Video scanning change discriminator

A method and apparatus is disclosed for determining the speed and direction and height/width dimensions of subject movement within a field of view. Two video frames are compared such that the dimensions of change within the two frames are determined, sorted and counted. One count is made of the vertically-occurring change; the other count is made of the horizontally-occurring change. The derived change dimensions and position is stored to be later compared with the change dimensions and position of a following comparison of two scans; the lateral displacement of one change position of a prior time with respect to the change position of the present time is determined and counted, the count representing the magnitude and direction of the subject movement that occurred. These determinors are `dumped` into a computer which detects certain types of change and ignores others and which may be operated to determine the velocity of horizontal movement as well as changes in velocity of vertical movement.

BACKGROUND OF THE INVENTION 
This invention relates to video systems and, more particularly, to a method 
and means for deriving from video signals, a set of second signals 
indicative of the characteristics of dynamic changes taking place in a 
second area and determining change, speed and direction. 
The improvement disclosed herein, lies in the selectors and counters which 
sum certain characteristics of change found in two to four video frames. 
The prior art methodology of determining change within two video frames is 
with the combination of camera, delay, comparator and timing generator. 
This invention discloses additional novel functions to the combination. A 
dimension selector is added. The selector selects and sorts vertical 
change from horizontal change and the associated accumulators sum the 
vertical change as distinct from the horizontal change. additionally, a 
horizontal direction selector is disclosed, the later selector determines 
the direction and magnitude of the change, the connected counters sum 
leftward movement as distinct from rightward movement. At the proper time, 
these sums are `dumped` into a computer. 
No prior art reveals a height/width determiner, derived from a moving 
subject. Prior art speed and direction determiners derive speed and 
direction through a differing process. In the prior art system, a wave 
comparator compares the centerline scan of one period of time with 
successive "skewed" lines of a different scan to find one line that 
matches the amount of "skew" of the matching line, thereby determining the 
direction and speed of the change or moving object. 
SUMMARY OF THE INVENTION 
It is, accordingly, an object of the present invention to provide an 
arrangement for measuring the characteristics of a change, more 
specifically, the measurement of height width dimensions coupled with 
lateral speed and direction measurement. 
Briefly, in accordance with the present invention, a video camera provides 
electrical signals representative of the intensity of the field of view. 
This electrical information is delivered in accordance with the invention, 
to an arrangement of a delay, a comparator, and a threshold detector which 
provides the first differential signals. The first differential signal is 
indicative of the difference between each picture element of the present 
video frame and the corresponding picture element of the previous frame. 
The first differential signal is counted and sorted, such that one count 
is representative of the horizontal dimension of change, the other count 
being representative of the magnitude of the vertical dimension. 
Additionally, the first differential signal, also designating position of 
change, is delayed and later compared with the position of the change of 
the presently produced first differential signal. The lateral position 
differences between the two change designations is counted and sorted, 
such that one count is representative of the magnitude of the rightward 
displacement and the other count is representative of the magnitude of the 
leftward displacement. In accordance with a particularly advantageous 
embodiment of the invention, the same circuitry is used to provide 
differential signals and previously described processing is utilized to 
identify the subject displacement by attached computer circuitry.

DETAILED DESCRIPTION 
Referring to the general block diagram of FIG. 1, the combination of the 
invention is disclosed in relation to the combination of the prior art. 
The operation of the combination of the prior art is briefly explained as 
follows. The camera 111 produces electrical signatures of the field of 
view. One output is supplied to delay 112. Timing generator 113 locks the 
camera 111 to the output of delay 112 such that as a picture element 
emerges from delay 112 the corresponding picture element of a common 
position is produced by the camera 111. The video input and output of the 
delay 112 is compared by comparator 115, which in the case of sufficient 
non-comparison, produces a signal of a logical "1" at its output. 
The following additional functions are the improvement over the prior art 
combination. The output of comparator 115 is supplied to dimension 
selector 121, horizontal direction selector 116 and delay 114. In 
dimension selector 121 a determination of the vertical dimension as 
distinct from the horizontal dimension of change is made. The connected 
vertical accumulator 120 sums the magnitude of vertical change. Similarly, 
the horizontal accumulator 122 sums the magnitude of the horizontal 
change. 
The derived non-comparison signal from comparator 115 is also applied to 
delay 114 which is equal to delay 112. The lateral position of the change 
from a prior frame emerges from delay 114 since the lateral position of 
change of a present frame is produced by comparator 115. These signals are 
applied to horizontal direction selector 116 which determines direction of 
lateral displacement. The magnitude of leftward change is summed in 
leftward accumulator 118 and the magnitude of rightward change is summed 
in rightward accumulator 117. Timing generator 113 produces a clock pulse 
signaling the connected computer 119 to read the counters and shortly 
thereafter, a clock pulse resets the counters. 
