Electro-optical system with scan-in illuminator and scan-out photosensor for scanning variable transmittance object

Billingsley, F. C.

Volkoff, J. J.

English

NASA Technical Reports Server

NOTICE 
- 
The invention disclosed in this document resulted from 
resea rch  in aeronautical and space activities performed under 
programs of the National Aeronautics and Space Administration. 
The invention is owned by NASA and is therefore available for 
licensing in accordance with the NASA Patent Licensing Regu- 
lation (14 Code of Federa l  Regulations 1245.200). 
To encourage commercial  utilization of NASA-owned inven- 
tions, it is NASA policy to grant nonexclusive, royalty-free, 
revocable l icenses to any company o r  individual desiring to use 
the invention while the patent application is pending in the U, S, 
Patent Office and within a specified period, presently two years ,  
af ter  issuance of the patent to NASA. If commercial  use of the 
invention does not occur during this period, NASA may grant a 
limited exclusive, royalty-free license thereby adding an  incen- 
tive to further encourage commercial  development, Any company 
desiring to make, use, o r  se l l  this invention is encouraged to 
obtain a royalty-free license from NASA. 
Address inquiries and a l l  requests for l icenses to Assistant 
General Counsel for  Patent Matters,  Code GP-1, National 
Aeronautics and Space Administration, Washington DC 2 0546. 
NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19700025381 2020-03-11T23:42:45+00:00Z
Appl i ca t ion  S/N 15,020 
F i l e d  : 02/27/70 
' Cont rac tor  : ~ a l t e c h / ~ ~ ~  
Con t r ac t  NAS7-100 
AWARDS ABSTRACT 
Inventors :  F r e d e r i c  Crocke t t  B i l l i n g s l e y  JP33--C-as-e---N@-. - 1-1106 
John Jay  Volkof f  NASA Case No. : 
Cont rac to r :  J e t  Propuls ion  Laboratory NPO-11106 
January 8 ,  1970 
ELECTRO-OPTICAL SCANNING APPARATUS 
A system %or e l e c t r o - o p t i c a l l y  scanning v a r i a b l e  
t r a n s m i t t a n c e  o b j e c t s  i s  d i s c l o s e d .  The system inc ludes  
a scan- in  i l l u m i n a t o r  1 f o r  scanning an o b j e c t  10 a t  a  
v a r i a b l e  dwel l  t i m e  w i t h  a  s p o t  d e f i n i n g  beam 2 of v a r i a b l e  
i n t e n s i t y .  A scan-out photosensor  20, which i n c l u d e s  a  
p h o t o s e n s i t i v e  s u r f a c e  i n  o p t i c a l  communication wi th  t h e  
beam t r a n s m i t t e d  by t h e  o b j e c t ,  i s  provided.  The photo- 
s e n s i t i v e  s u r f a c e  i s  scanned synchronously w i t h  t h e  scan- in  
i l l u m i n a t o r  beam, 
An i l l u m i n a t i o n  i n t e n s i t y  modulator 50 i n c r e a s e s  
t h e  i n t e n s i t y  of  t h e  scan- in  i l l u m i n a t o r  beam when t h e  
photosensor  o u t p u t  f a l l s  below a  predetermined l e v e l .  when 
an o b j e c t  a r e a  i s  reached which has  t o o  low a  t r a n s m i t t a n c e  
t o  b e  adequa te ly  compensated by i n c r e a s i n g  t h e  i l l u m i n a t i n g  
beam i n t e n s i t y ,  a scan and  dwell F.ime control 40 increases t h e  
dwe l l  t ime.  I n c r e a s i n g  t h e  dwe1.l t ime p rov ides  an increased.  
