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?