Lecture 3: Visualization Principles I Flashcards
Visual Perception
What qualifies as Perception?
‣ Identification and interpretation of sensory information
‣ First processing (edges, planes) in visual cortex
‣ From the physical stimulus to recognizing information
‣ Reflexes, not conscious
Visual Perception
What qualifies as Cognition?
‣ Processing of information, applying knowledge, conclusion drawing, problem solving, learning, relations between objects
What is Change Blindness?
Details of an image cannot be remembered across separate scenes – except in areas with focused attention
Interruption amplifies this effect (e.g., a blink, eye saccade, or blank screen)
No failure of vision system, failure based on inappropriate attentional guidance
Relevant for visualization when using animation to encode time-dependent data
What is Inattentional Blindness?
Person fails to notice stimulus in plain sight
Stimulus usually unexpected but fully visible
Depends on attention and expectations
Define Human Perception
Driven by goals, expectations, and prior knowledge.
Relies more on relative judgments (e.g., comparing sizes) than absolute ones.
What are Preattentive Features
Properties detected by the low-level visual system without conscious effort (processed in milliseconds).
Properties detected by the low-level visual system
‣ Very rapid, very accurate, processed in parallel
‣ 200-250 milliseconds Happens before focused attention -> „pre“attentive
Attention is very important for cognition
Can be used to draw attention to areas of interest
‣ Example: Item selection reflected in change of color across multiple visualizations
Independent of the number of distractors
What are the dimensions of colour?
Color Basics
Visible part of the electromagnetic spectrum
‣ 390-750 nm
Spectral colors
‣ Evoked by a single wavelength
Other colors
‣ Mix of multiple wavelengths
‣ e.g., magenta (pure red and pure blue light)
Hue
Saturation
‣ Purity of a color
Brightness, luminance, value,
‣ Lightness or darkness of a color
Which color scale should be used for encoding categorical attributes?
qualitative color scale
Which color scale should be used for encoding ordered data?
sequential scale
Why are rainbow colormaps uneffective?
Hard to order
Perpetually non-linear
Non-linear increase in brightness
What are some ways to use less color in your visualizations?
01Simply don’t show different colorsDoes your chart work without colors?
02Show shades, not huesCan you make the chart less confetti-like?
03EmphasizeCan you only use color for your most important categories?
04Label directlyCan you use the same or similar colors but label them?
05Merge categoriesCan you put categories together?
06Group categories, but keep showing themCan strokes help to tell categories apart?
07Change the chart typeWill another chart type rely less on colors?
08“Small multiply” itCan you split the categories into multiple charts?
09Add other indicatorsCan you add symbols, patterns, line widths, or dashes?
10Use tooltips and hover effectsCan smaller categories be hidden with them?
Which channel should be used for encoding ordered data?
Magnitude channels
What are Visual Marks?
Basic geometric elements in visualizations
Points, Lines, Areas
3D mark: volume (rarely used)
What are Channels (Visual Variables)?
Ways to control appearance of marks proportional to or based on attributes
Change appearance of marks based on attribute
Position, Color, Shape, Tilt, Size
What are the types of Channels?
Magnitude Channels
How much?
‣ Position ‣ Length ‣ Saturation …
Ordered Attributes:
Ordinal & Quantitative Attributes
Identity Channels
What? Where?
‣ Spatial region … ‣ Shape ‣ Color (hue)
Categorical Attributes
Which magnitude channel should be used for encoding categorical data?
Identity channels
‣ Spatial region … ‣ Shape ‣ Color (hue)
Which magnitude channel should be used for encoding ordered data?
Magnitude channels
‣ Position ‣ Length ‣ Saturation
What are the characteristics of channels?
Selective
‣ Is a mark distinct from other marks?
‣ Can we make out the difference between two marks?
Associative
‣ Does it support grouping?
Quantitative
‣ Can we quantify the difference between two marks?
Order
‣ Can we see a change in order?
Length
‣ How many unique marks can we see?
What is the strongest channel?
Position
What are Gestalt Principles?
Understand pattern perception
Proximity: Grouping based on closeness.
Similarity: Grouping based on shared properties (e.g., color, shape).
Closure: Perceiving incomplete shapes as whole.
Continuation: Viewing elements as part of a continuous flow.
Psychological principles that describe how we perceive patterns and group elements
