Ntsc Colour Tv System
Transcript of Ntsc Colour Tv System
-
7/26/2019 Ntsc Colour Tv System
1/50
ESSENTIALS OF COLORTRANSMISSION AND NTSC SYSTEM
-
7/26/2019 Ntsc Colour Tv System
2/50
It should produce a normal black
and h!te p!cture on a monochromerece!"er !thout an# mod!$cat!on o%rece!"er c!rcu!tr#&
A color rece!"er must be able toproduce a black and h!te p!cture%rom monochrome s!'nal&
Compatibility requirements of Color system.
-
7/26/2019 Ntsc Colour Tv System
3/50
It should occup# same band!dth as themonochrome s!'nal&
Locat!on and spac!n' o% p!cture and soundcarr!ers must be the same&
Same lum!nance !n%ormat!on as a monochromes!'nal transm!tt!n' the same scene&
Color !n%ormat!on should be carr!ed such that !tdoes not !nter%ere !th p!cture on the screen o%
a monochrome rece!"er&Same de(ect!on %re)uenc!es and s#nc s!'nals as
!n monochrome s#stem&
Requirements of colorsignal
-
7/26/2019 Ntsc Colour Tv System
4/50
E*pla!ned b# +elm+olt, theor# To t#pes o% l!'ht sens!t!"e or'ans- rods and cones Rods pro"!de br!'htness sensat!on and cones are
sens!t!"e to color Three sets o% cones !th each sens!t!"e to red- blue
and 'reen l!'hts respect!"el#& Thus each set o% cones detects the amount o% R./
components !n l!'ht& The opt!c ner"e s#stem !nte'rates d!0erent color!mpress!ons as per the response cur"e o% e#e toperce!"e the actual color&
How Color is Perceived by Eyes?
-
7/26/2019 Ntsc Colour Tv System
5/50
Response curve of eyes
-
7/26/2019 Ntsc Colour Tv System
6/50
Add!t!"e m!*!n' %orms the bas!s o% color tele"!s!on +ere l!'ht %rom to or more colors comb!ne
to'ether to '!"e sensat!on o% a ne color&The add!t!"e m!*!n' o% pr!mar# colors1 red- blue
and 'reen can create most o% the colors&
Additive Color Mixing &Grassmans law
-
7/26/2019 Ntsc Colour Tv System
7/50
GRASSMANS LAW
Eye is not able to distinguish each of thecolors that mix to form the new color
Eye beha!es as if the out"ut of di#erentset of cones are additi!e
$rightness im"ression created bycombined light source is e%ual to thenumerical sum of & "rimary colors thatconstitute that color
'he "ro"erty of eye "roducing a res"onsebased on algebraic sum of red( blue andgreen in"uts is called Grassmans law
-
7/26/2019 Ntsc Colour Tv System
8/50
/ased on spectral response cur"e and .rassman2s
la - the tr!st!mulus "alues ha"e been de"eloped&
Tr!st!mulus "alues are the component "alues o%three pr!mar# colors to produce "ar!ous othercolors&
Thus the re%erence h!te %or T3 has been chosen to
be a m!*ture o% 456 red- 786 'reen and 996 blue&There%ore 9 lumen o% h!te:5&4 lm o% red;5&78lmo% 'reen; 5&99 lm o% red&
Alternat!"el# 9lm o% h!te :5&
-
7/26/2019 Ntsc Colour Tv System
9/50
Luminance or Brigtness It !s the amount o% br!'htness asperce!"ed b# e#e re'ardless o% color& /etter l!'hted parts ha"e more lum!nance than dark areas&
Hue It !s the predom!nant spectral color o% rece!"ed l!'ht& D!0erent hues result %rom d!0erent a"elen'ths o% spectral rad!at!on&
Saturation It !s the spectral pur!t# o% color&
Ind!cat!on o% amount o% other colors present& Or can be de$ned as ho much the color !s d!luted b# h!te& A %ull# saturated color has no h!te&
Caracteristics of Color
-
7/26/2019 Ntsc Colour Tv System
10/50
+ue and saturat!on o% a color put to'ether !scalled chrom!nance&
