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SFU arial picture Color Calibration via Natural Food Colors Brian Funt and Milan Mosny Simon Fraser University Vancouver, Canada

Problem of Internet Shopping

Suppose we are considering ordering this sofa over the Internet.

What colour is it really?

Colorchecker chart might help

Memory of color chart is unreliable

Colorchecker chart might help

Memory of color chart is unreliable Really need actual color chart for comparison

Aren’t colours right anyway?  The 

problems

Cameras designed to make pretty pictures  Not

scientific instruments  sRGB is a standard (primarily) specifying output  

Camera spectral sensitivities differ from one another Camera image enhancement varies across models

Aren’t colours right anyway?  The 

problems

Cameras designed to make pretty pictures  Not

scientific instruments  sRGB is a standard (primarily) specifying output  

Camera spectral sensitivities differ from one another Camera image enhancement varies across models

 Ambient  White

scene illumination changes colours

balancing problem  Metamerism problems of illuminants of same colour but different spectra

Aren’t colours right anyway?  Problems  Viewing  sRGB 

(continued) conditions of display vary

standard specifies viewing conditions

Few consumers likely to pay attention to them

 Brightness  User

and Contrast display controls

adjusts  colours change

 Vendor

may ‘improve’ image via Photoshop

Balancing Input

R=G=B

White balancing is the first step, but it doesn’t correct all colours

Brightening Preserving R=G=B Balanced Original

Linear Brightening

Non-linear (gamma) Brightening

“Enhancements� Preserving R=G=B 204,202,206 Gamma

166,167,167 Photoshop Curves

The 4 Color Charts Do Differ

The 4 Color Charts Do Differ

The 4 Color Charts Do Differ

If you don’t care about sofas…

What to do Without Color Chart?  Need

some standard ‘ground truth’ colors for comparison. But what?  Considered  Printed

currency (Euros, US dollars, etc.)

 Gold  Colour

varies with purity

 Silver 

Not really a colour.

 Product

colours like Coca Cola red

What to do Without Color Chart?  Coffee

break at ISCC Rochester 2009

What to do Without Color Chart?  Coffee

break at ISCC Rochester 2009

What to do Without Color Chart?  Coffee

break at ISCC Rochester 2009

Aha!

Fruit-Based Color Chart

Color for Food --- Food for Color  Most

talks have been about using colour to evaluate foods

 This

talk is about using foods to evaluate colours

Suppose You’re Ordering a Colorchecker

 

Photo of scene with colorchecker for sale

Photo of LCD reproduction Oranges and lemons look wrong.

Colorchecker wrong too

Potential Problems of Food Colours  Is

food colour stable across samples?

 from

one orange to another  from one region to the next  In

Vancouver stores I’ve seen oranges from USA, Australia, Peru, and China

 Do

fruit colors change in parallel to the colorchecker colors?

Candidate Food Colours  Interior

of oranges, limes, lemons

 Not

exteriors which change with processing and ripeness  Not apples, which turn brown quickly  Cooked

egg white  Raw beets, carrots

Tests of Food Colour Stability Samples from 11 oranges

CIE a*b* chromaticities of various foods and papers within a single image of scene illuminated with cool white fluorescent

Stability under illumination variation

CIE a*b* chromaticities of the oranges (only) from 4 images of the same scene under 4 different illuminants.

Each symbol type represents multiple samplings of different oranges within a single image.

Correlation with Colorchecker Colors

a* of a lemon sample versus yellow patch across illumination change

Correlation with Colorchecker Colors

a* of a lemon sample versus yellow patch across illumination change

Image Enhancement Effects

a* of orange patch versus orange fruit for different image ‘enhancements’

Conclusion  Proposed

food-based colour chart  Colour of some foods quite consistent  Citrus fruits & egg white provide readily available ground truth colours  Food colours can be used to evaluate image colours for Internet sales  Also good that colours compared within actual viewing environment

Questions?

Questions?

Suggestions?

QUESTIONS Suggestions?