DK167420B1 - COMFILTER FOR TREATMENT OF REMOTE SIGNALS AND PROCEDURE FOR CAMFILTRATION OF REMOTE SIGNALS - Google Patents

Description

DK 167420 B1

The invention relates to a comb filter according to the preamble of claim 1.

Periodic electrical signals may be advantageously processed by storing copies of the signal, which copies 5 are separated during the repetition period, and then combining the stored copies to increase the information content of the signal. television broadcasts of a known kind (and most video recording / playback systems) are arranged such that a large portion of the brightness (luminance) information contained in an image is represented by signal frequencies which are concentrated around whole multiples of the horizontal line scanning frequency. Color (chrominance) information is encoded or inserted into a portion of the luminance signal spectrum around frequencies that are midway between the multiples 15 of the line scanning frequency (i.e., at odd multiples of half of the line scanning frequency).

By appropriately combing the spectrum of the complete signal, chrominance and luminance information can be separated and retail information highlighted. Comb 20 arrays take advantage of the fact that the odd multiplas relationship between chrominance signal components and the half line scanning frequency causes chrominance signal components for corresponding image regions in successive lines to be 180 ° out of phase (so-called interleaved 25 frequency components). Luminance signal components for corresponding image areas in consecutive lines are substantially in phase (and constitute non-interleaved components).

In a comb filter system, one or more copies of the complete image representative signal are generated, which copies are delayed by at least one line scanning interval (a so-called 1 H delay). The signals from a line are added to signals from a preceding line causing the interleaved frequency components 35 (e.g., chrominance) to be canceled, whereas the non-interleaved frequency components (e.g., luminance) are amplified.

DK 167420 B1 2

Subtracting the signals for two consecutive lines (for example, inverting the signals for one line and then adding the two) cancels the non-interleaved frequency components, whereas the interleaved frequency components are amplified. Thus, the luminance and chrominance signals can be combed between each other and thus can be advantageously separated.

The above-mentioned combing process is possible due to the large line-to-line signal redundancy in a typical video-10 scene. If a stationary image is considered and in particular a particular pixel (pixel element) in this scene, this pixel will have a redundancy that is essentially 100% on a total image by total image basis. Thus, if the combing was performed on a total image for total image basis, the percentage of residual luminance signal in the combed chrominance signal would be significantly reduced compared with a line by line combed signal. Likewise, the percentage of residual chrominance signal in the combed luminance signal will be significantly reduced relative to a line by line combed signal.

In particular, e.g. vertical detail does not accompany the warped chrominance signal. The chrominance signal in an NTSC complete signal is synchronized in such a way that there is a phase jump of 180 * from total image to total image. Therefore, the luminance component can be separated from consecutive total images by linear addition to the complete signal, and the chrominance component can be separated from consecutive images by linear subtraction from the complete signal.

30 The response characteristic of a line-based comb filter has zeros or spikes at a distance corresponding to the line frequency (15,734 kHz in the NTSC system), while the total image for the filter image response characteristic has spikes at 30 Hz intervals. The smaller image comb filter 35's smaller distance between points or zeros gives rise to a more complete combing process in all spatial directions than line for the line comb filter.

In the overall picture for the whole picture combing process, as is known, for example, from GB-OS 1 402 609 or DE-OS 3 007 520, non-stationary objects give rise to 5 distortions in the rendered images. These distortions are a consequence of incomplete cancellation of the luminance and chrominance components in the combed chrominance signals and the combed luminance signals, respectively, and a consequence of an effective bandwidth reduction for the luminance signal. A visible movement occurs when differences in image content occur within a period of 1/30 second or less by object movement or panning.

The motion-induced distortions produced by the total-frame for the full-frame combing process are 15 two-dimensional and are entirely the result of scene movement from one frame to another. The distortions can be observed in both horizontal and vertical directions in the plane of the image and appear as double or ghost images in the rendered scenes. The double images are separated by a distance corresponding to the speed of movement and may be accompanied by incorrect color at the edges of the moving objects. To prevent such phenomena, DE-OS 3 007 520 proposes a line for line comb filtration.

