Lec-02(a) Computer Graphics.ppt

8/9/2019 Lec-02(a) Computer Graphics.ppt

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Lecture # 02

Computer Graphics

Gauhar RahmanDept of Comp. Science

University of Peshawar


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VIDEO DISPLAY DEVICES

The primary output evice in a !raphics

system is a vieo monitor.

The operation of most vieo monitors is "aseon the stanar cathoeraytu"e $CRT%

esi!n& "ut severa' other techno'o!ies e(ist

an so'istate monitors may eventua''y

preominate.


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CRT )*+,T*R

cathode-

ray

tube


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-ow CRTs wor / isp'ay

1 CRT monitor contains mi''ions of tiny re& !reen& an "'ue phosphor ots

that !'ow when struc "y an e'ectron "eam that trave's across the screen

to create a visi"'e ima!e.

,n a CRT monitor tu"e& the cathoe is a heate fi'ament. The heate

fi'ament is in a vacuum create insie a !'ass tu"e. The e'ectrons arene!ative an the screen !ives a positive char!e so the screen !'ows.


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1vanta!es of CRT

The cathoe raye tu"e can easi'y increase the monitors "ri!htness "y

ref'ectin! the 'i!ht.

They prouce more co'ours

The Cathoe Ray Tu"e monitors have 'ower price rate than the LCD

isp'ay or P'asma isp'ay. The 3ua'ity of the ima!e isp'aye on a Cathoe Ray Tu"e is superior to

the LCD an P'asma monitors.

The contrast features of the cathoe ray tu"e monitor are consiere

hi!h'y e(ce''ent.


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Disavanta!es of CRT

They have a "i! "ac an tae up space on es. The e'ectroma!netic fie's emitte "y CRT monitors

constitute a hea'th ha4ar to the functionin! of 'ivin! ce''s.

CRTs emit a sma'' amount of 5ray "an raiation which canresu't in a hea'th ha4ar. Constant refreshin! of CRT monitors can resu't in heaache. CRTs operate at very hi!h vo'ta!e which can overheat

system or resu't in an imp'osion 6ithin a CRT a stron! vacuum e(ists in it an can a'so resu't

in a imp'osion They are heavy to pic up an carry aroun


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Co'or CRT )onitors

1 CRT monitor isp'ays co'or pictures "y usin! a com"ination

of phosphors that emit ifferent co'ore 'i!ht.

6ith the com"ination of phosphor a ran!e of co'ors can "e

isp'aye. There are two techni3ues use in co'or CRT monitors7

8eam Penetration )etho

Shaow )as )etho


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8eam Penetration )etho

,n "eam penetration metho two 'ayers of phosphor& usua''ycoate onto the insie of the CRT screen& an the isp'ayeco'or epen on how far the e'ectron "eam penetrates intothe phosphor 'ayers.

1t intermeiate "eam spees& com"inations of re an !reen'i!ht are emitte to show two aitiona' co'ors& oran!e anye''ow.

8eam penetration is an ine(pensive way to prouce co'ors as

on'y a few co'ors are possi"'e an the 3ua'ity of picture is a'sonot impressive


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Shaow mas metho

Shaow mas methos can isp'ay a wie ran!e of co'ors. ,n this techni3ue each pi(e' position is mae up of three

phosphor ots ca''e trias as shown in the fo''owin! fi!ure.

Three phosphor ots have ifferent co'ors i.e. re& !reen an"'ue an the isp'ay co'or is mae "y the com"ination of a''three ots.

Three !uns are use to throw "eam at the three ots of thesame pi(e'.

8y varyin! intensity at each ot a wie ran!e of co'ors can "e!enerate.

1 shaowmas is use which has ho'es a'i!ne with theots so that each !un can fire "eam to corresponin! ot

on'y.


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Shaow mas


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Shaow mas

1vanta!es

prouce rea'istic ima!es

a'so prouce ifferent co'ors an shaows scenes.

Disavanta!es

'ow reso'ution

e(pensive

e'ectron "eam irecte to who'e screen


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P'asma


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-ow oes it wor / isp'ay

The te'evision 'i!hts up thousans of tiny ots with a hi!h

ener!y "eam of e'ectrons. ,n most systems& there are three

pi(e' co'ours re& !reen an "'ue which are even'y

istri"ute on the screen.

8y com"inin! these co'ours in ifferent proportions& the

te'evision can prouce the entire co'our spectrum. The

phosphors on the screen of the p'asma enhances the viewin!

p'easure


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1vanta!es of p'asma

Lar!er viewin! an!'e& 9:0; compare to LCD


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Disavanta!es of p'asma

Compare to other isp'ay units the p'asma isp'ay unit has a

very short 'ife span& the manufactures estimate the 'ife span

to "e aroun 20&000 hours to >0&000 hours $at a rate of

Lec-02(a) Computer Graphics.ppt

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