VDU colorimetry

Digital input - luminance output gamma-correction channel interdependence local interdependence

Colour correction matrixHard-copy / soft-copy transformation

colour management cognitive effects

Video Display Unit (VDU)

White point setting differences

• CCT x y

D50 5000 .346.359

D65 6504 .313.329

D93 9300 .280.312

VDU monitor

Input: bit streamsDisplay processor:

converting for output device

Object oriented storage of characters: scaling, rotation, etc.

Buffer memory

Computer

Displ.proc.

BGR

Display

SyncmemoryBuffer

Buffer memory

Size: Number of pixels x Bits in pixel

3 bit colour 640 x 400 x 3 bit colour: 95 kbyte(3 bit colour: R, G, B: on - off)

8 bit per colour channel: 640 x 400 = 256 000 pixels256 000 x 8 x 3 = 768 kbyte Refresh rate:

640 x 400 x 3 = 768 000 bits,70 frames/sec: 54 Mbit/s

3 bit colour palette

Display processing

Character generation- ASCII 7 bit code: 128 characters- ISO 8 bit code: 256 characters- Code sheets- Additional information

- Font & colour- Character outline

Display processing

Graphics generation- Graphical user interface

- Windows- Icons (symbols)- Mouse & pointer

Colour systems

Basic 8-colour setR, G, B on - off: 3 bits per character

Logically defined colours: CLUTs

Dithering- spatial dithering; temporal dithering

Spatial dithering

2 x 2 groups: 5 luminance levels

2 x 2 arrays, 2 bits per pixel:

28=256 arrangements:

35 colours, 23 chromaticities

Colour look-up tables

Logical and actual colour CLUT: image as bit-codes per pixel in terms

of a set of logical colours.

g

b

Pixel address

Drive signals

Pixel data1001, 0101, ...

Computer CLUT

r

Display

R

DAC

DAC

B

G

DAC

Digital-to-Analogue Conversion

n bit code for primary colour: 2n levels: in CLUT -correction possible

RGB HVC conversion 8 bit palettes

Perceptual space:Levels L; 16 u*, 4 v*, 4

Bit 1 2 3 4 5 6 7 8

RGB:

Levels Red: 8 Green: 8 Blue: 4Bit 1 2 3 4 5 6 7 8

Anti-aliasing

Anti-aliasing processors: Real time interpolation in CLUT

System structure

Red byte

Green byte

Blue byte

2 entryCLUT

2 entryCLUT

2 entryCLUT

Bluebuffer

8

8

n x m

Greenbuffer

pixels

bufferRed

8

DAC

DAC

Blue signal

Display

DACRed signalGreen signal