We present a systematic approach for training and testing structural texture similarity metrics (STSIMs) so that they can be used to exploit texture redundancy for structurally lossless image compression. The training and testing is based on a set of image distortions that reflect the characteristics of the perturbations present in natural texture images. We conduct empirical studies to determine the perceived similarity scale across all pairs of original and distorted textures. We then introduce a data-driven approach for training the Mahalanobis formulation of STSIM based on the resulting annotated texture pairs. Experimental results demonstrate that training results in significant improvements in metric performance. We also show that the performance of the trained STSIM metrics is competitive with state of the art metrics based on convolutional neural networks, at substantially lower computational cost.

Cake customization services allow clients to collaboratively personalize cakes with pastry chefs. However, remote (e.g., email) and in-person co-design sessions are prone to miscommunication, due to natural restrictions in visualizing cake size, decoration, and celebration context. This paper presents the design, implementation, and expert evaluation of a social VR application (CakeVR) that allows a client to remotely co-design cakes with a pastry chef, through real-time realistic 3D visualizations. Drawing on expert semi-structured interviews (4 clients, 5 pastry chefs), we distill and incorporate 8 design requirements into our CakeVR prototype. We evaluate CakeVR with 10 experts (6 clients, 4 pastry chefs) using cognitive walkthroughs, and find that it supports ideation and decision making through intuitive size manipulation, color/flavor selection, decoration design, and custom celebration theme fitting. Our findings provide recommendations for enabling co-design in social VR and highlight CakeVR’s potential to transform product design communication through remote interactive and immersive co-design.

Millions of photos are shared online daily, but the richness of interaction compared with face-to-face (F2F) sharing is still missing. While this may change with social Virtual Reality (socialVR), we still lack tools to measure such immersive and interactive experiences. In this paper, we investigate photo sharing experiences in immersive environments, focusing on socialVR. Running context mapping (N=10), an expert creative session (N=6), and an online experience clustering questionnaire (N=20), we develop and statistically evaluate a questionnaire to measure photo sharing experiences. We then ran a controlled, within-subject study (N=26 pairs) to compare photo sharing under F2F, Skype, and Facebook Spaces. Using interviews, audio analysis, and our questionnaire, we found that socialVR can closely approximate F2F sharing. We contribute empirical findings on the immersiveness differences between digital communication media, and propose a socialVR questionnaire that can in the future generalize beyond photo sharing.

In computer graphics, illuminating a scene is a complex task, typically consisting of cycles of adjusting and rendering the scene to see the effects. We propose a technique for visualization of light as a tensor field via extracting its properties (i.e., intensity, direction, diffuseness) from (virtual) radiance measurements and showing these properties as a grid of shapes over a volume of a scene. Presented in the viewport, our visualizations give an understanding of the illumination conditions in the measured volume for both the local values and the global variations of light properties. Additionally, they allow quick inferences of the resulting visual appearance of (objects in) scenes without the need to render them. In our evaluation, observers performed at least as well using visualizations as using renderings when they were comparing illumination between parts of a scene and inferring the final appearance of objects in the measured volume. Therefore, the proposed visualizations are expected to help lighting artists by providing perceptually relevant information about the structure of the light field and flow in a scene.

Texture is an important visual attribute both for human perception and image analysis systems. We review recently proposed texture similarity metrics and applications that critically depend on such metrics, with emphasis on image and video compression and content-based retrieval. Our focus is on natural textures and structural texture similarity metrics (STSIMs). We examine the relation of STSIMs to existing models of texture perception, texture analysis/synthesis, and texture segmentation. We emphasize the importance of signal characteristics and models of human perception, both for algorithm development and testing/validation.

We focus on the evaluation of texture similarity metrics for structurally lossless or nearly structurally lossless image compression. By structurally lossless we mean that the original and compressed images, while they may have visible differences in a side-by-side comparison, they have similar quality so that one cannot tell which is the original. This is particularly important for textured regions, which can have significant point-by-point differences, even though to the human eye they appear to be the same. As in traditional metrics, texture similarity metrics are expected to provide a monotonic relationship between measured and perceived distortion. To evaluate metric performance according to this criterion, we introduce a systematic approach for generating synthetic texture distortions that model variations that occur in natural textures. Based on such distortions, we conducted subjective experiments with a variety of original texture images and different types and degrees of distortions. Our results indicate that recently proposed structural texture similarity metrics provide the best performance.