Also called chroma&
A color s#stem has to handle the chroma!n%ormat!on apart %rom lum!nance&
)hrominanance
-
7/26/2019 Ntsc Colour Tv System
11/50
)olor 'ele!ision )amera
-
7/26/2019 Ntsc Colour Tv System
12/50
)olor !oltage am"litudes
-
7/26/2019 Ntsc Colour Tv System
13/50
-
7/26/2019 Ntsc Colour Tv System
14/50
* signal am"litudes
-
7/26/2019 Ntsc Colour Tv System
15/50
In color s#stems the Y s!'nal !s transm!tted as !t!s&
/ut !nstead o% transm!tt!n' all three colors!'nals separatel# -onl# color d!0erence s!'nals
are transm!tted& Color d!0erence s!'nals are obta!ned b#
subtract!n'
lum!nance "olta'e %rom color "olta'e& Onl# R1Y and /1Y s!'nals are sent and the color
s!'nals are der!"ed %rom these at the rece!"er&
)olor +i#erence !oltages
-
7/26/2019 Ntsc Colour Tv System
16/50
-
7/26/2019 Ntsc Colour Tv System
17/50
>e ha"e Y:5&4R; 5&78.; &99/ !e- ?5&4; 5&78 ;5&99@Y:5&4R ;5&78. ;5&99/ Rearran'!n' -
!y "#$ signal not transmitted?
-
7/26/2019 Ntsc Colour Tv System
18/50
/ut !% .1Y !s transm!tted-
9& I% R1Y !s the m!ss!n' s!'nal- then
R1Y:?15&785&4@ .1Y ; ?1&995&4@ /1Y
Th!s !mpl!es a 'a!n %actor !n the res!stor matr!*&
B& I% /1Y !s not sent then
/1Y: ?15&785&[email protected] ?O&45&99@R1Y
-
7/26/2019 Ntsc Colour Tv System
19/50
Moreo"er- proport!on s!nce proport!on o% .
!s lar'e !n man# s!'nals then- "alue o% .1Y!ll be small&
It !s e!ther the smallest o% the s!'nals or
almost e)ual to smallest o% other to
The smaller ampl!tude o% .1Y !ll also!ntroduce s!'nal to no!se rat!o problems !%selected %or transm!ss!on&
-
7/26/2019 Ntsc Colour Tv System
20/50
COLOR !" S#S!$MS
The bas!c color t" s#stems are
9@ The Amer!can NTSC ? Nat!onal Tele"!s!onS#stems Comm!ttee@ s#stem
B@ The .erman AL ? hase Alterat!on b#L!ne@
4@ The French SECAM?Se)uent!al Couleuresa memo!re@ s#stem&
-
7/26/2019 Ntsc Colour Tv System
21/50
In color t" s#stems- the problem o% con$n!n'color s!'nals !th!n the same band!dth o%monochrome s!'nal !s ach!e"ed us!n' Fre)uenc#Interlea"!n'&
Fre)uenc# Interlea"!n'
It has been %ound that the ener'# content o%
compos!te "!deo s!'nal occur as bundles h!choccur at harmon!cs o% l!ne %re)uenc#? 97&B7-49&B75G&&Hh,@
Shape o% ener'# bundle shos a peak at e*actharmon!cs o% l!ne %re)uenc#
-
7/26/2019 Ntsc Colour Tv System
22/50
Compos!te 3!deo s!'nal
Ener'#
-
7/26/2019 Ntsc Colour Tv System
23/50
From the $'& e can see that ener'# contentdecreases s!'n!$cantl# a%ter !ncrease !nharmon!cs
and !s much smaller a%ter 4&7 Mh,&
Also a part o% monochrome s!'nal band!dth 'etunused due to spac!n' beteen the bundles&
It !s here the color !n%ormat!on !s packed b#modulat!n' color d!0erence "olta'es us!n' hat!s knon as a color sub carr!er&
Th!s %re)uenc# !s so chosen that !ts s!deband %alle*actl# m!da# beteen harmon!cs o% l!ne%re)uenc#&
-
7/26/2019 Ntsc Colour Tv System
24/50
-
7/26/2019 Ntsc Colour Tv System
25/50
Thus the %re)uenc# o% subcarr!er must be anodd mult!ple o% hal% the l!ne %re)uenc#&
In order to a"o!d crosstalk !th p!cture !n%o-!t !s selected at the h!'her s!de o% channelband!dth&
In NTSC s#stem the subcarr!er !s 77 t!mesone hal% the l!ne %re)uenc# !e-
?BJBB= ;9@J?97=75B@ : 4&7< Mh,
-
7/26/2019 Ntsc Colour Tv System
26/50
The problem o% transm!tt!n' to colord!0erence "olta'es !th same carr!er !ssol"ed us!n' %uadrature &odulation.
