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.

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.

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.

Cel-Shading

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

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.