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Questions and Answers
What causes changes in the spectrum during light passage through matter?
What does the hue of a color refer to?
Which of these is an example of a non-spectral color?
What is a psychophysical description of brightness?
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How can color be produced by addition?
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What characterizes desaturated colors?
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What is the primary cause of colour blindness?
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Why is the overlap of sensitivity curves crucial for colour vision?
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What happens when all three cone types are equally stimulated?
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How do video displays create the illusion of colours?
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What effect does the colour of incident light have on perceived object colour?
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What is the apparent colour of an apple when illuminated with only blue/cyan light?
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Why might our visual system be fooled into perceiving colours that aren’t really present?
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How do objects’ interactions with light contribute to their observed colour?
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Study Notes
Colour Recognition with 3 Cone Types
- Having three cone types with slightly different sensitivity curves allows us to distinguish colours by associating each with a specific set of response rates.
- Overlap of sensitivity curves is crucial for colour vision.
- Colour blindness is caused by the absence or dysfunction of one or more cone types.
- We can be fooled into perceiving colours that aren't really there, and all video displays make use of this kind of illusion.
Colour Perception
- Illumination of the world rarely involves only one wavelength.
- The solar spectrum is roughly "constant" in the visible spectrum.
- Equal stimulus of all three cones produces a "white" sensation.
- Interaction with objects' surfaces changes (filters) the spectrum, making the colour of an object correspond to the set of wavelengths that are NOT absorbed, but are instead reflected/transmitted.
- Object colour is complementary to that which is absorbed.
The Origin of Colour
- Light can interact with matter through reflection, transmission, absorption (often wavelength-dependent), and interference (leading to iridescence).
- The colour of an object corresponds to the set of wavelengths that are NOT absorbed, but are instead reflected/transmitted.
- Examples:
- Apple skin strongly absorbs light in the blue and green bands, but reflects wavelengths in the red band.
- Banana skin strongly absorbs light in the blue band.
Colour Production
- Two ways to produce colour:
- Subtraction of ranges of wavelengths from white light.
- Addition of a few specific wavelengths.
- Changes in spectrum may occur due to scattering of light during passage through matter (e.g., blue sky).
Psychophysical Description of Colour
- Hue: The spectral colour associated with the "dominant" wavelength in the spectrum presented.
- Saturation: The amount of white in a spectrum.
- Brightness: The degree (or intensity) with which light seems to be coming from a colour.
Spectral and Non-Spectral Colours
- Spectral: A sensation that can also be produced by a single wavelength of light.
- Non-Spectral: A sensation that cannot be reproduced using only one wavelength of light.
- Examples:
- Magenta: Simultaneous red and blue stimulus with little/no green.
- Greys: Low-brightness whites.
- Desaturated colours: Containing at least some level of equal stimulus of all cone types.
- The range of human colour perception extends to a much wider palette than just spectral colours.
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Description
Discover how the three cone types in our eyes allow us to perceive a wide range of colours. Learn about the role of sensitivity curves and response rates in colour distinction.