When designing with young children, designers usually select user centred design methods based on the children’s required level of engagement and the inspiration expected to be created according to the designer. User centred design methods should be selected for their suitability for children and for the quality of the output of the design method. To understand the suitability of design methods, a framework was developed to describe design methods in terms of required design skills as identified by the Theory of Multiple Intelligences. The proposed framework could provide the basis for a tool to compare design methods and to generate hypotheses about what design method would work optimally with children in a specific school grade. The initial examination of the viability of the framework is a comparison of design methods by the number of skills involved; earlier work showed that the involvement of more skills (as with, e.g. low-fi prototyping) could result in more options for a design problem than the involvement of fewer skills (as with e.g. brainstorming). Options and Criteria were counted to understand the quality of the method in terms of the amount of design-information. The results of the current paper indicate that 8-to-10-year-old children generate significantly more options in prototyping sessions than when they are involved in sessions applying a Nominal Group Technique. The paper indicates that (a) with the framework we can generate hypotheses to compare design methods with children and (b) that the outcome of various design methods, which might lead to very different representations, can be compared in terms of Options and Criteria. Further usage of the framework is expected to result in empirical support for selecting a design method to be applied with young children.

Human perception of sign language can serve as inspiration for the improvement of automatic recognition systems. Experiments with human signers show that sign language signs contain redundancy over time. In this article, experiments are conducted to investigate whether comparable redundancies also exist for an automatic sign language recognition system. Such redundancies could be exploited, for example, by reserving more processing resources for the more informative phases of a sign, or by discarding uninformative phases. In the experiments, an automatic system is trained and tested on isolated fragments of sign language signs. The stimuli used were similar to those of the human signer experiments, allowing us to compare the results. The experiments show that redundancy over time exists for the automatic recognizer. The central phase of a sign is the most informative phase, and the first half of a sign is sufficient to achieve a recognition performance similar to that of the entire sign. These findings concur with the results of the human signer studies. However, there are differences as well, most notably the fact that human signers score better on the early phases of a sign than the automatic system. The results can be used to improve the automatic recognizer, by using only the most informative phases of a sign as input.

A recent focus is on creating engaging user experiences with digital products and services such as voicemail. This study aims to design towards increased levels of engagement in voicemail browsing by using the ‘Richness, Control and Engagement’ (RC & E) framework. This framework explains the levels of engagement in terms of the levels of richness and control that are shaped by the features of a product and the user’s expertise. A product was developed that utilized gestures and sound to access digital voicemail contents. An experiment was conducted in which 28 participants interacted with the product while varying (1) the number of features of the user interface, (2) the amount of voicemail content and (3) the type of task. Results showed that the levels of engagement could be predicted according to the levels of richness and control experienced when a task-term was added to the framework. Implications of the refined RC & E framework for interaction design practice are discussed.

This paper describes a study in which the outcome of early design sessions with eight-to-twelve-year old children is assessed through expert judgment. Experts compare the outcomes of two early design methods: brainstorming and prototyping. The design case was to come up with a solution for incapacitated children that need to attend class from home. The hypothesis is that children will generate more creative design solutions when prototyping than when brainstorming, because we reason that prototyping requires a wider range of intelligences according to Gardner's Theory of Multiple Intelligences. The outcome of the sessions is assessed on creativity and five explanatory criteria. The results show that a brainstorming method generates design solutions that are more creative. However, both methods produce creative design solutions; the brainstorming sessions generate more surprising and novel design solutions, the prototyping results are considered more relevant and workable.

We have developed a prototype for a learning environment for deaf and hard of hearing children. This demonstration consists of hands-on experience with the prototype. In total, there are three exercises: 1) an introduction of all pictures and corresponding signs, 2) multiple choice sign-to-picture and 3) performing the sign that corresponds to the picture shown on the screen. The live recognition from a wide-angle stereo camera provides immediate feedback for the third exercise where the sign must be performed.

This study explores issues of consistency and inspectability in usability test data analysis processes and reports. Problem reports resulting from usability tests performed by three professional usability labs in three different countries are compared. Each of the labs conducted a usability test on the same product, applying an agreed test protocol that was collaboratively developed by the labs. Each lab first analyzed their own findings as they always do in their regular professional practice. A few weeks later, they again analyzed their findings, but then everyone applied the same method (SlimDEVAN: a simplified version of DEVAN, a method developed for facilitating comparison of findings from usability tests in an academic setting). It was found that levels of agreement between labs did not improve when they all used SlimDEVAN, suggesting that there was inherent subjectivity in their analyses. It was found that consistency of single analyst teams varied considerably and that a method like SlimDEVAN can help in making the analysis process and findings more inspectable. Inspectability is helpful in comparative studies based on identified usability problems because it allows for tracing back findings to original observations as well as for laying bare the subjective parts of the data analysis.

