Television image positioning and combining system

• US 4,393,394 A
• Filed: 08/17/1981
• Issued: 07/12/1983
• Est. Priority Date: 08/17/1981
• Status: Expired due to Fees

• Current Assignee: Reginald F.H. Mccoy
• Original Assignee: Reginald F.H. Mccoy
• Inventors: McCoy, Reginald F.H.
• Primary Examiner(s): Masinick, Michael A.
• Application Number:
  US06/293,525
• Time in Patent Office: 694 Days
• Field of Search: 358/22, 358/183
• US Class Current: 348/587
• CPC Class Codes: H04N 9/75 Chroma key

Abstract

Method for producing a background television image which moves corresponding to motion of a camera viewing a foreground scene, the image of which is to be combined with the background image by chroma-key, thus creating the appearance that both background and foreground are viewed by the same camera, although the background actually originates from separate cameras or recordings. Employs multiple cameras, or a single anamorphic camera with subsequent electronic horizontal expansion of the image, or recordings therefrom, to form the background image which can then be displaced in position, by variation of synchronizing pulse timings, while continuing to fill the full screen area. Also employs a backing for the foreground scene including a distinctive marker, the position of which in the foreground image is detected and used to control the position of the background image.

Claims

1. Apparatus for use with equipment producing a first television image, originating from a first television camera capable of being pointed in a variable direction so as to view differing parts of a foreground scene, said apparatus having the capability of producing a second television image formed by combination of parts of a pair of further images originating from a pair of further television cameras pointing in fixed directions so as to view different parts of a background scene, with horizontally displaced overlapping fields of view, said second television image moving coincident with, and corresponding to, horizontal motion of said first television image arising from change in the direction of viewing of said first television camera, in such manner that said first television image and said second television image may subsequently be combined, by the method of chroma-key, being known art, to form a combined image, said combined image then having the appearance of having been viewed by said first television camera, the position of objects portrayed in said combined image undergoing displacement in accordance with the horizontal motions of said first television camera, said displacement applying equally to that part of said combined image deriving from said first television camera capable of being pointed in a variable direction, and to that part of said combined image deriving from said second television image itself being derived from said further television cameras pointing in fixed directions, comprising:

a. means for sensing the direction of viewing of said first television camera, comprising a backing surface placed behind those parts of said foreground scene viewed by said first television camera, said backing surface having areas of a first color and an area of a second color different from said first color such as to cause said first television camera to generate two distinct and different values of its electrical output, the boundaries between said areas of said first color and said area of said second color being vertical lines, said boundaries performing the function of markers, the positions of said markers in the image formed by said first television camera being dependent on the direction of viewing of said first television camera,

b. marker detector means for detecting transitions between said distinct and different values of said electrical output generated by said first television camera when viewing said first color and said second color, thereby detecting said markers,

c. means for determining the positions within the image originating from said first television camera at which said transitions corresponding to said markers occur, and thereby producing indication of the direction of viewing of said first television camera,

d. displacement generator means for generating displacements of the positions of said pair of further images originating from said pair of further television cameras, consisting of means for accepting a first reference signal having synchronizing pulses in accordance with standard television practice;

means for generating a second reference signal likewise having synchronizing pulses in accordance with standard television practice; and

means for effecting a controllable variable time delay between the synchronizing pulses of said second reference signal and the synchronizing pulses of said first reference signal,

e. means for generating a pair of further reference signals also having synchronizing pulses in accordance with standard television practice,

f. means for effecting individually changeable time delays between the synchronizing pulses of said pair of further reference signals and the synchronizing pulses of said second reference signal,

g. means for supplying to each camera of said pair of further television cameras a timing signal, being a distinct one of said pair of further reference signals, in such manner that the timing of the synchronizing pulses of said timing signal controls the time at which said camera generates the electrical output signals corresponding to specific points in the scene viewed by said camera,

h. means for controlling said controllable variable time delay between the synchronizing pulses of said second reference signal and the synchronizing pulses of said first reference signal by an amount dependent on the direction of viewing of said first television camera derived from the detection of the positions of said markers in the output of said first television camera, said amount being such that the variation in said time delay so produced results in a variation in the timing of the video output signals derived from said pair of further television cameras equal to the variation in the timing of the occurrence of said markers in the video output signal of said first television camera;

