Techniques On Non-Photorealistic Rendering

Based on the compare between photorealistic and non-photorealistic, the author gives a systematic survey on the objective, methods and the state and applications of non-photorealistic graphics, and then presents some key techniques on non-photorealistic rendering (NPR).The first technique the author presents is silhouette detecting, a fundamental technique in non-photorealistic rendering. Silhouette plays a critical role in NPR. NPR effect greatly depends on the silhouette performance. And it's also a key technology for speedup in real-time NPR applications. Silhouette plays an important role in our visual interpretation of 3D shape, and they are necessary for both perception and taste, which represents the contour and basic shape of the model. Artists and designers therefore often emphasize silhouettes, either by drawing them explicitly or by contrast enhancement across silhouette boundaries. In cartoon, silhouettes are used for shape expressing, and broad brushes for main characters, and this method also frequently applies in the technical drawing. Silhouette detecting algorithms can be divided into two aspects, image space algorithm and object space algorithm. This paper presents a modified hybrid silhouette detecting algorithm both take the advantages of image space and object space algorithms; hardware accelerating techniques are also used to solve the bottle-neck in silhouette detecting. We mainly focus on the fist three types of silhouette, contours and feature lines. Using previous presented algorithms; we use two methods to detect these three types of silhouette. We use back-face wire-frame drawing technique on the first type and vertex shader on the others. Further more, by computing dot matrix on the vertex shader; we successfully reduce the computations on CPU. By this algorithm we not only lighten the geometry information dependence, extend our algorithm to dynamic models, but also get a flexible control on the width of the silhouette and thus a better final result.Stylized silhouette is an important artistic effect in non-photorealistic rendering. We can simulate many natural materials. Based on the discussion of the current popular stylize algorithms, we present a hybrid stylize algorithm base on image space stroke reconstruction mainly. The system starts at the 3-D model of the scene, by specific rendering the 3-D model, we get a ID reference image, then we link pixels with the same color into stroke particles, by applying connecting rules on these single particles and referencing the geometry information of the 3-D model, we get strokes as long as possible. These strokes are the basic of the stylized silhouette. Appling brush tools on these strokes product different art styles. The algorithm we presenttakes the facilities of the stencil buffer and vertex shader to render the ID reference image, add feature lines on the previous algorithms. Reconstructing stroke particles on ID reference avoid visibility testing, so the main bottleneck in stylized silhouette rendering is solved. At the same time, we solved the weakness applying stylized rendering on the result of image space silhouette detecting algorithms. Our algorithm is more robust than previous algorithms on stroke connecting problem etc.Cartoon rendering or cel shading is a new application of non-photorealistic rendering raised in recent years. The motivation of cartoon rendering is auto generating conventional cartoon style pictures by the computer. Cartoon rendering techniques will be widely used in games and education service. Many games applying cartoon rendering give a new strike in the game production. We discuss the key technologies in cartoon rendering and presented a real-time hardware accelerated cartoon rendering model. Profit from our silhouette detecting algorithm, we do better in drawing the outlines of the cartoon model and enhanced the interior features. Compare to the previous CPU based shading algorithm, we use vertex shader to simulate the lighting model in cel shading with real-time speed. We also apply ambient light; specula...