DE1209759B - Method and device for searching for homologous points in stereo images - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

tnt. CL:

GOIc

German class: 42 c -10/02

Number: 1 209 759

File number: P 23359 IX b / 42 c

Filing date: August 12, 1959

Opening day: January 27, 1966

The invention relates to a method and a device for searching for homologous points in Stereo images, especially for photogrammetric purposes

It is known to match homologous points in stereo images by photoelectrically scanning Make the images and compare the scanning signals, taking the information simultaneously and obtained independently of each image using a moving scanning spot and a special scanning signal is generated for each desired coordinate direction and the scanning spot according to this signal is moved simultaneously on the two images about a scanning axis.

In this known method are used to determine the misregistration of the two Information obtained from images is mixed subtractively. However, it is not possible to use a direction-dependent Error signal for the purpose of adjusting the scanning axes to homologous points in the two To win pictures. Such an error signal can, however, then according to an earlier proposal derive when the information obtained from the two images are mixed multiplicatively. An error signal corresponding to the time difference between the two pieces of image information can then be generated, and from the comparison of this error signal with the scanning signals, control signals for control can be obtained of the scanning axes can be obtained on homologous points in the two images.

The time difference between the two pieces of image information required to generate the error signal can be found in can be generated in different ways. For example, circular scan paths become different Diameter is used, or the two images are in circles of equal size with constant temporal Difference sampled. The two scanning paths can also be run through synchronously, however In this case, the two pieces of image information are treated in such a way that they are a differential quotient first order differentiate according to time. After the multiplicative mix lets measure the time difference between the two signals.

To detect the homologous points, in all these cases the two scanning paths are initially selected to be so large that a correlation occurs over large areas. Then the scanning paths are gradually drawn together and the two scanning axes or the two images are controlled simultaneously in such a way that the time difference between the two pieces of image information always disappears. In this way, the method and device for searching
homologous points in stereo images

Applicant:

Hunting Survey Corporation Limited,

Toronto, Ontario (Canada)

Representative:

Dipl.-Ing. G. Weinhausen, patent attorney,

Munich 22, Widenmayerstr. 46

Named as inventor:
Gilbert Louis Hobrought,
Oshawa, Ontario (Canada)

finally find the point of the other image that is homologous to a certain point of one image. In this method with known scanning paths, however, certain disadvantages are inevitable. By a periodic trajectory can only scan a finite area at any point in one direction will. This can lead to insufficient or incorrect information if the Detail or its boundary line is perpendicular to the corresponding direction, as is often the case Case is. In addition, the entire area is covered evenly by the periodic scanning paths, see above that all parts of the picture are given the same meaning. In contrast, an increase in sensitivity would be desirable in the vicinity of the homologous points.

The invention has succeeded in avoiding these disadvantages. The inventive method of The type specified at the beginning is characterized by the combination of the following measures:

a) The deflection signals for the simultaneous movement of the scanning spots on the two images in the different coordinate directions are independent of one another, statistically around the scanning axis distributed signals.

b) An error signal corresponding to the time difference between the two pieces of image information is generated, and from the comparison of this error

509 780/99

signals with the scanning signals become control signals for controlling the scanning axes homologous points obtained in the two images.

Because of the statistical distribution according to the invention of the scanning paths around the scanning axis, the The greatest likelihood of capturing the surroundings of the points under consideration. On the other hand, however, any large deflections of the scanning spot also come with a correspondingly reduced amount Frequency so that the scan is not limited to a specific area. Be like that Apparent signal matches that are mismatched from the similar environment Points originate, after more or less a short time automatically recognized as accidental and corrected.

Thanks to the aperiodic statistical distribution of the scanning signals, any interaction with the Avoided image structure, which is the main source of error in image analysis with periodic scanning paths is eliminated.

To form a time difference between the two pieces of image information, one of the different The method mentioned at the outset is used. For example, the image information and the Sampling signals for obtaining the manipulated variables before the multiplicative mixing, depending on the Differentiated time.