This paper presents the design of pOwerball, a novel augmented reality computer game for children aged 8-14. The pOwerball was designed to bring together children with and without a physical or learning disability and to encourage social interactions surrounding the play. The contribution of this design case is two fold. From a design perspective, pOwerball exemplifies an emerging class of computer games where the interaction style and game mechanics support social interactions amongst the players. From a methodological perspective, we describe the various ways children became involved in our design process; we highlight the related difficulties and successes in the context of relevant research literature.

A tool was developed for structured and detailed analysis of video data from user tests of interactive systems. It makes use of a table format for representing an interaction at multiple levels of abstraction. Interactions are segmented based on threshold times for pauses between actions. Usability problems are found using a list of observable indications for the occurrence of problems. The tool was evaluated by having two analysts apply it to three data sets from user tests on two different products. The segmentation technique proved to yield meaningful segments that helped in understanding the interaction. The interaction table was explicit enough to discuss in detail what had caused the differences in the analysts' lists of usability problems. The results suggested that the majority of differences were caused by unavoidable differences in interpretations of subjects' behaviour and that only minor improvements should be expected by refining the tool.

The article describes a user study to support the design of a personalizable EPG (Electronic TV Programme Guide), and of its user interface for editing user preference profiles regarding TV channels and categories. This study focuses on issues related to users' behaviour and perceptions regarding a personalizable EPG, and especially regarding the personalization process. Users were presented with a paper-and-pencil procedure to indicate their TV viewing preferences, as well as with an electronic version. Their strategies were observed and their opinions asked, especially on trusting a system that uses this data. Moreover, their viewing behaviour was monitored over a period of two weeks, and recommendations for the second week were based on the viewing behaviour of the first week. The results indicate that users are reasonably comfortable and consistent in describing their viewing habits in terms of preferences, both for the paper-and-pencil and electronic preference-indication procedures, but that fine tuning this profile on the basis of habit watching would considerably improve the efficacy of the recommendations. It was found that subjects trust the system with the task of preselecting their TV programmes on the basis of their preference indications, although they are not sure whether a habit-watching system would be capable of following their changing habits over time.

The problem of quantifying perceived quality of processed images is traditionally solved by associating quality with the deviation from the undistorted original. This paper presents experiments challenging two underlying assumptions, namely (1) the original always possesses the highest quality and (2) quality cannot be determined without a direct comparison between the original and processed image. In doing so, percentage scaling is introduced as a scaling procedure for evaluating multiply impaired images.

Two experiments are presented that were aimed to investigate the effects of stereoscopic filming parameters and display duration on observers' judgements of naturalness and quality of stereoscopic images. The paper first presents a literature review of temporal factors in stereoscopic vision, with reference to stereoscopic displays. Several studies have indicated an effect of display duration on performance-oriented (criterion based) measures. The experiments reported were performed to extend the study of display duration from performance to appreciation-oriented measures. In addition, the present study aimed to investigate the effects of manipulating camera separation, convergence distance, and focal length on perceived quality and naturalness, In the first experiment, using display durations of both 5 and 10 s, 12 observers rated the naturalness of depth and the quality of depth for stereoscopic still images. The results showed no significant main effect of the display duration. A small yet significant shift between naturalness and quality was found for both duration conditions. This result replicated earlier findings, indicating that this is a reliable effect, albeit content-dependent. The second experiment was performed using display durations ranging from 1 to 15 s. The results of this experiment showed a small yet significant effect of display duration. Whereas longer display durations do not have a negative impact on the appreciative scores of optimally reproduced stereoscopic images, observers do give lower judgements to monoscopic images and stereoscopic images with unnatural disparity values as display duration increases. In addition, the results of both experiments provide support for the argument that stereoscopic camera toe-in should be avoided if possible.

This paper deals with two current issues in visual quality assessment, namely, contextual effects in quality judgments and the evaluation of time-varying image quality. A scaling experiment is described showing that contextual effects due to stimulus spacing are negligible when a method based on difference judgments is used. It is also shown that subjects can record their impressions of time-varying image quality by means of moving a slider along a graphical scale. The research on contextual effects as well as on the continuous assessment of time-varying image quality illustrate the important role psychological factors play in image quality evaluation.