Cartes mémoires Interactive Computer Graphics (Seite 2 von 7)

Cartes-fiches	272
Langue	English
Catégorie	Informatique
Niveau	Université
Crée / Actualisé	27.07.2022 / 31.07.2022
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Asking small children, what the number halfway in between 1 and 9 is, often results in the answer of 3 instead of 5. Why is that the case?

Smaller numbers are more familiar at young age and larger numbers therefore seem to be further away.

The number is in half way in between on the logarithmic scale.

Steven’s Power Law

The Uncertainty Principle

Most visual sensors and displays have a characteristic nonlinear relationship of input and output signal levels. How can we compensate for this distortion?

Use Gamma correction.

It is not possible, because we would need to have the relationships of all devices.

Find the inverse function of the distortion and apply it to the signal.

Increase / Decrease the brightness by multiplying with a factor.

Which postulation describes the connection between a stimulus’ intensity and the perceived intensity?

Stephen’s Power Law

Exponential Stimulus Law

Stelato’s Increase Law

Weber-Fechner Law

How does a stimulus’ intensity and the perceived intensity relate to one another?

differential relationship

nonlinear relationship

oscillating relationship

For which areas is the eye more sensitive?

dark

bright

The eye ... discontinuities of brightness.

smooths

accentuates

An intensity of 1 is mapped onto an 8 bit number with ɣ = 0.3. Which value is assigned to the number?

0

1

76

255

256

The definition of picture elements (or pixels for short) given does not match the structure and principles of human vision and the eyes on a fundamental level. What are reasons for this mismatch?

Different geometry of displays and visual fields.

No homogeneous distribution of receptors

Specialized cells not for image formation but for movement.

There is no single framerate in nature.

Cone cells have no primary color.

The graphics card is sending pixel information to the screen for every frame to be rendered. Let us assume a display resolution of 1920 (h) x 1080 (v) with a fixed refresh rate of 60 Hz, 8 bits per pixel primary color channel, three channels, and no compression. How much net bandwidth do the components have to provide.

100 Mbit/s

1,43 Gbit/s

2,99 Gbit/s

9.001 Gbit/s

In which situations does it seem advisable to choose a vector graphic over a raster graphic.

User interface objects

Sensory input & Display output

Logo Design & Text

Image Manipulations

CAD Modeling

Which formats use primarily Vector Graphics?

Postscript

TIFF

HTML

SVG

PNG

Which formats use primarily Raster Graphics?

TIFF

JPG

Postscript

HTML

PNG

Which image descriptions are resolution independent?

scanned art

text

bélèr curves

polygons

How can color be described by a limited amount of bits?

By indicating values of a particular color model.

By entangling quants with the appropriate natural occurrence.

By using a pointer into a color table.

By describing a factor on top of a predefined value.

Which color model codings typically uses 8bits?

256 colors out of a color table

Real Color: 256 shades for RGBA values

512 colors out of a color table

True Color: 256 shades for each primary color

Which color model codings typically uses 24bits?

256 colors out of a color table

Real Color: 256 shades for RGBA values

512 colors out of a color table

True Color: 256 shades for each primary color

What is aliasing?

An effect that causes different signals to become indistinguishable.

A rasterization approach for smooth lines.

A sampling method to reconstruct the original, continuous signal.

What types of aliasing exist?

Spacious Aliasing

Continuous Aliasing

Temporal Aliasing

Random Aliasing

Spatial Aliasing

What is true of the Supersampling approach?

Supersampling uses multiple samples per pixel.

Supersampling uses multiple pixels per sample.

Supersampling averages colors.

Supersampling maximizes colors.

What is true of grid sampling?

Grid sampling samples in regular intervals.

Grid sampling avoids moiré patterns.

Grid sampling amplifies grids.

Grid sampling prevents aliasing.

What is true of stochastic sampling?

Stochastic sampling samples at random points.

Stochastic sampling samples every pixel uniformly.

Stochastic sampling produces coarse grained images.

