Computer Graphics Flashcards

Flashcards for reviewing computer graphics concepts.

Motion capture

Capturing the motion of a model from a real life actor, usually done by placing markers on the actor’s body to record motion in real time. The markers are tracked using calibrated cameras and the joint position is estimated using triangulation.

Rendering Pipeline

Includes stages like modelling, transformation, lighting, rasterisation, and pixel shading. It transforms 3D objects into a 2D image by projecting vertices onto the screen, applying lighting and shading calculations, and rasterising the result into pixels for display.

Alpha Channel in Texture Mapping

Represents transparency. It allows textures to have varying levels of opacity, enabling the rendering of transparent objects like glass, while maintaining realistic interactions with other objects.

MIP Mapping

Improves texture rendering by creating a series of prefiltered texture images at different resolutions. Its advantages include better texture quality at varying distances, enhanced performance, and prevention of texture popping artefacts. Particularly useful in real-time graphics and scenarios where consistent texture quality across distances is critical.

Global Illumination

Simulates how light interacts with surfaces and scatters throughout a scene, considering specular and diffuse lighting. Examples include ray tracing, path tracing and radiosity. It differs from local illumination models, which does not consider any object to object interactions.

Gouraud shading

L[D|S]E (single diffuse or specular reflection).

Phong shading

L[D|S]E (single diffuse or specular reflection).

Ray tracing

LDS*E (single diffuse but multiple specular reflections).

Radiosity method

LD*E (multiple diffuse reflections).

Normals in Lighting Calculations

Normals determine how light interacts with a surface, affecting its brightness and shading. Different lighting models use normals to compute diffuse and specular reflections accurately.

Normals in Bump Mapping and Displacement Mapping

Normals are employed in bump mapping and displacement mapping to simulate fine surface details without altering the geometry. By perturbing normals these techniques create the illusion of bumps and deformations.

Normals in Surface Smoothing

Normals play a role in creating smooth surfaces. In techniques like Gouraud and Phong shading, normals are interpolated across vertices to create the illusion of smooth shading.

Phong Model for Caustics

Only takes into account the local geometry and the direction of incoming light. It would estimate a reflection intensity that would not be affected by the presence of the gemstone at all. The colours of the velvet surface would be represented without any shadows or caustics.

Whitted Ray Tracing for Caustics

Since the velvet surface is approximated as an ideal diffuse surface, for any point on the surface, the backward tracing of the corresponding ray would stop there. Then, a shadow ray from this point to the light source would be created. Since the gemstone occludes the path of this shadow ray from the point to the light source, the point would be classified as being in the shadow. The area would be rendered as being completely in the shadow, without any caustics.

Path Tracing for Caustics

For every pixel on the cushion surface, many rays would be shot and each one of them would follow a random walk. Some of them would be refracted within the gemstone and, for the bright regions of the caustics, would eventually hit the light source. Aggregating the contributions of all random rays, path tracing would simulate in a very realistic way the complex interactions between the light and the objects in the scene. The illumination on the cushion surface would be very realistic and would include the caustics.

Z-buffer algorithm

Handles occlusions by recording the depth of each rendered pixel and overwriting it if a new, closer surface is rendered on the same location.

Painters Algorithm

A better choice to render a scene with translucency because Z-buffer cannot deal with translucency easily as it requires to store multiple depths in the depth buffer. Painters can render a translucent bar by blending the pixel’s colour with the previous colour using the appropriate alpha instead of overwriting it.