Perceptually-motivated non-photorealistic graphics

In my chapter I want to highlight some important episodes in the history of the technologies and procedures that form the bases for photorealistic computer graphics, as well as fields of practice and related aesthetic strategies. Firstly, I discuss its root in flight simulation, and secondly, I underline that simulation is related fundamentally to realism. Thirdly, I will address the notion of photorealism and discuss some of the properties of photography that have to be simulated to generate a photorealistic image, as the “realism” of the computer-generated images is judged in comparison to photography. Following that, I draw some more generalized inferences on the relation of computers and photography and finish the chapter with a short conclusion.

2000

The advent of photography and computer graphics has not replaced artists. Imagery generated by artists provides information about objects that may not be readily apparent in photographs or real life. The same goal should apply to computer-generated images. This is the driving force behind non-photorealistic rendering. The term non-photorealistic rendering (NPR) is applied to imagery that looks as though it

Proceedings of the 3rd international symposium on Non-photorealistic animation and rendering - NPAR '06, 2006

Pen-and-ink line drawing techniques are frequently used to depict form, tone, and texture in artistic, technical, and scientific illustration. In non-photorealistic rendering (NPR), considerable progress has been made towards reproducing traditional pen-and-ink techniques for rendering 3D objects. However, formal evaluation and validation of these NPR images remain an important open research problem. In this paper we present an observational study with three groups of users to examine their understanding and assessment of hand-drawn pen-and-ink illustrations of objects in comparison with NPR renditions of the same 3D objects. The results show that people perceive differences between those two types of illustration but that those that look computer-generated are still highly valued as scientific illustrations.

Traditionally, computer graphics has been concerned with producing imagery that is as physically accurate as possible. But accurate physical simulation of geometry, lighting and material properties of a visual scene can be cumbersome and time-consuming. At the same time, human vision is far from accurate, which offers an enormous opportunity to create imagery at a reduced computational cost as well as with less reliance on human modelers. As a result, a recent trend is towards accepting perceptual plausibility instead of physical accuracy as a guiding principle in the design of modeling and rendering systems. This requires us to understand visual realism, which involves both learning statistical regularities of the world, for instance by employing huge amounts of data, as well as humans visual perception of it. This paper addresses issues related to understanding realism, presents several applications, and discusses what this interesting approach may lead to in the future.

2005

In this paper, two problems concerning truthfulness of computer-generated visualization are considered. The fi rst one concerns relationships between reality and its representation by computer renderings. The second problem concerns the kind of representations people need. These problems are analyzed for static perception of architectural forms based on computer visualization, and for dynamic walk-through perception of urban space. The thesis of the paper is that many photorealistic renderings are excessively realistic and thus not true. In this context, a new question arises: do we need the true representation of an object? The author claims that we need “adequate” pictures. Adequate means a picture that is satisfactory in particular situation. The problem of equivalence of media (renderings and animations) and reality is not that important here. Much research is concerned with the truthfulness and falsity of information. However, they do not take into consideration that frequently...

2002

This paper draws from art history and perception to place computer depiction in the broader context of picture production. It highlights the often underestimated complexity of the interactions between features in the picture and features of the represented scene. Depiction is not always a unidirectional projection from a 3D scene to a 2D picture, but involves much feedback and influence from the picture space to the object space. Depiction can be seen as a pre-existing 3D reality projected onto 2D, but also as a 2D pictorial representation that is superficially compatible with an hypothetic 3D scene. We show that depiction is essentially an optimization problem, producing the best picture given goals and constraints. We introduce a classification of basic depiction techniques based on four kinds of issue. The spatial system deals with the mapping of spatial properties between 3D and 2D (including, but not restricted to, perspective projection). The primitive system deals with the di...

Proceedings of SPIE, 2012

Painters reproduce the appearances they see, or visualize. The entire human visual system is the first part of that process, providing extensive spatial processing. Painters have used spatial techniques since the Renaissance to render HDR scenes. Silver halide photography responds to the light falling on single film pixels. Film can only mimic the retinal response of the cones at the start of the visual process. Film cannot mimic the spatial processing in humans. Digital image processing can. This talk studies three dramatic visual illusions and uses the spatial mechanisms found in human vision to interpret their appearances.

Computers & Graphics, 2012

Non-photorealistic rendering (NPR) algorithms are used to produce stylized images, and have generally been evaluated on the aesthetic qualities of the resulting images. NPR-produced images have been used for aesthetic and practical reasons in media intended to produce an emotional reaction in a consumer (e.g., computer games, films, advertisements, and web sites); however, it is not understood how nonphotorealistic rendering affects the emotion portrayed in an image. We conducted a study of subjective emotional response and visual attention to five common NPR approaches, two blurring techniques, and the original image with 42 participants, and found that the NPR algorithms dampened participants' emotional responses in terms of arousal (activation) and valence (pleasure). Gaze data revealed that NPR rendering of images might reduce emotional response to an image by producing confusion, creating distracting visual artifacts, causing the loss of meaningful semantic information, or causing users to lose interest in the resulting image.

This project discusses interactive non-photorealistic rendering techniques. It is split up into two sections – outlining merhods and shading methods. Three outlining methods were implemented – stencilling, front-face culling and ink-sketching. Sten- cilling uses the stencil buffer to create a mask to draw the outline. Front-face culling uses edge localisation methods to draw the silhouette as well as the outline. Ink- sketching builds on front-face culling to make the edges look like they have been sketched with an ink pen. The second section discusses three shading methods – cellshading, ‘simple’ crosshatching and ‘fine’ crosshatching. The cellshading method uses 1D textures to make the shading of the model discrete. ‘Simple’ crosshatch- ing uses textures to shade shade the polygons. ‘Fine’ crosshatching moves beyond current research and refines the ‘simple’ crosshatching to make it more accurate on models with low polygon counts. All of the work presented in this paper is designed to work in real-time with speeds ranging from 24 to 60 frames per second.

2000

Abstract Now that technology allows us to present photorealistic animations of scenically lit objects acting in realtime, the problem of computer graphics has changed from making displays recognisable, to ensuring that users notice what they are intended to see, without being distracted by irrelevant information. Worse than that, the use of veridical displays that are intended to be lifelike runs the risk of introducing unpredictable sources of information, that can lead users to infer all sorts of unwanted details.