The early adoption and subsequent interest in photorealistic rendering by the graphics community is most likely due to the “mission statement” of photorealistic rendering: “Create an image that is indistinguishable from a photograph.” This mission statement gives photorealistic rendering a visual “Turing test”, and an easily defined metric for a successful image. Artistic computer graphics does not have a single mission statement. Instead, researchers are pursuing a number of image creation goals. The goals of Artistic computer graphics include simulating traditional artistic media, understanding the human visual system, communicating effectively with low bandwidth, abstracting images, enhancing learning, and improving user interaction.
The control of detail in an image for purposes of communication is becoming the hallmark of artistic computer graphics. Often this control of image detail is combined with stylization to evoke the perception of complexity in an image without an explicit representation. Artistic images also provide a more natural vehicle for conveying information at different levels of abstraction and detail. Seven occasions when an artistic computer generated image has an advantage are listed below.
1. Image Reproducibility: In a technical journal printed in black and white, fully shaded three-dimensional geometry may not print well. For example, photographic images do not copy or fax as well as line art images.
2. Medical Visualization: Researchers are focusing on providing artistic algorithms, which can be manipulated interactively, for real time visualizations of volume data. A good example is the visualization of electric fields inside the human body.
3. Communication of Abstract Ideas: The human visual system expects realistically rendered characters to behave realistically. Therefore, nonphotorealistic animation can be used to express ideas beyond the physical and logical norm, in a way that is acceptable to a general audience. An example of this is force diagrams used in physics textbooks.
4. Evoking the Imagination: Simple line drawings can communicate abstract ideas in ways that a photograph cannot. In a photorealistic image, everything in the scene is rendered in fine detail, leaving little to the imagination. In comparison, by not depicting every detail, a nonphotorealistic image allows the viewer to share in the interpretive process.
5. Animation: When creating an animation it is necessary to focus the attention of the audience on the relevant actions and elements in the scene. A viewer inspecting the fine details of a photorealistic scene can miss the big picture. Most nonphotorealistic techniques employ an economy of line, limiting the detail in a scene, which makes directing the attention of the viewers easier for an animator.
6. Compression: By not depicting all the detail required for photorealistic images, nonphotorealistically rendered computer graphics images typically take less time to create, can be rendered to the screen faster, and use less storage space. For example, half-tone images yield the same shape from shading cues as traditionally rendered computer graphics images when viewed from a distance. However, the half-tone images require between one tenth and one one-hundredth of the storage space.
7. Communication of Design or Process Completeness: Photorealistic rendering implies an exactness and perfection that may overstate the fidelity of the simulated scene to a photograph. Artistic computer graphics can aid a viewer in understanding that the image they see is only an approximate depiction of a scene. An excellent example of this phenomena is architectural rendering. Architects have found that on-site building conditions and variations in regional building codes can lead to last minute changes in building plans. If clients are shown realistic images of the proposed building these last minute changes can come as a shock, leading to angry, disappointed clients. However, if the clients are shown nonphotorealistic images of the proposed building clients tend to accept the design process as incomplete and the plans as changeable. Therefore, the clients usually accept on-site changes.
