CA2040145C

CA2040145C - Image pickup system comprising a memory of a small capacity

Info

Publication number: CA2040145C
Application number: CA 2040145
Authority: CA
Inventors: Riichi Nagura
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1990-04-12
Filing date: 1991-04-10
Publication date: 1996-07-16
Anticipated expiration: 2011-04-10
Also published as: US5134473A; EP0451837A2; JP2626152B2; DE69117557T2; CA2040145A1; EP0451837B1; EP0451837A3; JPH03295364A; DE69117557D1

Abstract

In an image pickup system which is used on a craft flying over an object zone and comprises a first (photoelectric) transducer (21) for producing a first partial (electric) signal representative of a partial image of a partial zone lying forwardly of the craft flying at a first position and a second transducer (22) for producing a second partial signal representative of another partial image of the partial zone lying directly under the craft flying, an interval of time later, at a second position spaced from the first position by a distance between two partial zones picked up by the first and the second transducers when the craft is at the first position, a compression unit (90 ) compresses the first and the second partial signals into first and second compressed signals. A delay circuit ( 54-1) gives the first compressed signal a delay equal to the interval of time and produces a delayed signal. A
subtracter (55-1) calculates a difference between the delayed signal and the second compressed signal and produces a difference signal. The first compressed signal and the difference signal are transmitted by a transmitter to a ground station to obtain a stereo image of the object zone. Preferably, the image pickup system should comprise a third transducer (23), another delay circuit (54-2), and another subtracter (55-2). The delay circuit is implemented by a memory.

Description

- 204Q14~

IMAGE P~CKUP SYSTEM COMPRISING
A MEMORY OF A S~A~I, CAPACITY

Back~round of the ~nvention:
-. .
This invention relates to an image piokup sys~em for use in combination with a craf~, such ~s a spa~ecraft, ~lying c~ver an object zone whi~h i~
5 tyE).ical ly on the groun~ surfac~ O~c ~he earth . Such an imag~ pickup system is E~rticularly useful in a remote sensing system for the earth.
An im~ge pickup sy~tem o~ th~ type d~6crib~
used tG remately sen~e an c~b~ct zone on bo~rd a ~raf~
10 l~lying 4v~r the object 20n~ ~lon~ a flying d~rc~tion A~
- a predetermilled flight ~ltit~lde. In a remote ~ensing ~y~tcm, i~ i9 often n~ce~ry to pick up a stereo lmage, ~uch as a stereo topographi~ lmage, from ~e obj ect zone ~y the use o~ the image pickup system. In order ~o 15 provide the stereo image, the objec~ zone sh~l}ld be E~icked ~p, along the flying direc:tion at two positions spaced apar~ from each other, so as to fo~m two optical irnages of the obj ect zorle .

A conventional im~ge pickup syste~ is disclosed in United State~ Application seri~l No. 410,104 ~iled Septe~ber 2n, 1~8~, by Naoshi Suzuki and for assignnlent to the instant assignçe. ~n the i~age pickup system, an optical system is used on the c~aft ~o form! on ~
focusing area of the optical syst~m, opti~al images of forward and b~kward zones lyi~ transversely of the ~lying direction in th~ object ~one. The forward and the backward zones are positioned a~ a predetermlned 10 distance ~long ~he flying direction. ~orw~rd and hackward optical images are ~icked up from the forward and the backward zones, The forward and ~he backward optical i.m~es are tran$duced into forward and backward ~.lectrlc sisn~ls by usin~ forward a~d b~ckward L5 photoelectric 1:ransduc~rs, re~ectlvely, pla~ed on the fo~using area with a gap left there~e~ween. ~he f~rward and the b~ckward electric sign21s are transmitted ~rom t~ansmitter ~ ~he craft to ~ ~rhund 6tation ~t a pred~te.rmin~d tran~mi~;6ion r~t~.

2 0 Tran~mitted from the çr~2Ct, the forw~rd ~nd t~e bac~ward electric ~ignals ~re produced so ~hat the forwhrd ~nd the b~ckward c)ptic:al images are reprc)duced in the ground sta~ion to provl~e the stereo image. In practice, the forward elec~ric signal is delay~d by a 25 pre~termin~d time flurat~on into a ~layed signal in the ~ronn~ st.at.i.ol-. The pre~let~brmi.ned ti~lle ~u~ati.on is suoh that the delayed electric signal appears concurrent with the backward electric sign~ n o~her words, the `` - 20401~ -delayed signal is produced after the craft ~lies ~he predetermined distance.
A ~eccnt requirement is to provide the stereo topographic or a li~e image ~t ~ high ~esolution ~o as 5 to make up a precise stereo topog~ap~ or the like.
~is re~ulrement gives rise to an in~rease o the forward and the ~ackward electric sign~ls in number.
~hi~ means that it is necessary to carry out data com~ression o~ the forward ~nd t~e backward elec~ri~
.1.0 signals. In t.hi.s ev~nt~ ~he cr~f~ must carry the ~e~ory havin~ a large ~apacity. ~t is undesirahle ~hat the mem~ry has a large capacit~ ~ecau~e the craft is restri~ted in size, power consumption, and weight.
Summary o~ the Invention:
It i.s therefore an object of this invention to provide an im~ge pickup system whi~,h comprises a me~ory c)f a reduced memory çapAcity for use as a delay circuit.
It is another object nf thi.s invention to provide an im~e piçkup sy~terl~ th~a type de~csribed which 20 compri~ss a data co~npr~ic)n ciraui.t: o~ a e~imple structure for ~se in reducing the memory capa~ity of the manlory .
Other o1~je~:t o~ thi~ invention will become c:lear ~s ~he descrlption procee~s.
On describi.n~ the gist of this inven~ion, i~ is pos~ible ~o understand tha~ an image pickup çystem is for a ~raft having a predete~mined dire~tion and ~l~ing over an objec~ zone. The system comprises an optical - - 20401-~5 - --sys~em for producing an optical image of the obje~t zone, image proces~ing means in~ludi.ng first ~nd ~econd photoelectric transduc~rs for transducing the optical image to irst and s~cond partial eleckric si~nals S representative o firs~ and se~ond partial zones of the object zone, respecti~ely, whi.çh are spaced apart by a ~irst preselected dist~nce along the predeter~ined direction. The ~ixs~ and ~he secon~ photoelectric transducers are spaced apart from e~ch other ~long the 10 ~redetermined direction by a ~irst predetermined distan~e and lie tr~nsve~sely of the prede~ermined directio~. ~he first predetexmi~ed distance de~er~ines for the optic~ system ~ first visual angle related ~o the first preselected di~tance. The sys~em ~urther 15 comprises an i~a~e signal processor for proçeSsing the firs~ and the se~ond paxtial e~.ectric signals to produçe a processed signal 2nd for supplying the proces~ed ~ignal to a transmitter. ~he cra~ flies for a ~irst duration from a ~irst posi.t.ion t~ a ~ec~nd p~si~io~
~0 spa~ed ~p~rt fxom ~he ~irst p4sition ~y th~ fir~t preselected distance.
~ ccox~ to thi~ inven~ion, the image ~ign~l pxc~ce~:~or cc~rnp~i~e~; compre~ ion ~irc~it c:onnc~ted to ~he first ~nd ~e seconA photoe~.ect~ic trans~ucers ~or 25 compressing the first and the second partial electric signals into first and second compressed signals; ~irst de-ay circuit c~nnected to the compression ~ir~uit for giving the first compr~ssed si~n~l ~ first delay equal 2û40145 to ~he first duration to produce a firs~ delayed signal ha~ing the first dela~ relati~e to ~he first compressed ~ignal; a f~rst sub~xacter connec~ed to ~he first delay cirçuit and the compression ~irct~it for cal~ulating a 5 fir~t difference between the ~i~st del~yed signal and the second compressed signal to pro~e ~ ~irs~
difference signal repre~entative o~ the first diference: and suppl~in~ mean~ connecte~ to the compre~si.on circuit and the first subtracter for 10 supplying the first ~ompressed si~nal and the first differ~nce signal to the transmitter collectively as the proces~ed signal.
Brief ~e~cription o~ the ~rawing:
Fig. 1 is a pictorial schematic view of an 15 object zon~ and a craft at three positions for use in describing a con~ention~l image pickup system;
Fig. ~ block diagram of a ground stati~n operable as a part of the image pickup ~ystem illu~ ed in ~ig. 1 Fi~, 3 i~ a block di~g~am o~ a ~i~n~l proce~in~
unit of an image pickup sys~m accord~ng to a first çm~odi~çn~ o~ ~hi3 invention;
Flg. 4 illustrates signal ~a~eforms for use in ~escri~ing operation of he signal processing unit ~5 ill~lstrated in Fig. 3;
Fig. 5 i~ a block diagram of a reception signal pro~e~in~ unit operable as a counterpart of ~he signal processin~ unit illu~trated in Fig~ 3;