A cathode ray tube is preferably used to carry out the method according to the invention provided, which generates the scanning spot for both images together. Form two optical systems the scanning spot on the two images. With the cathode ray tube baffles are two independent noise generators connected to the sampling in the two to each other cause perpendicular coordinate directions. As a noise generator, for example, the known Noise diodes are used.

An embodiment of the invention is described below with reference to the drawings. In here is

1 shows a schematic diagram of a device which is used for scanning two Stereo images are suitable according to the method according to the invention,

F i g. 2 is a block diagram of an inventive Circuit for generating a statistically distributed scanning pattern for the cathode ray tube of

F i g. 3 is a circuit diagram of a noise generator which is used for the circuit according to FIG. 2 can be used,

F i g. 4 shows a block diagram of a device for processing the information signals resulting from the two simultaneously scanned images are obtained,

Fig. 5 shows a representation of the ideal shape of the signals that occur when the light spot passes over Detail boundaries occur, the pulse height being a measure of the difference in intensity at the boundaries is,'

F i g. 6 shows the time relationship between the information signals obtained from the two stereo images, when the scanning spot is as shown in FIG. 5 exceeds a limit, the scanning axis being more corresponding Points in the two images is precisely aligned,

F i g. 7 shows an illustration of the information signals of the two stereo images when the scanning axes in FIG Scanning direction are shifted against each other,

F i g. 8 shows an illustration of an original information signal and its first derivative,

F i g. FIG. 9 is an illustration of the waveforms used in the circuit of FIG. 4 occur, and

10 shows an overall circuit diagram of the device according to the invention.

In the preferred embodiment of the invention according to FIG. 1 is on two parallel Rails 10 and 11 a displaceable carriage 12, the direction of displacement z. B. the X direction represents. A second slide 13 is displaceable in the ^ direction on guides 14 and 15 of the slide 12 stored. On this two frames 16 and 17 are attached to the recording of stereo images 18 and 19 or the like, which are to be compared according to the invention. The frame 16 is

ao attached to the carriage 13, while the frame 17 is displaceable in the X and Y directions, either by hand or preferably automatically by two motors 20 and 21 attached to it, which by friction wheels 22 and 23 a displacement along the top 24 of the carriage 13 in the X or F direction. The carriages 12 and 13 and the frames 16 and 17 have large openings below the pictures 18 and 19 in order to let the light through.

A single cathode ray tube or other light spot generator (25) is used to generate a scanning spot 26 on the screen 27, which is imaged with lenses 28 and 29 along scanning axes 30 and 31 at 26 a and 26 b on the image planes 18 and 19 . The respective blackening found by the scanning spot in each image determines the brightness or density of the spot images 26 a and 26 b, which are imaged by lenses 32 and 33 on photocells 34 and 35, which are located in the optical axis of the two scanning spots.

If the light spot generator 25 in the manner shown as a cathode ray tube 36 with deflection plates is formed, the baffles 37 and 38 can be used for scanning in the F-direction and the baffles 39 and 40 are used for scanning in the Z direction by they influence a beam of electrons which emanates from the cathode 41 and on the screen 27 a

This is how Leuchtfleck 26 designs. The voltage supply of the cathode ray tube 36 offers no special features, apart from the supply of the deflection plates. In the ideal case, the scanning is carried out in a purely statistical manner around the scanning axis, so that the greatest probability of information in the scanning axis and lower probabilities occur at radial distances from it, corresponding to the known probability distribution on a bell curve. This can be achieved by means of a deflection circuit according to FIG. For the Z-direction and the Y-direction a noise generator 42 and 43 are provided, of which the generated noise signal is passed through filters 43 α and 44 in order to cut the noise spectrum within suitable limits, which result from the frequency limits of the subsequent switching elements result. Amplifiers 45 and 46 are used to generate deflection signals at deflection plates 39 and 40 and 37 and 38 in FIG

5 6

X and F directions for the cathode ray tube 36 of the mean image density are less influential

in Fig. 1. to make while at the same time small blackening

A noise generator 42 or 43 can be better resolved according to differences from point to point

Fig. 3 be constructed. Be a noise diode 47 with.