Stochastic sampling substitutes aliasing with noise.

What is true of stratified sampling?

Stratified sampling produces less noise than grid sampling

Stratified sampling samples in homogenous subgroups.

Stratified sampling maximizes the variance in random selection.

Stratified sampling limits the variance in random selection.

Stratified sampling reduces the noise.

Audiophiles do love analog and lossless digital records. The most prominent argument is recognizable sound quality manifesting itself in less noise. Under which circumstances is the Nyquist-Shannon Theorem contradicting better sound quality and renders the lossy compressions like MP3 a competitive alternative.

Data is sampled with 48kHz.

There are no frequencies in the scene to be recorded higher than the sampling rate allows.

At the time of recording, higher frequencies than the theorem allows are cut off by a filter.

Data is sampled with 128kHz.

What can a recorder do before recording to diminish aliasing within audio and visual data?

Nothing, there will always be noise when using digital sampling.

Using a high enough sampling frequency so that the artifacts are not as prominent

Averaging over the sampled data.

Avoid high frequencies by compatible countermeasures in the setup

Which formular describes a sphere with center c = (h, j, k) and radius r?

(x - h)² + (y - j)² + (z - k)² = r²

(x + h)² + (y + j)² + (z + k)² = r²

(x - h)³ + (y - j)³ + (z - k)³ = r³

Which statements about photogrammetry are correct ?

… the measurement of light, in terms of its perceived brightness to the human eye.

… obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant imagery and other phenomena.

… is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film.

Which of the following steps are correct for ray tracing?

Transform objects.

Trace rays into scene.

Intersection? → rebound.

Trace rays to edges.

Calculate/combine pixel color.

Which of the following steps are correct for rasterization?

Transform objects.

Calculate vertex color.

Project geometry to screen.

Raster geometry to colors.

Calculate/combine pixel dimension.

Which of the following color to wavelength assignments are correct?

Yellow: 600 nm

Violet: 380 nm

Orange: 600 nm

Blue: 680 nm

Green: 510 nm

Which color space is biology-oriented?

CIE XYZ

RGB

HSV

Which color space is hardware-oriented?

CIE XYZ

RGB

HSV

Which color space is user-oriented?

CIE XYZ

RGB

HSV

How can we have negative values here from the CIE experiment?

By adding color to reference patch.

By removing color from target patch.

Captures human variance in color perception.

What are correct assertions about the CIE Chromaticity Diagram?

The curved line runs along colors of spectrum.

Purple line crosses white point.

Hue is endpoint of segment (x, y)-edge.

Fully describes color.

What does Steven’s Power Law (Weber-Fechner Law) describe?

Relationsship between the magnitude of a physical stimulus and its perceived intensity

What's ψ(I) in Steven’s Power Law?

ψ(I) = kI^a

Magnitude of physical stimulus

Perceived intensity of stimulus

Propotionality constant that depends on the units used

What's k in Steven’s Power Law?

ψ(I) = kI^a

Magnitude of physical stimulus

Perceived intensity of stimulus

Proportionality constant that depends on the units used

What's I in Steven’s Power Law?

ψ(I) = kI^a

Magnitude of physical stimulus

Perceived intensity of stimulus

Proportionality constant that depends on the units used

What are consequences of intensity sensitivity of human eye for integer encoding?

Too many bits to encode higher brightness range humans cannot differentiate and too few bits to encode lower shadow values that humans are sensitive to.

Too few bits to encode higher brightness range humans cannot differentiate and too many bits to encode lower shadow values that humans are sensitive to.

Requires more bits to maintain same visual quality.

An intensity of 1 is mapped onto an 8 bit number with ɣ = 0.3. The result is 255.

How is this achieved?

By using Linear Quantization into n bit representation.

By applying n = I · 2^N

By using Gamma Transfer Function Quantization into n bit representation

By applying n = ⌊I^-ɣ · 2^N⌋

Interactive Computer Graphics

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