~040~

Fig. ~ is a block diagram of a signal processing ~nit of an im~ge pi.ckup system accordin~ to a se~ond emb~diment of this invention;
Fig. 7 i.l.l.ustrates signa~ w~veforms for use in 5 descri.bing oper~tion of the si~na~ processing uni~
illustrated in Fig. 6;
Fig. 8 is a block diagram o~ a subsidiary decoding circuit which is included in the signal processing unit illustrated in Fig. 6;
Fig. 9 is a blo~k diagram of a recep~ion signal proces~ing uni~ operable as a counterpart o~ the signal pro~essin~ unit illustrated in Fig. ~; and Fig. 10 is a bloc~ diagram of ~ signal p~ocessing uni.t of an image pickup sy~te~ accordin~ to a 15 third embodiment of this inve~tion.
~escription of the Pre~erred Embodime~t:
R~erring to ~ig. 1, description ~ill be made 2s xega~ds a conventional image ~ickup sYs~em in order to facilitate a c~ear understandin~ of thi~ inven~ion. Th~
2n çc~nverlt~onAl im~ pi-::kup . y~-t~m i~; of t~e typ~
disclosed in the Suzuki patent application referred to here in~ove~ .
ïn Fig . 1, an imn~e pickup appa:~tus 15 i~
carried on a craf~ WhiCh is sy~bc~l1c~ll y Cleplcte~ at 16 .
25 It is assumed that the ~raft 16 has a velocity V
(meter/second) and f~ies over an object zone 17 at a ~light altitude l~ an~ ~long a flying direc~tion depic~ed by an arrow labelled V. The image pickup apparatus 15 2040i~5 serves ~o pick up a s~ereo i~age and a nonstexeo or mono image Prom th~ object zone }7, T~e cra~t 16 ls a~sumed to be present at a fir~t position Pl at a firs~ in8~ant.
The appara~us 15 ~omprises an optical system 1~
5 directed towards the object ~one 17. The object zone 17 forms a vis~al angle ~ ~t the op~ical syste~ 18. The optic~l s~stem 18 forms an op~ical image of the objeçt zone 17 on a Xoc~sing area 1~. A~ will la~er be described more in d~tail, Xir~t throug~ third ln photoele~tric transducers ~1, 22, and ~3 are arran~ed parallel on the focusing area J.9 tran~versely of the flying dire~ti.on. Th~ first photoel~ctric tr~nsducer 21 is ~pa~ed apart from the second pho~oelectri~ transducer 22 by a ~ir~t prede~ermined di~tance dl bAckw~rdl~
15 the flyin~ direc~io~. l'he ~hird p~otoele~tric txAn~ducer 23 i8 sp~ce~ Ap~rt som the se~ond ~hotoelec~ric ~ransducer ~ by a seçond predetermined ~lstance ~2 forwardly o~ the ~lylnq ~ireç~ion, The visual ~ngle ~ defines ~orward and backward 20 partial zones 24 and 25. The ohject zone 17 i divided along ~he flying direction into a plurality of partlal ~ones fro~ which partia? optical i~ages are picked up to be focused on the focusing area 19. In the example being illustrated, only a right or di~ectly under 2~ parti.al zone ~6 and the forwa~d and th~ b~ckward partial 20ne~ 24 and 2S are illustrated. 'rhe right under partial zone 26 lB }~etween the for~ard ~nd the backward partial zones 24 and 25 and lie~ right under the cra~t 20~01~

