coding of a large amount of information. These codes are readable if (i) we have a sharp image, (ii) the camera is close enough (about 20–50 cm) and (iii) we are working under good lighting conditions. These requirements prevent dense markers from being detected in certain situations, namely from large distances, while the device is moving (due to the motion blur effect), or when lighting conditions are not ideal. In this group, we find several well-known types of markers, such as QR codes or the Datamatrix system [13]. These codes are usually dichromatic (consisting of black and white eleme
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