ILLUMINATION AND COLOUR MODELS

1.What is a color model?

A color model is a method for explaining the properties or behavior of color within some particular context. Example: XYZ model, RGB model.

2. Define intensity of light, brightness and hue.

Intensity is the radiant energy emitted per unit time, per unit solid angle, and per unit projected area of source. Brightness is defined as the perceived intensity of the light. The perceived light has a dominant frequency (or dominant wavelength). The dominant frequency is also called as hue or simply as color.

3. What is purity of light? Define purity or saturation.

Purity describes how washed out or how “pure” the color of the light appears. Pastels and pale colors are described as less pure. Purity describes how washed out or how "pure" the color of the light appears.

4. Define chromacity and intensity.

The term chromacity is used to refer collectively to the two properties describing color characteristics:

purity and dominant frequency. Intensity is the radiant energy emitted per unit time, per unit solid angle, and p:r unit projected area of the source.

5. Define complementary colors and primary colors.

If the two color sources combine to produce white light, they are referred to as 'complementary colors.

Examples of complementary color pairs are red and cyan, green and magenta, and blue and yellow. The two or three colors used to produce other colors in a color model are referred to as primary colors.

6. State the use of chromaticity diagram.

Comparing color gamuts for different sets of primaries. Identifying complementary colors. Determining dominant wavelength and purity of a given color.

7. How is the color of an object determined?

When white light is incident upon an object, some frequencies are reflected and some are absorbed by the object. The combination of frequencies present in the reflected light determines what we perceive as the color of the object.

8. Explain about CMY model.

A color model defined with the primary colors cyan, magenta and yellow is useful for describing color output to hard copy devices.

9. How will you convert from YIQ to RGB color model? (AU MAY/JUNE 2012 IT)

Conversion from YIQ space to RGB space is done with the inverse matrix transformation:

R       1.000    0.956    0.620 Y

G   =  1.000  −0.272  −0.647 I

B       1.000  −1.108   1.705 Q

10. What isIlumination and the Ilumination models?

The transport of light from a source to a point via direct and indirect paths is called Ilumination.

Illumination Models:

Empirical - approximations to observed light properties

Physically based - applying physics properties of light and its interactions with matter