lfi at the fi.r~t instant. ~he forward par~ial zone 24 is positioned at a first zone distance Ll ~meter~) forwar~
~rom the ba~kward par~ial zone 25 along the flyi~g direction. The backward p~rti.al zone ~ is po~itioned 5 at ~ second zone distanc~ L2 back~rd f~om the right unde~ partial zone 2 6 . The f irst predetermined distan~e ~1 is defined by a first visual angle ~1 which correspond~ to the firs~ zone dis~ançe Ll, namel~, the forward and the right un~r parti~ zones 24 and 2~.
10 The ~e~ond predeter~ined distance d2 is de~ined by a seeond ~isual angle ~2 which corresponds ~o the se~ond zone dlstance L2, namel~, the b~ckward and the right ~nder partial zones ~5 and 26.
The fir~t pho~oeleo~ri~ transducer 21 txans~u~es lS the p~rtial optical im~ge pi~ked ~p from the ~orwar~
p~rtial æone 24 to a forward ele~txic signal. The second and the third ~hotoelectric ~ransducer~ ~ and 23 transduce the p~rti~l op~i.cal i.mage~ o~ the right u~der partial zone 26 and the ba~kward partial r4ne ~ t~
20 right under and ~ackward electrl& signal~ 6p~ctivel~.
~ e ç~ft 1~ flies from the first position Pl to ~ccond po~ition P2 in a fir~t ~ime dur~tion tl ( sccond~ ) ~nd flies from ~he sec~nd position PZ to a third positiorl P3 ln a seconCl tlme Cluration t2 25 (seconds~ The first and ~.he se~ond distances Ll and L~
are given ~:
L1 = H~an~l, and L2 - Htan~2.

20401~

The first and the se~ond time dur~ions t~ and t2 are given by:
tl - I.l/~, and t2 - L2/V.
As wel~ known ln the art, the stereo im~ge is ormed by processing ~e forward electri~ signal derived ~rom ~he ~irst photoelec~xic transducer ~1 at ~he position Pl and the bac~ward electric signal later derived from the thi~d pho~oelectric ~ransducer 23 at 10 the third po~i.tlon P3.
Each of the f i~st ~hrough the ~h i~d photoelectric transducers 2~ ~o 23 may be, for exampler a cha~ge-~oupl.ed device ~CCD~, ~ccordingly, the first through the third photoelectric tran~duce~s ~1 ~o 23 15 produce ~uc~essions of im~ge pulse~ ha~in~ a constan~
readout frequency and a variable ampli~ude as image pulse ~uccessions, Each of the image pul~es has ~
predetermined pulse wid~h an~ corresponds to ~ne of pictur~ ~lements.

q'he oraft 16 carrie~ ignal pro~sing unit 3~, a modulator 31, a transmitter 32, and an antenna 33.
Thc imAge puleie ~uC:c~Ssi.on~ ~re sen~ from the first through the third pho~oelectric transducers ~1 ~o 23 to tne ~lgnal processing uni~ 3n~ The signal processi~
25 unit 30 encodes the image pulse successions in~o an en~oded image data ~uccession. The encoded image data ma~ be called a pro~essed si~nal. The encoded i~age data are modulated by the modulator ~ to modulated 20~0145 l.maqe ~ata. The modulate~ lmage da a are trans~itted fro~ the ~ran~mitter 32 thro~l~h the antenna 33 to a ~round ~tation which w.ill be described i.n the fo~lowing.
Referring to ~ig. 2, ~he ground ~tation is 5 ~ymbolic~lly depicted a~ 40 and is oper2ble as a part of the ima~e pic~up system. Transmit~ed from the cra~t 16, the ~odulated im~ge data are received at an antenna 41, sent to a demo~ulator 42, and demodul~ted into demodulated image ~ata. Responsive ~o the demodulated 10 image data, a signal dist~ihuting unit 43 divides the ~emodulated image data in~o firs~, s~cond, and thi~d image d~ta trains Il, I2~ and I3 ~hich eorrespond to the ~irst throu~h ~he third photoelect~ic transducer~ 21, 22, and 23, respecti.ve].y.
1~ The irst and the second image d~ta trains Il and I2 ~re delivered to first ~nd ~eeond delay uni~s 46 and 47 ha~ing first and second del~ intervals. ~he ~irgt and the second delay interval~ will be represented by (~1 + t2~ and tl, xesPe~tively. ~he fir~t and the 20 sec~nd ima~e da~a train~ Il and I2 are ~pplied t~ An image reproducing unit 48 ~hrough th~ first and the ~ec~nd del~y unit~ 46 and 47, reelpectivel~. The third imA~e dAtA tr4in I3 i~ sent ~irectly to th~ ~m~g~
repr~d-l~in~ unit 48. The image reproducing unit 48 2S rep~adu~es the fo~ward, the ri~ht under, and the ~ac~ward ele~ signals ~o ~or~ t~e stereo image.
~ efer~ing back to Fig. 1, le~ the first and the sec~nd zone distances ~1 and L2 be equ~l to eaeh o~e~.