whereby a displacement in the timing of said markers resulting from a motion of said first television camera will cause an equal displacement in the timing of the video output signals from said pair of further television cameras,

i. means for setting said individually changeable time delays between the synchronizing pulses of said pair of further reference signals and the synchronizing pulses of said second reference signal such that the timings of each distinct one of said pair of further reference signals supplied to each one of said pair of further television cameras are such that, there being a first object viewed by the first one of said pair of further television cameras, being that camera placed to the left of the second one of said pair of further television cameras, said pair of further television cameras having horizontally overlapping fields of view, said first object being so positioned as to produce a video signal output from said first one of said pair of further television cameras at a time corresponding to the time of scanning of a part of the field of view close to the right side of the limit of the field of view of said first one of said pair of further television cameras, said first object being viewed by said second one of said pair of further television cameras then producing a video signal output from said second one of said pair of further television cameras at a time coincident with the time of production of the corresponding video signal output due to said first object from the first one of said pair of further television cameras; and

conversely a second object being viewed close to the left limit of the field of view of said second one of said pair of further television cameras producing a video signal output coincident in time with the video signal output produced said second object when viewed by said first one of said pair of further television cameras;

whereby said pair of further television cameras may have overlapping fields of view and the timings of said timing signals controlling the scannings of each of said pair of further television cameras may be so set that objects simultaneously appearing in the fields of view of both of said pair of further television cameras will produce video signal outputs coincident in time,

j. means for generating a switch control signal so timed as to occur during the time of overlap of the fields of view of said pair of further television cameras such that said switch control signal will occur during the simultaneous presence of the video output signals from said first and second objects, both being viewed by both of said pair of further television cameras, in the video outputs of both of said pair of further television cameras, the timing of said switch control signal being directly related to the timings of said pair of further reference signals, said timings being set by way of said means for setting said individually changeable time delays such as to produce time coincidence of the video output signals from said pair of further television cameras deriving from objects within the overlapping fields of view of said pair of further television cameras, such as said first object and said second object, said switch control signal therefore being derivable from said pair of further reference signals by detection of the time of overlapping of the images of said pair of further television cameras;

additionally means being provided to cause said switch control signal to be reset to its initial condition during the synchronizing pulses of said first reference signal;

whereby the output of said first one of said pair of further television cameras will be selected following said synchronizing pulses of said first reference signal, being coincident with the start of scanning of a standard television display device on which the output of the system may be viewed, and

k. means for switching between the video signal outputs of said pair of further television cameras controlled by said switch control signal such that only one of said video signal outputs is selected at any one time, the selection being performed at those times at which the video signal outputs from a single object appearing in the fields of view of both of said pair of further television cameras are coincident in time;

whereby a single continuous video output signal corresponding to a field of view part of which is derived from one, and the remainder from the other, of said pair of further television cameras, may be derived.

2. Apparatus as recited in claim 1 wherein said pair of further television cameras have vertically overlapping fields of view;

said boundaries between said areas having said first color and said second color being horizontal lines;

said first one of said pair of further television cameras being placed above said second one of said pair of further television cameras;

said first object producing a video signal output from said first one of said pair of further television cameras at a time corresponding to the time of scanning of a part of the field of view close to the bottom of the limit of the field of view of said first one of said pair of further television cameras, said first object being viewed by said second one of said pair of further television cameras then also producing a video signal output from said second one of said pair of further television cameras at a time coincident with the time of production of the corresponding video signal output due to said first object from the first one of said pair of further television cameras, and, conversely, said second object, being viewed close to the top limit of the field of view of said second one of said pair of further television cameras, producing a video signal output coincident in time with the video signal output produced by said second object when viewed by said first one of said pair of further television cameras;

the magnitude of said variable time delay between the synchronizing pulses of said second reference signal and the synchronizing pulses of said first reference signal being sufficiently great, and being a multiple of the period of a horizontal television line, such that a displacement of said markers from one television line to another resulting from a vertical motion of said first television camera will cause a displacement of timing of the video output from said second television camera by a time equal to the time occupied by the number of television lines by which said markers have been displaced;

whereby the apparatus will cause said second television image to move vertically coincident with and corresponding to vertical motions of said first television camera.

