Week 8 - Rasterisation and Anti-Aliasing Flashcards

1
Q

Name 2 examples of vector displays.

A

Pen plotters
Tektronix cathode ray tubes

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2
Q

Name 5 examples of raster displays.

A

Monitors
Televisions
Laser, ink-jet, dot matrix printers
Liquid crystal displays
Arrays of LEDs

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3
Q

What is rasterisation?

A

The conversion of ideal, mathematical graphics primitives onto raster displays

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4
Q

What is scan conversion?

A

Rasterisation line by line of the raster display

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5
Q

How does scanline interpolation work?

A

Use Z-buffer algorithm to determine screen locations of vertices

Intensities or normals interpolated from vertices

Interpolate along scanline from edges

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6
Q

What is the parity rule for filling polygons?

A

A point is inside a polygon if a line to a distant point intersects boundary an odd number of times

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7
Q

What is the non-zero winding number rule for filling polygons?

A

A point is inside a polygon if the polygon winds clockwise around the point a non-zero number of times

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8
Q

What is scan-line coherence?

A

An interior pixel is adjacent to another interior pixel unless a boundary is encountered

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9
Q

How does scan-line coherence work?

A

For each scan line:
- Find intersections of scan line with all polygon edges
- Sort intersections into increasing order of x coordinate
- Fill alternate segments of scan line (spans) according to parity rule

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10
Q

What are the two ways to choose which pixels to illuminate for a line?

A

Every pixel the line intersects

The vertically closest pixel

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11
Q

What algorithm is used to illuminate the pixel vertically closest to a line?

A

Naïve midpoint algorithm

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12
Q

What does DDA stand for?

A

Digital Differential Analyser

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13
Q

What is the Bresenham circle algorithm?

A

Choose pixel with centre closest to circle

Work on a single octant and draw others by symmetry

Can be written in integer arithmetic

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14
Q

What causes aliasing?

A

Undersampling (not taking enough discrete samples to capture a fast rate of change)

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15
Q

What does ADC stand for?

A

Analog-to-Digital Converter

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16
Q

What does DAC stand for?

A

Digital-to-Analog Converter

17
Q

Why will there always be aliasing, no matter how densely we sample?

A

Repetitive patterns can have arbitrarily high frequencies due to perspective effects

Object edges create sharp changes -> high frequencies

18
Q

How does anti-aliasing work in computer graphics?

A

The scene is rendered

No access to a continuous image

Low-pass filtering of continuous image has to be simulated/approximated

19
Q

What are the three filtering approaches?

A

No filtering

Pre-filtering (simulation)

Post-filtering (approximation)

20
Q

What does SSAA stand for?

A

Super-Sampling Anti-Aliasing

21
Q

What is SSAA?

A

Take many point samples per pixel, and assign grey level as the (weighted) average value

22
Q

What is a pro and a con of SSAA?

A

Pro: smoother, nicer looking results

Con: ridiculously expensive and can lead to low performance and framerate

23
Q

What is multisample anti-aliasing?

A

Faster processing by processing fragment shaders only once, and only supersampling depth and stencil buffers

24
Q

What does FXAA stand for?

A

Fast Approximate Anti-Aliasing

25
What is FXAA?
Pixel-level fast algorithm (implemented as fragment shader) identifies depth edges in the image, and smooths edges at pixel level
26
What are two issues to be aware of with anti-aliasing and texture maps, and how are they fixed?
Compression (several texels map to a single pixel) - texture image should be sampled many times to calculate pixels, but this is very expensive Magnification (single pixel lies deep within texel) - higher resolution texture map required
27
What are the three types of filtering in MIP mapping?
Bilinear filtering, trilinear filtering, anisotropic filtering
28
What is bilinear filtering?
Approximate pixel value from pixels around it
29
What is trilinear filtering?
Also approximate between levels of MIP mapping
30
What is anisotropic filtering?
Sample texture with different horizontal and vertical scale ratios
30
What is anisotropic filtering?
Sample texture with different horizontal and vertical scale ratios