Color fundamentals and color models - Digital Image Processing

This presentation is based on Color fundamentals and Color models.
~ Introduction to Colors
~ Color in Image Processing
~ Color Fundamentals
~ Color Models
~ RGB Model
~ CMY Model
~ CMYK Model
~ HSI Model
~ HSI and RGB
~ RGB To HSI
~ HSI To RGB

1. Color fundamentals And Color models

2. Introduction Color is the aspect of things that is caused by differing qualities of light being reflected or emitted by them. The characteristics used to distinguish one color from another are: Hue – refers to primary and secondary colors (Yellow, Red, Blue, and Green) Brightness – refers to amount of intensity Saturation – the degree of purity of a hue.

3. Color in image processing Motivation to use colors in image processing: Humans can perceive thousands of shades of color as opposed to only about two dozen shades of gray Color is a powerful descriptor that greatly simplifies object segmentation and identification

4. Color in image processing Color image processing is divided into two major areas Full-color processing – images are acquired and processed in full color Pseudo-color processing – images are by nature grayscale and are converted to color images for visualization purposes

5. Color Fundamentals In 1666, Isaac Newton discovered that when a beam of sunlight passes through a glass prism, the emerging beam of light is split into a spectrum of colors ranging from violet at one end to red at the other.

6. Color Fundamentals Three basic quantities are used to describe the quality of a chromatic light source: Radiance is the total amount of energy that flows from the light source - measured in watts (W). Luminance gives a measure of the amount of energy an observer perceives from a light source - measured in lumens (lm) Brightness is a subjective descriptor that is practically unmeasurable CONTD…

7. Hue and saturation taken together are called chromaticity A color may be characterized by its brightness and chromaticity. The amounts of red , green and blue needed to form any color are called the tristimulus values and are denoted, X,Y and Z. A color is then specified by its trichromatic coefficients which means x + y + z = 1 Color Fundamentals CONTD…

8. Color Fundamentals Primary colors of light red (R) green (G) blue (B) Secondary colors of light cyan (green + blue) magenta (red + blue) yellow (red + green) CONTD… Mixing the three primaries, or a secondary with its opposite primary color, produces white light.

9. Color Fundamentals CONTD… Primary colors of pigment cyan (C) magenta (M) yellow (Y) Secondary colors of pigment red (R) green (G) blue (B) Mixing the three pigment primaries, or a secondary with its opposite primary color, produces black.

10. Color MODELS The color model aims to facilitate the specifications of colors in some standard way.  In Digital Image Processing, commonly used models are: RGB CMY CMYK HSI

11. Color MODELS R G B Each color appears in its primary colors red, green, and blue Based on Cartesian coordinate system All color values R, G and B have been normalized in the range [0, 1] We can represent each of R, G and B from 0 to 255 CONTD…

12. Color MODELS R G B Each RGB color image consists of three component images, one for each primary color CONTD…

13. Color MODELS R G B The three images are combined to produce color image Number of bits used to represent each pixel is referred to as pixel depth 24-bit image is often referred as full-color image CONTD…

14. Color MODELS Applications of R G B Used in the representation and display of images in electronic systems like computers and televisions.  Used in conventional photography as well. Image scanner which scans images and converts it to a digital image mostly supports RGB color. Used in web graphics. CONTD…

15. C M Y This model is made of secondary colors of light - Cyan, Magenta and Yellow It is a subtractive model appropriate to absorption of colors -  white is at (0.0, 0.0, 0.0) and black is at (1.0, 1.0, 1.0) Any CMY color when passed through white light will not reflect the color from which the combination is made. Color MODELS CONTD…

16. C M Y Example Color MODELS CONTD… C, M, Y components of an image

17. Relation between C M Y and R G B CMY coordinates are the complements of RGB values. The conversion formula is Color MODELS CONTD…

18. Applications of C M Y It is used in color printing as it uses colored inks. It is used in most commercial printing like magazines, books, etc. Color MODELS CONTD…

19. C M Y K CMYK color space is a variation on the CMY model It adds black (Cyan, Magenta, Yellow, and blacK ) Closes the gap between theory and practice. When equal components of cyan, magenta, and yellow inks are mixed, the result is usually a dark brown, not black. Adding black ink solves pr oblem . Color MODELS CONTD… CONTD…

20. C M Y K Example Color MODELS CONTD…

21. HSI Stands for Hue, Saturation, Intensity Human perceptual description of colors Decouples the intensity component from the color carrying information (hue and saturation) Ideal tool for developing color image processing algorithms Color MODELS CONTD…

22. Color MODELS CONTD… HUE SATURATION INTENSITY Component that describes a pure color (pure yellow, orange or red) Component represents the measure of the degree to which color is mixed with white color. 0 degree – Red 120 degree – Green 240 degree – Blue 60 degree – Yellow 300 degree – Magenta Component refers to grey level. Range is [0, 1] 0 means white 1 means black

23. HSI Example Color MODELS CONTD… HSI Components of full color image

24. HSI AND RGB Hue, Saturation and Intensity values can be obtained from the RGB color cube. Angle from the red(R) axis gives the Hue Length of the vector is the saturation Position of the plane on the vertical axis gives intensity

25. Conversion from RGB to HSI We can convert any RGB point to a corresponding point in the HSI model by the geometrical formulas: The hue H is given by where The saturation S is given by The intensity I is given by

26. Conversion from RGB to HSI

27. Conversion from RGB to HSI HSI Components of RGB Cube

28. Conversion from HSi TO RGB Applicable equations for converting colors from HSI to RGB depends on the value of H:

29. Manipulating hsI component images

30. Thank you!