What is color fundamentals?

Color Fundamentals

• The process followed by the human brain in perceiving and interpreting color is a physiopsychological phenomenon that is not yet fully understood, the physical nature of color can be expressed on a formal basis supported by experiment and theoretical results.

• In 1666, Sir Isaac newton discovered that when a beam of sunlight passes through a glass prism, the emerging beam of light us not white but consist instead of a continuous spectrum of colors ranging from violet at one end to red at the other.

• Visible light is composed of a relatively narrow brand of frequencies in the electromagnetic spectrum.

• If the light is achromatic (void of color), its only attribute is its intensity, or amount.

• Achromatic light is what viewers see on a black and white television set.

• Chromatic light spans the electromagnetic spectrum from approximately 400 to 700 nm.

• Three basic quantities are used to describe the quality of a chromatic light source: radiance, luminance, and brightness.

- Radiance is the total amount of energy that flow from the light source, and it is usually measured in watts (W).

- Luminance, measured in lumens (lm), gives a measure of the amount of energy an observer perceives from a light source.

- Brightness is a subjective descriptor that is practically impossible to measure. It embodies the achromatic notion of intensity and is one of the key factors in describing color sensation.

• 6 to 7 million cones in the human eye can divided into three principal sensing categories, corresponding roughly to red, green, and blue.

• Approximately 65% of all cones are sensitive to red light, 33% are sensitive to green light, and only about 2% are sensitive to blue (but that blue cones are the most sensitive).

• Due to these absorption characteristics of the human eyes, colors are seen as variable combinations of the so-called primary colors red (R), green (G), and blue (B).

• It is important to keep in mind that having three specific primary color wavelengths for the purpose of standardization does not mean that these three fixed RGB components actin alone can generate all spectrum colors.

• The primary colors can be added to produce the secondary colors of light - magenta (red plus blue), cyan (green plus blue), and yellow (red plus green).

• The characteristics generally used to distinguish one color from another are brightness, hue, and saturation.

• Hue is an attribute associated with the dominant wavelength in a mixture of light waves.

• Hue represent dominant color as perceived by an observer.

• Saturation refers to the relatives purity or the amount of white light mixed with a hue.

• The pure spectrum color are fully saturation.

• Hue and saturation taken together are called chromaticity, and therefore, a color may be characterized by its brightness and chromaticity.

• CIE chromaticity diagram (Fig 6.5), which show color composition as a function of x (red) and y (green).

• Any point not actually on the boundary but within the diagram represents some mixture o spectrum colors.

• A straight-line segment joining any two points in the diagram defines all the different color variations that can be obtained by combining these two colors additively.

• The triangle in Figure 6.6 shows a typical range of colors (called the color gamut) produced by RGB monitors.

• The irregular region inside the triangle is representative of the color gamut of today's high- quality color printing devices.

• The boundary of the color printing gamut is irregular because color printing is a combination of additive and subtractive color mixing, a process that is much more difficult to control than that of displaying colors on a monitor.

Color Models

• RGB (red, green, blue) model for color monitors and a board class of color video cameras.

• CMY (cyan, magenta, yellow) and CMYK (cyan, magenta, yellow, black) models for color printing.

• HIS (hue, saturation, intensity) model, which corresponds closely with the way humans describe

and interpret color.

• The HIS model also has the advantage that it decouples the color and gray-scale information in an

image, making it suitable for many of the gray-scale techniques.

N. Barman