Line by line cam filters produce one-dimensional distortions that result from the vertical structure of a scene, even when stationary. The distortions accompanying line by line combing process act as an effective reduction in the bandwidth of the signal representing the vertical scene structure, causing vertical transitions in the image to become blurred.

DE-OS 3 214 607 discloses how the output of a low pass filter 35 (which is influenced by the chrominance output of a line by line comb filter) is compiled with the luminance output of line by line comb filter for the purpose of recovering the vertical detail information which has been lost below line by line combat process- DK 167420 B1 4 sen. When using a total image for total image cam system, such a recovery is not required, since the vertical detail information is not lost when generating a total image for total image combed luminance signal.

Furthermore, the total image for total image combed chrominance signal cannot act as source for vertical detail information for recovery purposes since it does not contain vertical detail information.

It is the object of the invention to mitigate the unfortunate effects produced by image movements in a total image for total image core system.

The object is achieved with a comb filter of the type mentioned in the preamble of claim 1 and a method according to the characterizing part of claim 8.

A comb filter provided by the invention for processing television (TV) signals includes a delay means for delaying the TV signal by a frame period.

First means are provided for combining the TV signal with the delayed TV signal from the delay means 20 to produce the sum thereof corresponding to a first component of the TV signal. Another means is provided for combining the TV signal with the delayed TV signal from the delay means to produce the difference therebetween corresponding to another component of the TV signal. A linear phase low pass filter is provided, which low pass filter has an input terminal connected to the second combiner for receiving the second component of the TV signal. The low pass filter has an output terminal and generally rejects the frequency spectrum normally occupied by the other component of the TV 30 signal. A third means is provided which is connected to the first combining means and to the low-pass filter output terminal to combine the first component and the TV signal with the low-pass filtered signal, thereby correcting the first component 35 of the signal for errors therein due to motion from an image. to another.

In a particular embodiment of the invention, motion detection means are connected to the output terminal of the low-pass filter and, depending on the low-pass filtered signal, detects the occurrence of scene movement from a total image 5 to another. The motion detection means produces a control signal in response to such motion.

A fourth signal combiner is provided with a first input terminal which is connected to the second combiner to receive the second component of the TV-10 signal. The fourth signal combiner has a second input terminal and an output terminal. Switching means are connected to the motion detection means and selectively, depending on the control signal, leads the first component to the second input terminal of the fourth signal combining means 15 when scene motion is detected from one total image to another.

According to yet another feature of the invention, a linear phase bandpass filter is connected in series to the output terminal of the fourth signal combiner. The bandpass filter is designed to pass the chrominance signal frequency spectrum only. The invention will now be explained in more detail with reference to the drawing, in which: FIG. Fig. 1 is a block diagram of a total image for combining cam filters as known from DE-os 3,070,520 in connection with TV signal processing; 2a-2d show amplitude waveforms as a function of time, which waveforms are associated with the circuit of FIG. 1, while FIG. 2e shows a waveform resulting from a modification of the circuit of FIG. 1, 30 FIG. 3, which includes Figures 3a-3c, is a block diagram of a total image of the overall image comb filter according to the invention.

In FIG. 1, there is shown a total picture for a total cam comb filter of known kind. The comb filter will be described in connection with the separation of luminance and chrominance signals from a complete TV signal. However, the comb filter is not limited to this particular application. For example, the comb filter may be used to comb filter a luminance signal in order to insert a chrominance signal therein to form a complete video signal.

5 In FIG. 1, there is shown a storage means 10 capable of storing electrical signals in a total picture (for example, two sub-frames in an NTSC video format) in a video signal. The storage means 10 continuously inputs an input signal at an input terminal 11 and outputs this signal on an output terminal 14, which output signal is delayed by the duration of a total frame period. The means 10 may comprise a digital storage, for example a random access memory (RAM) with supporting electronics or an analog storage, for example a serial charge transfer device (CTD) such as a charge coupled charge coupled device (CCD) with the required support circuit. In terms of invention, it is irrelevant whether the means 10 is a digital or analog circuit, however it is assumed to be of a digital nature. The other 20 circuit means in connection therewith are therefore believed to be digital in order to avoid digital analog signal conversion between the circuitry single parts.