3. Apparatus as recited in claims 1 or 2 wherein the electrical signals generated by each of said pair of further television cameras are recorded and subsequently reproduced by a pair of reproducing means prior to being combined to form said second television image, and wherein means are provided for supplying to each of said pair of reproducing means a timing signal, being a distinct one of said pair of further reference signals in such manner that the timing of the synchronizing pulses of said timing signal controls the time at which said reproducing means reproduces the electrical signals corresponding to specific points in the scene viewed by that one of said pair of further television cameras the recorded electrical signals of which it is reproducing, and wherein said means for supplying a timing signal to each of said pair of reproducing means replaces said means for supplying a timing signal to each camera of said pair of further television cameras.

4. Apparatus as recited in claim 1 wherein said means for separately setting said individually changeable time delays between the synchronizing pulses of said pair of further reference signals includes distortion corrector means whereby said individually changeable time delays may be separately caused to change in opposing sense at a rate synchronous with the vertical synchronizing pulses of said first reference signal, whereby the relative horizontal displacement of the images originating from said pair of further television cameras may be caused to change during the vertical scanning period of said further television cameras, thus effecting correction for geometrical distortion of said images and providing time coincidence of said video signal outputs from said first and said second of said pair of further television cameras, deriving from said first object and said second object, both being viewed by both of said pair of further television cameras, independent of the vertical positions of said first object and said second object in the vertical fields of view of said pair of further television cameras.

9. Apparatus as recited in claims 1 or 5 wherein said means for controlling said controllable variable time delay comprises:

a. means for generating a sawtooth waveform synchronous with the horizontal synchronizing pulses of said first reference signal,

b. means for sampling the instantaneous value of the voltage of said sawtooth waveform with pulses coincident with transitions of one sense of said transitions between said distinct and different values of said electrical output generated by said first television camera when viewing said two different colors and retaining the voltage so sampled to form a control voltage,

c. means for comparing the instantaneous value of the voltage of said sawtooth waveform with said control voltage and for generation of a comparison signal indicative of the greater of said instantaneous value and said control voltage, whereby a change in said comparison signal occurs at the time of equality of said instantaneous value and said control voltage,

d. means for generating further synchronizing pulses in accordance with standard television practice,

e. means whereby said change in said comparison signal controls said means for generating further synchronizing pulses causing the horizontal component of said further sychronizing pulses to coincide with said change in said comparison signal, and

f. means for supplying said further synchronizing pulses to form the synchronizing pulses of said second reference signal, whereby the time delay of said second reference signal will be caused to vary by an amount corresponding to the variation in timing of said transitions of one sense.

10. Method and apparatus as recited in claim 9 wherein said sawtooth waveform is synchronous with the vertical synchronizing pulses of said first reference signal, and said change in said comparison signal controls said means for generating further synchronizing pulses causing the vertical component of said synchronizing pulses to coincide with said change in said comparison signal.

5. Apparatus for use with equipment producing a first television image, originating from a first television camera capable of being pointed in a variable direction so as to view differing parts of a foreground scene, said apparatus having the capability of producing a second television image originating from a single second television camera pointing in a fixed direction so as to view a background scene, said second television image moving coincident with, and corresponding to, horizontal motion of said first television image arising from change in the direction of viewing of said first television camera, in such manner that said first television image and said second television image may subsequently be combined, by the method of chroma-key, being known art, to form a combined image, said combined image than having the appearance of having been viewed by said first television camera, the positions of objects portrayed in said combined image undergoing displacement in accordance with the horizontal motions of said first television camera, said displacement applying equally to that part of said combined image deriving from said first television camera capable of being pointed a variable direction, and to that part of said combined image deriving from said second television image itself originating from said second television camera pointing in a fixed direction, comprising:

a. means for sensing the direction of viewing of said first television camera, comprising a backing surface placed behind those parts of said foreground scene viewed by said first television camera, said backing surface having areas of a first color and an area of a second color different from said first color such as to cause said first television camera to generate two distinct and different values of its electrical output, the boundaries between said areas of said first color and said area of said second color being vertical lines, said boundaries performing the function of markers, the positions of said markers in the image formed by said first television camera being dependent on the direction of viewing of said first television camera,

b. marker detector means for detecting transitions between said distinct and different values of said electrical output generated by said first television camera when viewing said first color and said second color, thereby detecting said markers,

c. means for determining the positions within the image originating from said first television camera at which said transitions corresponding to said markers occur, and thereby producing indication of the direction of viewing of said first television camera,

