COLOURS (W3)

Question 1

What do prisms and diffraction grating do

Answer 1

Splits a white light source into the colour light spectrum

Question 2

How do we get a color signal

Answer 2

Illumination x Reflectance = Colour signal

Question 3

3 cones in our eyes

Answer 3

They are light receptors
Called S, M, L
All light has a value for each 3 cone type
A response for a cone can be computed as an integral over all wavelengths multiplied by the cone response

Question 4

3 primary colours

Answer 4

RGB

Question 5

What is Additive light

Answer 5

Coloured light are called additive when they sum up - white in the centre
Intensity is added in the graph

Question 6

What is Subtractive light

Answer 6

Like ink or paint
Have black in the middle
Eg red+yellow=orange
Intensity is subtracted in the graph

Question 7

Issue with Additive light

Answer 7

If we have values in the S cone, our light graph overlaps so we will also have unwanted values in the M and L cone
SML cones are always related in a ratio
Note that negative values are not physical

Question 8

What is Intensity

Answer 8

unit = candela per square metre
Defines the absolute brightness
Governed by the area of the curve
So as intensity increases, so does the amount of wavelength

Question 9

What is Hue

Answer 9

The predominant wavelength that defines the colour
Essentially the mean of the graph

Question 10

What is saturation (chroma)

Answer 10

The variance from the mean defines the saturation
low saturation = closer to white

Question 11

Interrelation of Intensity, Hue and chroma

Answer 11

They cannot be changed independently
Downwards cone model:
Hue is the circumference
Chroma is the radius from centre
Intensity is the height going upwards (how far from black centre)

Question 12

Standard Colour Space (CIE XYZ)

Answer 12

We have a test light and 3 RGB primary lights
We point all lights at a white screen and adjust the singular RGB lights until they match the test light
In turn we have the correct RGB value for each light
These can be converted to any other light due to their linearality
Some light cannot be defined by RGB if they give negative values

Question 13

Tristimulus Values

Answer 13

Resulting values for R,G,B

Question 14

Solving a negative RGB value

Answer 14

If we have a negative R value, we remove it and add to the G and B values to compensate

Question 15

Relationship between x and X, y and Y

Answer 15

x = X / X+Y+Z
y = Y / X+Y+Z

Where x,y are the axis in the 2D chromaticity diagrams
and X,Y,Z and the axis in the 3D complex chromaticity diagram

Question 16

Using matrices

Answer 16

We can use matrices to convert between XYZ in the chromaticity diagram and RGB values

Question 17

Other colour spaces

Answer 17

All show up as triangles in the chromaticity diagram because we can only add lights and there are no negative lights

Question 18

Problem with using the logarithmic for modelling light

Answer 18

Gets crazy exponential around 0
Use gamma2.2 instead

Question 19

What is Metamer

Answer 19

When 2 different tristimulus values result in the same perceived colour

Question 20

What is colour gamut

Answer 20

The colour pallet that a device has/uses

Question 21

What is gamma encoding

Answer 21

A method of encoding brightness