An input signal from terminal 11 and a delayed signal from terminal 14 are summed in the add circuit 12. 25 The phase luminance components which are in phase are added, whereas the chrominance components which are 180 ° out of phase are phase-phased and produce a substantially chrominance-free luminance signal Y 15. An input signal and a delayed signal are also applied to the subtraction circuit 13, in which the chrominance components of the two total images are summed constructively, whereas the luminance components cancel each other out and produce a substantially luminance-free chrominance signal on the connection 16 (at least when consecutive total image signals are same stationary scene).

35 In FIG. 2, the effects of motion on the aforementioned total image for total image combing process are illustrated graphically. FIG. 2a represents a portion of the complete signal applied to the terminal 11 at any time interval.

FIG. 2b, the complete video signal from the same scene represents exactly a total frame period later and in which there is some motion in the scene. In waveform 2a, it is assumed that the signal component between time points T1 and T3 represents an object with luminance and chrominance signal parameters L2 and C2, respectively. It is assumed that the object is located in an area of uniform scene content with 10 luminance and chrominance signal parameters Li and C1, respectively.

Between the total images, the object performs spatial motion causing the object's video signal representation to be time-shifted, ie. so that it is between the times T2 and T4 of FIG. 2b. Signal luminance 15 and chrominance component relative signal parameters L and C

remains the same between the waveforms of FIG. 2a and fig. 2b, although there is a time lag relative to the object represented by L2, C2. However, the chrominance component of the signal has a 180 ° phase relationship between the waveforms 2a and 2b (i.e., between the total images).

The sum and difference of the waveforms of FIG. 2a and fig. 2b is represented by the waveforms 2c and 2d, respectively.

It will be seen that for the time segments in which the absolute value of the chrominance vector component between the waveforms 25 of FIG. 2a and fig. 2b is the same, essentially the complete cancellation of the chrominance components due to the summation of the two waveforms (Fig. 2c). Also, where the amplitude of the luminance component of the signal is the same between the two waveforms (2a and 2b), complete cancellation of the luminance component as a result of a subtraction of the two waveforms (Fig. 2d) is also substantially eliminated. FIG. 2a, 2b, 2c and 2d are representative of the signals present at the terminals 11, 14, 15, 16 of the circuit of FIG. First

35 Over the period during which motion occurs between the total images, ie. between times Ti and T2 and 0 times T3 and T4, the different signals are summed differentially and incomplete cancellation of the undesirable component occurs.

Furthermore, movement distorts the desired signal.

5 The motion causes an averaging of the signal over the periods during which motion occurs. These averages are shown in FIG. 2c with the signal segments designated (L1 + L2) equal to (2L1 + 2L2) / 2. Usually, the signal from the two total images is weighted by a factor of 1/2 before combining. The amplitude of the combed signal will be half of the values shown and the signal during the period of motion will be (L1 + L2) / 2. The mean values (L1 + L2) of the luminance signal try to repeat signal transitions to produce a double or ghost image surrounding the moving object.

15 The averages (C1 + C2) of the warped chrominance signal during periods of motion from one total image to the next attempt to distort the color around the object in motion.

If a low pass filter is provided at connection 16 of FIG. 1, the cored chrominance signal of FIG. 2d. 2e. In FIG. 2e, the chro-minance signal spectrum has been removed and back is only the uncontaminated luminance component resulting from the movement from one total image to the next. If the signal of FIG. 2e is added to or subtracted from the signal of FIG. 2c, the edges of the luminance signal are reset to produce a luminance component equivalent to that which has not been combed. Addition of the signal of FIG. 2e will recover the luminance signal of FIG. 2c between the times T1 and T2 to the level 2L2 and decrease the luminance signal between the times T3 and T4 to the value 2L1 as indicated by the dashed lines.