d. displacement generator means for generating displacement of the position of said second television image originating from said second television camera, consisting of means for accepting a first reference signal having synchronizing pulses in accordance with standard television practice;

means for generating a second reference signal likewise having synchronizing pulses in accordance with standard television practice; and

means for effecting a controllable variable time delay between the synchronizing pulses of said second reference signal and the synchronizing pulses of said first reference signal,

e. means for supplying said second reference signal to said second television camera in such manner that the timing of the synchronizing pulses of said second reference signal controls the time at which said camera generates the electrical output signals corresponding to specific points in the scene viewed by said camera, and

f. means for controlling said controllable variable time delay between the synchronizing pulses of said second reference signal and the synchronizing pulses of said first reference signal by an amount dependent on the direction of viewing of said first television camera derived from the detection of the positions of said markers in the output of said first television camera, said amount being such that the variation in said time delay so produced results in a variation in the timing of the video output signal derived from said second television camera equal to the variation in the timing of the occurrence of said markers in the video output signal of said first television camera;

whereby a displacement in the timing of said markers resulting from a motion of said first television camera will cause an equal displacement in the timing of the video output signal from said second television camera, thus causing said output of said second television camera to follow in time, and thus in position when displayed on a television screen, any displacement of said markers resulting from motion of said first television camera.

7. Apparatus as recited in claim 5 wherein said second television image moves coincident with and corresponding to vertical motion of said first television image arising from change in the direction of viewing of said first television camera;

said boundaries between said areas of said first color and said second color being horizontal lines;

the magnitude of said variable time delay between the synchronizing pulses of said second reference signal and the synchronizing pulses of said first reference signal being sufficiently great, and being a multiple of the period of a horizontal television line, such that a displacement of said markers from one television line to another resulting from a vertical motion of said first television camera will cause a displacement of timing of the video output from said second television camera by a time equal to the time occupied by the number of television lines by which said markers have been displaced;

whereby the apparatus will cause the positions of objects portrayed in said combined image to undergo displacement in accordance with the vertical motions of said first television camera, said displacement applying equally to that part of said combined image derived from said first television camera and to that part of said combined image derived from said second television camera.

8. Apparatus as recited in claims 5 or 7 wherein the electrical signal generated by said second television camera is recorded and subsequently reproduced by a reproducing means prior to being utilized to form said second television image and wherein means are provided for supplying said second reference signal to said reproducing means, in place of to said second television camera, in such manner that the timing of the synchronizing pulses of said second reference signal controls the time at which said reproducing means reproduces the electrical signals corresponding to specific points in the scene viewed by said second television camera.

6. Apparatus as recited in claim 22 wherein the image originating from said second television camera is compressed in the horizontal direction and wherein means are provided for effecting expansion in the horizontal direction of a selected part of said image, selection of said selected part being determined by said controllable variable time delay between said synchronizing pulses of said second reference signal and said synchronizing pulses of said first reference signal, whereby horizontal displacement of the content of said selected part of said image may be effected, said means for effecting expansion in the horizontal direction of a selected part of said image comprising:

a. a source of first clock pulses,

b. a source of second clock pulses having a lower frequency than said first clock pulses,

c. first and second storage means each capable of storing a plurality of samples of a television signal supplied to its input and subsequently providing said samples at its output in the sequence of supplying to said input, the temporal separation between said samples supplied to said input being determined by said first clock pulses and the temporal separation between said samples provided at said output being determined by said second clock pulses,

d. means for producing a control voltage alternating between a first value maintained for a time equal to the time of scanning of one horizontal television line and a second value maintained for a like time,

e. means for selecting between said output of said first storage means and said output of said second storage means to form a selected output, and

f. means for supplying samples of a television signal being that signal originating from said second television camera and said first clock pulses to said first storage means and supplying said second clock pulses to said second storage means and selecting said output of said second storage means to form said selected output when said control voltage has said first value; and

for supplying said samples of said television signal originating from said second television camera and said first clock pulses to said second storage means and supplying said second clock pulses to said first storage means and selecting said output of said first storage means to form said selected output when said control voltage has said second value;

whereby said samples will alternately be stored in, and retrieved from, each of said first and second storage means, and whereby, consequent upon said second clock pulses having a lower frequency than said first clock pulses, the temporal separation of said samples provided at said outputs of said first and second storage means, and consequently at said selected output, will be greater than the temporal separation of said samples of said signal originating from said second television camera supplied to said first storage means and to said second storage means, resulting in said selected output being expanded in time by comparison with said signal originating from said second television camera, such temporal expansion then resulting in a horizontal expansion of the image when subsequently displayed on standard television display equipment.