Directly heated cathode consisting of a pentode in 5 The filters 59 and 60 are band filters that are used for

Diode circuit can produce a sta- attenuation of the noise, which result from the

tistically distributed shot emission from the cathode 48, corpuscular nature of the light with low

which is amplified by a triode 49, the grid gives sities. These filters also differentiate that

51 information signal coupled directly to the diode anode 50, so that it is inside of boundary lines. As a result, the current flow through the triode io half of the stereo images originating signals modulated according to the noise signal. The anode will be lifted. As a result of these filters and the

52 of the triode 49 is provided with a positive voltage flow of the size of the scanning spot, which is used here as a con source 53 connected, to which the anode 50 of the stant is also assumed, results in the shape of the Diode 47 through a high resistance 54 electrical signal that is connected at the transition of the light is so that the diode 47 with high 15 spots over sharp boundary lines from a dark one Noise power works. The amplified signal from to a bright spot and back to a bright one of triode 49 is created at the cathode via a point from curve 64 in FIG. 5 where the Coupling capacitor 54 removed and the boundary lines 65 and 66 between the dark and Terminals 55 and 56 are supplied, where a light area is drawn.

low impedance occurs. 20 An information signal of the general type shown in FIG. 5

As can be seen, the filament 48 of the diode 47 shown always occurs when a light spot

in series with the triode 49 to the voltage source, a detail boundary line of the image crosses. Each

d. H. between the positive pole 53 and the earth image consists of small areas of different

57 connected. The flow of current is determined by the blackening that is separated by such boundary lines

variable series resistance 58 is determined, which are 25. These boundary lines contain the actual in-

in the present example in the order of magnitude of formation necessary for alignment, arrangement

4000 ohms. The in and / or correlation has been found to be useful. The amount of the

Fig. 3 shown noise generator self-regulating at the transition of the resulting pulse is a measure

and a satisfactory noise signal for the

written arrangement supplies. By applying 30 line.

two independent noise generators of this type. If now in the arrangement according to FIG. 1 equal

for deflection in the X and Y directions, there are similar images that are oriented towards one another and which

so a completely randomly running scanning scanning axes hit identical points of the images, so

The path of the electron beam in the cathode can be the relative time sequence of the information signals

ray tube on the screen of the same generated 35 ^{in the} two channels when the light spot border

Luminous spot. A statistical trajectory is drawn as shown in FIG. 5 exceeds, according to FIG. 6th

produced by that the light spot are represented in each time. Here is the state of full

point in any direction with any speed alignment of the optical axes

running. The probability that the sample-corresponding pixels will be shown. With D and H are

spot the center point of the screen surface of the cathode 40 in FIG. 6 and subsequent figures those

the tube goes through is higher than designated for any parts of the signals, the dark and light, respectively

other point of the screen. The probability places correspond. The letter E indicates that

becomes smaller, the further a point is from the center - the waveforms shown are

point away. The sampling density has its own voltages.

Maximum at the midpoint, and its value falls according to 45 If the images at a given point in time

the probability function decreases radially outwards. a slight shift in the direction of the scanning

The further processing of the spots from the photocells have so that the scanning spot in one

34 and 35 supplied signals is shown in FIG. Fig. 4 shows each boundary line in front of the scanning spot in the second

represents. The signal from each photocell is reached in filters image, so the information differs

59 and 60 sifted to include DC components and 50 signals in time and the signal of the second sample

to separate high-frequency noise components. is compared to that of the first scan

One of the scanning signals, which is shown below as information, as shown in FIG. 7. The tension

mationssignal is designated, a differential curve of the F i g. 6 to 9 are each shared with

First order decoration drawn by an electronic samer time base to allow comparison of the