am0ur.t of t o t a l  l i g h t  t o  t h e  photosensor  t o  enab le  an ou t -  
p u t  s i g n a l  of adequate  S/N r a t i o  
AppLication ~ / k 4  15, w%O 
Fi Led : u2/2?17b 
Gonicrac tor r ~ a l t e . c ? h ! ~ ~ ~  
Con-is;;rac.t HAS'7-POQ 
TO ALL WHOM I T  MAY CONCERN: 
5 BE I T  KNOWN THAT WE FREDERIC CROCKETT BILLINGSLEY 
and JOHN JAY VOLKOFF, c i t i z e n s  of t h e  United S t a t e s  of 
America, r e s i d i n g  a t  Altadena and S i e r r a  Madre re spec t ive ly ,  
i n  t h e  County of Los Angeles, S t a t e  of C a l i f o r n i a  have 
invented a new and u s e f u l  
10 ELECTRO-OPTICAL SCANNING APPARATUS 
of which t h e  following i s  a s p e c i f i c a t i o n :  
ABSTRACT OF THE DISCLOSURE 
A system f o r  e l e c t r o - o p t i c a l l y  scanning v a r i a b l e  
t ransmi t tance  o b j e c t s  inc ludes  a modulated scan-in i l lumina to r  
15  and a scan-out photosensor. The scan-in i l lumina to r  provides 
a s p o t  of l i g h t  of requi red  i n t e n s i t y  upon t h e  ob jec t .  The 
t r ansmi t t ed  l i g h t  from t h e  o b j e c t  i s  then o p t i c a l l y  read by 
t h e  scan-out photosensor. The scanning sequence of  the  scan-in 
i l lumina to r  i s  synchronized with t h a t  of t h e  scan-out photo- 
20 sensor .  Since a v a r i a b l e  l i g h t  i n t e n s i t y  and a v a r i a b l e  dwell  
time f o r  t h e  read-out a r e  provided i n  t h i s  system, t h r e e  con- 
t r o l l e d  read-out phases a r e  a v a i l a b l e ;  cons tan t  reduced l i g h t  
i n t e n s i t y  and cons tan t  dwell  t ime, v a r i a b l e  l i g h t  i n t e n s i t y  
and cons tan t  dwell  time, and cons tan t  maximum l i g h t  i n t e n s i t y  
25 and v a r i a b l e  dwell time. These read-out phases enable  t h e  
. system t o  read-out an extended dynamic range of t h e  ob jec t .  
The dynamic range i s  determined by t h e  maximum a v a i l a b l e  l i g h t  
i n t e n s i t y  and/or maximum a l l o t t e d  dwell time f o r  t h e  read-out. 
O R I G I N  OF THE INVENTION 
30 The invent ion  descr ibed  h e r e i n  was made i n  t h e  per- 
formance of work under a NASA contract and is subject to 
the provisions of Section 305 of the National Aeronautics 
and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 
42 USC 2457). 
5 BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to systems for electro- 
optically scanning variable transmittance objects and more 
particularly to apparatus for electro-optically scanning 
10 such objects for purposes of monitoring, recording, displaying, 
or digitizing the derived video signals. 
2. Description of the Prior Art 
Electro-optical scanning systems for acquiring data 
relating to variable transmittance objects such as photographic 
15 film are known. Such known devices typically include a 
scan-in illuminator component such as flying spot scanning 
cathode ray tube. The scan-in illuminator sweeps a spot of 
light across the photographic film. A pk;otosensitive device 
intercepts the light transmitted through the film. The degree 
20 to which light is attenuated as it passes through the associated 
film area represents the transmittance of that associated film 
area. 
It has been difficult in such systems to obtain suf- 
ficient light at the photosensitive component to insure an 
25 adequate signal-to-noise ratio when an area of low transmittance 
is read. To compensate for this, it has been known in the 
prior art to increase the intensity of the scanning beam when 
scanning such low transmittance areas. While such an approach 
has proven advantageous, significant limitations remain. For 
30 example, the light intensity for a given system is limited 
e i t h e r  by t h e  maximum l i g h t  i n t e n s i t y  a v a i l a b l e  from t h e  
source o r  by t h e  photographic f i l m  o b j e c t  which may be 
photometr ica l ly  degraded by very  h igh  i n t e n s i t y  l i g h t .  
OBJECTS AND SUMMARY OF THE INVENTION 
I n  accordance wi th  t h e  p r e s e n t  invent ion ,  an e l e c t r o -  
o p t i c a l  scanning system i s  provided which overcomes t h e  above- 
noted d i f f i c u l t i e s .  The system inc ludes  a scan-in i l lumina to r  
f o r  scanning an o b j e c t  a t  a v a r i a b l e  scan r a t e  wi th  a def ined  
s p o t  of l i g h t  t h e  i n t e n s i t y  of which can be  va r i ed .  A scan- 
o u t  photosensor,  which inc ludes  a pho tosens i t ive  su r face  i n  
o p t i c a l  communication wi th  t h e  l i g h t  t r ansmi t t ed  by t h e  o b j e c t ,  
i s  provided. The scanning sequence of t h e  scan-in i l lumina to r  
i s  synchronized wi th  t h a t  of t h e  photosensor. 