11. Apparatus for use with equipment producing a first television image, originating from a first television camera capable of being pointed in a variable direction so as to view differing parts of a foreground scene, said apparatus having the capability of producing a second television image originating from a single further television camera pointing in a fixed direction so as to view a background scene, the image originating from said further television camera being compressed in the horizontal direction and wherein means are provided for effecting expansion in the horizontal direction of a selected part of said image from said further television camera, said selected part of said image, having been expanded in the horizontal direction, forming said second television image, said second television image moving coincident with, and corresponding to, horizontal motion of said first television image arising from change in the direction of viewing of said first television camera, in such manner that said first television image and said second television image may subsequently by combined, by the method of chroma-key, being known art, to form a combined image, said combined image then having the appearance of having been viewed by said first television camera, the positions of objects portrayed in said combined image undergoing displacement in accordance with the horizontal motions of said first television camera, said displacement applying equally to that part of said combined image deriving from said first television camera capable of being pointed in a variable direction, and to that part of said combined image deriving from said second television image itself originating from said further television camera pointing in a fixed direction comprising:

a. a backing surface placed behind those parts of said foreground scene viewed by said first television camera, said backing surface having areas of a first color and an area of a second color different from said first color such as to cause said first television camera to generate two distinct and different values of its electrical output, the boundaries between said areas of said first color and said area of said second color being vertical lines, said boundaries performing the function of markers the positions of said markers in the image formed by said first television camera being dependent on the direction of viewing of said first television camera,

b. marker detector means for detecting transitions between said distinct and different values of said electrical output generated by said first television camera when viewing said first color and said second color thereby detecting said markers,

c. means for determining the positions within the image originating from said first television camera at which said transitions corresponding to said markers occur, and thereby producing indication of the direction of viewing of said first television camera,

d. displacement generator means for generating displacement of the position of said second television image originating from said further television camera, consisting of means for accepting a first reference signal having synchronizing pulses in accordance with standard television practice;

means for generating a second reference signal likewise having synchronizing pulses in accordance with standard television practice; and

means for effecting a controllable variable time delay between the synchronizing pulses of said second reference signal and said synchronizing pulses of said first reference signal,

e. means for controlling said controllable variable time delay between the synchronizing pulses of said second reference signal and the synchronizing pulses of said first reference signal by an amount dependent on the direction of viewing of said first television camera derived from the detection of the positions of said markers in the output of said first television camera, and of such amplitude as to produce a variation in said time delay of magnitude proportional to any change in the times of occurrence of the signals produced by said markers in the output of said first television camera relative to previously obtaining times of occurrence of said signals produced by said markers, but having the opposite sense, a reduction in the amount of said time delay resulting from increase in the delay between the times of occurrence of said signals produced by said markers by comparison with previously obtaining times of occurrence of said signals produced by said markers,

f. means for effecting expansion in the horizontal direction of a selected part of said image originating from said further television camera, including;

a source of first clock pulses;

a source of second clock pulses having a lower frequency than said first clock pulses;

first and second storage means each capable of storing a plurality of samples of a television signal supplied to its input and subsequently providing said samples at its output in the sequence of supplying to said input, the temporal separation between said samples supplied to said input being determined by said first clock pulses and the temporal separation between said samples provided at said output being determined by said second clock pulses;

means for selecting between said output of said first storage means and said output of said second storage means to form a selected output,

g. means for producing a storage input control signal, being a pulse having a low value and a high value, the transition from said low value to said high value occurring during the time of said horizontal synchronizing pulses contained in said second reference signal, and the duration of said pulse being such as to permit a sufficient number of said first clock pulses to occur as to cause each of said first and second storage means, said first clock pulses being supplied thereto, to be filled to its storage capacity with said plurality of samples of a television signal supplied to its input,

h. means for producing a storage output control signal alternating between a first value maintained for a time equal to the time between successive horizontal synchronizing pulses contained in said first reference signal, and a second value maintained for a like time, the transitions between said first value and said second value occurring during the time of said horizontal synchronizing pulses contained in said first reference signal, and

