11-12. color (phys/percep factors) Flashcards
Chromatic aberration?
- in a photo, it creates a thin green line on one side of an object and red line on the other side
- light rays of diff. wavelengths focus on slightly diff. parts of the image sensor
Spectral power distribution def?
- describes the INTENSITY (power) of a light at each wavelength emitted by a SOURCE (ex. florescent bulb)
- ALSO used to describe ILLUMINATION when talking about color constancy and the light (wavelengths) that’s actually being reflected by an object
Spectral reflectance def?
- proportion of light at each wavelength that the object will reflect (instead of absorb)
- what KINDS of light does the object reflect if illuminated?
What does the spectral reflectance curves look like for black, white, and grey? How do they differ?
- they are all approximately horizontal
–> reflect same % of all wavelengths - differ in OVERALL AMOUNT of light reflected
–> black reflects only 20% of all light
– curve is really low on graph
–> white reflects 80% or more
– curve is really high on graph
Is color a property? What 2 things are properties?
- Color is NOT a property
- Spectral Power Distribution of a light source IS a property
- Spectral Reflectance IS a property
Monochromatic light? Ex?
Light that consists of only one wavelength
ex. laser
3 PHYSICAL parameters of light?
- wavelength
- intensity
- spectral composition
3 psychological correlates?
- Hue (color)
- Brightness
- Saturation
What does saturation measure? What colors are high/low sat?
- Measures richness
- rich reds/greens/etc. –> HIGH
- pastels –> LOW
- greys (blacks&whites)
–> completely UNSAT
What type of color mixture for light? For paint?
additive = light
subtractive = paints & filters
How do additive mixtures work?
- most light we see is not monochromatic –> its a mixture
- a mixture contains ALL wavelengths present in individual COMPONENTS
How can we measure additive mixtures?
For computers…
- amounts of R/G/B light are measured from 0-255
- if you know the amount of R, G, & B you want, it will give you the color
On the color wheel… mixing 2 lights will fall…?
on the line segment connecting the 2
On the color wheel… mixing 3 lights will fall…?
within the triangle defined by the 3
Primary colors def?
Any three colors that can be combined in different proportions to produce a range of other colors.
Complementary colors def?
Pairs of colors (opposite sides) that, when combined in equal proportion, are perceived as a shade of gray.
Ex. 50% yellow and 50% blue
–> 25% G, 25% R, and 50% blue
How do subtractive mixtures work?
paints:
- the only wavelengths reflected by mixture are those that are reflected by ALL COMPONENTS
- components always absorb/reflect the same things
- mixture color is the wavelengths that both components reflect
EX:
blue & yellow paint –> only color they both reflect is green
How do sub. mixtures work in filters?
- the wavelengths in “mixture” / result are those that pass through every filter in use
EX.
white –> yellow (G&R pass, not B)
–> magenta (R passes, not G)
result: red light on wall
(when white light passes through a filter, all wavelengths NOT in the color of the filter get absorbed)
What physical and perceptual factors does color perception depend on?
PHYSICAL:
- SPD of light source illuminating the object
- Spectral reflectance of the object
PERCEPTUAL:
1. Adaptation after-effects
2. (Simultaneous) Color contrast
3. Color assimilation
4. Color constancy
Color adaptation after-effects (after-images) explanation?
- you become adapted by staring at an image for a long time. When you switch to staring at a blank/white/grey box, you see a version of the image where pairs of colors have switched
–> R switches with G
–> Y switches with B - suggests that the perceptual system inherently links pairs of colors (Y/B & R/G)
ex. 4 colors in boxes, american flag
(Simultaneous) color contrast explanation?
- target color (usually grey) seems tinged with the COMPLEMENTARY color of the surround
EX. (12. pg 9)
- Y diamond in B background looks normal yellow
- Y diamond in Y background looks bluish
Color assimilation explanation? AKA?
- AKA spreading effect
- perception of a color is shifted towards a surrounding color
–> not necessarily a complementary color
EX. (12. pg 11, esp. 12)
- green surrounded by red looks reddish, or brighter green
- green surrounded by blue looks blueish, or muted green
Color constancy explanation? Why?
- the color we perceive remains constant regardless of illumination
- if identifying color is important for survival (ex food), you need perception to be the same in diff lighting (ex. noon vs dusk)
What is white balance?
- a camera’s way of figuring out what “white” is in the image, so it can decide what the illumination is
- if the camera knows what the illumination is, it can better represent the colors in the image
Best explanation for why people argue ab “the dress”?
- the photo allows for a variety of perceptual interpretations about the illumination of the dress
- observers make different implicit assumptions about illumination –> we perceive color differently
Chromatic adaptation as an explanation for color constancy means…?
- if you’re OVEREXPOSED to a certain wavelength, you adapt to it –> overcorrect –> NOT AS SENSITIVE
- you don’t perceive those wavelengths as well as others
ex.
- stare at screen with cyan | yellow
- image of plane below (tinged with cyan | yellow illumination) looks normal
