images and colour Flashcards
(38 cards)
What is a spectral power distribution (SPD)?
It is a function that describes how much energy light has at each wavelength in the visible spectrum.
What is the typical wavelength range of visible light?
Visible light typically ranges from about 380 nm to 750 nm.
How does a surface determine the colour of the light it reflects?
By its reflectance spectrum, which modifies the incident light’s spectral distribution.
What is the formula for calculating reflected radiance?
R(λ) = E(λ) × S(λ), where E is the incident light and S is surface reflectance.
Why do we see different colours in different lighting?
Because the reflected radiance depends on both the light source and surface properties.
What is the role of cone cells in human vision?
Cone cells detect colour by responding to different wavelengths of light.
How many types of cone cells do humans have?
Humans have three types of cone cells: S (short), M (medium), and L (long) wavelength cones.
What is the function of S-cones in the eye?
S-cones are sensitive to short wavelengths, corresponding to blue light.
What is the function of M-cones in the eye?
M-cones are sensitive to medium wavelengths, corresponding to green light.
What is the function of L-cones in the eye?
L-cones are sensitive to long wavelengths, corresponding to red light.
How does the brain perceive colour using cone responses?
By comparing the relative activation levels of the S, M, and L cones.
What are rods and how are they different from cones?
Rods are photoreceptors for low-light vision and do not detect colour, unlike cones.
How many rods are in the human retina?
About 120 million rods.
How many cones are in the human retina?
About 6 million cones.
What is colour constancy?
It is the brain’s ability to perceive an object’s colour consistently under different lighting conditions.
Why do two spectrally different lights appear the same colour?
Because they produce the same cone responses — a phenomenon called metamerism.
What is a digital image?
A digital image is a 2D array of discrete samples (pixels) of a continuous scene.
What is a pixel?
A pixel is the smallest unit in a digital image that holds a sampled colour or intensity value.
What is the standard colour representation for a pixel in digital images?
Pixels are typically represented using RGB — red, green, and blue values.
How are pixels stored in memory for greyscale images?
They are stored in scanline order: left to right across rows, and top to bottom.
What is the memory address formula for a pixel at (x, y) in a greyscale image?
Address = y × width + x
How many values are stored per pixel in a greyscale image?
One value per pixel.
How many values are stored per pixel in a colour RGB image?
Three values per pixel — red, green, and blue.
What is the memory address formula for a pixel at (x, y) in a colour image?
Address = 3 × (y × width + x)
