Gaining Colour Stability in Live Image Capturing

Motivation Colour Capturing Colour Management Solution Summary

Gaining Colour Stability

in Live Image Capturing

Guy K. Kloss

Computer ScienceMassey University, Albany

International Conference onApplications and Principles of Information Science

29 January 2008

Guy K. Kloss — Gaining Colour Stability in Live Image Capturing 1/30


Outline

1 Motivation

2 Colour Capturing

3 Colour Management

4 Solution



Outline

1 Motivation

2 Colour Capturing

3 Colour Management

4 Solution



The Basic Problem

We do not recognise light changes

Cameras do!

Colour measurements are off!



The Basic Problem

We do not recognise light changes

Cameras do!

Colour measurements are off!



The Basic Problem

Anticipated Solution

Create a systemthat is able to adapt to the conditions automatically.



Outline

1 Motivation

2 Colour Capturing

3 Colour Management

4 Solution



(Human) Colour SensingReflection Model



(Human) Colour SensingSpectral Light Composition

Light Source

wavelength λ [nm]re

lativ

e sp

ectr

al p

ower

D65F2

400 450 500 550 600 650 700

Object

wavelength λ [nm]

rela

tive

refle

ctan

ce

400 450 500 550 600 650 700



(Human) Colour SensingSpectral Light Composition

wavelength λ [nm]

rela

tive

sens

itivi

ty

S M L

400 450 500 550 600 650 700

S M L

wavelength λ [nm]

rela

tive

sens

itivi

ty

B G R

400 450 500 550 600 650 700

Relative sensitivities of cone cells (spectrum top). Typical camera sensors (spectrum bottom).



Colour Capturing

Werner Heisenberg, Physics and Philosophy (1958)

“What we observe is not nature itself,but nature exposed to our method of questioning.”



Colour Capturing

Capturing Process

Sensing

Rendering

Encoding



Colour Capturing

Problems

Sensor readings are not passed through,they are “interpreted!”

Measurement dependent on . . .

IlluminantSurface ColourCamera



Colour Spaces

Lost in Colour Space?

RGB, sRGB, Adobe RGB, . . .

YUV

HLS, HSV

CMYK

YCrCb

XYZ

CIE LAB, CIE LUV



Colour SpacesCrash-Course in Sensible Colour Spaces

RGB != RGB



Colour Spaces

Categorisation

Dependency

Device dependentDevice independent

Linearity

physical (with intensity)physical (for a specific output device)visual (CIE LAB)

Number of ChannelsHere: Building a system based on visible colours(trichromatic colour spaces)



Colour Spaces

Categorisation

Dependency


Linearity





Colour Spaces

Categorisation

Dependency


Linearity





Colour SpacesCIE LAB

1976, CIE L*a*b* (and L*u*v* )

Linear (visually), Device Independent,Opponent Colour Space(Only CIE LAB is shown in the diagrams.)Guy K. Kloss — Gaining Colour Stability in Live Image Capturing 20/30


Outline

1 Motivation

2 Colour Capturing

3 Colour Management

4 Solution



Colour Management(static)

Using ICC profiles and CIE colour spaces

Independent, linear PCS(usable for visual processing)



Colour Management(static)

Using ICC profiles and CIE colour spaces

Independent, linear PCS(usable for visual processing)



Colour ManagementInput Device Calibration

Preconditions:

Colour characterisation targetReproducible conditions (illumination)A specific camera

1 Capturing of target

2 Comparison of measurement vs. true values

3 Computation of ICC profile (lookup table)




Preconditions:








Preconditions:








Preconditions:







Colour ManagementProblems for Live Capturing

The Problem:

This does not work in changing/live environments!



Outline

1 Motivation

2 Colour Capturing

3 Colour Management

4 Solution



Approaches for a Solution

Usable Clues:

A priori knowledge

Infering by image analysis(Colour Constancy methods)

Advantage of slow changes:

Image segmentationObserve background changes




Usable Clues:

A priori knowledge







Usable Clues:

A priori knowledge






Putting it Together

De-coupled live process:Processing loop with “pay load”Adaptation process



Summary

Overview in Colour Science→ Colour Sensing/Measuring, Colour Representation

Colour Management→ Industry Standards and Best Practices,

Static Characterisation

Dynamic/Live Solution→ Usable Clues, Implementation



Questions?

What colour is the lemon?If you look closely, you may be surprised!

[email protected]


Economy & Finance

Gaining Colour Stability in Live Image Capturing