20~01~S

In thi~ ~v~nt, the ~raft L6 flies from the first posi~ion Pl to the third position ~3 in a time interval (tl ~ t2~ The time interval (tl + t~) is ~iven ~y:
~tl ~ t2~ = ~Ll ~ L2)/V, This means t~a~ t~e forward parti~l zone 24 is again picked ~p ~y the third photoelectric tran~ducer 23 thç ti~e interval (~1 + t2~ after the ~orward partial zone 24 is previously pic~ed up ~y the first photoelectric trans~ucer 21. T~king the above int~
10 consideration, the ~irst delay time of th~ first delay uni~ 46 is rendered eq~l to the t1me interval (tl ~ t2 so ~s to form the stereo image of t~e forward partial zone 24. The stereo image o~ the forward pax~1al zone 2~ can be obtained by procesSin~ the first image data lS train Il delayed by the first dela~ uni~ 46 and the third imag~ data train ~3.
On the other ~and, t~e ~raft 1~ ~orwardly flies throu~h the irst zone ~istance Ll f~om ~he right u~der partial zone 26 to the forward ~artial zone 24 during 20 th~ tim~ int~rv~l tl. As a r00ult, th4 orw~rd partial zone 24 is picked up by the second pho~oelec~ric tr~n:3duçer 22 . Af~ter t:he tlme intervAl ~tl + t 2 ~ he cr~ft 16 re~Ghes the third position P3, In order to ~e~lve ~h~ stereo i~ags o~ the forward partial zone 24, 25 the -~e~ond del~y inter~al is given to ~he second im~ge dat~ trai.n ~2 by the second delay uni~ 47.
Referring to Figs. 3 a~d 4, th~ d~scription will proceed to a si~nal processin~ unit of an i~age pi~kup ~040145 syste~ accord:ing to a firs~ embodimen~ o~ this i.nvention~ The signal processing unit is opera~le a~ a par~ of the image pickup system of the t~pe illustrated i.n Fig. L. Although thç signal processing uni~ deals 5 with digi.tal .signals, sign~l waveforms are illustrated in Fig. 4 in an analog ~orm for brevity of the description. The signal processin~ ~nit comprises first through third data com~res~ion cir~ui~s S~, 52, and 53 whi~h are connected to the fir~t thr~ugh the third 10 photoelectri~ t~nsducers ~ to 23, respecti~ely, I~ Fi.~. 4, the forward electric signal is i.ll~strated along a firs~ or top line lahelled (aj and is produced within a predetermined time period T. The forward electric signal is derived from the ~orward 15 partial zone 24 at t~e ~irst posi.tion Pl. ~s illustra~ed along ~ seco~d li.ne labelled ~b), the right under ~lectric signal appear~ a~ter lapse o~ the first time duration tl from ~ppe~rance of the forward electri~
&ignal and is pr~du~ed w~thin ~e pred~termined ti~e 20 p~riod ~, ~h~3 right ~nder electric ~ignal i~ de~ived fro~ the forw~rd partial zone 24 ~ the second po~ition P2. As ~h~wn alon~ ~ third line ~a~ell~d tc), the baGkwa~d elec~ri~ signal ls sent rr~ the thl~d photoelectric tran~ducer 23 ~cer ~apse Or the ~econ~
25 ti~e duration t2 from appearance of the r~ght under electric æignal and is produced within the predetermined time period T. Th~ backward el~ctric signal is derived from th~ forward partial z~ne 24 at the third position 20~0145 P~. ~açh o~ the ~orward, the right under, and the ~ackward elect:ric ~ignal~ is a su~oession o~ im~ge pulses which h~ve a varlable a~plitude.
Supplied with ~h~ forward, the right under, and 5 the ~ackw~rd electric signals, the first throug~ the third data compression circuits 51 to 53 compress the forward, ~he right under, and the b~ckward electric ~ignal~ into first through third compressed si~nals, re~pectively, in a manner which is ~alled a pr~dic~ive 10 en~odin~ ~ethod. The first through the third ¢ompress~d sig~a~s have a ~a~ia~le amplitude and ~re illus~rated along fourth through sixth lines la~elled (d~, ~e), ~nd (f). I~ is ~o ~e noted here that each of the first throu~h the third compressed signa~s i~ illus~rated on a 15 twi.ce magni~ied amplitude scale.
Let each of the forward, the right underl a~d the backw~rd eleçtriç si.~na3.s is represented by an OU~pU~ hit number e~ual to ten ~its per ~ sin41e pictu~e el~ent.. In this event, the first through the third 20 data compression circuitc 51 t~ 53 ~ompres~ ~h~ f~rward, ~he right under~ and ~ the backward electric si~nal~ into ~he fi~t through ~he third compre~ed ~ignalR which ~re repre~ented ~y thc output bit number eqUA~ to ~n~ of four through six bits per a single pi~ture elem~nt. In 25 othe~ word~, the first throu~h the third compres~ed slgnals have a reduced amplitude r~l~tive to the forward, the right under, and the ~kward electric signals. T~e first through the third oompression clrcuits 51 ~o 53 may ~e put in ope~ation in accordance with ~ vari~ble word length ~ethod in addition to ~he pre~ictive encoding method.
The first compressed signal is supp~ied to a 5 first delay ci.rcuit 54-l. The first del~y ci~cuit 54-l give~ the ~i~st compr~ssed signal a ~i~st delay equ~l ~o the first ~ime dura~io~ ~l and produces a first delayed sign~l having the firs~ delay relative to the first compressed siynal~
A first sub~racter 55-l is ~upplied wi~h the first del~yed signal and the second c~mpressed signal and c~lcul~tes a first ~ eren~e betwee~ the ~irst de1ayed ~igna}. and the se~ond ~ompressed sign~l. The ~ir~t ~u~tracter 55-l produces a firs~ differen~e signal l~ repre~ntati~e of the ~irst differen~e. It i~ to be noted here that ~here is a high degree of similarity betwee~ the first delay~d si~nal ~nd the second compressed signal ~çcause both of ~he first delayed signal and the second co~pressed ~.i.gnal are derived fxom 20 the forw~rd partial zone ~4. This means that ~h~ ~irst diff~rence signa-l h~s a reduced amplitude. As sho~n alon~ ~ ~eve~th Line labelled ~g), ~he fir~t di~ference ~i~nAl hA~ ~ red~ce~ ~mplitude ~el~tiv~ to the ~e~nd comprcs~ed ~ign~l shown ~long the Eifth line labelled 25 (e). In o~her words, the first differ~nee signal can be xepresente~ ~y the Outpll~ bit numb~r e~ual t~ two o~
~hree, 2~01~5 ~ secon~ delay circu~t 54-Z is supplied with the second compre~sed s~gnal and gives the second compressed signal a second delay equal to the second ~ime duration t2. The second del~y circui~ 51 2 produce~ a se~ond S delayed signal having the se~ond delay rel~tive to t~e second compre~ed signal.
The ~e~ond delayed si~nal and the third compres~ed signal are supplied to a se~ond ~u~tracter S5-2. The second subtracter 55-2 c~lculates a second lO dl~ç~e~e ~etween the second delayed signal and the thi~d co~pressed si~nal and produce~ ~ second difference si~nal representative o~ the second difference. As illu~trated along an eighth or bottom line l~belled (h~, the second di~ference si.~nal al~o has a redu~ed 15 amplitude relative to the second compressed signal, It is to be no~ed here that ~he first and the second differen~e signals are illustrated on ~n eight ~ime~
ma~nified a~plitude ~cale. The first and the ~econd dela~ cir~ui~s 54~1 and 5~-2 should ~e imple~ented by 20 memory. In this event, the memory memorizes the first and the second compressed signa~s as first and second memorized ~ignals. The ~irs~ memorized ~ignal i~ read out of the memory ~ ~ke ~ir~ del~y~d ~ign~ ter lap~e of ~he first time dur~ion ~l fr~m ~ppearance of 25 the forward ele~t~ic signal. The second me~orized si~nal is read out of the memory as ~he second delayed signal after lapse of the se~ond ~i~e duration t2 ~rom appearanc~ o~ the ri~ht under electric signal. ~et the 20~ 0145 char~e-couple~ ~evice bç Or the unidimensional type and has picture elements, 4,000 in number. The optical ima~e of the obj ect zone has pi.~ture elements, 16 ~ 10 (40~0 x ~000~ in numbex. In this ~ent, ~he conventional image piçkup system may nçed the memory having a capacity approximately equ~l ~o 100 ~eg~by~es.
In contras~, it is pos~ible ~ccordin~ ~o this invention to reduce the çapacity of the memory to one-f~urt~
through one-third when the first through the third dat~
~0 compre~sion cir~uits 51 to 53 are used. It is fur~her possible to reduce the capacity to one-tenth when ~he first and the second subtracteræ S5~1 and 55-2 are used in addition ~o the flrst ~h~ou~h the third data compression ~ircuits 51 to 53.
T~rou~h o~tput lines of the fir&t data compresion circuit 51f and ~he first ~nd the s~cond s~btracters SS-l and 55-2, t~e firs~ compres~ed sign~lt and the first and the second di~erence siqnals are .
supplied to the modulator 31 ~ig. 1) as the processed 20 signal. I!he autput lines of the ~irst d~ 4mpre~ion circuit 51, and th~ first and th~ ~econd ~ubtra~te~s 55-1 and 55-2 m~y be called a ~upply unit. ~he modul~to~ 31 modulates the first c~mpressed ~ignal, and the flrst an~ the ~econ~ ~ir~erence signals lnto first 25 throuqh third modulated ~ignals. The transmitter 32 transmits the first through t~e third modulated signals to the ground st~tion through the antenna 33~