Referring to FIG. 2, a detailed description of operation of the system is 
given. The circuit elements of FIGS. 1 and 2 correspond as follows: 
______________________________________ 
FIG. 1 FIG. 2 
______________________________________ 
111 1 
112 4 
113 2 
114 3 
115 8-9 
116 11 
117 36 
118 37 
119 38 
120 7 
121 5 
122 6 
______________________________________ 
The camera 1 provides electrical information representative of the 
intensity of the scanned field of view. This electrical information is 
delivered, in accordance with the invention, to a comparison arrangement 
comprising a delay 4, a comparator 8, and a threshold device 9. In this 
case, delay 4 has a storage of many video frames, i.e. t.sub.1 =(T) (X), 
where t.sub.1 =time delay of delay 4. T=frame period, X=number of frames. 
Timing generator 2, synchronized to the output of delay 4, provides the 
time base synchronization, i.e., the field synchronization pulse occurring 
at time t.sub.2, where t.sub.2 = T/2, and the line synchronization pulse 
occurring at time t.sub.3, where t.sub.3 = T/525, to the camera 1 such as 
an electrical signature or signal indicative of a presently generated 
element emerges from the delay 4 the corresponding picture element of the 
present frame indicative of a common geometric location is produced by the 
camera 1. comparator circuit 8 utilizes the simultaneous input and output 
signals of delay 4 to produce a differential signal indicative of change 
of intensity of brightness of each picture element of the present video 
frame with respect to the corresponding picture element of a previous 
video frame. This differential signal is applied to the threshold detector 
9 which provides a first differential output indication signal, a logical 
"1" signal, each time the amplitude of difference exceeds a predetermined 
threshold. The signals from detector 9 supply dimension selector 5 with 
one input to the three input AND gate 28. Similarly, astable multivibrator 
30 produces a clocked input for AND gate 28. As a third input to AND gate 
28, timing generator 2, after an initial delay equal to time t.sub.1, 
provides a logical "1" output, allowing gate 28 to be enabled only when 
both instantaneous and delayed video values are present. The clocked 
output of AND gate 28 is applied to counter 32 of horizontal change 
accumulator 6, which accumulates the clock pulses indicative of the length 
and duration of change. It should be readily apparent that with horizontal 
lines of scan, the comparator 8 produces, horizontally, first differential 
signals of the field of view. Therefore counter 32 sums the horizontal 
dimensions of change. The clock pulse, t.sub.3, coinciding with the end of 
each scan video line, is provided by the timing generator 2 to reset 
flip-flop 27, in every case setting output Q at a logical "1". The output 
thereof, is applied to one input of two input AND gate 29. Following the 
reset pulse and the occurrence of a first differential change indication, 
a logical "1" pulse from AND gate 28, the output of AND gate 29 provides a 
through path for the pulse. The connected flip-flop 27, in response to the 
trailing edge of the pulse, shifts logical "0" to output Q. The output 
thereof is applied to one input of AND gate 29, the latter producing in a 
negative transition, an output signal of a logical "0". As a consequence 
to this negative transition of gate 29 the connected counter 31 in the 
vertical change accumulator 7 is clocked one. It should now be clear that 
AND gate 29 cannot produce additional negative transitions, without 
resetting the output Q of flip-flop 27 to a logical "1". The reset pulse 
occurs at the end of each line of scan at time t.sub.3, allowing only one 
change count per scan line. Because each present line of scan is 
vertically displaced from the prior line, the accumulation of vertical 
change accumulator 7 of each line of scan with a first differential signal 
indicative of change, is representative of the vertical length of change. 
In speed and direction determination, the horizontal direction selector 
circuitry 11 compares the lateral position of a first differential change 
indication of a prior comparison with respect to the lateral position of 
the first differential signal change indication of the present comparison 
of an additional two video scans. As set forth, the stored designation of 
prior change is recalled from delay 3, which, in any case, is equal to 
delay 4, i.e., t.sub.1 =(T) (X). The storage time of delay 3, equal to 
time t.sub.1, is such that as a first differential signal, indicative of 
differences of presently compared picture elements, is produced, the 
corresponding derived first differential signal of previously compared 
picture elements indicative of a common geometric location emerge from the 
delay 3. After an initial time delay equal to twice the period of delay 3, 
i.e., t.sub.4 = 2t.sub.1, timing generator 2 provides a logical "1" signal 
which closes hereinafter called an "enhance mode gate." Hence the present 
first differential signal as well as a previous first differential signal 
are simultaneously applied as inputs to AND gate 13; in absence of a first 
differential change indication, such that a logical "1" is not present at 
both inputs, the output of AND 13 is a logical "0". As a consequence, the 
connected gates 14 and 15, hereinafter called "dehancement mode gates", 
are closed such that signals presented at their respective inputs are 
passed through to their outputs. Gates 10, 22, and 23 are conventional 
logical switching elements which provide a through path for the input 
signal when a logical "1" is applied to the gating control input line and 
block the input signal when "0" is applied to the control input. Gates 14 
and 15 are similar circuits but have inverting elements at their control 
inputs (designated by the symbol "o"). Thus gates 14 and 15 are "closed" 
(pass the input signal) in response to a "0" gating input and are "opened" 
(block the input signal) in response to a "1" gating input. 
