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 scene illumination changes colours   White balancing problem   Metamerism problems of illuminants of same

colour but different spectra

Aren’t colours right anyway?

 Problems (continued)   Viewing conditions of display vary

  sRGB standard specifies viewing conditions   Few consumers likely to pay attention to them

  Brightness and Contrast display controls   User adjusts colours change

  Vendor may ‘improve’ image via Photoshop

Balancing

R=G=B Input

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

Brightening Preserving R=G=B Linear Brightening

Non-linear (gamma) Brightening

Balanced Original

“Enhancements” Preserving R=G=B

Photoshop Curves Gamma

166,167,167 204,202,206

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

CIE a*b* chromaticities of various foods and papers within a single image of scene

illuminated with cool white fluorescent

Samples from 11 oranges

Stability under illumination variation

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

CIE a*b* chromaticities of the oranges (only) from 4 images

of the same scene under 4 different illuminants.

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?