The FIG. 3a is a total image for full image comb filter arranged in accordance with the principles of the present invention and capable of correcting distortions such as double images or smears as a result of movement between consecutive two number images. In FIG. 3 performs individual parts designated by the same reference numerals as the individual parts of FIG. 1, identical functions. At the terminals 15 and 16 of the circuit of FIG. 3a, chromed luminance and chrominance signals are thus produced which contain crosscomponent components as well as imperfectly combed signal components as a result of movement from one total image to the next.

The cored chrominance signal at connection 16 is applied to a linear phase low pass filter 27 to remove the 10 chrominance signal spectrum and output the unresolved low frequency luminance components. The low-pass filtered signal from filter 27 is added in the adder circuit 31 back to the cored luminance signal from terminal 15 to produce a corrected luminance signal Y at connection 32.

C

15 luminance signal is thus generated at connection 32 in accordance with the principles of the present invention. The remainder of the uncontaminated chrominance component of the cored luminance signal from connection 15 attempts to produce only a second-order distortion which cannot be observed except by careful inspection of the displayed image.

The low-pass filter 27 must have a linear phase to properly re-insert the motion detail into the combed luminance signal. Namely, this insertion occurs incorrectly if the motion detail is not properly re-inserted due to phase differences between the motion affected segments of the warped luminance signal and the motion detail separated from the warped chrominance signal. In this case, the combustion conditions of the comb filter will be adversely affected.

The residual chrominance (C2-C1, C1-C2) of the luminance channel due to movement from one total image to the next does not produce significant distortions in the rendered image. However, the intermediate or transition chrominance signal (C1 + C2) in the chamfered chrominance signal component occurring during 35 periods of motion can produce unfavorable color distortions. The chrominance signal is a vector size.

o DK 167420 B1 10

Thus, the vector sum C2 + C1 during periods of motion can produce colors quite different from the colors represented by one of the signals C1 or C2. In order to maintain the color unit at the edges of moving objects, it is often desirable that the chrominance component can be corrected for motion-induced errors produced during the comb filtration process.

The information needed for the correction of the combed chrominance signal is located in the combed luminance signal. This information can be re-entered in a manner similar to the method of recovering the motion detail of the combed luminance signal. However, chrominance recovery should not be a continuous process, but should be able to perform relief movement sequences. The reason for this is the relatively high energy density of the luminance signal compared to the cross components of the chrominance signal. Continuous addition of the nucleated luminance signal to the nucleated chrominance signal would effectively counteract the nucleation process. However, addition of the nucleated luminance signal to the nucleated chrominance signal during periods of movement produces a signal which is preferable in comparison to the chrominance reincorporation.

It is usually necessary to band-pass filter the cored chrominance signal to eliminate the residual luminance signal, i.e. luminance motion detail, the cored luminance component added to the cored chrominance signal being substantially eliminated from the corrected chrominance signal * 'f' ·

Only luminance components located in the spectral band of the chrominance signal remain in the corrected chrominance signal, and the luminance signal energy in this band is relatively small.

The luminance signal comprises components of the chrominance signal, i.e. red, blue and green signals, and therefore the amplitude of the luminance signal denotes the amplitude of the chrominance signal. The occurrence of signals beyond a predetermined value emitted from the low-pass filter 27 indicates the occurrence o 11 of motion, and the amplitude of this signal denotes the amplitude of the chrominance errors. Therefore, chrominance signal errors large enough to cause unfortunate distortions in the rendered image can be detected by measuring the amplitude of the luminance signal passed by the low-pass filter 27.

In FIG. 3a, a motion detector 28 which is connected to the output terminal of the low-pass filter 27 compares the low-pass filtered combed chrominance signal with a threshold. The threshold is set to a level corresponding to a signal level which has been found to cause unfortunate chrominance distortions. When the low-pass filtered signal from the filter 27 exceeds the threshold, the motion detector 28 produces a control signal which terminates the switch 29.

