Non-photorealistic rendering Marko Täht

Topics Rendering Photorealism Non-photorealistic rendering

Rendering Rendering is the process of generating an image from a 2D or 3D model by means of computer programs. Multiple models are collectively called a scene file. Scene file contains: geometry, viewpoint, texture, lighting and shading. Data in scene files is passed to rendering program to be processed and output as digital image or raster graphics. Rendering image from scene file is called graphics pipeline along rendering device.

Graphics pipeline Graphics pipeline or rendering pipeline refers to sequence of steps in order to make 2D raster representation of a 3D scene. https://en.wikipedia.org/wiki/Graphics_pipeline#Stages_of_the_graphics_pipeline

Photorealism

Photorealism is a genre of art that encompasses painting, drawing and other graphic media, in which an artist studies a photograph and then attempts to reproduce the image as realistically as possible in another medium. https://www.youtube.com/watch?v=NxXwfT3LeyE

Clay-render Final picture

“If photorealism is the holy grail of CG, then a photorealistic face Face made in blender “If photorealism is the holy grail of CG, then a photorealistic face must be the holy, HOLY grail.” http://www.blenderguru.com/articles/24-photorealistic-blender-renders/

Non-photorealistic rendering Non-photorealistic rendering (NPR) is an area of computer graphics that focuses on enabling a wide variety of expressive styles for digital art. It is inspired by artistic styles. In movies and video games NPR has appeared in form of “Toon shading”. Modern use of this is cel-shaded animation.

Paint brush

Technical drawings Photorealistic images not reasonable Give better overview Exploded view

Exploded view

Leonardo da Vinci Reciprocating motion machine

Wireframe Only edges are drawn Used in making models Visualizes the structure of object Simple and fast to calculate Often used when high- framerate is needed

Pen and ink Strokes - wavy lines of varying thickness Texture - collection of strokes Tone - lines of equal weight and spacing Outlines – Boundary line of the structure to separate it from background http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.116.7335&rep=rep1&type=pdf

Watercolor Suspension of pigment particles in water, binder and surfactant Each stroke needs fluid simulation Paper affects fluid flow http://grail.cs.washington.edu/projects/watercolor/paper_tiny.pdf

http://grail.cs.washington.edu/projects/watercolor/paper_tiny.pdf

Toon shading Also known as cel-shading Designed to make models look flat by using less shading color The name comes from cels (short for celluloid), the clear sheets of acetate, which are painted on for use in traditional 2D animation. Spongebob Squarepants season 4-8

Sobel filter Creates image emphasizing on edges. It is a discrete differentiation operator, computing an approximation of the gradient of the image intensity function. Operator is based on convolving the image with a small, separable, and integer-valued filter in the horizontal and vertical directions and is therefore relatively inexpensive in terms of computations. https://en.wikipedia.org/wiki/Sobel_operator

Why not in real life

Games that use cel-shader https://www.youtube.com/watch?v=tWVLDq661H Q

Borderlands

Antichamber

The Simpsons Game

Creating cel-shader Vertex shader: uniform vec3 lightDir; //Defined in world space varying float intensity; void main() { intensity = dot(lightDir, gl_Normal); gl_Position = ftransform(); }

Fragment shader: Sets the fragment color based on intensity varying float intensity; void main() { vec4 color; if (intensity > 0.95) color = vec4(1.0, 0.5, 0.5, 1.0); else if (intensity > 0.5) color = vec4(0.6, 0.3, 0.3, 1.0); else if (intensity > 0.25) color = vec4(0.4, 0.2, 0.2, 1.0); else color = vec4(0.2, 0.1, 0.1, 1.0); gl_FragColor = color; }

Result