An i l lumina t ion  i n t e n s i t y  modulator i s  included i n  
t h e  system t o  r e g u l a t e  t h e  i n t e n s i t y  of l i g h t  scanned onto 
t h e  o b j e c t  a s  determined by t h e  t r ansmi t t ed  l i g h t  i n t e n s i t y .  
The i n t e n s i t y  of t h e  l i g h t  scanned onto t h e  o b j e c t  ranges 
from a predetermined minimum l e v e l  t o  a gpeci f ied  maximum 
l e v e l .  
For those o b j e c t  a reas  read having such low f i l m  
t r ansmi t t ances  t h a t  t h e  t r ansmi t t ed  l i g h t  onto t h e  photosensor 
i s  n o t  s u f f i c i e n t  t o  develop an adequate output  s i g n a l ,  t h e  
dwell  t ime f o r  t h e  read-out is  increased.  The dwell  time i s  
increased  t o  t h a t  per iod  requi red  t o  a s su re  t h a t  t h e  output  
s i g n a l  has  an adequate s ignal- to-noise r a t i o .  
I t  i s  t h e r e f o r e  an o b j e c t  of t h i s  invent ion  t o  provide 
an e l e c t r o - o p t i c a l  scanning system t h a t  enables  t h e  read-out 
of  very low t ransmi t tance  regions  of t h e  f i l m  o b j e c t  with an 
improved s ignal- to-noise r a t i o  i n  t h e  r e s u l t i n g  output  s i g n a l .  
I t  i s  a f u r t h e r  o b j e c t  of t h e  p r e s e n t  invent ion  t o  
provide a scan-in/scan-out electro-optical scanning system 
wherein a minimum of total light transmitted onto the scan- 
out photosensitive element is provided by varying the scan-in 
light intensity or varying the dwell time at the allotted 
5 maximum scan-in light intensity. 
It is a further object of the present invention to 
provide an electro-optical scanning system wherein a scan-out 
photosensitive element is utilized to accurately define the 
illuminated ob'ject area which the output signal represents. 
10 It is still a further object of the present invention 
to provide an electro-optical scanning system to extend the 
dynamic range of transmittance read-out capability of the 
system beyond that achievable by prior ark devices. 
Still other objects, features and attendant advantages 
15 of the present invention will become apparent to those skilled - 
in the art from z reading of the following description of a 
preferred embodiment constructed in accordance therewith taken 
in conjunction with the accompanying dra~ings. 
BRIEF DESCRIPTION OF THE DRAWINGS 
20 FIGURE 1 is an exemplary electro-optical scanning 
system constructed in accordance with the principles of the 
present invention. 
FIGURES 2A-C graphically depict various signal 
characteristics which are helpful in understanding the operation 
25 of the system of FIGURE 1 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGURE 1, there is shown an exemplary 
electro-optical scanning system constructed in accordance with 
the principles of the present invention. The system of FIGURE 1 
30 is adapted to acquire information relating to the transmittance 
c h a r a c t e r i s t i c s  of a f i l m  frame loca ted  a t  f i l m  plane 10, 
A scan-in i l lumina to r  1 genera tes  an i l lumina t ing  
def ined  s p o t  of l i g h t  ind ica ted  a t  2 .  The scan-in s p o t  of 
l i g h t  i s  i n t e r m i t t e n t l y  and s e q u e n t i a l l y  swept across  f i l m  
, 5 plane 10. The scan-in i l lumina to r  1 i s  p re fe rab ly  a cathode 
r a y  tube of t h e  f l y i n g  s p o t  scanner type.  However, t h e  
i l lumina to r  i s  n o t  l i m i t e d  t o  any p a r t i c u l a r  l i g h t  source 
and may inc lude  incandescent o r  a r c  lamps and l a s e r s  with 
appropr ia t e  i n t e n s i t y  and scan c o n t r o l  devices  provided. 