+ere to separate modulators are used-one %or the /1Y and other %or R1Y& /ut thecarr!er %re) %ed to one modulator !s '!"en arelat!"e phase sh!%t o% 85 !th respect to
another&Thus the to s!'nals are sa!d to be !n)uadrature and the to outputs arecomb!ned to #!eld C- the subcarr!er phasor&
&odulation of Color 'i(ererencevoltages
-
7/26/2019 Ntsc Colour Tv System
27/50
The !nstantaneous ampl!tude o% C !e-chrom!nance s!'nal- '!"es the color
saturat!on at that !nstant& Ma*!mum amp& Impl!es 'reatest saturat!onand ,ero to no saturat!on !e- h!te&
The !nstantaneous phase an'le o% C "ar!es
%rom 5 to 45 and '!"es !n%o on the hue o%the color&
Thus phasor C conta!ns %ull !n%o on hue andsaturat!on&
% d M d l i
-
7/26/2019 Ntsc Colour Tv System
28/50
%uadrature Modulation
-
7/26/2019 Ntsc Colour Tv System
29/50
Suppressed carr!er !th double s!debands !sthe normal method %or modulat!n' color d!0"olta'es !th color sub carr!er&
In order to ensure proper demodulat!on atthe rece!"er - a short sample o% subcarr!erosc!llator- ?ha"!n'
-
7/26/2019 Ntsc Colour Tv System
30/50
Location of Color Burstsignal
-
7/26/2019 Ntsc Colour Tv System
31/50
The chrom!nance s!'nal phasor- C !s addedto lum!nance s!'nal- Y be%ore modulat!n' !t!th channel carr!er&
The ampl!tude o% Y s!'nal becomes thele"el l!ne %or th!s purpose&
/ut d!rectl# us!n' th!s "alues !ll lead to'ross o"ermodulat!on& To a"o!d th!s
e!'ht!n' %actorsare used&
Weighting factors and why are theyre%uired,
-
7/26/2019 Ntsc Colour Tv System
32/50
For e'& The peak to peak ampl!tudes o%'reen s!'nal?;1 5&
-
7/26/2019 Ntsc Colour Tv System
33/50
-
7/26/2019 Ntsc Colour Tv System
34/50
There%ore to a"o!d o"ermodulat!on- the"alues o% color d!0erence "olta'e s!'nal arereduced be%ore the# are modulated us!n'color sub carr!er&
Th!s !s ach!e"ed b# scal!n' don the color
s!'nal "olta'es b# mult!pl#!n' !th "aluesknon as the K>e!'ht!n' Factors2 The e!'ht!n' %actors are 0.877%or R1Y
component and 5&84 %or /1Y component&
Then $nall# %or proper recept!on theuncompensated "alues are obta!ned at therece!"er s!de us!n' su!table netork&
-
7/26/2019 Ntsc Colour Tv System
35/50
-
7/26/2019 Ntsc Colour Tv System
36/50
-
7/26/2019 Ntsc Colour Tv System
37/50
T#p!cal "alues o% ampl!tudes o% color subcarr!ers are 5&4 %or red and c#an- 5&78 %or'reen and ma'enta and 5& %or blue and
#ello&Thou'h these ampl!tudes !ll st!ll cause
o"er modulat!on b# about 446 !t !sacceptable& Th!s !s because saturat!on o%
