Computer science Color image processing.pdf

Color image processing

1. Unit 3
Color Image Processing

2. Color Image Processing
Color fundamentals, Color models: RGB, CMY, CMYK, HIS, Pseudocolor
Image Processing, Intensity Slicing, Gray Level to Color Transformations,
Full color Image processing, noise in color images.

3. Color is the most important aspect of an Object

4. Color Image Processing (CIP)
•One of the most important aspect of any object is color
•CIP provides an overview of the following
•Color fundamentals
•Color models
•Pseudo color image processing
•True color image processing

5. Color Fundamentals
•Use of color in image processing is motivated by two factors
•Color is powerful descriptor that often simplifies
object identification and extraction from a scene.
•Humans can discern thousand of color shades and
intensities compared to about only few shades of
gray.

7. In1966ISSACNewtondiscoveredthatwhen
whitelightispassedontheprism,itwillbe
dividedintosixbroadregions

8. (Electromagnetic )

9. Amount of reflection will indicate the color.

11. Color Models
•Color models are also called as color system or color
space.
•In terms of digital image processing hardware
oriented models most commonly used in practice are:
•The RGB model for color monitors and broad class of
color video cameras
•The CMY and CMYK models for color printing
•The HSI (Hue, Saturation and Intensity) model which
corresponds closely with the way humans describe and
interpret color.

12. RGB Model
•Each color appears in its primary spectral components of red, green
and blue.
•This model is based on cartesian coordinate system
•The color subspace of interest is the cube shown in figure (Next slide)
•RGB values are three corners
•CMY are at the other 3 corners
•Black is at the origin and white is at the corner farthest from the
origin.
•When fed into RGB monitor, these three images combine on the
screen to produce a composite color image

13. RGB color model
•Consider an RGB image in which each of the red, green and blue
images is an 8 bit image.
•So 24 bits are used to represent the color in RGB colors.
•With this we can have more than one crore colors.
•However systems normally uses 256 colors only.

14. Illustration of color components

21. CMY, CMYK

26. Subtract from 1 means : Subtract from White

30. HSI color model
•The HSI color modelrepresents every color with three components:
hue (H), saturation (S), intensity (I).
•The Hue component describes the color in the form of an angle
between [0,360] degrees.
•The Saturation component describes how much the color is diluted
with white light.
•The range of the S varies between [0,1].

35. HSI color model

36. HSI color Model

38. Example: Consider R=24, G=98 and B=118

39. Compute S

40. Compute Hue

44. Pseudo color image processing
•It is to assign to different colors to different intensity of gray.
•So we need to have slicing of gray intensity

45. Pseudo Colour Image Processing (false colour)

47. Intensity Slicing

59. Gray to Color
Transformations

60. Intensity to color transformations
•3 independent transformations done.
•They are Red, Green and Blue transformation.
•They are separately fed.
•f(x,y) is the image.
•They are fed together to the color monitor.
•In the previous method we used piece wise linear function. (Intensity
slicing)
•Here non-linear method is used