10 . The scan-in i i lumina to r  produces a s p o t  of l i g h t  I .  
whose i n t e n s i t y  can be va r i ed  and c o n t r o l l e d  by s i g n a l s  appl ied  
t o  an i n t e n s i t y  c o n t r o l  te rminal  3. The scanning sequence 
per iod  of t h e  i l lumina to r  can be v a r i e d  and i s  c o n t r o l l e d  " 
by s i g n a l s  appl ied  t o  a dwell  time c o n t r o l  te rminal  4 ,  The 
15  manner of c o n t r o l l i n g  t h e  i l lumina t ion  l i g h t  i n t e n s i t y  and 
dwell  time t o  provide t h e  requi red  system s i g n a l  output  w i l l  
be  descr ibed  h e r e i n a f t e r .  
The t r ansmi t t ed  l i g h t  8 i s  in te rdep ted  by a scan-out 
s i g n a l  genera tor  20. Scan-out s i g n a l  genera tor  20 p re fe rab ly  
20 inc ludes  a pho tosens i t ive  su r face  pos i t ioned  t o  i n t e r c e p t  t h e  t r a n s -  
mi t ted  l i g h t  8. Areas of t h e  pho tosens i t ive  su r face  a r e  sequen- 
t i a l l y  read-out a s  an output  s i g n a l  2 1 .  The s i g n a l  l e v e l  i s  a 
func t ion  of t h e  t o t a l  amount of l i g h t  t r ansmi t t ed  through t h e  
r e spec t ive  a r e a s  of t h e  pho tosens i t ive  su r face  read-out. Pos i t ion  
25 c o n t r o l  i s  provided by t h e  scan and dwell  time e l e c t r o n i c s  40 
a which i s  u t i l i z e d  t o  synchronize t h e  dwell  time and p o s i t i o n  of 
' the  scan-in i l l u m i n a t o r  with t h e  scan-out s i g n a l  genera tor .  
P re fe rab ly  t h e  a rea  of t h e  s p o t  of l i g h t  from t h e  scan- 
i n  i l lumina to r  is  l a r g e r  than  t h e  r e spec t ive  a r e a  of the photo- 
30 s e n s i t i v e  su r face  read-out by t h e  scan-out s i g n a l  genera tor  
t o  minimize scan-in/scan-out misalignment and l i g h t  f l a r e  
from ad jacen t  f i l m  a reas .  A smal ler  number of t o t a l  move- 
ments requi red  f o r  t h e  scanning sequence of t h e  scan-in 
component can be f a c i l i t a t e d .  
5 The a rea  of t h e  pho tosens i t ive  su r face  read-out a t  
a  given i n s t a n t  can be c o n t r o l l e d  f o r  accura te  c o r r e l a t i o n  
with t h e  r e spec t ive  a reas  of t h e . o b j e c t  f i lm.  The scan-out 
s i g n a l  genera tor  20 may p re fe rab ly  be a  non-storage type of 
e l e c t r o - o p t i c a l  component such as  a  photomul t ip l ie r  tube o r  
10 an image d i s s e c t o r  tube.  Storage type camera tubes  such a s  
v id icons ,  image o r th icons ,  emitrons,  e t c . ,  may a l s o  be used 
wi th in  t h e i r  r e spec t ive  dynamic range c a p a b i l i t i e s .  
Because of inhe ren t  e l e c t r o n  noise  introduced with 
output  s i g n a l  2 1 ,  it i s  necessary f o r  accura te  determinat ion 
15 of t h e  s i g n a l  l e v e l  t o  have t h e  l e v e l  of t h e  output  s i g n a l  
l a r g e  enough t o  ensure an adequate s ignal- to-noise (s/N) 
r a t i o .  The a t t e n u a t i o n  f a c t o r  of t h e  i l lumina t ing  spot  of 
l i g h t  from t h e  i l lumina to r  it passes  through t h e  f i l m  
i n v e r s e l y  p ropor t iona l  t o  t h e  t ransmi t tance  of t h e  r e spec t ive  
20 f i l m  a rea  i l luminated .  For those  a reas  read-out which have 
f i l m  t ransmi t tances  t o o  low t o  r e s u l t  i n  an output  s i g n a l  of 
adequate S/N r a t i o  over t h e  minimum read-out dwell  time 
per iod ,  t h e  i n t e n s i t y  of t h e  s p o t  of l i g h t  onto t h e  o b j e c t  
f i l m  i s  increased  r e s u l t i n g  i n  an inc rease  i n  t h e  output  s i g n a l  
25 l e v e l .  Furthermore, should t h e  a r e a  des i red  t o  be  read-out 
. r equ i re .  a  g r e a t e r  l i g h t  i n t e n s i t y  onto t h e  o b j e c t  f i l m  than 
t h a t  provided by  t h e  scan-in i l lumina to r ,  t h e  dwell  time 
dur ing  t h e  read-out i s  increased.  Thus, t h i s  invent ion  d i v i d e s  
t h e  read-out c a p a b i l i t y  of t h e  system i n t o  t h r e e  phases cover- 
30 ing  t h r e e  recognizable  t ransmi t tance  regions  I, I1 and 111 of 
the object film having reference to FIGURES 2A-C, 
FIGURES 2A, 2B and 2C show respectively the scan-in 
light intensity, dwell time, and S/N ratio curves for the 
three object transmittance regions I, I1 and 111. 
