Evaluating the Impact of V-Ray Rendering Engine Settings on Perceived Visual Quality and Render Time a Perceptual Study
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Bachelor of Science in Digital Game Development September 2019 Evaluating the Impact of V-Ray Rendering Engine Settings on Perceived Visual Quality and Render Time A Perceptual Study. Andreas Linné Faculty of Computing, Blekinge Institute of Technology, 371 79 Karlskrona, Sweden This thesis is submitted to the Faculty of Computing at Blekinge Institute of Technology in partial fulfilment of the requirements for the degree of Bachelor of Science in Digital Game Development. The thesis is equivalent to 10 weeks of full time studies. The authors declare that they are the sole authors of this thesis and that they have not used any sources other than those listed in the bibliography and identified as references. They further declare that they have not submitted this thesis at any other institution to obtain a degree. Contact Information: Author(s): Andreas Linné E-mail: [email protected] University advisor: Dr. Valeria Garro Department of Computer Science Faculty of Computing Internet : www.bth.se Blekinge Institute of Technology Phone : +46 455 38 50 00 SE–371 79 Karlskrona, Sweden Fax : +46 455 38 50 57 Abstract Background. In computer graphics, it can be a time-consuming process to render photorealistic images. This rendering process, called “physically based rendering” uses complex algorithms to calculate the behavior of light. Fortunately, most ren- derers offer the possibility to alter the render-settings, allowing for a decrease in render time, but this usually comes at the cost of a lower quality image. Objectives. This study aims to identify what setting has the highest impact on the rendering process in the V-Ray renderer. It also examines if a perceived difference can be seen when reducing this setting. Methods. To achieve this, an experiment was done where 22 participants would indicate their preference for rendered images. The images were rendered in V-Ray with different settings, which affected their respective render time differently. Addi- tionally, an objective image metric was used to analyze the images and try to form a correlation with the subjective results. Results. The results show that the anti-aliasing setting had the highest impact on render time as well as user preference. It was found that participants preferred images with at least 25% to 50% anti-aliasing depending on the scene. The objective results also coincided well enough with the subjective results that it could be used as a faster analytical tool to measure the quality of a computer-generated image. Prior knowledge of rendering was also taken into account but did not give conclusive results about user preferences. Conclusions. From the results it can be concluded that anti-aliasing is the most im- portant setting for achieving good subjective image quality in V-Ray. Additionally, the use of an objective image assessment tool can drastically speed up the process for targeting a specific visual quality goal. Keywords: V-Ray, Computer-Generated Imagery, Rendering, Perception, Subjec- tive Evaluation Contents Abstract i 1 Introduction 1 1.1 Aim, Objectives and Research Question ................. 2 2 Related Work 3 3 Background 5 3.1 Physically Based Rendering . ..................... 5 3.1.1 Biased Render Engines ...................... 5 3.1.2 Unbiased Render Engines .................... 5 3.2AutodeskMaya.............................. 6 3.3V-Ray................................... 6 3.4 V-Ray Quick Settings ........................... 6 3.4.1 Render Settings Overview .................... 7 3.5 Image Quality Assessment ........................ 9 3.5.1 Subjective IQA .......................... 9 3.5.2 Objective IQA .......................... 10 4 Method 13 4.1Scenes................................... 13 4.2 V-Ray Quick Settings ........................... 14 4.3 Preliminary Study ............................ 15 4.4 Rendering ................................. 15 4.4.1 Rendering Hardware ....................... 15 4.5 Experiment Setup and Procedure .................... 15 4.6Ethics................................... 16 4.7 Experiment Specifications ........................ 16 4.8 Custom Software Implementation .................... 16 4.9 DSSIM IQA Metric ............................ 17 5 Results 19 5.1 Preliminary Study ............................ 19 5.2 Subjective Results ............................ 22 5.2.1 How Render-Settings Affect Votes ................ 23 5.2.2 Survey Results .......................... 27 5.2.3 Previous Experience vs No Experience ............. 27 5.3 Objective Results ............................. 28 iii 5.3.1 DSSIM Results .......................... 28 5.3.2 Render Time ........................... 