hues !n natural and sta'ed scenes seldome*ceed =76&
)ormation of Crominance signal
-
7/26/2019 Ntsc Colour Tv System
38/50
Due to e!'ht!n' %actors the phase an'leso% color c!rcle chan'es to '!"e ne "alues
Pasor diagram of Croma signal
-
7/26/2019 Ntsc Colour Tv System
39/50
Th!s s#stem !s compat!ble !th the 7B7 l!neAmer!can monochrome s#stem&
+ere band!dth %or color transm!ss!on !sreduced b# us!n' propert!es o% human e#e&
+ere ad"anta'e !s taken o% the l!m!tat!ons o%human e#e to restr!ct color s!'nal band!dth&
E#e2s resolut!on o% color2s o the redd!sh blue#ello!sh 'reen a*!s !s much less than colors
around #ello!sh red 1'reen!sh blue a*!s &There%ore to ne color s!'nals I and are
'enerated&
*+,C ,$,+E&
-
7/26/2019 Ntsc Colour Tv System
40/50
I signal lies in a region 33 degree counter
clockwise to R-Y where eye has max resolution.
I=0.7!R-Y" # 0.$7!%-Y"
&hich gi'es I as
I=0.(0 R- 0.$8)-0.3$%
I signal is located at *7 degree with res+ect to the,urst signal.
-
7/26/2019 Ntsc Colour Tv System
41/50
imilarly / signal is deri'ed as
/=0.8!R-Y"0.1!%-Y"
=0.$1R-0.*$)0.31% It is located 33 degree counter clockwise to !%-Y"
and is in 2uadrature with I signal.
-
7/26/2019 Ntsc Colour Tv System
42/50
ince eye is ca+a,le o resol'ing ine details ocolors in the I region it is gi'en a ,andwidth o u+
to 1.* 4h5.6s eye is less sensiti'e to colors in the / region it
is gi'en a ,andwidth o only -0.* 4h5 withres+ect to color su,carrier. ou,le side,and transmission is allowed or /
signal and it occu+ies a ,andwidth o 14h5!-0.*"
%ut or I signal the % is restricted to 0.*4h5,ut 9% is allowed to ha'e re2uencies u+ to
1.*4h5.
-
7/26/2019 Ntsc Colour Tv System
43/50
:hereore o'erall a ,andwidth o $ 4h5 isre2uired or color signal transmission.
:his im+lies a sa'ing o 1 4h5 i color di 'oltages
were directly sent. :his reduced ,andwidth results in reduced
intererence with +icture and sound carriers.
C i C l S '
-
7/26/2019 Ntsc Colour Tv System
44/50
:he exact 'alue o color su, carrier in ;:$($.*=*?.? @5 instead o (0@5.
:hus A=!$$$71"1*73.$(>$=3.*7?** 4h5. It isderi'ed rom a crystal controlled oscillator.
:he small changes n line re2 a,out 1*.7@5 and ield
re2 0.0( @5 has +ractically no eect on delectionoscillators as an oscillator which can ,e triggered ,y (0
@5 +ulses can also ,e synchronised or *?.? @5
6lso 6A< circuit can easily adBust the line re2
-
7/26/2019 Ntsc Colour Tv System
49/50
-
7/26/2019 Ntsc Colour Tv System
50/50