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VDU

VDU- Video Display Unit has two basiccomponents video screen and video display

adapter or graphics adapter

Microprocessor does not have the ability tosend the signals necessary to produce the images

on the screen. This is done by graphics adapter.

Adapter consists of VDU memory in which

microprocessor writes and circuitry which

transfers this information from VDU memory to

the screen.

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VDU

!ach address in the VDU memory

corresponds to the specific location on the

screen. Display adapter reads from VDU memory

repeatedly "#$-%$ times per second & and

place it on screen.This is called as screenrefreshing

'ow refresh rates cause screen flic(er

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MONITORS

Two types of monitors are used with V)A

*. V)A mono monitors

+. V)A color monitors V)A monitors are based on analog system

,n olor monitors ed)reen and /lue

electron beam is generated by the electronguns

Mi0ing of these colors generate re1uired

color

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Digital display

,n digital display * bit signal controls each

beam i.e. on or off. Additional* bit controls

intensity of generated color.

This gives +2combinations of color

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3 /,T 3 /,T 3 /,T

,45MM,4) 6 /,T

7,8!' VA'U! T5

'559 U7 54! +#3

+2 /,T 5:

!),;T!;

DA !),;T!;

!D )!!4 /'U!

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!ach DA register contains *6 bit value

corresponding to 3 bit red 3 bit green and 3

bit blue.

DA converts this +2 bit value into analog

signal and sends to the monitor

!ach pi0el can have one of ++2 values

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GRAY IMAGE DISPLAY

Value of red green and blue must be e1ual

to display gray shades

There are +#3 such DA registers hence

+#3 combinations possible

!ach register is 6 bit only +#3 possible gray

shades are possible

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Graphics Mode

V)A supports many graphics modes.two popular

are

32$ 8 26$ - *3 color

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VGA prograi!g

Three levels of programming

*. )eneral purpose video libraries that can be

called from high level language +. V)A services provided by operating

systems.These include 5M-/,5; M;-D5; orother operating system

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VGA Prograi!g

All 5M-/,5; services for programming video hasbeen gathered under interrupt no.*3 "*$h&

7rogramming operations for calling a 5M- /,5;video services is consists of loading A> register withdata and pointers as re1uired by the function and thentransferring e0ecution to the 5M-/,5; handler bycalling int63" & function

To set video mode no.*? "

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)ray image display

;TAT

8C 75;,T,54

;!T )A7>,;

M5D!"*,;7,8!'

!4D 5: :,'!

!4D

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>eader *2 bytes >!AD!

;ignature + bytes E/ME

:ile;iFe 2 bytes :ile siFe

reserved 2 bytes unused "@$&Data5ffset 2 bytes :ile offset to Data

,nfo>eader 2$ bytes /,TMA7,4:5>!AD!

;iFe 2 bytes ;iFe of ,nfo>eader @2$

idth 2 bytes /itmap idth

>eight 2 bytes /itmap >eight

7lanes + bytes 4umber of 7lanes "@*&

/itount + bytes /its per 7i0el

* @ monochrome palette.

2 @ 2bit palletiFed. olors@ *3

6 @ 6bit palletiFed. olors @ +#3

*3 @ *3bit )/. olors @ 3##

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ompression 2 bytes Type of ompression

$ @ no compression

* @ 6 6bit '! encoding

+ @ 2bit '! encoding,mage;iFe 2 bytes ;iFe of ,mage

,: no ompression @ $

8pi0els7erM 2 bytes horiFontal resolutionG

Cpi0els7erM 2 bytes vertical resolution

olorsUsed 2 bytes 4umber of actually used colors

olors,mportant 2 bytes 4umber of important colors

$ @ all

olorTable 2 H 4umolors bytes

ed * byte ed intensity)reen * byte )reen intensity

/lue * byte /lue intensity

reserved * byte unused "@$&

repeated 4umolors times

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T,:: :ile format

TIFF, a tag based fle ormat that isdesigned to promote the

interchange o digital image data. The general scenario or whichTIFF was invented assumes that

applications sotware or scanningor painting creates a TIFF fle,which can then be read

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Tiff structure

/yte order

version

5ffset to

$th ,:D

+ /CT!;

+ /CT!;

2 /CT!;

,: $02D2D most

significant byte first

,f $02?2? listsignificant byte first

$0+A for all T,::

>eader

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,:D

!ntry count

Directory entry

$Directory entry

*Directory entry

+

5ffset to ne0t

,:D

*+ /CT!;

+ /CT!;

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Directory entry

Tag

Type

'ength

Value offset

+ bytes

+ bytes

2 bytes

2 bytes

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TC7!

Type length of the type

*@ byte 6 bit unsigned

+@ A;,, 6 bit bytes that store A;,,