Graphics or Images.ppt

8/10/2019 Graphics or Images.ppt

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Graphics & Images


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Introduction

Imageis a partial representation of an object or ascene. (image of a person, place, object)

Graphicis a broader and general denition which

includes: Pictures or Photographs

Drawings or Line arts

lip arts

!uttons and !anner harts and graphs

!ac"grounds

#cons


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Types of Graphic

!itmap graphics

$ector graphics


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Bitmap graphics

%he most common and comprehensi&e form of

storage for images on computers is bitmapimage.

!itmap use combination bloc"s of di'erent

colours ("nown as pixels) to represent animage. ach piel is assigned a speciclocation and colour &alue.

%here are also called pixelized or rastergraphics.


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Bitmap graphics

!itmaps * arra+ of dots or piels

olor depth per piel

igh -ualit+ pictures

Photo realistic

Larger than drawt+pe

/ile si0e 1 piels color depth 2 3

4oftware to edit bitmapped graphics are :

5dobe Photoshop

Paint 4hop Pro


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Bitmap graphics

Advantage

an ha&e di'erenttetures on thedrawings6 detailed andcomprehensi&e.

Disadvantage Large le si0e.

7ot eas+ to ma"emodication toobjects2drawings.

8raphics become9bloc"+9 when the si0eis increased.


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Vector Graphics

$ector images are based on drawing

elements2objects to create an image.

%he elements and objects are stored as a series ofcommand that dene the indi&idual objects.

Pac"ages that allow to create &ector graphicsinclude :

acromedia /reehand ;

acromedia /lash ;

5dobe #llustrator

orel Draw


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Vector Graphics

Draw t+pe

8eometric shape stored as set of instructions

4maller than bitmap


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Vector Graphics

Advantage

4mall le si0e. aintain -ualit+ as the

si0e of the graphics isincreased.

as+ to edit the

drawings as each objectis independent of theother.

Disadvantage

=bjects2drawings cannotha&e teture6 it can onl+ha&e plain colours orgradients 6 limited le&elof detail that can bepresented in an image.


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Resolution

%here are three t+pes of resolution measuring di'erent aspects of the-ualit+, detail and si0e of an image:

Colour resolution Image resolution Display resolution

Image Resolution:%he term resolution often associated with an images degree ofdetail or quality.

Display Resolution:


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Image resolution

#mage resolution measures the piel dimension

of an o&erall image or how man+ piel theimage has.

#mage resolution is measured in width and

height.

/or eample, >?? @ >??piel image has a totalof >?,??? piels.


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Display resolution

Displa+ resolution is also measured in piels in terms of

height and width.

#t simpl+ means how man+ piels can be displa+ed onthe computer screen.

Displa+ resolution normall+ uses a setting ofAB?B3?($85), 3??A?? (4$85), >?CBA3, etc.

Eou can change the displa+ resolution under Displa+Properties in ontrol panel.

#f +our image resolution is bigger than the displa+resolution, the result would be part of the image will beout of the displa+ area.


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Memory/Storage requirement

/actors to consider:

%he height of the graphics

%he width of the graphics

%he colour depth or bit depth

%he le si0e of a bitmap image (in b+tes):

%eight & 'idth & !Colour depth $ ("


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olour Resolution/olour Depth

ach piel can represent at least C possible

colours or more. olour resolution or olour depth2channel depth

is measured in bits.

Colour Depth Calculation )umer of Colours

> bitB bits3 bits (> b+te)>A bits (C

b+tes)CB bits (F

b+tes)

C> 1 CCB1 >AC31 CGAC>A1 AG,GFACCB1 >A,,C>A

C colours>A coloursCGA coloursAG,GFA colours>A,,C>A colours


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Binary !Bitonal" Image

%hese images ha&e two possible

&alues of piel intensities: blac" andwhite.

5lso called >bit monochrome image,since it contains onl+ blac" andwhite.

%+pical applications of bitonalimages include oHce2businessdocuments, handwritten tet, linegraphics, engineering graphics etc.

%he scanned output contains ase-uence of blac" or white piels.!inar+ > represents a blac" piel andbinar+ ? represents a white piel.


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Grayscale Image

%he+ contain se&eral shades of

gre+.

%+pical applications of gra+scaleimages include newspaperphotographs (noncolor), magneticresonance images and catscans.

5n uncompressed gra+scale imagecan be represented b+ n bits perpiel, so the number of gra+ le&elssupported will be Cn.

/or eample, 3bit 8ra+scale #mage.#t consists of CGA gra+ le&els. 5 dar"piel might ha&e a piel &alue of ?,a bright one might be CGG.


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olour Image

%he+ are characteri0ed b+ the

intensit+ of three primar+colours (A,,C>A (CCB) possiblecolours. #n other words, 3 bitsfor Adi'erent colours.


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RGB# / $%'it images

5n important point: man+ CBbit colour images

are actuall+ stored as FCbit images, with theetra b+te of data for each.

5llows


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Image olour Schemes


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Various olour Schemes

4e&eral colour schemes (also called colour space,

models or formats) ha&e been de&eloped torepresent colour mathematicall+.