29 6 Analysis and Discussion 39 7 Conclusions and Future Work 41 References 43 A Supplemental Information 45 A.1 Acronyms ................................. 45 iv Chapter 1 Introduction Achieving photorealism in computer graphics has been widely chased ever since the ’70s [9]. With current software and technology, this has been possible for the layman for almost 20 years. While big corporations take advantage of render farms with enormous computing capabilities, personal computers and workstations still linger behind when it comes to rendering times. Even still, results which are similar to that of render farms can be achieved on any hardware, given enough time. As of today, there is a diverse number of rendering engines that are used in computer graphics. One of the primary functions of these engines is to calculate global illumination by using different algorithms such as ray tracing [22, 24]. One of these engines is V-Ray, developed by Chaos Group [4], and is widely used in the field of computer graphics. V-Ray is available as a plugin for Autodesk Maya [1], Autodesk 3ds Max [1], and Maxon Cinema 4D [6], to name a few. To reduce rendering times, image quality must be sacrificed. In V-Ray, different render settings can be used to modify the quality, thus changing the render time. These settings range from different methods of primary diffuse bounces, Irradiance map, light cache, and brute force. Additionally, these methods also have their specific options that can be modified. Shading rate and anti-aliasing are two other settings that can also be modified. To add to this, while there have been many studies where the focus lies in opti- mizing render times [15, 20, 26], they require the implementation of their technique to take advantage of the improvements. Although these techniques decrease render times, they come with the disadvantage of not being able to be implemented by an end-user in V-Ray. It should however still be possible to achieve lower render time with the software tools currently available, as is. In other words, using V-Ray with optimal settings could reduce the render times, without a perceived loss in quality. With this in mind, a problem is created: Which of these settings can be reduced without negatively affecting a users perceived quality of the image? If one or more of these settings can be lowered without users noticing a difference in perceived quality, rendering times will surely decrease. Reduced rendering times will save the artist time and possibly even money in the long run. Furthermore, it can also be of interest for those who do not have access to a render farm, for example, students, amateur artists, startup companies, indie game developers, and possibly even AAA studios. 1 2 Chapter 1. Introduction 1.1 Aim, Objectives and Research Question The overall aim of this study is to have a better understanding of how some of the rendering settings in V-Ray affect the rendering time as well as the perceived quality of the image. To achieve this, three objectives will be the focus of this report. • Determine what setting or settings in V-Ray have the most impact on render times. • By developing an image quality perceptual study, let participants compare rendered images with different settings. • Analyze the gathered data and propose a solution to the problem above. With these objectives in mind, a research question is asked: Can a perceived difference in image quality be noticed when reducing the most impacting render settings in V-Ray? When determining the most impacting render setting it was hypothesized that every setting would increase the render time based on its increased value, but global illumination would have more impact than shading quality and anti-aliasing. Chapter 2 Related Work This section provides a brief overview of the related work in this field. Studies in visual quality perception in the area of computer graphics are not uncommon. Some of the previous works include [23] by Rademacher et al. where the perception of visual realism in images was measured. Participants were instructed to rate an image as either real or not. Rademacher et al. point out the difficulty of communicating to the participants what they mean by the term “real”, as the goal of the experiment itself was to find out what makes an image realistic. Therefore one of the key points of the experiment design was to give participants as little information as possible to what was considered “real” and instead let the participants decide. The images used were real photographs and computer-generated. Rademacher et al. state that physics is not the only key to photorealism, as some of the real photographs were not all equally realistic. Finally, Rademacher et al. mention that if we can understand what visual factors have an impact on the perception of a photorealistic image, new rendering algorithms can be developed to take advantage of these factors