Illumination Model

• Shading is the process of adding light and color effects to surfaces in computer graphics to make objects look realistic and three-dimensional.
• It determines how light interacts with the surface of an object.
• Shading is important because, i.e., without shading, objects look flat, no depth perception. no realistic appearance, etc.
• Shading creates smooth surfaces, realistic lighting, shadow effects, depth illusion, etc.
• The shadow concept is used in software like Blender and Autodesk Maya.

Types of Shading

• Flat Shading

  • This shading has one color per polygon.
  • In this, lighting is calculated once per surface.
  • It is fast but not smooth.
  • It is used in simple graphics.
  • It produces sharp edges.

• Gouraud Shading

  • In this, the lighting is calculated at the vertices.
  • In this, colors are interpolated across the surface.
  • It is smoother than flat shading.
  • It is faster than Phong.
  • It reduces sharp edges.

• Phong Shading

• • In this, lighting is calculated at every pixel.
  • It produces smooth and shiny surfaces.
  • It is more realistic. 
  • It is developed based on the work of Bui Tuong Phong.
  • It has the best visual quality.
  • It is slower than Gouraud.

Ray Tracing

Definition

• Ray tracing is a computer graphics technique for generating a digital image by tracing the paths of light as it passes through a scene and strikes the image plane.
• Ray tracing is an advanced and powerful rendering technique in multimedia graphics to create realistic images by simulating the real-world light behavior (how light rays travel and interact with objects) to produce highly realistic images. 
• Ray tracing is a technique that generates images by tracing the path of light rays from the viewer’s eye (camera) into the scene and calculating how they interact with objects.

Features

• It simulates the physics of light.
• It doesn’t fake effects; it calculates them. This is why it produces incredibly realistic results but is computationally very expensive. Although this technique is computationally expensive, it is widely used in films, gaming, and advanced visualization systems.
• It produces highly realistic images with reflections, refractions, shadows, transparency, global illumination effects, etc.
• Ray tracing is a revolutionary graphics technique that simulates the physical behavior of light to create incredibly lifelike images.
• It produces realistic shadows.
• It gives accurate reflections.
• It gives natural refractions.
• It gives soft shadows.
• It shows global illumination effects

Ray Tracing Working Mechanism

• The basic steps of ray tracing are –
  • Ray Generation – Rays are shot from the camera into the scene.
  • Ray-Object Intersection – The system checks which object the ray hits first.
  • Shading Calculation – Lighting is calculated at the intersection point.
  • Secondary Rays –
    • Reflection rays (for mirrors).
    • Refraction rays (for glass/water).
    • Shadow rays (to check light blockage).
  • Color Calculation – Final pixel color is computed using lighting models.

Example

Suppose we see a glass ball-

• Ray tracing calculates how light enters,
• How light bends inside (refraction),
• How light reflects on the surface,
• How light casts a shadow behind it,
• How light produces realistic image.

Types of Rays

• Primary Rays – From the camera to the objects.
• Shadow Rays – To light sources.
• Reflection Rays – For shiny surfaces.
• Refraction Rays – For transparent objects.

Advantages

• It gives a very realistic output.
• It is an accurate light simulation.
• It has better quality than rasterization.

Disadvantages

• It has a high computational cost.
• It has a slower rendering time.
• It requires powerful hardware.

Use/Applications

• Ray tracing is widely used in-
  • Animated movies by studios like Pixar.
  • Modern video games like Cyberpunk 2077.
  • GPUs such as the NVIDIA RTX series.
  • Architectural visualization.
  • 3D modeling software like Blender.