~efe~in~ to Fi~. 5, the descr~ption will be 20~014~

ma~e as regards a reception signal processing unit operable ~ a pa~t of the ground ~ation d~scri~ed in ~onjunction with Fig, ~. The reception sign~l pro~essing unit i~ used instead of ~he flrst ~nd the 5 ~econd delay units 46 and 47 and is conneated between the si~na~ di~rihuting unit 43 and the i~age reproducin~ unit 48. The recep~ion ~ignal processing uni~ upplie~ with the first through the third image data trains ~l to I3 from ~he si~nal distributing unit l.O 43. The first ~hrou~h the third irnRge data trains Il to I3 correspond to the firs~ compressed signAl and th~
firs~ and the second di~erence signals described in conjunction with ~ig. 3. The recep~ion signal procer.sing unit i~ ~or cArryi.n~ out inverse process 15 operation relative to the signal proce~sing unit described in ~onnec~ion with ~i~. 3. The reception signal processin~ unit compri~es ~i.rs~ through third reception deco~ing cir~uits 61, 62, and 63 which cor~espond to the first through ~he thixd dAta ~o cc~mpres~;~on cir~uitC SL to ~3, re~pea~ively.
The first image d~ta train I~ i~ supplied to the ir~t reception decodin~ circuit 61 o.nd ~ fir~st reccption dc~ ~y circuit 64-1. The first r~ce~tlon decoding circult 61 1~ for carrying ou~ lnverse 25 operation relative to the ~irst data compression circuit 51 ~ig. 3) and deco~es the first image d~ta ~rain Il in~o a first decoded si~nal. The first decoded signal may be called a first reproduced electric si~nal of the 204014~

rOrwara electr~.c ~l~nal that is ~ran~duced by the $irst photoelectric transducex ~1 when the craft 16 is present at ~he flrs~ position P1.
Tne r ~.rst reception delay circ~it 64-1 gives the 5 ~lrst lmage d~ta train ~1 the firs~ d~lay equal to ~he fi.rst time duration tl a~d produce~ a flrst delayed ~rain hav~ng the fir~t d~lay r~ative to the ~irst image data txain ~1.
A first ad~er 65-1 i.s supplied with the first 10 delayed train and the ~ec~nd i~age da~a train I2. The first adder 65-1 calculates ~ ~7rst ~um o~ the firs~
dela~e~ t~ain and the second I mage da~a train I~ and produces a first sum si~nal represent~ive of the ~irst sum. The ~irst s~ signal is a reproducçd signal o~ ~h~
15 ~econd compres~ed si~nal produced hy the ~econd data compression circuit 52 (Fig. 3~.
The ~irs7~ sum signal is supplied to a se~ond reception delay circuit 64-2 and the seco~d reception decodi~g cireuit 62. The second reception decoding ~0 c:i~cuit 62 i~ ~or C~r~ing out inverBe oper~tion - relative to the second data compression circuit 52 (Fig.
3) ~nd decode~ the fir~t ~u~ ~i~n~l in~o A ~econd decoded 7ignAl. Th~ ~econd de~oded signal may ~e called a ~ec:~nd reproduc~ed electrlc ~lgnal Or ~he rlgnt urlder 25 eleGtric signal that is transdu~ed ~y the second ~ho~oelectri.c tran~ucer 22 when th~ craft 16 is pre~ent at the ~econd position P2.

20~01~5 Tne ~econd reçeption delay cirçuit 64-2 gives the firs~ sum signal the second delay eq~al to t~e se~ond time dura~ion t2 and produces a second del~yed train havinq the se~ond delay relative to the fir~t sum 5 signal.
~ seçond adder 65-2 is supplied with ~he second delayed train and the third im~ge data train I3. T~e second adder 65-~ calculates a second sum of the second delayed train and the thi~d image data train I3 and 10 produce~ a second sum signal represen~ative o~ the second sum. The second sum signal is a reproduced signal of the third compressed signal produced by the ~hird data comp~ession ~irauit S3 (Fi~. 3)~
The ~hird reception ~ecoding cirçuit ~3 is 15 supplied with the second sum si~nal. The third reception decoding cir~uit ~3 is for carrying out inverse opera~ion rel.ative to ~he third data compression circuit 53 (~i~, 3) and decodes ~e secon~ sum signa~
into a third decoded signal. The third dec~ded ~'ign~l ~o may be called a third reprodu~ed ~l~c~ric ~ig~l of the backward electric ~ignal that is transduced ~ the third photoelectric trAn~d~ce~ ~3 ~hen the çr~f~ pre~en~
at the thi~d po~ition P3.
The flrgt ~nrou~h tne third decoded sign~ls are 25 supplied ~o the image reproducing uni~ 48 (~ig. ~). The image reproducing unit 48 processes the ~irst thro~gh the third decoded signals and reproduces the ~tereo image of ~he fo~ward p~rtial zone ~4. It i~ to be notçd here tnat t~e ~tereo i~age of the ~orwa~d par~ial zone 24 can be ob~a.ined hy processing the firs~ and the second decoded signals. In this event~ it is possible to omi~ the third pho~oel~ctric ~r~nsducer 2~, the 5 second delay cir~uit 54~2, the third compressio~ circuit 53, and the second s~btrac~ex 55-2 which ~re o~rried by ~he craft 1~. Similarly, i~ is possi~le to omit the second reception delay circuit 64-2, the second adder 65~, and the third reception deco~ing cirçui~ ~3 which 10 are included in ~he reception sign~l p~o~essing unit.
Referring to ~igs. ~ and 7, the description will proGeed to a signal processing unit o~ an image pickup ~ystem ac~ord.ing to a second embodiment of this invention. The s.ign~l processing unit is similar to 15 that illust~ted i.n Fi.~. 3 and comprises similar pa~ts design~ted by like reference numer~Ls. It sho~d b~
~o~ed i.~ this connection ~h~t the second de~ay cir~uit 54-2 is conne~ted to a~ ou~ut line of the fir~t ~ubtra~ter 55~1 ana ~hat a sub~idiary decoding circ~
20 71 is conneated be~ween the second dslay Cl~Uit 54-2 and the second subtrac~er 55-2.
In ~ig. 7, aignAl w~fbrm~ ~re illustrated ~long fir5t t~rouyh seventh lines. The waveform~ a~e simil~r to those llLustrAte~ in Fig. 4.
As descri.bed in conjun~tion with Fig. 3, th~
~i.rst compression circuit Sl produces the ~irst comp~essed sign~l. The fir~t sub~xacter 55--1 produ~e~