In camera 1, scanning from left to right, picture elements and first 
differential signals are produced and compared likewise from left to right 
and a previous element of the same line is always leftward of the present 
element. It follows that in comparing the present first differential 
signal (i.e., the signal at the output of enhance mode gate 10) with the 
previous first differential signal (i.e., the signal from delay 3), the 
direction of movement can be detected by determining which of the two 
signals comes up first. If the previous first differential signal comes up 
first, the direction of movement is rightward and if the present first 
differential signal comes up first, the direction of movement is leftward. 
The direction determination is made in the horizontal direction selector 
11. 
Now referring to the circuitry of the selector 11, at the end of each video 
line a clock pulse, t.sub.3, representing the end of the line period, from 
timing generator 2, is applied to the reset of flip-flops 16 and 19, 
thereby providing a logical "1" at the reset outputs Q which are connected 
respectively to one input of AND gate 17 and AND gate 20. Accordingly, on 
the occurrence of leftward subject movement, a first change designation, a 
logical "1" is encountered first in the presently produced first 
differential signal which is applied to both one input of AND gate 13 and 
to the input of gate 15. However, the other input to AND gate 13, as well 
as its output, remains a logical "0". Accordingly dehancement mode gate 15 
remains closed providing a through path to the first (present) 
differential signal to the gating control input of enhancement mode gate 
23 and to AND 17. A first differential indication signal of a logical "1" 
to gate 23 provides a through path for pulses supplied by astable 
multivibrator 24 to counter 26 of leftward accumulator 37. The pulses are 
accumulated until the secondly encountered first differential indication 
signal, a logical "1" emerges from delay 3 and is applied to AND gate 13. 
Now the two logical "1" signal inputs to AND gate 13 drive the output 
thereof to a "1". As a result dehancement mode gate 15 is opened, blocking 
the change indication from AND gate 17 and enhancement mode gate 23. 
Accordingly, counter 26 is now isolated from the astable multivibrator 24 
and the output of AND gate 17, in a negative transition, becomes a logical 
"0". The negative transition of AND gate 17 toggles connected flip-flop 16 
and simultaneously increments counter 18 of leftward change accumulator 
37. In response to the toggle, reset output Q of flip-flop 16, which is 
one input to AND gate 17, becomes a logical "0". The remaining set output 
Q of flip-flop 16, after being toggled, becomes a logical "1", which, as a 
gate signal, opens both dehancement mode gate 14 and gate 15. It should 
be clear that no further counting is possible until flip-flop 16 is reset 
by the timing generator 2, at the end of each video scan line. For 
rightward movement, the selector circuit 11 is symmetrical to the one 
described in leftward movement. The differing factor in rightward movement 
is that the value "1" is first encountered in the signal from delay 3, 
rather than first encountered in the signal from threshold detector 9, as 
in the case of leftward movement. At the end of the frame, the vertical 
pulse i.e., t.sub.2 = T/2, triggers the trailing edge sensitive single 
shot 33 which signals a computer system 38 to read the counters. When the 
single shot 33 collapses, the trailing edge triggers single shot 35, 
preclearing all counters. 
It is thus seen that during each video frame interval counter 25 
accumulates a count which is proportional to the rightward distance 
travelled by the trailing edge of the moving object during the time of 
delay 3 (i.e., t.sub.1). In the event of leftward movement, counter 26 
accumulates a count proportional to the leftward distance travelled by the 
leading edge of the object during t.sub.1. The counts thus represent both 
direction and magnitude of movement and, since t.sub.1 is constant, can be 
used to determine velocity of movement by means of the formula X/t.sub.1, 
where X represents a given count. Computer 38 may be used to perform such 
calculation, it being fully within the skill of the ordinary computer 
programmer to implement the indicated division operation using any known 
type of computer. 
Counters 18 and 21 accumulate counts Y representing the number of scan 
lines in each frame for which horizontal movement is detected. This is an 
indication of the sum of the vertical dimension of the moving object and 
the vertical distance travelled during t.sub.1. Since the vertical 
dimension of the object remains substantially constant, variations in the 
difference .DELTA. Y between successive counts Y.sub.i and Y.sub.i+1 
represent changes in the vertical velocity of the moving object relative 
to the video frame. Computer 38 may thus be operated in accordance with 
well known techniques to calculate successive .DELTA. Y values and to 
determine velocity variations from such values. 
ALTERNATE EMBODIMENTS 
It should be understood that the methodology underlining the embodiments 
described above could be utilized with substantial variations and for 
different purposes. This is so as the number of scans can be varied from a 
minimum of three scans to a maximum of four scans in a complete cycle of 
operation. 
Though the invention has been described with respect to specific preferred 
embodiments thereof, many variations and modifications will immediately 
become apparent to those skilled in the art. It is therefore the intention 
that the appended claims be interpreted as broadly as possible in view of 
the prior art to include all such variations and modifications.