Differentiation circuit 61 subject to the known 55 delay properties of the information signals

Way is constructed. To enable the differentiated signal from due to lack of alignment,

the first sample is then screened with the. The waveforms discussed so far occur in the

Information signal from the second sample ideal case after the filters 59 and 60 of FIG. 4th

multiplied in a multiplication circuit 62. The rest of the circuit is used to

and results in a signal which, for the purpose of smoothing the difference between the individual transitions, is an alignment

can be screened in a filter 63, whereupon an error signal is generated at the output terminal 67,

it has an amplitude and a sign which, for this purpose, the differentiating circuit 61 forms the first

are proportional to the time difference between the derivative of the first sample with respect to time,

the information obtained from the two scans. 8 shows the effect of the differentiating circuit

mation signals exists. 65 to boundary line pulses according to FIG. 5. How

Preferably the photocells are chosen so that one sees the derived signal 68 at each

their sensitivity curve logarithmically with the point proportional to the slope of the original

Light intensity passes to larger changes in information signal 69. The multiplication circuit

I 209

62 combines the filtered signal from channel 2 with the differentiated signal from channel 1 and delivers at its output a waveform whose amplitude is the product of the instantaneous values of these two Represents signals.

In Fig. 9 are the waveforms of the signals of the circuit of FIG. 4 at the points L, M, N, O and P for three different states, namely for complete coincidence of two corresponding points, for a state in which the first scan precedes the second, and finally for a state where the second scan the first precedes. As can be seen, the output voltage of the multiplier 62 at point O is predominantly positive or negative, depending on the direction of the misalignment of the two optical axes with respect to the current scanning direction. The filter 63 serves to smooth the product voltages and to generate an error signal P which corresponds in amplitude and sign to the size and direction of the misregistration. The circuit according to Fig. 4 thus has the following properties:

a) With perfect alignment, ie the optical axes of the two scans coincide with respect to corresponding points in the two stereo images 18 and 19 of FIG. 1 is the error signal, ie the sieved product at P zero.

b) If there is insufficient coverage, a positive or negative error signal results depending on the Direction of misregistration with respect to the scanning direction of the light spot.

c) A misregistration perpendicular to the current scanning direction supplies an instantaneous value of the error signal with the value zero.

Assuming a purely statistically distributed scanning process, an error signal is generated in the ideal case generated, which is also distributed purely statistically. In this case, the error signal disappears as often as the Scanning direction is perpendicular to the direction of misalignment. It also turns changes the sign of the error signal when the scanning direction changes. Accordingly, it must be used for manufacture a continuous manipulated variable that can be used to produce the coverage, the error signal in two mutually perpendicular components, e.g. B. in the direction of the X and F axes, and the The dependence of the sign of the error signal on the scanning direction must be suppressed. One A circuit for solving this problem is shown in FIG. 10 shown. Here is an error signal according to the Invention used to excite adjusting motors for the X and Y coordinates, so that a Picture frame 17 according to FIG. 1 can be moved automatically in such a way that identical image locations which are intersected by the scanning axes, come to cover.

In Fig. 10, the required reference signals in the X and Y directions are obtained by differentiating noise signals from the sampling circuits. The noise signal for the X direction is differentiated in the differentiating circuit 70 and results in a reference signal R _x for the X direction. The noise signal for the Γ coordinate is also differentiated in the differentiating device 71 and results

a reference signal R _y for the Γ direction. The sign and amplitude of these reference signals are a function of the direction and speed of the scanning spot. The reference signal R _x is multiplied by the error signal μ occurring at G in the multiplier 72. Likewise, the reference signal R _{y is} multiplied by the error signal μ in the multiplication circuit 73. The output signals μ _χ and μ _{ν of} the multiplication circuits 72 and 73 are shown in FIG

ίο low-pass filters 74 and 75 sieved and result on Output at 76 and 77 are the manipulated variables for the X-direction and the F-direction.