the first difference ~i.gnal. The first dif~erence 20401~

5ignal is supplied to the second dela~ c t rcult 54-~. AS
described with r~feren~e to Fig. 3, the second ~la~
c~rcuit 54-2 glves the ~rs~ e~ence slgnal ~he secona ael~y e~ual tO the second tlme ~uration t2. The 5 secon~ ~el~y clrcu~ 54-2 produces the second delayed signal havin~ the second delay rel~ive ~o the ~i~s~
differenc~ signal. ~t is to be noted here that the ~ir~t diffe~ence signal has a re~uced amplitude relative to the second compres~ed signal p~oduced by ~hç second 10 data compression circuit 52. Th~s mean~ that the secon~
delay circuit 5~-2 can be implemented by a memory havi~g a capacity whi~h is ~ur~her smaller than tha~ ~ the second delay circuit 54-2 descri.bed in conjunction with Fig. 3-If the second dela~ed signal is directly supplied to the sec~nd s~ racter 55-2, the second su~tra~ter 55-~ ~ay produoe ~he second difference signal whioh is ~ub~tantially ~quivalent ~o the third compressed signal. This is because ~he ~econd delayed 20 ~i~nal has the reduced amplitude. ln other words, the second subtrac~er S5-2 is useless, although desir~ble unl~-~ th~ ~ub~idiary d~coding ~ircuit 71 i~ u6Qd. ~he ~oond d~l~y~d ~ignal i~ ~uppli~d ~o ~e 6ubsidiary ~ec~ding circui~ 71. The ~ub~idi~ry deco~ing circuit 71 25 is for decodi~g the ~econd delayed sign~l by in~erse opexatlon relatl~e ~o the predic~ve en~o~lng metno~
lnto a su~sidi~ry decoded si~nal which is substanti~lly equivalent to the first delayed ~i~nal.

2~401~

~ s lllust~ted ~long an eighth line la~elled (h) in Fig. 7, the subsidia~y decoded ~ignal has the amplltude ~igher than that o~ the first difference sign~l illustrated ~long the ~even~h line labelled (g~
i~ Fig~ 7. It is ~o be noted here tha~ ~he sub~idi~ry dec~ded si~nal is ill.ustrated on a twi~e magni~ied amplitude scale.
The se~ond sub~r~c~er 55-2 is s~tpplied with ~he subsidia~y deco~ed 5ignal and the third ~ompressed ln si.gna.l and calculates ~he sec~nd diEference between the ~ubsidia~ de~oded signal and the t:hird ~ompressed signal. ~he seco~d subtracter 55-2 produ~es the second dif~erençe signal representative of the second dif~erence. As ~ result, the se~ond di~ference signal 15 has ~ reduced amplitude as illustrated ~long a ninth or bot~om li.ne labelled (i~ in ~ig. 7. It should be note~
here that the second differen~e si~nal i~ illustrated on ~n ei~ht times magnified amp.Litude scale.
Referring to ~ig. 8, the ç~b~idiary decodin~
20 c:irc~lit 71 c4mprise~ a suh~idiary ~dder 71-1 and A
prediction circuit 71-2. The subsidiary adder 71-1 is ~or ~lcul~ting ~ $u~sidi~ry ~um ~f ~n additional signal ~n~ the ~çon~ ~elaye~ ~lgnal pro~uce~ ~y tne second delay c~xcult 54-2. The subsl~lary ~d~er 71 1 produces ~5 a subsidia~y sum si~nal rep~esentative of the gub~idi~ry ~tlm. Th~ p~edic~ion ci~cui.l: 71-~ c~ompr.i.ses an element delay circuit 71-2a and a co~f~icient multiplie~ 71-2b, A~ well kn~wn in ~he art, the element delay ci~cuit 20401~