5 In region I the object transmittance is equal to or 
greater than the transmittance level TQ. Within this region 
the dwell time and light illumination intensity for the . .  
read-out process are held constant at minimum levels %in 
and Imin respectively as shown by FIGURES 2B and 2A. The 
10 dwell ,time and light intensity are regulated by the illumina- 
tion intensity modulator 50 and scan and dwell time electronics 
40 (FIGURE 1). The measured signal 21 within this region will 
have a S/N ratio which is equal to or greater than the 
desired minimum S/N ratio (s/Nmi,). 
In the transmittance region 11, the film transmittance 
is less than TQ but equal to or greater than TB. Since the 
minimum illumination intensity Imin is inadequate to provide 
an adequate S/N ratio at minimum dwell time ~k~~ within this 
region, the light illumination onto the film object is in- 
creased. Illumination intensity modulator 50, FIGURE 1, senses 
the output signal level 21' and provides a signal to control 
terminal 3 of the scan-in illuminator causing the required 
change in the light intensity 2. For example, if the film 
'transmittance the output signal ineasured 
25 modulator 50. Modulator 50 causes the scan-in light intensity 
2 to change to the required illumination intensity level IX 
corresponding to the desired S/N ratio s/Nmin. Within this 
region the dwell time for the read-out is at the minimum level 
Kmin' as shown by FIGURE 2B. 
transmittance region the film transmittance 
l e s s  than  TB. Within t h i s  region t h e  maximum l i g h t  i n t e n s i t y  
Imax a v a i l a b l e ,  FIGURE 3A,  t oge the r  with t h e  dwell time Gin 
a r e  no t  s u f f i c i e n t  t o  r e s u l t  i n  an adequate S/N r a t i o .  How- 
eve r ,  by inc reas ing  t h e  dwell time f o r  t h e  read-out, F I G U R E  2B, 
5 t h e  t o t a l  amount of l i g h t  accumulated a t  t h e  photosens i t ive  
su r face  r e s u l t s  i n  a s u f f i c i e n t  l e v e l  of output  s i g n a l  t o  pro- 
v ide  t h e  adequate S/N r a t i o  s/Nmin. The dwell  time f o r  t h e  
read-out and t h e  scanning synchronizat ion a r e  c o n t r o l l e d  by 
t h e  scan and dwell  time e l e c t r o n i c s  40, FIGURE 1. 
The f i l m  t ransmi t tance  value a t  any p o i n t  may be 
determined by t h e  u t i l i z a t i o n  apparatus  60, FIGURE 1. U t i l i z a -  
t i o n  apparatus  60 i s  provided wi th  t h e  s i g n a l  output  2 1  from 
scan-out s i g n a l  genera tor  20, t h e  i l lumina t ion  i n t e n s i t y  
modulator s i g n a l  from t h e  modulator 50, and t h e  dwell  time 
15 s i g n a l  from t h e  scan and dwell time e l e c t r o n i c s  40. These 
t h r e e  s i g n a l s  can be used t o  determine a l g e b r a i c a l l y  t h e  
t ransmi t tance  T which i s  assoc ia ted  wi th  t h e  p i c t u r e  element 
read-out. 
The system thus  descr ibed provides f o r  t h e  read-out 
2 0  of a wider range of f i l m  t r a n s m i s s i v i t y  with an adequate S/N 
r a t i o  than  has  here tobefore  been a t t a i n a b l e  by p r i o r  a r t  
devices .  




Electro-optical scanning apparatus Patent Application

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