# Creating Colour: Self-Luminous Devices

`Self-luminous' means producing light without an external illuminant.

## Calibrating a Colour CRT

Calibration

• putting a device into a standard configuration

Characterization

• having a reliable mapping from device coordinates to standard colour coordinates (tristimulus coordinates)
• ideally one-to-one
• which allows give me colour X
• could be the basis for broadcast applications

### Modelling a Colour CRT

#### The colour gamut

The colour cube

The colour cube in colour space

The colour cube in chromaticity coordinates

### Measuring the Colour of CRT Output

Geometry

Problems

• temporal stability
• spatial variation

### Building a Mapping for XYZ input

#### Model-based

Forward

1. X = A Ii(vi) + Black
2. Ii(v) = Gi f(vi)
3. f(vi) = vi^\gamma

Invert

1. Ii(vi) = invA (X - Black)
2. fi = Ii(v) / Gi
3. vi = invf( fi ) = fi^{-\gamma}

### Calibrating a Colour CRT

#### Viewing Conditions

Reference white

• D6500 at 70 lumens per square metre

Viewing distance

• 5 screen heights from image
• about 10 degrees of visual angle

Surround

• 3 times the linear dimensions of the image
• 10 degree surround
• total field of view 30 degrees
• D65 at 10 lumens per square metre

#### The White Axis

• black
• white
• grey: test of how well the gamma functions match

Colour of grey (all guns equal: vR = vG = vB) depends on surround

#### Gamma Correction

What do you want gamma to be?

• For artists
• mode of luminance histogram is at 18%
• gamma = 2.6 based on ...
• For untrained eyes
• mode of luminance histogram is at 25%
• gamma = 2.0 based on ...

## Colour LCD

Technological basis

• backlight
• polarizers
• liquid crystal between the plates of a capacitor
• colour filters

What if we had four filters?

• Why? We are surely overdoing the blue

## Colour OLED

Solid state photodetectors and LEDs are very closely related

• high efficiency