%here are B commonl+ used colour schemes :


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(" RGB olour Scheme

olours are represented b+

a numeric triplet specif+ing


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%" M)/M)* olour Scheme

CMYK(+an,agenta,Eellow,!lac") scheme is widel+ used

for colour printing. %o print a particular colour on a whitepage, one must appl+ in"s that subtract (absorb) all coloursother than the one desired.

+an, magenta, and +ellow are the subtracti&e primaries and

are the complements of red, green and blue. olour isspecied b+ what is subtracted from white light (which is thesum of


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M)/M)* olour Scheme

%heoreticall+, if +an, agenta, and Eellow are

mied, then all the


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#dditi+e Mi,ing

Mhite Light : #t consists of energ+ throughout the &isible

light spectrum.

Primar+ colours :


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*econdary colours: +an, agenta and Eellow (CMY)are secondar+ colours or subtracti&e primar+ colours.

*utractive +ixing: 4ubtracti&e colour miing is basedon reNecti&e colours rather than emissi&e colours.

#t generates colour b+ miing secondar+ colours. /oreample, miing magenta and +ellow +ields red.

#n subtracti&e miing, unwanted colours are selecti&el+absorbed and the re-uired colour is reNected. %he +ellowcolour absorbs the blue component, and the magenta

absorbs the green component, resulting in red.

4ubtracti&e miing is used primaril+ in the printingindustr+, b+ printing the three subtracti&e colours indi'ering proportions on white paper can generate all thecolours in the spectrum.

Su'tracti+e Mi,ing


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#dditi+e and Su'tracti+e Mi,ing

Cyan

Blue Magenta

YellowGreen

RedBlack

White

Additive Colour Mixing Subtractive Colour Mixing

R

GB

M

C

Y

W


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$" -SB/-SI olour Scheme

omputer monitors displa+ colours b+ emitting colour dots (red,

green, blue).

reation of colour is based on function of three characteristics:

O hue, saturation rightness2 lightness. !%*, $ %*-"

olours are represented b+ a triplet representing hue (hue isdominant colour of a sample and is represented b+ an angular&alue &ar+ing from red to green to blue at >C?Q inter&als),saturation (purit+ of the colour) and brightness (luminance, orintensit+ of the colour).


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-SB/-SI olour Scheme

%ue:#t is the colour sensation produced in an obser&er due to the presenceof certain wa&elengths of colour. ach wa&elength presents a di'erenthue. ue is based on a &ector &alue mo&ing from ? to FA? degrees ona colour wheel.

*aturation:

%his is a measure of colour intensit+, for eample, the di'erencebetween red and pin". 5lthough the two colours ha&e the samepredominant wa&elength, one ma+ ha&e more white colour mied inwith it and hence appear less saturated. (>??R 1 pure colour, ?R 1blac", white , gra+)

Intensity $ -uminance or ,rightness :

%his is a measure of the light emitted or reNected b+ an object.ertain colours appear brighter than others as the human e+e doesnot respond in the same wa+ to all colours. %he human e+es see nerdetails in image scene more because of brightness &ariations thanbecause of colour &ariations.


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." )V olour Scheme

%his is the basic colour format used b+composite colour %$ standards (7%4, P5Land 45).

. represents the luminance2brightness andcan be thought of as containing blac" andwhite or gra+scale information.

/ and 0carr+ the chrominance or colourinformation. %here are a &ariet+ of E$li"ecolour models.

%he ad&antage of using E$ for broadcast

is that the amount of data needed to denea tele&ision picture is greatl+ reduced.

%he disad&antage is that man+ colours thatappear on a computer displa+ cannot berecreated on %$.


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olour Dithering

suall+, digitised images are CB bit, >Amillion colour depth.

#f displa+ s+stem is limited to less than>A million colours, the image must betransformed for displa+ in the lessercolour en&ironment (colour dithering).

Colour Dithering * the processthrough which colours are changed tomeet the closest a&ailable colourbased on the a&ailable palette.

olours are substituted with closest

a&ailable colours (output de&ice).

%he -ualit+ of dithering will depend onthe algorithm used to select theclosest colour.


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Image 0rocessing


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Image 0rocessing

5nal+0ing and manipulating images with a

computer. #mage processing generallyinvolves three steps:

>. #mport an image with an optical scanner or directl+

through digital photograph+.

C. anipulate or anal+0e the image in some wa+. %hisstage can include image enhancement and datacompression.

F. =utput the result. %he result might be the imagealtered in some wa+.


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Image 0rocessing Techniques

#mage processing operations ma+ operate directl+ on piel

data or on higher le&el features such as edges, surfaces,and &olumes.

#mage processing operations ma+ be roughl+ di&ided intosi categories.

1 2diting

1 3oint operations

1 4iltering

1 Compositing

1 Geometric transformations

1 Conversions

4upport for a &ariet+ of image operations is now becominga&ailable in page la+out and paint programs (such asPhotoshop).


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(" 1diting

%he most basic operation is changing

individual pixels#

#mage editors also support cutting, cop+ing, andpasting selected groups of piel. 5 selection

might be a simple rectangular subimage or anarbitraril+ shaped region.

