1. Definition

Ray tracing is a rendering technique in computer graphics used to generate realistic images by simulating the physical behavior of light.

• It traces the path of light rays from the eye (camera) into the scene, following reflections, refractions, and shadows.
• Produces highly realistic effects like mirrors, transparency, soft shadows, and global illumination.

Key Idea: “Simulate light paths to compute color and brightness of pixels.”

2. Basic Concept

• Each pixel on the screen corresponds to a ray shot from the eye (camera) into the scene.

• The ray may:

  1. Intersect an object
  2. Reflect off the object
  3. Refract through transparent materials
  4. Reach a light source

• The color and intensity of the pixel are computed by combining ambient, diffuse, specular, reflection, and refraction contributions.

3. Steps in Ray Tracing

Step 1: Ray Generation

• Generate primary rays from the eye through each pixel on the view plane.

Step 2: Ray-Object Intersection

• Determine which object the ray intersects first in the scene.
• Solve geometric equations for intersections (spheres, planes, triangles, etc.).

Step 3: Shading

• Compute color at the intersection point using a lighting model (e.g., Phong illumination).

• Consider:

  • Ambient light: general background light
  • Diffuse reflection: light scattered evenly
  • Specular reflection: shiny highlights

Step 4: Reflection and Refraction

• Generate secondary rays:

  • Reflection rays: bounce off reflective surfaces
  • Refraction rays: pass through transparent materials

Step 5: Shadow Rays

• Check if intersection points are in shadow by sending rays to the light sources.
• If blocked, that point is in shadow.

4. Advantages of Ray Tracing

• Produces highly realistic images
• Handles shadows, reflections, and transparency naturally
• Supports complex lighting effects like caustics and refraction

5. Disadvantages

• Computationally expensive – slow for complex scenes
• Requires optimization techniques (like spatial partitioning, bounding volume hierarchies)

6. Summary Table

Key Points:

• Ray tracing is fundamental in photorealistic rendering.
• Modern graphics use hybrid approaches combining ray tracing with rasterization for speed.
• Used extensively in movies, simulations, CAD visualization, and visual effects.