Editing Cel shading (section)

==Outlines==
===Wireframe method===
Black ink [[Outline drawing|outlines]] and [[contour line]]s can be created using a variety of methods. One popular method is to first render a black outline, slightly larger than the object itself. [[Hidden surface determination|Back-face culling]] is inverted and the back-facing triangles are drawn in black. To dilate the [[silhouette]], these back-faces may be drawn in [[Wire frame model|wireframe]] multiple times with slight changes in translation. Alternatively, back-faces may be rendered solid-filled, with their vertices translated along their [[vertex normal]]s in a [[vertex shader]].  After drawing the outline, back-face culling is set back to normal to draw the shading and optional textures of the object.  Finally, the image is [[Compositing|composited]] via [[Z-buffering]], as the back-faces always lie deeper in the scene than the front-faces.  The result is that the object is drawn with a black outline and interior contour lines.  The term "cel-shading" is popularly used to refer to the application of this "ink" outlining process in animation and games, although originally the term referred to the flat shading technique regardless of whether the outline was applied.<ref>{{cite book|url=http://raulreyesfinalproject.files.wordpress.com/2012/12/dissertation_cell-shading-raul_reyes_luque.pdf|title=The Cel Shading Technique|last1=Luque|first1=Raul|date=December 2012|access-date=December 2, 2014}}</ref>

The [[Utah teapot]] rendered using cel shading:

[[File:Celshading teapot large.png|700px|The Utah Teapot rendered using cel-shading.]]

# The back faces are drawn with thick lines
# The object faces are drawn using a single color
# Shading is applied

Steps 2 and 3 can be combined using [[multitexturing]] (part of texture mapping).

=== Edge-detection method ===
{{multiple image

|perrow=3
|align=center
|header=2D [[image processing]] outlining technique

|image1=Cel shading no outlines.png
|caption1=First, the scene is rendered with cel shading to a screen-sized color texture.
|width1=250
|caption2=Then, [[z-buffer|depth information]] of the scene is rendered to a screen-sized texture.

|image2=Cel shading depth.png|width2=250

|caption3=[[World space|World-space]] [[surface normal]]s are rendered as a screen-sized texture.

|image3=Cel shading normals.png|width3=250

|caption5=Finally, a [[Sobel filter]] or similar [[Edge detection|edge-detection]] filter is applied to the normal and depth textures to generate an edge texture. [[Texels]] on detected edges are black, while all other texels are white.

|image5=Cel shading edge detection.png|width5=250

}}
{{multiple image

|align=center
|image1=Cel shading composite final image.png|
|width1=800|
|caption1=Finally, the edge texture and the color texture are [[Compositing|composited]] to produce the final [[Rendering (computer graphics)|rendered]] image.
}}