The circuit shown in the right part of FIG. 10 operates as follows: It is assumed that that there is a misregistration in the X-direction. Then the following cases have to be distinguished:

Case 1:

SO scanning spot moves in Γ direction; Error signal μ = 0.

Thus μ _χ and μ _{ν are} both zero, since one of the factors of the product vanishes in each case.

Case 2:

The scanning spot moves in the X direction in such a way that μ and R _{x are} positive.

a) Since the scanning spot speed in the Y direction is equal to zero, this results

and thus

35 Ry = O

, Wy = O.

b) μ _χ is positive because both factors R _x and μ are positive.

Case 3:

The scanning spot moves in the X direction in the reverse direction as before, ie μ negative and R _x negative. Thus μ _{χ is} positive because both factors are negative.

It follows that the signal μ _χ does not depend on the scanning direction and that a misregistration in the X direction generates a manipulated variable μ _ν = 0.

It can also be shown that in the event of a misregistration, a continuous signal μ $ is generated only in the Y direction, while the manipulated variable μ _χ = 0.

In the case of random scanning and the presence of a misregistration in the X direction, the manipulated variable μ _χ disappears every time the scanning spot stops or moves purely in the Y direction. The manipulated variable receives its maximum value when the scanning spot moves in the X direction. The task of the filters 74 and 75 is to smooth these fluctuations and to generate constant manipulated variables in the X and Γ directions, which are suitable for feeding servo amplifiers, which can be used to compensate for the misregistration.

If, instead of a noise diode, another noise generator is used, it must be ensured that that the noise spectrum does not become too narrow. So in the example of the invention is the bandwidth of the used noise signal of the order of 2000 Hz, with the lower frequency limit at around

200 Hz. The lower frequency limit determines the resolution of the device and thus the sensitivity for fine image details. If the lower frequency limit is set too low, e.g. B. at about K) Hz, then the whole scan pattern may show a tendency to wander.

The influence of the light on the photocell or the like results in a noise generated by the light continuous spectrum superimposed on the desired information signal according to the invention is. This disruption of the operation of the arrangement can largely, if not entirely, thereby be eliminated that the upper frequency limit of the noise signal in the coordinate direction accordingly is restricted. The upper frequency limit can be set by the switching elements behind the Photo cells be determined, whereby a band filtering occurs by itself and only the desired information is let through.

Instead of a natural noise generator, an artificial noise generator can also be used become, the z. B. consists of an endless magnetic tape on which a uniform noise of the desired bandwidth is recorded with the ideal spectrum.

Claims (3)

Patent claims: 1. Method of finding homologous points in stereo images by photoelectric scanning corresponding positions of the images and comparing the scanning signals in which the information can be obtained simultaneously and independently of each image by using a moving scanning spot and for each desired Coordinate direction generates a special scanning signal and the scanning spot accordingly this signal is moved around a scanning axis on both images at the same time, while the information obtained from the two images is mixed multiplicatively to determine the misregistration, characterized by the combination of the following Measures: a) The deflection signals for the simultaneous movement of the scanning spots on the two images in the different coordinate directions are independent of one another and are statistically distributed around the scanning axis Signals. b) There is an error signal corresponding to the time difference between the two pieces of image information generated, and from the comparison of this error signal with the sampling signals Control signals for adjusting the scanning axes to homologous points in the two Images won. 2. The method according to claim 1, characterized in that the image information and the scanning signals for obtaining the manipulated variables before the multiplicative mixing depending on differentiated over time. 3. Device for performing the method according to claim 1 or 2, characterized through a cathode ray tube (36) to generate the scanning spot for both images two optical systems (28, 29) for imaging the scanning spot on the two images and through two independent of each other connected to the baffles of the cathode ray tube Noise generators. Considered publications:
U.S. Patent Nos. 2,679,636, 2,896,501;
Belgian patent specification No. 546 732. For this purpose 2 sheets of drawings 509 780/99 1.66 © Bundesdruckerei Berlin