Advanced Computer Graphics Interview Questions: Algorithms, Transformations & 3D
This advanced guide prepares you for in-depth computer graphics interviews by exploring complex algorithms, 3D transformations, and display technologies. We delve into fractal generation (Mandelbrot, Julia sets, Koch curve), animation techniques (morphing, tweening), and curve representations (B-splines, Bézier curves). This resource provides detailed answers to challenging computer graphics interview questions, covering topics like space partitioning, projection types (parallel, perspective), and color models (RGB, CMY, HSV). Prepare for expert-level discussions on advanced graphics concepts with this comprehensive guide.
Computer Graphics Interview Questions and Answers
What is Computer Graphics?
Computer graphics involves generating, manipulating, storing, and displaying images using computers. It's a vast field used in many applications, from simple diagrams to complex 3D models and animations. A computer graphics system typically consists of a host computer, processor, memory, frame buffer, display device, and input devices.
Properties of Video Display Devices
Key properties of video display devices include:
- Persistence: How long a pixel remains illuminated.
- Resolution: The number of pixels displayed.
- Aspect ratio: The ratio of width to height.
Applications of Computer Graphics
Computer graphics is used in diverse applications including:
- Computer-aided design (CAD).
- Creating illustrations and presentations.
- Film and television (special effects).
- Video games.
- Simulations and modeling.
Raster vs. Vector Graphics
| Raster Graphics | Vector Graphics |
|---|---|
| Made up of pixels; resolution-dependent (quality degrades when scaled). | Made up of paths and mathematical equations; resolution-independent (scales without quality loss). |
| Suitable for photorealistic images. | Better for illustrations, logos, and designs with sharp lines and solid colors. |
Advantages and Disadvantages of Direct View Storage Tubes (DVSTs)
| Advantages | Disadvantages |
|---|---|
| No refresh needed; can display complex images at high resolution without flicker. | No color; parts of the image cannot be erased; redrawing complex images can be slow. |
Aspect Ratio
Aspect ratio is the ratio of an image's width to its height. For example, a 4:3 aspect ratio means the width is four units for every three units of height.
Raster vs. Vector Graphics (Details)
| Raster Graphics | Vector Graphics |
|---|---|
| Image is composed of a grid of pixels. | Image is composed of lines and curves defined mathematically. |
| Resolution-dependent; quality degrades when scaled. | Resolution-independent; scales without quality loss. |
DDA (Digital Differential Analyzer) Algorithm
The DDA algorithm is a simple line-drawing algorithm. It's relatively fast but can be less accurate than other algorithms due to its reliance on floating-point arithmetic, potentially resulting in rounding errors.
DDA vs. Bresenham's Line Algorithm
| DDA | Bresenham's |
|---|---|
| Uses floating-point arithmetic. | Uses integer arithmetic. |
| Slower. | Faster. |
| Less accurate. | More accurate. |
| More computationally expensive. | Less computationally expensive. |
Translation in Computer Graphics
Translation moves an object along a straight-line path. For a 2D point (x, y), translation by (tx, ty) results in a new position (x + tx, y + ty).
Reflection in Computer Graphics
Reflection creates a mirror image of an object about a specified line (axis of reflection).
Shearing in Computer Graphics
Shearing distorts an object by shifting its points along a specified direction. It creates a skewed or slanted effect.
Viewing Transformation
A viewing transformation maps a 3D scene to a 2D view on the screen. It defines the camera's position, orientation, and field of view.
Clipping and Clip Window
Clipping is the process of removing parts of an object that lie outside a specified viewing area (clip window). It determines what's visible on the screen.
Parallel vs. Perspective Projection
| Parallel Projection | Perspective Projection |
|---|---|
| Projection lines are parallel; preserves relative proportions. Used for technical drawings. | Projection lines converge at a point; creates a realistic effect but doesn't preserve proportions. |
Space Partitioning Representations
Space partitioning divides 3D space into smaller regions to improve rendering and searching efficiency. Octrees are a common space partitioning structure.
Quadric Surfaces
Quadric surfaces are 3D shapes defined by second-degree equations. Examples include spheres, ellipsoids, paraboloids, and hyperboloids.
Critical Fusion Frequency (CFF)
CFF is the minimum frequency at which a flickering light source appears as a continuous, steady light. This is dependent on factors such as brightness and contrast.
CMY vs. HSV Color Models
| CMY (Cyan, Magenta, Yellow) | HSV (Hue, Saturation, Value) |
|---|---|
| Subtractive color model; used for printing. | Additive color model; intuitive for users. |
Dithering
Dithering is a technique used to create the illusion of colors or shades not directly available on a display device by using a pattern of existing colors or shades. This allows for simulating more colors than are physically present in the display device's palette.