i. means for supplying samples of a television signal being that signal originating from said further television camera and said first clock pulses to said first storage means when said storage input control signal has said high value and said storage output control signal has said first value and supplying said second clock pulses to said second storage means and selecting said output of said second storage means to form said selected output also when said storage output control signal has said first value; and

for supplying said samples of said television signal originating from said further television camera and said first clock pulses to said second storage means when said storage input control signal has said high value and said storage output control signal has said second value and supplying said second clock pulses to said first storage means and selecting said output of said first storage means to form said selected output also when said storage output control signal has said second value;

whereby said samples will alternately be stored in, and retrieved from, each of said first and second storage means, the times of commencement of storage being determined by the times of transition of said storage input control signal from said low value to said high value, said selected output forming the video signal capable of producing said second television image and whereby, consequent upon said second clock pulses having a lower frequency than said first clock pulses, the temporal separation of said samples provided at said outputs of said first and second storage means, and consequently at said selected output, will be greater than the temporal separation of said samples of said signal originating from said further television camera supplied to said first storage means and to said second storage means, resulting in said selected output being expanded in time by comparison with said signal originating from said further television camera, such temporal expansion then resulting in a horizontal expansion of the image when subsequently displayed on standard television display equipment, such that said second television image will have standard aspect ratio, the horizontal compression of the image originating from said further television camera being canceled by said horizontal expansion and whereby, consequent upon the timings of the transitions from said low value to said high value of said storage input control signal being dependent on the times of occurrence of said markers in the output of said first television camera, but in reversed sense, a retardation in the time of occurrence of said markers consequent upon a motion of said first television camera to the left will cause said storage input control signal to change state earlier thus commencing storage of the signal from said further television camera at an earlier time corresponding to the scanning of a part of the image of the background scene displaced to the left of that previously obtaining;

thus a motion to the left of said first television camera will cause selection of a portion of said background scene to the left of that previously selected, and conversely motion to the right of said first television camera will cause selection of a portion of said background scene to the right of that previously selected, thus said second television image, being derived from the selected portion of the output of said further television camera, will move coincident with, and corresponding to, the motions of said first television image arising from motion of said first television camera.

12. Apparatus as recited in claim 11 wherein the electrical signal generated by said further television camera is recorded and subsequently reproduced by a reproducing means the output of said reproducing means being supplied to said means for supplying samples of a television signal to said first and second storage means in place of said signal originating from said further television camera.

13. Apparatus as recited in claim 11 wherein said means for controlling said controllable variable time delay comprises:

a. means for generating a sawtooth waveform synchronous with the horizontal synchronizing pulses of said first reference signal said sawtooth waveform including both negative and positive voltage parts and passing through zero voltage at a time occurring between said horizontal synchronizing pulses,

b. means for sampling the instantaneous value of the voltage of said sawtooth waveform with sampling pulses coincident with transitions of one sense of said transitions between said distinct and different values of said electrical output generated by said further television camera when viewing said two different colors and retaining the voltage so sampled to form a control voltage,

c. means for inverting the polarity of, and means for adjusting the amplitude of, said control voltage to form an inverted control voltage,

d. means for comparing the instantaneous value of the voltage of said sawtooth waveform with said inverted control voltage and for generation of a comparison signal indicative of the greater of said instantaneous value and said inverted control voltage, whereby a change in said comparison signal occurs at the time of equality of said instantaneous value and said inverted control voltage, and whereby, in consequence of said means for inverting the polarity of said control voltage, a retardation of said sampling pulses will cause an advance in the time of said change in said comparison signal, and conversely an advance of said sampling pulses will cause a retardation in said time of said change in said comparison signal, the amount of alteration in said time of said change in said comparison signal being dependent on the adjustment of said means for adjusting the amplitude of said control voltage;

coincidence of said sampling pulses with the time of said zero voltage of said sawtooth waveform resulting in coincidence of said change in said comparison signal with said sampling pulses,

e. means for generating further synchronizing pulses in accordance with standard television practice,

f. means whereby said change in said comparison signal controls said means for generating further synchronizing pulses causing the horizontal component of said further synchronizing pulses to coincide with said change in said comparison signal, and

g. means for supplying said further synchronizing pulses to form the synchronizing pulses of said second reference signal, whereby the time of said transition from said low value to said high value of said storage input control signal becomes controlled by said time of said change in said comparison signal.