Flashcards
SCC 202 - Vision and Visualisation
Cards in this deck (52)
- 1What do we use to see light?Light receptor cells in the retina
- 2Why can Rods be largely ignored?Rods can be largely ignored
Hardly used in modern lifestyles
More for getting around in the dark
Completely maxed out in daylight and lighted environments - 3What are the three Light Sensitivity conesL -Cones
M-Cones
S-cones - 4What frequency and wavelength do L-cones cover and what are they most sensitive to?L-cones: low frequency / long wavelength
Covering most of the spectrum
But most sensitive to the middle (yellow) and low (red) frequencies - 5What frequency and wavelength do M-cones cover and what are they less sensitive than?M-cones: medium frequency / wavelength
From high-frequency blues to middle-frequency yellow/orange
Less sensitive than L-cones - 6What frequency and wavelength do S-cones cover and what are they less sensitive to?S-cones: high frequency / short wavelength
Violets and blues
Much less sensitive, and less numerous - 7What are the three different signal calculation frequencies for seeing Difference?Subtract medium- from low-frequencies: “red-green” difference
Subtract high- from low-frequency signals: “yellow-blue” signal
Add low- and medium frequencies: luminance (or “black-white”) - 8What happens to the signals of channels we distinguish most easily?The colours that we can distinguish most easily cause a strong signal (positive or negative) on one of the channels, and none on the other two
- 9Describe the process "Seeing the Difference"?Converting original signals into colour-opponent channels
- 10What is more optimized in Human vision, Edge Contrast or Brightness?Human vision is optimised for edge contrast, not brightness
- 11What affects our sensitivity to contrast? Give examples of what are we more sensitive to and less sensitive to?Difference signals makes us more sensitive to contrast n e.g.,
more sensitive to difference between green circle an its surround
We are less sensitive to absolute brightness levels - 12Why is our sensitivity to color contrast over absolute color important?Sensitivity to colour contrast over absolute colour is important for perception of objects as the same, under different light conditions
- 13Limitations in how colors individually convey information, what should you do to solve this in relation to design and visualization?Design with colour differences
- 14What are we much better at seeing?We are much better at seeing differences than absolute colours, but our ability to detect differences also depends…
- 15What other factors does our ability to detect colours apart is affected by:Ability to tell colours apart is affected by three presentation factors:
paleness, patch size and separation - 16How does paleness affect our ability to detect differences?The paler (less saturated) two colours, the harder to tell apart
- 17How does smaller and thinner affect our ability to detect differences Relate this to text?The smaller/ thinner the objects, the harder to distinguish their colours
Text is usually thin -> colour hard to determine - 18How does the separation of patches affect ourThe more separated the patches, the harder to distinguish their colours
- In particular when separation so great that we need to move our eyes - 19What is colour blindness?Colour blindness is a vision deficiency that affects our ability to
discriminate colours - 20What can't people with red/green colour-blindness distinguish?- Dark red from black
- Blue from purple
- Light green from white - 21What happens to the colour subtractions that leads to colour blindness?One or more of the colour subtraction channels are not functioning
normally, making it harder to distinguish certain pairs of colours
- More common in men (8%) than in women (0.5%) - 22State external factors affecting colour discrimination?Variation among colour displays
Display angle
Ambient light - 23How can variation among colour displays affect colour visualisation?Computer displays vary in how they display colour, depending on display technologies, driver software, or colour settings
- Colour that may look different on one
can look the same on another - 24How can display angle affect colour perception?Viewing straight versus at an angle alters percpetion
- 25How can ambient light affect colour visualisation?- Strong light washes out colour before it washes out light and dark
- Display in direct sunlight reduced to greyscale - 26State guidelines for using colours?- Use the most distinctive colours
- Distinguish colour by saturation and brightness as well as hue.
