CZ1102 Computing & Problem Solving Lecture 11

8/8/2019 CZ1102 Computing & Problem Solving Lecture 11

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Imageand

pictures


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Digitalimage

processing

Imageprocessingistochangethenatureof

imagefor

Type1:improvingitspictorialinformationfor

humaninterpretation

Type2:renderingitmoresuitableforautonomous

machineperception.

Digital

image

processing involvesusingacomputertochangethenatureof

adigitalimage


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Type1:

Image

sharpen

Enhancingtheedgesofanimagetomakeit

appearsharper


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Type1:

Image

de

noising

Removingnoisefromanimage

Noise:random

errors

in

the

image


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Type1:

Image

de

blurring

Removingblurringfromanimage


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Type2:

Edge

detection

Formeasurementofobjects,suchastheir

spread,and

the

area

contained

within

them


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Type2:

Image

segmentation

Partitioning imageintointerestingregions


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Imagetypes

and

matrices

Binary

Eachpixel

is

just

black

or

white

Greyscale Eachpixelisashadeofgrey,normally0(black)to255

(white)

Color Hereeachpixelhasaparticularcolour (~sixmillon

colours)

Indexed haveasmallsubsetof~sixteenmillionpossible

colours


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Binaryimage

Thereareonlytwopossiblevalues0or1for

eachpixel,

we

only

need

one

bit

per

pixel.

text(printedorhandwriting),fingerprints,or

imageedgemap


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Greyscale image

Valueofeachpixelrangingfrom0to255,can

berepresented

by

eight

bits

(one

byte)

Datatype:mbynmatricesofuint8number


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Colorimages

(RGB

images)

eachpixelhasaparticularcolour;thatcolour

beingdescribed

by

the

amount

of

red,

green

andblueinit.

Bitsrequiredforeachpixelis24

Numberofcolours:

Datatype:mbynby3matricesofuint8

number


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(cont)


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(cont)


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(cont)>> im = imread('peppers.png');

>> whos im

Name Size Bytes Class Attributes

im 384x512x3 589824 uint8 imshow(im);

>>imshow(im)


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Writingimages

imwrite(im,filename) writeanimagedefinedby

im with

name

filename,

image

type

is

inferredfromitsfileextension

>> imwrite(im,'mypeppers.jpg');

>> dir *.jpg

mypeppers.jpg

>>


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Dataconversion

Datareaded fromimageisuint8,convertitto

doublebefore

applying

some

operations

Beforewritingdatatoimagefilesorfor

display,convertittouint8.

>> moon=imread('moon.tif');

moon=double(moon);

>>moon=moon/2;

imshow(uint8(moon));


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Creatingimages

in

Matlab

>> black =80*ones(100,100);

>> imshow (uint8(im))

>> I=127*eye(100,100);

>> imshow (uint8(I))


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(cont)

384x512x3 96x128x3


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Croppingimage

Onlytakingaregionofimage

>> im = imread('peppers.png'); imshow(im);

>> figure; imshow((im(201:end-100,201:end-200,:));


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Colorimage

to

greyscale image

Brightness=0.2989*R+0.5870*G+0.1140

*B

>> im = imread('peppers.png');

greyim = 0.2989*im(:,:,1) + 0.5870*im(:,:,2)+ 0.1140im(:,:,3);


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Imageaddition

>> I=imread('rice.png');

J

=

imread('cameraman.tif');

K=(double(I)+double(J)));

imshow(uint8(K))

>> I=imread('rice.png');

J

=

imread('cameraman.tif');

K=1/2*(double(I)+1/2*double(J)));

imshow(uint8(K))


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>> bw =imread('text.png');bw2=1bw;

subplot(1,2,1),imshow(bw);subplot(1,2,2),imshow(bw2);

Imagecomplemention

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CZ1102 Computing & Problem Solving Lecture 11