Texture Rendering

Texture Rendering

© Alican Alma

When we are in physical interaction with objects, our sensory receptors located under the skin transmit signals to the brain. Particularly, texture information is a multimodal event that is mainly perceived via tactile receptors and kinesthetic sensations. However, touch devices do not involve kinesthetic feedback and haptic feedback, therefore, is limited to tactile information. This makes rendering on touch displays a challenging event, but recent researches and current technologies enable the reproduction of haptic textures on tactile surfaces. This research field is particularly known as "surface haptics", and it relies on replicating surface roughness or modulating friction force when a fingertip and a surface are in active or passive contact. Friction modulation in touch interfaces can be enabled by two popular methods: Ultrasonic vibration and electrostatic attraction. Also, surface roughness can be reproduced by a vibrotactile feedback system since it is the most feasible approach in contrast to electrostatic and ultrasonic-vibration methods.

In the chair, an industrial AIF project called "Multimodal Inspection of Product Surfaces" was successfully conducted, between 2017-2020, together with TU Dresden-Textile Research Group and various companies (AscoLab, Assyst, Audi, Birkenstock, Biehler, Born, Hugo Boss, and many more), which are interested in rendering textures for the purpose of better online shopping. Nowadays, there are numerous commercial devices available on the market that can present single or multiple modalities with varying quality. These devices are currently subject to very short innovation cycles. Hence, the quality and functionality of solutions are concerned for touch-based interaction on touch screen devices such as smartphones and tablets, and the devices for virtual and augmented visual presentation. Approaches to solving this problem are based on model-based software development (MDSD). MDSD is a generic term for techniques that automatically generate executable software models. International standardization bodies already specify means of description for the visual, auditory, and haptic modality (e.g. for audio: loud, quiet; haptics: smooth, soft, metallic, sticky, etc.). For haptic interactions, the W3C (World Wide Web Consortium) standard specifies a Vibration API for accessing the vibration mechanisms of a mobile device such as a smartphone or tablet. Although this interface only supports simple methods, it allows the formulation of "tactile patterns". A standardization team at NOKIA for tactile user interfaces proposes extensions in cascading style sheets (stepped design sheets) for tactile outputs. Also, predefined values for textures are suggested such as smooth, grainy, sharp, and raised. Even if these W3C standards are essentially developed for the development of websites, the underlying abstractions represent a valuable, but above all a uniform starting point for reusable, standardized user interfaces. As part of this project, the multimodal HMI solution could be configured directly with the help of the description of the devices to be used and further developed in a targeted manner. 

© Alican Alma

Another research topic on texture reproduction, called "Perceptual Substitution-based Haptic Texture Rendering for Narrow-Band Reproduction", has been completed successfully as well. This work was found remarkable and original by the editorial members of IEEE Transaction of Haptics Journal, and published in March 2023, (click here to see). This work offers a simple and plausible perceptual texture rendering model on mobile touch devices considering the limited capabilities of small haptic actuators in commercial mobile devices. It is because accurate reproduction of recorded texture vibration is often infeasible for widely available haptic reproduction systems on mobile devices. Usually, haptic actuators can only reproduce narrow-bandwidth vibration. With the exception of research setups, rendering strategies need to be developed, that utilize the limited capabilities of various actuator systems and tactile receptors while minimizing a negative impact on the perceived quality of reproduction. According to the set of experiments, the narrowest band-noise vibration with frequencies between 90 Hz to 400 Hz can be assigned to fine textures. Furthermore, amplitude-modulated vibrations are found to be more congruent to reproducing too coarse textures. To see the rendering parameters in detail, the research paper above can be examined. 

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