-Avoid pairs that colour-blind people can not distinguish
- Separate strong opponent colours - 27How can using the most distinctive colour be a useful guidelines?Distinct signal in colour-opponent channels; all other colours cause
signals on more than one channel, so will need longer processing in the
brain to be discriminated - 28How can Distinguish colour by saturation and brightness as well as hue be a useful guideline?Test by viewing in greyscale
- 29How can you verify that you have pairs that colour-blind people can distinguish?Use Vischeck to see how your images or web pages would appear to
colour-blind people: - 30Why shouldn't you mix strong opponent colours together?Causing shimmer when placed together
- 31Approximately how many cone cells does each eye have and where are they more tightly coupled?Each eye has approx. 6 million cone cells– much more tightly
packed in the centre (the fovea)
High in the center, much lower at the
edges - 32What is spatial resolution?Spatial resolution is a term that refers to the number of pixels utilized in construction of a digital image. Images having higher spatial resolution are composed with a greater number of pixels than those of lower spatial resolution.
- 33How many dots are there in fovea? What does it drop to? What happens at the edges?- Several thousands dots in fovea
(thumbnail-size at arm’s length)
- Dropping to a few dozen dots per inch just outside fovea
- At the edges, pixel resolution is size of a melon at arm’s length - 34What percentage of the retina and visual cortex is devoted to fovea input? State one of the fovea prime use?Fovea: ~1% of the retina but 50% of
visual cortex devoted to foveal input - 35Our eyes move rapidly and tirelessly to sample different bits of our environment , what is fixation?Fixations: ‘looking at something’
- Aligning an object in the scene with the fovea, for at least 200ms - 36What are saccades?Fast movement from fixation to fixation; for short movements
(e.g. reading) only 20-30 ms but suppresses vision - 37Why does the brain fill in bits that are not sampled?The brain fills in bits that are not sampled, to create an illusion of
seeing the entire environment in focus - 38How many saccade fixation cycles can you do per second?3-4 saccade-fixation cycles per second
- 39What do you have to do in principle, to solve a complex task?- Need to attend to all objects in the scene/image?
- Then recognize each attended object?
- Finally evaluate set of recognized objects against our goals? - 40When using your peripheral vision, what are you looking for? Relate the use of the term "parallel processing"Looking for low-resolution cues to guide our eye movements
- Massively parallel processing, in real-time across the entire scene - 41When should you use pre-attentive processing? What is it faster than?Extracting features from the scene without focussing
- Faster than a fixation - 42When should we use attentive processing?More detailed analysis only of those regions that we attend to
- 43State some UI design implications of attention detail and give examples?- Placing important information where the user’s attention is
Example: Error messages
- Design to provide low-resolution cues to guide attention
Example: Structure “at a glance”
Blur test
- Pre attentive features
Features that ‘pop out’:
e.g., different colour, shape, or movement
Motivates data visualisation: seeing patterns in data faster - 44What does data visualisation make easier?Make it easier to see patterns in data
- 45If objects or group of objects have a unique visual property, what can users do in regards to detecting them?If objects or group of objects have a unique visual property, users
can detect them without having to pay attention - 46State some visual properties?Color Hue - type of colour
Orientaiton - transformation
Texture
Positon and Alignment
Colour Brightness
Colour Saturation
Size
Shape - 47What do soe visual properties do to pre-attentive processing?Some features pop out more than others
- 48Complete this statement Data visualization is about harnessing automatic process?Data visualisation is about harnessing automatic processes
- 49In relation to how we process colour, what are better at seeing?How we process colour; better at seeing contrast than colour levels
- 50Where is spatial resolution high?Spatial resolution high in a very small area, and poor in the periphery
- 51What balance does data visualisation shift?Data visualisation shifts the balance from slow thinking to fast
visual processing - 52How do we find information?How we find information using parallel processing across the scene,
and attention to sample detail
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- Flashcards on SCC 202 - Vision and Visualisation, created by Ayo Olutobi on 28/01/2017.
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- Ayo Olutobi · Jan 2017
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- Apr 24, 2017
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