Properties of Light
- Reflection
- Refraction
- Dispersion
- Interference
- Diffraction
Computer Animation
Computer animation creates the illusion of motion by rapidly displaying a sequence of slightly different images.
Keyframe Systems
Keyframe animation systems allow animators to specify key poses (keyframes), and the system automatically generates the intermediate frames.
Fractals
Fractals are shapes that exhibit self-similarity at different scales; they appear similar no matter how much they are magnified or reduced.
Turtle Graphics
Turtle graphics is a programming method where you give instructions to a "turtle" to draw shapes, lines, etc. This creates visual outputs. It's often used in educational programming and for creating fractal images.
Turtle graphics is a method of creating vector graphics using a relative cursor on a Cartesian plane. It's a common feature in programming languages like Logo.
Turtle Graphics Attributes
- Position: (x, y) coordinates.
- Orientation: Angle (usually in degrees) relative to the x-axis.
- Pen State: Whether the pen is up (no drawing) or down (drawing).
Mandelbrot Set vs. Julia Set
| Mandelbrot Set | Julia Set |
|---|---|
| A set of complex numbers that do not diverge when repeatedly subjected to a specific mathematical transformation (zk+1 = zk² + c). Forms a famous fractal. | A family of fractals, each generated by a specific constant value (c) in the transformation: zk+1 = zk² + c. Extremely complex shapes. |
Koch Curve
The Koch curve is a fractal curve constructed by recursively replacing line segments with four smaller segments forming an equilateral triangle. It demonstrates self-similarity and infinite length within a finite area.
Morphing and Tweening
- Morphing: Gradually changing an object's shape from one form to another.
- Tweening: Generating intermediate frames between keyframes in an animation.
Peano Curves
Peano curves are space-filling curves; they have a dimension of 2, meaning they can completely fill a two-dimensional area.
Scripting Systems in Computer Graphics
Scripting systems allow users to define objects and animation sequences using a scripting language. This provides a flexible and efficient way to create and control complex graphical scenes.
Refresh Buffer (Frame Buffer)
The frame buffer is a memory area that stores the pixel data for an image. This data is used to refresh the display, creating the visual output.
Resolution in Computer Graphics
Resolution refers to the number of pixels used to represent an image. Higher resolution means more detail.
Window and Viewport
A window is a region in world coordinates that you want to display. A viewport is the area on the screen where the window is mapped.
Window Port vs. Viewport
A window port specifies a portion of the image to be displayed in the window. The viewport specifies where this portion appears on the screen.
Blobby Objects
Blobby objects are shapes that don't have a fixed, well-defined surface, often changing based on interactions or other factors. Their surfaces appear soft and deformable.
Spline Curves
Spline curves are smooth curves created by connecting polynomial segments. They are widely used in computer graphics for modeling smooth shapes and surfaces.
B-Spline vs. Bézier Curves
| B-Spline Curves | Bézier Curves |
|---|---|
| The degree of the polynomial is independent of the number of control points; offers local control. | The degree of the polynomial is fixed by the number of control points; does not offer local control (changing one control point affects the entire curve). |
Rasterization
Rasterization is the process of converting vector graphics into a raster image (a grid of pixels) for display on a screen.
Representing Curves in Graphics
Curves can be represented mathematically (using equations) or as a sequence of points. Both methods are used in computer graphics, each with its own advantages.
Chromaticity Diagram
A chromaticity diagram is a tool for visualizing colors and determining whether a color is reproducible on a given device.
Interactive Computer Graphics
Interactive computer graphics involve real-time interaction between the user and the computer-generated image. This allows for manipulation and modification of the image.
RGB Color Model
The RGB (Red, Green, Blue) color model is an additive color model where red, green, and blue light are combined to create a wide range of colors. It's used in electronic displays like computer monitors and televisions.
VDU (Visual Display Unit)
A VDU is a display device for showing images generated by a computer. Modern VDUs use LCD technology; earlier models used CRTs.
Projection in Computer Graphics
Projection transforms 3D objects into a 2D representation for display on a screen. Various projection techniques (parallel, perspective) exist.
Advantages of Electrostatic Plotters
- Faster than pen plotters.
- High resolution.
- Color capability.
Advantages of Laser Printers
- High speed.
- High resolution.
- Cost-effective.
- Low maintenance.
3D Viewing Devices
- Stereoscopic systems
- Virtual reality (VR) systems
Addressability
Addressability is the number of individually addressable points on a display device.
Scan Code
A scan code is a unique code generated by a keyboard when a key is pressed.