71-2a ls for glvlng ~he subsidiary sum ~ignal a predeter~ined delay i.n~erval of a single picture elemen~. The element ~elay ~ircui~ 71-~a produ~e~ a delayed ~ignal ~aving the predetermined delay rel~tive 5 to the sub~i.diary ~um signal. The element de~ay cir~uit 71-2a ~ay ~e called ~ ~ird delay circuit. The coefficient mul.~iplier 71-2b is for ~ultlplying the subsldiar~ sum by the pre~etermined coefficient to produce a multiplied value and supplies a mul~iplied 10 signal re~resentati.ve of the multiplied v~lue to the subsidiary ~dder 71~1 as the additional sign~l. The predetermined c~e~icient is ~p~roximately equ~l to uni~y.
The subsidiary decoding ~i~cuit 71 m~y be 15 implemented by ~n amplifier having a prede~er~ined amplification factor for ampli~ying the se~ond delayed sig~al into an amplified ~igna~. The ampli~ier delivers the amplified si~nal t~ the æecond QU~t~ er a~ ~he ~ubsidiary decoded sign~l. The pr~d~termin~d 20 amplificati~n ~tor should be d~rmi~e~ to be grcAtcr ~han unity.
Refe~ring ~o Fig. 9, the d~cription wlll proceed to ~ rccep~ion signal proce~ing un~t whic~ i~
used in the ~roun~ s~atlon 40 (Fig. 2~ and ix sui~able 25 for ~he signal processin~ unit described in ~annectlon with Fig. ~. The reception signal pro~essin~ unit is similar to that illustra~ed in Fi~. 5 ~nd compri~es similar parts designated by like reference numerals 20~0145 excep~ that the second reception delay cixcuit 64-~ is connecte~ ~o ~n input l}ne of the fi~st adder 65-l and tha~ a re~ep~ion subsidiary decoding circuit 80 is conneGted between the second recep~i~n del~y ci~cuit 5 64-2 and ~he c;econd adder 65-2. The second recep~ion del~y Cl~CUit 64-2 is simila~ to the second delay circu.it 54 2 de~cribed in conjunc~ion ~ith Fig~ ~.
Likewi~e, the reception subsidiary de~oding cirçuit 80 is si~ilar to t~e subsidi~ry de~oding circuit 71 1~ descri~ed in connection ~ith Fig. 6.
The reception si~nal processing unit is supplied with the first through the third image da~a ~rains ~l to I3 from the sign~ di~tributing ~nit 43. The flrst imag~ dat~ ~rain Il i~ supplied to the ~irst reception 15 decodin~ cir~uit ~1 and the firs~ reception delay circ~ 4-l. The first recep~i.on decodin~ ~ircuit 61 decode~ the firs~ image d~t~ train Il into the first decoded signal. The first re~ep~i4~ delay oircuit 64-1 gives the f irs~ image data train ~l the f ir~ delAy 20 ~ual to th~ fir~t time duration tl and produo~s the ~irst delayed train having the firs~ delay relati~e to the ~ t imAge data ~ain ~l, The ~lr~ adder ~5~ supplied ~ith the fir~t ~e~ayed t~ain ~nd the second i~age d~ta train I2~ The 25 firs~ adder 65-l ~aLculates the first sum of ~he ~irst delayed train and the seco~d i~age data train I2 and deliv~rs ~he i.rst sum signal representati~e of the first sum to the second reception decoding cir~uit 62.

20401~a The second re~eption de~ding ~ircuit 62 ~eaodc~ th~
first sum sign~1 into the second decoded signal.
The secon~ recep~i4n delay clrcuit 64-2 gives the second image ~ata traln IZ the secon~ aelay e~1 to 5 the se~ond ~ime duration t2 and produce~ the second ~elayed train havin~ the second del.~y ~lativ~ to the ~econd image data ~rai.n I2. The reçeption subsidiary de~oding circuit 80 i~ ~upplied with the second d~layed train and decodes ~he seçond ~el~yed t~ain into a eption decoded sign~1 by like operation which i~
carried out by the subsidiary deco~ing circui~ 71 describefl in conjun~t1on w~th Fig~ 6, The reception decoded ~ignal i8 suppLied to the second adder 65-~ as a reproduced æi~na1 of t~e SU~s tdi~ry decoded signa1 15 produced by ~he subsidiary decodin~ circuit 71.
The se~ond adder ~5-2 calc~ es the second sum of ~he reception deçoded signa1 and the thir~ im~e da~a train I~ and produces the second sum signa1 ~epresentative o~ the second sum~ The second sum sign~1 20 i8 decoded by the third reçeption decoding circui~ ~3 into the third decoded signal. The irst through the ~hird ~eaoded ~i~n~l~ ara oupplied ~o the imag~

reproducin~ unit 48 (Fig. 2 ) .
Referring to P'ig. 10, th~ ~le~cription will be 2 S m~de as regards a signal prc~cessing unit ac:co~ding to a third embo~lment o~ this inventlon, The s ~ gnal proce~sing ~lnit i.s similar to th~t illustrated in Fig.
3. The signal pro~essing uni~ comprises simil~r parts 20401~

de5i~na~ed by ll~ce reference numeral~ ~xcept ~h~t the signal proce~sing ~lnit is suppl~d wit~l the forward, the rlg~t under, 2nd ~he backward electric signals collec~ively as a time divisiona} multil~exed signal and that ~ data compression unlt 90 is used instead of the fi.rst through the third data compression cir~uits 51 to 53. This is based on the followin~ ~act. When used as a combination o~ the ~irst through the third photoelectric transducer~ 21 to 23r the charge ~oupled 10 deviçe produc~s ~ device output signal in ~he form o~ a suc~essi.on of the forward, the right under, and the b~ckward electric signals as the time di~iæio~al multiplexed si.gnal.
The data compression uni~ 90 i5 supplied with 15 the ~i~e divis~.onal mul~iplexed signal and compres~es ~he ti~e ~ivisional m~ltiplexed si.-~nal into a compressed signal~ The c~mpres~ed signal consists o~ fir~t through third par~ial compressed signals whic~ correspond ~ the forwaxd, the right u~der, and the ~ackward electric 20 signals, respecti.~rely The data c~pre~ion unit ~0 ~upplies a~ first the firs~ par~ial compressed sign~l to the fir~t dçl~y ci~cuit 54-1 ~nd th~ modulAtc~r 31 ~Fig.
13 ~nd supplie:~ the: second pa~tia~ compress~ slgnal to th~ fir~t s~lbt~ac;:ter SS-l and ~he ~econd del~y clrcult ~5 ~4-2 after l~pse of ~he ~irst time duration tl from Supply 0~ the first partial compxessed signal.
Further~ore, the da~a compression unit 90 sends the third partial compres~ed signal to the second ~u~rac~er 20401 1~

55-2 a~ter lapse o~ the second time duration t~ from supply of the second p~rtial compres~d signal.
The ~irst sub~racter 55-1 ealculates the fir~t difference between ~he first d~l~yed signal prod~ced by 5 the fir~t delay circuit 54-1 and the second par~ial compressed sign~l a~d produces the first di~fere~ce signal representativ~ of the firs~ ~if ference The ~econd ~btracter S5-2 calculateg the second dif ferenç~ be~ween the second del~yed signal produced ~y 10 the second delay ci~cuit 54-2 and the third parti~l co~pxessed signal and produces the second difference ~gnal repr~sentative of the second diffe~ence;
The first partial compres~ed ~ignal and the ~irs~ and ~he se~ond di~erence ~ign~ls a~e supplied to lS the modula~or 31 as the pro~essed sl~nal.
While thi~ in~ention has thus far been described in conjunc~ion wi~h a ~ew embodiments thereof, it will readily be possible fo~ thos~ skilled in the art to ~ut thi~ invention int~ practi.ce in various ~ther manners.
2a For exampl~, the optical syctem may for~ a plurality o~
optica~ im~ge~ of ~he object zone on ~ plurality of ~ocu~ing ~re~s at a time by u~ing A plurality of æpectral filters which ha~re spectr~l c~a;~acteristics dlfference ~roln one ~no~cher. In ~ls c:ase~ a pl~rality 25 of pho~oelectric transducer~ ~re arranged on the ras~ective focu~ing area~.

