MEMO(Sanitized) [RE: A NEW CRISPENER CIRCUIT FOR TELEVISION IMAGES]

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04770A002700030024-5
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 9
• Document Creation Date: December 28, 2016
• Document Release Date: May 18, 2005
• Sequence Number: 24
• Publication Date: November 1, 1963
• Content Type: MEMO

25X1
25X1
Declass Review by NGA.
Ap roved- or Rt
FORM NO ? '101
!DATE )
lp,7 7 F4002700030 24-5
f
tali
 CPYPQ. up
r-T New CrIS ueuer Circuit
or Tel evasion Images By EARL F. BROWN
'[he subjective definition of a television image msy be improved by overemphasiz-
ing and/or increasing the steepness of its luminance transitions. A new crispener
circuit capable of performing either or both these functions using linear circuitry is
described and illustrated with low-resolution television images. It is shown that the
effect of overemphasizing or steepening the rise-times of the luminance transitions
appear to be comparable in improving the subjective quality of the resulting pic-
ture: whereas a combination of the two is superior to either. Applications of the
crispener circuit in outlining television images and reducing overshoot and ring
due to sharp cutoff filter characteristics are also described and illustrated. It is
shown that when the ring and overshoot in an image are reduced, the sharpness of
the image is likewise reduced.
Introduction the sharp cutoff characteristics of filters
is also described.
ion is to place
The objective of televis before an observer a satisfactory and
pleasing image of a distant scene. Some
researchers believe that of the ingredients
of a reproduced image among the most
important are the edges or brightness
boundaries of the image. Surely this
must have some substance since many
scenes are identifiable from an outline of
their luminance. boundaries alone. The
;filling in of tones between the boundaries
in general serves to enhance the aesthetic
value of the image.
In their natural setting luminance
boundaries appear with varying degrees
of abruptness. It behooves us to recreate
these boundaries as accurately as pos
title. The steepness of luminance bound-
aries in a television image is proportional
':o the bandwidth of the system. In tele-
vision systems of narrow bandwidth, the
slowly changing boundaries are normally
accurately reproduced, but the initially
abrupt boundaries are smoothed out,
sometimes radically. It appears advisable
to operate on the resolved boundaries,
at the receiver. in such a way that only
the degraded boundaries, i.e., the for-
merly abrupt boundaries, are affected.
Earlier researchers'? have demon-
itrated that steepening and/or over-
?mphasizing these boundaries will pro-
vide some restoration or apparent restor-
ation of these boundaries towards their
Crispcning
Crispcning is here defined as the addi-
tion of art inverted second derivative (or
approximate) of the image signal to the
image signal. A crispening signal may be
used to steepen and/or overemphasize
the luminance transitions of the image.
With signal amplitudes and bandwidth
held constant, the ratio of the duration
of the crispening signal to the duration of
the luminance transition signal is the
controlling factor in determining the
aniount of steepening obtained. When
this ratio becomes unity (i.e., the ct;spen-
intt signal becomes a true second deriva-
tive of the transition signal) the maxi-
mum increase in steepness is obtained.
The maximum ratio of crispening signal
duration to image signal duration is two
to one, where steepening of the lumi-
nance transitions is negligible. Above this
ratio the crispening signal has a dete-
riorating effect similar to echoes in an
image. The degree of overemphasis is a
function of the amplitude of the crispen-
ing signal.
The subjective impression on the
observer of crispening is a sharper pic-
ture, apparent increase in resolution,
improved contrast and an improvement
in the perception and clarity of liminal
detail.
of a step waveform by limiting the
frequency hand, as shown in Fig. 1(a), we
decrease the sharpness of the luminance
step. We may increase the sharpness of
luminance boundaries along a line by
crispening the image signal as illustrated
with the step signal in Fig. 1(c). Crispen-
ing requires that we derive an inverted
second derivative or approximate, Fig.
1(b), from the step signal and subse-
quently add the derived signal to the step
signal as shown in Fig. 1(c).
Crispener Circuit
The crispener circuit is shown sche-
matically in Fig. 2. It is composed of an
electromagnetic delay line, the input end
of which is terminated in the character-
istic: impedance of the line while the
other end is left open-circuited. A pickup
coil is inductively coupled to the delay
line. A bandlimited step signal, Fig. 3(a),
converted into a current wave is im-
pressed onto the delay line. As the current
step wave passes the pickup coil on its
Fig. 1. Crispcning of a degraded step
signal: (a) top, input step signal; (b)
muddle, inverted second derivative of
step signal; (c) bottom, crispcned ste
signal, i.e., addition of wavciorrns (a)
and (b).
nrii,ginal steepness. A linear crispening Design Considerations
circuit has been designed with this
purpose in mind. This circuit is capable In television the abruptness of lumi-
of steepening and/or overemphasizing nance changes in the direction perpcndic-
the deteriorated luminance signal bound- ul