Color Appearance Model: Understanding Perception and Representation in Computer Vision

By Fouad Sabry

What is Color Appearance Model

A color appearance model, often known as a CAM, is a mathematical model that aims to capture the perceptual elements of human color vision. This model is used to describe viewing settings in which the appearance of a color does not coincide with the corresponding actual measurement of the stimulus source.

How you will benefit

(I) Insights, and validations about the following topics:

Chapter 1: Color appearance model

Chapter 2: CIELAB color space

Chapter 3: Colorimetry

Chapter 4: Chromatic adaptation

Chapter 5: CIECAM02

Chapter 6: Color space

Chapter 7: RGB color spaces

Chapter 8: Colorfulness

Chapter 9: CIE 1931 color space

Chapter 10: LMS color space

(II) Answering the public top questions about color appearance model.

(III) Real world examples for the usage of color appearance model in many fields.

Who this book is for

Professionals, undergraduate and graduate students, enthusiasts, hobbyists, and those who want to go beyond basic knowledge or information for any kind of Color Appearance Model.

• Language: English
• Publisher: One Billion Knowledgeable
• Release date: Apr 29, 2024

Book preview

Chapter 1: Color appearance model

Mathematical models called color appearance models (CAMs) attempt to characterize the perceptual elements of human color vision, such as the circumstances in which an object's perceived color differs from the corresponding physical measurement of the stimulus source. (In contrast, a color model, such as the RGB or CMYK color models, establishes a coordinate space to represent colors.)

The goal of a uniform color space (UCS) is to create a color model in which the apparent differences between colors are proportional to their physical separation in space. A UCS is the outcome of applying a CAM to a static viewing environment, while a CAM is the consequence of applying a UCS to a dynamic viewing environment. Even without this kind of modeling, a UCS can serve as a crude CAM.

The observer is the source of all color; objectively, The only thing visible is the light's spectral power distribution.

With this in mind, Everybody sees colors differently.

However, Many researchers have attempted to quantitatively link the spectral power distribution of light to the human sensory response, with some success.

In 1931, utilizing techniques of psychophysics, The XYZ color space, developed by the CIE (International Commission on Illumination), accurately represents human color perception at this sensory level.

However, there are assumptions built into the XYZ color model that limit its use (such as the retinal locus of stimulation, the luminance level of the light that meets the eye, the background behind the observed object, and the luminance level of the surrounding light). Two stimuli with identical XYZ tristimulus values will appear to have the same hue to a human observer only if all other factors are held constant. Different colors may be perceived from two identical stimuli with the same X, Y, and Z tristimulus values if the initial conditions differ (and vice versa: two different stimuli with thereby different XYZ tristimulus values might create an identical color appearance).

To represent human color perception, a color appearance model is necessary rather than the static XYZ color model if the viewing environment varies.

Humans do not perceive colors using XYZ tristimulus values but rather appearance parameters, which presents a significant problem for any color appearance model (hue, lightness, brightness, chroma, colorfulness and saturation). Therefore, the X, Y, and Z tristimulus values need to be transformed (taking into account the viewing conditions) into these appearance parameters as part of any color appearance model (at least hue, lightness and chroma).

Some color appearance phenomena that color appearance models attempt to account for are discussed below.

Chromatic adaptation is the human eye's capacity to see a reflected object without being affected by the white point (or color temperature) of the light source. A sheet of white paper appears white to the human eye regardless of whether the light is bluish or yellowish. This is the most fundamental and fundamentally significant color appearance phenomenon, and hence any model of color appearance must include a chromatic adaptation transform (CAT) that attempts to mimic this behavior.

This clearly separates elementary tristimulus-based color models from more complex color appearance models. When describing the surface color of an illuminated item, a simple tristimulus-based color model does not take into account the white point of the illuminant, therefore if the white point of the illuminant changes, so does the surface color. A color appearance model, on the other hand, accounts for the illuminant's white point (thus the need for this value in the model's calculations) and, as a result, reports the same color for a surface even if the white point of the illuminant changes.

In the situation of chromatic adaptation, two stimuli with differing XYZ tristimulus values might produce the same color appearance. The white paper's reflected light will have a different spectral power distribution and, consequently, different X, Y, and Z tristimulus values depending on the color temperature of the light shining on it (white).

Multiple factors alter an observer's color perception:

Bezold–Brücke hue shift: The hue of monochromatic light changes with luminance.

Abney effect: the addition of white light alters the color of monochromatic light (which would be expected color-neutral).

Multiple factors alter an observer's contrast perception:

Stevens' effect: brightness improves contrast.

The Bartleson-Breneman effect states that the perceived contrast of an emissive image (such as an LCD screen image) rises when the ambient light level rises.

The human eye is subject to an effect that alters the perceived vibrancy of colors:

Hunt effect: higher light levels result in more vibrant colors.

The human eye is subject to an impact that alters how light is perceived:

The Helmholtz-Kohlrausch effect: Saturation-dependent enhancement of brightness.

Because the human brain assigns each pixel a unique set of contextual meanings, spatial phenomena only influence color where they really occur in an image (e.g. as a shadow instead of gray color). The term optical illusion might be used to describe these events. They are notoriously challenging to model because of their contextual nature; models that attempt to do so are known as picture color appearance models (iCAM).

Due to the