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Non-Photorealistic Rendering: Exploring Cel-Shading and Pen-and-Ink Illustration

This project explores non-photorealistic rendering (NPR) techniques, specifically focusing on implementing cel-shading and pen-and-ink illustration algorithms from scratch.

Implemented Algorithms

Sobel Edge Detection

  • Post-render edge detection using Sobel Operator on depth values.
  • Produces outlines by comparing z-buffer values instead of color.

Sobel Outline On Utah Teapot

First and Second Order Sobel

  • Distinguishes internal and external edges using first and second-order operators.
  • Captures abrupt and subtle depth changes within the model.

Internal and external edges of teapot model

Sobel with Normalization

  • Normalizes gradients to improve edge distinction.
  • Enhances accuracy and reduces artifacts in edge detection.

Cross-Hatching and Stippling Techniques

  • Utilizes luminance-based cross-hatching and stippling for artistic rendering.
  • Adjusts line frequency based on luminance, enhancing visual aesthetics.

Progression of pen-and-ink illustration

Cel-Shading

  • Implements cartoon-like shading by refining lighting techniques.
  • Focuses on ambient lighting and scene illumination for a cel-shaded effect.

Utah teapot with cel-shading

References

  • Freeman, H., & Serger, O. (1990). Generalized and separable sobel operators.
  • Saito, T., & Takahashi, T. (1990). Comprehensible Rendering of 3-D Shapes.
  • Parameter Values for the HDTV Standards for Production and International Programme Exchange: Recommendation ITU-R Bt. 709-5.
  • Decaudin, P. (1996). Cartoon-Looking Rendering of 3D Scenes.