orgb: a practical opponent color space for computer ... · orgb: a practical opponent color space...

oRGB: A Practical Opponent ColorSpace for Computer Graphics[1]

Bratkova, M. and Boulos, S. and Shirley, P.

Review by Massimo Fierro

Color and Imaging LabKyungpook National University

March 14, 2009

M. Fierro (CILAB) Skin separation Mar 14, 09 1 / 16

Outline

Introduction

Testing

References


Introduction

Opponent color theory

Ewald Hering

Hering was the first to notice in the 1970s that there appeared to be twocouples of “pure” colors with respect to each other: red and green, blueand yellow.


Introduction

Opponent color spaces

Opponent color space characteristics

I 1 luminance axis

I 2 chrominance axis based on the opponent color theory.

Currently available opponent color spaces

Device dependant (magenta-cyan axis)

I YCbCr

I YIQ

I YCC

I NCS

Device independant

I L∗a∗b∗

I lαβ


Introduction

Proposed color space ideas

Desired features

I Opponent color space

I Similar in spirit to lαβ and L∗a∗b∗

I Useful for graphics applications

Design choices

I Device dependant color space (directly from R′G′B′)I Non-linear luma channel (instead of linear luminance)


Introduction

Magenta-cyan vs red-green


Introduction

Considerations on R′G′B′


Introduction

Proposed algorithm

Algorithm outline

1. From R′G′B′to L′C′C′: linear transform to white-black, yellow-blue,magenta-cyan color space

2. From L′C′C′to oRGB: nonuniform rotation around luma axis toobtain red-green axis

Notes

The second step is a compression/decompression of angles depending onthe quadrant to which the color attains.


Introduction

Proposed algorithm: mathematically

Steps

1.

24 L′

C′1

C′2

35 =

24 0.2990R′ + 0.5870G′ + 0.1140B′

0.5(R′ + G′)− B′

0.866(R′ − G′)

352. θo(θ) =

((3/2)θ if θ ≤ π/3

π/2 + (3/4) + (θ − π/3) if π ≥ θ ≥ π/3

3.

"C′

yb

C′rg

#= R(θo − θ)

»C′

1C′

2

–

where L′C′1C

′2 is Y CC and L′C′

ybC′rg is oRGB.


Introduction

oRGB properties

Properties

I Similar to HSV/HSB

I It’s axes reflect common “color naming”

I C ′yb and C ′rg are in the [−1, 1] range

I L′ is normalized ([0, 1])


Testing

oRGB testing

Sample applications

I Color adjustment

I Gamut mapping: custom algorithm

I Color transfer: various methods

I Cool to warm shading: similar to Amy Gooch et al.


Testing

Color adjustment


Testing

Cool to warm shading


Testing

Color transfer


Testing

Gamut mapping


References

Bibliography

M. Bratkova, S. Boulos, and P. Shirley.orgb: A practical opponent color space for computer graphics.Computer Graphics and Applications, IEEE, 29(1):42–55, Jan.-Feb.2009.


orgb: a practical opponent color space for computer ... · orgb: a practical opponent color space...

Documents