color image processin in digital image processing

8/13/2019 Color Image Processin in digital image processing

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6. COLORIMAGEPROCESSING

Introduction

In early days, whole image processing is done on monochrome images only but due

to advances in technology, it is possible to work on color images. So the processing of colorimages is called color image processing.

The study of color is important in design and development of color region system.

The use of color in image processing is motivated by two reasons as,

1. Color gives a better look and appearance to the images.

2. Color helps in obect identification and e!traction from the images.

Color Images Fundamentals

The color image processing is widely categori"ed into 2 separate areas as,

1# $ull Color Images %rocessing.

2# %seudo Color Image %rocessing

The processing of $ull Color Images or True Color Images having a pi!el depth of 24 bitsis

called as &$ull Color Image %rocessing'. (e can do the image processing steps like

enhancement, compression, segmentation etc. with full color images. The %rocessing of

pseudo color images is called pseudo color image processing. %seudo Color Images are not

the true color images. These are created by providing some false color to the group of

intensities of grey images. Such types of color images are called %seudo Color Images. In

this area a user can also develop the application for compression, segmentation etc. but the)uality output is not good as compared to full color image processing. Therefore pseudo

color image processing is rarely used for image processing work.

In 1***, ISS+C euton first discovered that when a beam of sunlight passes through

a prism, the emerging light is not a white light but it consist of - different colors. This

combination of - colors is called electromagnetic spectrum. These colors are violet, indigo,

blue, green, yellow, orange and red /I0345. These colors are used for color image

processing.

+mong /I034, 4ed, reen, 0lue are the fundamental primary colors. Since any

color is generated by a proper combination of 4, , 0 colors. These colors are the primary

colors. To represent each of the planes a Computer system needs 6 bits hence a total pi!el

depth of color image is 27 bits.

The total number of colors supported by color images is 2271*,---,21*5 from such huge

no. of colors, we can reduce the re)uired number and process that amount of pi!els only.These operations can be done in color image processing.

The set of all these colors form a vector space and it is called color space or colormodels. These colors spaces are nothing but the representation of colors in a standard way.


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The popular color models are,

1. 40 Color 8odel2. 9S/ Color 8odel

:. C8; Color 8odel

Color models (or Color spaces):

The color spaces are the standard way of representation of colors. The colors can be

represented using standard techni)ues called color spaces or color models. The widely usedcolor models are,

40 Color 8odel

9S/ Color 8odelC8 or C8; Color 8odel

1) RBG Color Model

In 40 color model each color appears in its primary component of 4, , 0 %lanes.

This model consist of : fundamental colors as 4ed, reen and 0lue from this three colors auser can obtain three secondary colors such as Cyan, 8agenta, ellow by combining 4,,0colors together.

40 Color model is based on Cartesian co


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2) HSV COLOR MODELTo overcome the drawbacks of 40 color model, a new color space called 9S/ Color

8odel is used. This model consist of : independent planes such as 9ue95,, Saturation S5and /alue /5. This model is also called as 9IS 9ue, Saturation = Intensity5 Color 8odel.

The characteristics that are generally used to distinguish one color from another are9ue, Saturation and Intensity value. 9ue is an attribute associated with the actual color or

true color of the obect. Therefore hue describes pure color of an obect. Saturation is theamount of white color added with the actual color of the obect. Saturation indicates howdilute the color is. The value plane represents the brightness of the image.

$or e!ample, let us consider a pink color. This color is generated by combining red

and white color together. Therefore red represents the hue of the obect, Saturationrepresents the percentage of white color mi!ed and valuerepresents the brightness or

intensity of the image.9S/ color model doesn't have high co-relationshipamong the pi!els of 9S/ planes.

Therefore it is the ideal tool for developing image processing algorithms based on 9S/ colormodel. 9S/ color model also decompiles the intensity from color carrying information 9

and S5. 9ence this color model is widely used for >9igher Image +nalysis (ork?.

3) CMY OR CMYK Color Model

This color model is also sometimes called as secondary color model. This color modelconsists of : secondary colors as CyanC5, 8agenta85 and ellow5. +ll these secondarycolors are obtained from the : primary colors such as 4ed, reen and 0lue.

C8 /alues can be obtained from 40 color using following e)uation.

The e)ual amount of C, 8, values produces black color, while mi!ing of 4, , 0 colors

produces white color.Those 9@( devices such as printers, photocopier machine Aero!5, fa! machine uses

C8 color model. Sometimes a black color is used with C8 to generate C8; color space

cyan, magenta, yellow, black5.Since this color space is used in devices, it is not generally used for image analysis

work, To do image analysis 9S/ color space, c0c4 color space, TSC Color space arewidely used.

imcomplement5 function can be used to convert from 40 to C8,

cmyBimageimcomplementrgbBimage5D

+lso, imcomplement5 function can be used to convert from C8 to 40,

rgbBimage imcomplementcmyBimage5D

Converting to Oter Color S!aces

To convert color image from one color space to another 8atEab provides some

predefined functions as,


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1.4029S/5

2.402c0c45:.402TSC5

To obtained reverse operation following functionFs are used,

1. 9S/24052. c0c42405

:. TSC2405


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! "#$ to Di%&la( !/'&0 !&+ and !+i* i'a+e%!

clear allD

close allD

iimreadFShailu.bmpF5DiimreadFaprichit.pegF5DiimreadFShailesh.gifF5D

figureDimshowi5D

figureDimshow5D

figureDimshowk5D

! -a& to onvert RGB olor i'a+e to HSV olor %&ae

clear allDclose allDiimreadFS.bmpF5D

figureDimshowi5D

4029S/i5DfigureD

imshow5D

! -a& to onvert a *ile alled e'+'ole+e!&e+ *ro' RGB olor %&ae to HSVolor %&ae

.

clear allDclose allD

iimreadFeGHmgmHcollege.pegF5DfigureD

imshowi5D

4029S/I5D

figureDimshow5D

! -a& to onvert the i'a+e *ro' HSV olor %&ae to RGB olor %&ae

clear allD

close allD

iimreadFs.bmpF5DfigureD

imshowi5D

9S/240i5DfigureD

imshow5D


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! "#$ to onvert RGB Color %&ae to YBR and YBR olor %&ae to RGB Color%&ae4

clear allD

close allDiimreadFs.bmpF5D

imshowi5D

402c0c4i5Dkc0c4240i5D

figureD

imshow5D

figureDimshowk5D

! -a& onvert RGB olor 'odel to HSV olor 'odel 5 HSV olor 'odel and%e&arate the o'&onent o* HSV olor i'a+e%

clear allD

close allDiimreadFs.bmpF5D

figureDimshowi5D

4029S/I5DfigureD

imshow5D

1G,G,15D2G,G,25D

:G,G,:5D

figureD

imshow15DfigureD

imshow25DfigureD

imshow:5D

color image processin in digital image processing

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