Claims

WHAT IS CLAIMED IS:

1. An image pickup system for a craft having a predetermined direction and flying over an object zone, said system comprising an optical system for producing an optical image of said object zone, image processing means including first and second photoelectric transducers for transducing said optical image to first and second partial electric signals representative of partial zones of said object zone, respectively, which are spaced apart by a first preselected distance along said predetermined direction, said first and said second photoelectric transducers being spaced apart from each other along said predetermined direction by a first predetermined distance and lying transversely of said predetermined direction, said first predetermined distance determining for said optical system a first visual angle related to said first preselected distance;
and an image signal processor for processing said first and said second partial electric signals to produce a processed signal and for supplying said processed signal to a transmitter, said craft flying for a first duration from a first position to a second position spaced apart from said first position by said first preselected distance, said image signal processor comprising:
a compression circuit connected to said first and said second photoelectric transducers for (Claim 1 continued) compressing said first and said second partial electric signals into first and second compressed signals;
a first delay circuit connected to said compression circuit for giving said first compressed signal a first delay equal to said first duration to produce a first delayed signal having said first delay relative to said first compressed signal;
a first subtracter connected to said first delay circuit and said compression circuit for calculating a first difference between said first delayed signal and said second compressed signal to produce a first difference signal representative of said first difference; and supplying means connected to said compression circuit and said first subtracter for supplying said first compressed signal and said first difference signal to said transmitter collectively as said processed signal.

2. An image pickup system as claimed in Claim 1, wherein said compression circuit is put in operation in accordance with a predictive encoding method

3. An image pickup system as claimed in Claim 2, wherein said compression circuit is put in operation in accordance with variable word length encoding method in addition to said predictive encoding method.

4. An image pickup system as claimed in Claim 3, said image processing means further comprising a third photoelectric transducer spaced apart from said second photoelectric transducer by a second predetermined distance forwardly of said predetermined direction, said second predetermined distance determining for said optical system a second visual angle related to said second partial zone and a third partial zone which are spaced apart from said second partial zone by a second preselected distance backwardly of said predetermined direction, said third partial zone being in correspondence to said third photoelectric transducer, said craft flying in a second duration from said second position to a third position spaced apart from said second position by said second preselected distance, wherein:
said compression circuit is connected to said third photoelectric transducer to produce a third compressed signal;
said image signal processor further comprising:
second delay circuit connected to said compression circuit for giving said second compressed signal a second delay equal to said second direction to produce a second delayed signal having said second delay relative to said second compressed signal;
a second subtracter connected to said compression circuit and said second delay circuit for calculating a second difference between said second (Claim 4 continued) delayed signal and said third compressed signal to produce a second difference signal representative of said second difference; and supplying means connected to said compression circuit and said first and said second subtracters for supplying said first compressed signal and said first and said second difference signals to said transmitter collectively as said processed signal.

5. An image pickup system as claimed in Claim 3, said image processing means further comprising a third photoelectric transducer spaced apart from said second photoelectric transducer by a second predetermined distance forwardly of said predetermined direction, said second predetermined distance determining for said optical system a second visual angle related to said second partial zone and a third partial zone which are spaced apart from said second partial zone by a second preselected distance backwardly of said predetermined direction, said third partial zone being in correspondence to said third photoelectric transducer, said craft flying in a second duration from said second position to a third position spaced apart from said second position by said second preselected distance, wherein:
said compression circuit is connected to said third photoelectric transducer to produce a third compressed signal;

(Claim 5 Continued ) said image signal processor further comprising:
second delay circuit connected to said compression circuit for giving said second difference signal a second delay equal to said second duration to produce a second delayed signal having said second delay relative to said second difference signal;
partial decoding circuit connected to said second delay circuit for decoding said second delayed signal into a decoded signal;
a second subtracter connected to said compression circuit and said partial decoding circuit for calculating a second difference between said third compressed signal and said decoded signal to produce a second difference signal representative of said second difference; and supplying means connected to said compression circuit and said first and said second subtracters for supplying said first compressed signal and said first and said second difference signals to said transmitter collectively as said processed signal.

6. An image pickup system as claimed in Claim 5, each of said first through said third partial electric signals comprising a succession of image pulses, each of said image pulses having a pulse width, wherein said partial decoding means comprises:
an adder circuit connected to said second delay circuit and supplied with an additional signal and said (Claim 6 continued) second delayed signal for calculating a sum of said additional signal and said second delayed signal to produce a sum signal representative of said sum;
a third delay circuit connected to said adder circuit for giving said sum signal a third delay equal to said pulse width to produce a third delay signal having said third delay relative to said sum signal; and a multiplier connected to said third delay circuit for multiplying said sum by a predetermined coefficient to produce a multiplied signal representative of a multiplied value as said additional signal.

7. An image pickup system as claimed in Claim 5, wherein said partial decoding means is an amplifier connected to said second delay circuit and having a predetermined amplification factor for amplifying said second delayed signal into an amplified signal to produce said amplified signal as said decoded signal.

8. An image pickup system for a craft having a predetermined direction and flying over an object zone, said craft flying for a predetermined duration from a first position to a second position spaced apart from said first position by a first preselected distance, said system comprising:
an optical system for producing an optical image of said object zone;

(Claim 8 continued) first and second photoelectric transducers for transducing said optical image to first and second partial electric signals representative of first and second partial zones of said object zone, respectively, which are spaced apart by said first preselected disitance, said first and said second photoelectric transducer being spaced apart from each other along said predetermined direction by a first predetermined distance and lying transversely of said predetermined direction, said first predetermined distance determining for said optical system a first visual angle related to said first preselected distance;
means for delaying said first partial electric signal by said predetermined duration to produce delayed signal;
means for calculating a difference between said delayed signal and said second partial electric signal to produce a difference signal; and means for transmitting said first partial electric signal and said difference signal.