4elections are either drawn b+ the user or

calculated b+ software (for instance, b+eamining colour di'erences betweenneighboring piels).


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%" 0oint 2perations

5 point operation consists of appl+ing a functionto e&er+ pielin an image (or selection).

%he function is such that in calculating a new piel &alue, the onl+image data used is the pixels current value and exclude theneighoring pixels#

amples include:

5hresholding:5 piel is set to > or ? depending uponwhether it is abo&e or below the threshold &alue. %his createsmonochrome (binar+) images which are often used as mas"swhen compositing6.

@ Compositing: creating ne7 images or moving images ycomining images from di8erent sources 9 lie real1 7orlddigital video; 1D animations;painted acdrops; digital still photographs; and text#

colour correction:5n image ma+ be modied to increase orreduce contrast, brightness, and to strengthen or wea"enparticular colours.


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$" 3iltering

/ilter operations, li"e point operation, in&ol&e

appl+ing a function to e&er+ piel in an image orselection.

%he function determines a pixels ne7 value

ased on its current value and that ofneighoring pixels#

Depending on the denition of the function,

ltering is used to blur or sharpen the image,introduce distortions, and produce a &ariet+ ofspecial e'ects.


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." ompositing

#mage compositing is the combination of two or

more images to produce a new image.

5lpha channels are fre-uentl+ used to controlblending and mas"ing.

#n general, compositing is specied b+mathematical relationship between the &ariousimages. /or instance one image might be

produced from the sum of two eisting images.

5 &er+ large &ariet+ of e'ects are possible.


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4" Geometric Transformations

!asic geometric transformations include

displacing, rotating, mirroring, and scaling animage.

=ther geometric transformations include

s"ewing (slanting) and warping (an eample ofwarping is mapping a rectangular selection toan arbitrar+ foursided pol+gon)


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5" on+ersions

Mith the &ariet+ of image formats a&ailable, there is

a fre-uent need to con&ert from one format toanother.

/ortunatel+, there are a number of public domainsoftware pac"ages which handle man+ format

con&ersion tas"s. #n addition, image processingsoftware will usuall+ import and eport images in anumber of formats.

!esides format conversion, there are other

operations that can be considered forms ofcon&ersion. %hese include image compression ordecompression; changing colour schemes !ormodels" and changing image depth orresolution#

G hi 3il f t


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Due to the number of choices a&ailable in

determining image representation, it is notsurprising that a number of image formatsha&e e&ol&ed. 4ome eamples of imagele formats used for storing images are

GI4(8raphics #nterchange /ormat)

,itmap

3ost*cript

?32G

5I44(%agged #mage /ile /ormat)

5GA (often called %arga)

3)G, and etc.

Graphic 3ile formats


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Graphics Interchange 3ormat !GI3"

3bit per piel, bitmap image format commonl+ used b+ the worldwide web

ses lossless compression technique

ompress line art well

#mage can ha&e transparent portion

#nterlaced images possible

5nimation possible (Sasc 5nimation 4hop )

an onl+ ha&e a maimum of CGA colours

Does not compress photographs well

op+righted format such that de&elopers must pa+ ro+alt+


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6indo7s Bitmap !BM0"

!itmapped 8raphics /ormat

ost common format containing piel b+ piel &alue

Platform independent

4upport up to CBbit colour depth

7o compression

5 FCbit &ersion with integrated alpha channel has beenintroduced with Mindows ;P. (support transparenc+)

7o animation


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8oint 0hotographic 1,pert Group !801G"

ommonl+ used standard method of compression forphotographic images

4upport a maimum of >A. million colours

ompresses photographs well

Possible to select compression ratio &ersus -ualit+

Progressi&e (interlaced) images possible

-ossy compression technique:Losses some image information

Degradation of image possible with repeated editing and sa&ing

7o transparenc+

7o animation


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0orta'le 9et7or: Graphic !09G"

7o colour information lost

an use all colour depth supports more than >A.million colours

ompresses well Lossless ompression %echni-ue

#mage can ha&e transparent portion

7o animation


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2ther Graphic 3ile formats RA' Graphics 4ile 4ormat (.raw)

5 Neible basic le format for transferring les between

applications and computer platforms. %his format consists ofa stream of b+tes describing the colour information in the le.

5agged Image 4ile 4ormat(.tif, .ti')%#// is mainl+ used for echanging documents betweendi'erent applications and di'erent computer platforms. #t

supports the LTM method compression for image t+pes.

5ruevision 5arga(.tga)De&eloped b+ %rue&ision #nc. %85 les is a le format that willsupport images suitable for displa+ on %arga hardware but issupported b+ man+ applications on a wide range of platforms.

@ *oft 3aintrush (.pc)!itmap graphics le format, originall+ de&eloped b+ T4oft foruse with PPaintbrush. %his le format is now used andgenerated b+ man+ applications and scanners.


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2MM29 V1T2R 32RM#TS

5dobe #llustrator le (.ai) =


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Summary

>. %+pes of graphics

bitmap graphic &ector graphic

C.


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Summary

G. #mage colour schemes

Documents

Graphics or Images.ppt