FIG. 3b and fig. 3c shows examples of analog signal and digital signal motion detectors, respectively. Analog version 28 'comprises a differential amplifier 40 with a large gain factor and a source of reference voltage 41. The signal from filter 27 is applied to a non-inverting input terminal 42 on amplifier 40 and signal from reference source 41 is applied to the inverting terminal of amplifier 40.

When the voltage at terminal 42 exceeds the reference voltage, the output of the amplifier 40 assumes a high value, otherwise it remains at a low value. Connected to the output terminal of amplifier 40 is an N-type field effect transistor 29 'which can be used as the switch 29 in FIG. 3a. A high voltage applied to the transistor port (G) terminates the switch and a low voltage opens the switch.

As shown in FIG. 3c, the digital edition 28 "of the motion detector comprises a binary reference source 45, a subtraction circuit 43 (comparator), a sign detector 44, and an AND circuit switch 29". (In the drawing, the double-line connections indicate parallel bit lines). The subtraction circuit 43 subtracts the reference number (45) from the binary signal at the output 42 of the filter 27 *. The difference value 35 is examined by a sign circuit 44 to determine whether it is positive or negative. If the difference is positive, the sign circuit generates a positive output pulse which enables the OG circuit 29 "to pass the signal to its data lines. Note that if the subtraction circuit performs two complementary arithmetic, the sign circuit may is removed and replaced by an inverter circuit which is directly connected between the most significant bit, i.e. the sign bit, from the subtraction circuit's output connections and the AND circuit.

The circuits of FIG. 3b and fig. 3c, as shown 10, responds only to input signals of one polarity, however, it is well known in the circuit art to parallel connect two such circuits so that they respond to signals of both polarities. Alternatively, the comparator may be of the "window comparator11 type.

Switch 29 selectively switches the combed luminance signal from terminal 15 to one input of the add circuit 30. Another input of the add circuit 30 is directly connected in such a way that it receives the combed chrominance signal from the terminal 16. When the motion detector-20 which, exceeding the threshold, is detected, switch 29 is terminated and the combed chrominance and luminance components are added in the add circuit 30. When no motion detail is detected, the switch 29 remains open and the add circuit leaves the churned pass chrominance signal 16 unchanged.

The output of the adding circuit 30 is fed to a linear phase bandpass filter 34 which only passes the chrominance signal frequency spectrum at its output terminal 35.

The circuit single portions 31 and 30 may either be additional.

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30 ring or subtraction circuits as indicated by the (-) signs at their input terminals in FIG. 3a. However, they can both be circuits of the same kind, viz. both addition circuits or both subtraction circuits. Whether the leading rear flank motion-distorted signal segments are recovered respectively depends on whether these circuits are adding circuits or subtracting circuits.

Claims (10)

A comb filter for processing television (TV) signals and of the nature comprising: a) a delay means (10) for delaying the television signal one frame of images, b) a first means (12) for combining The TV signal and the delayed TV signal from the delay means to produce the sum thereof corresponding to a first component (Y) of the TV signal, 10 c) a second means (13) for combining the TV signal and the delayed TV signal from the delay means to produce the difference therebetween corresponding to another component (C) of the TV signal, d) a low phase filter (27) of linear phase and with an input terminal connected to the second combining means (13), and with a output terminal, which low pass filter essentially rejects the frequency spectrum occupied by the second component, characterized by, e) a third means (31) connected to the first combining means (12) and the output terminal of the low pass filter to combine the first component of TV signal one with the low pass filtered signal to correct the first component of the TV signal for errors therein due to movement from one image to the next. A comb filter according to claim 1, characterized by a) a motion detection means (28) which is connected to the output terminal of the low-pass filter (27) and which responds to the low-pass filtered signal by detecting the occurrence of scene movement from one image to the next and generating a control signal in response to such a movement, b) a fourth signal combiner (30) having a first input terminal connected to the second combiner (13) to receive the second component, which o The fourth signal combining means has a second input terminal and an output terminal, and c) a switching means (29) which is connected to the motion detection means and which responds to the control signal 5 by selectively passing the first component to the second input terminal of the fourth signal combiner when scene motion is detected from one image to the next. Comb filter according to claim 2, characterized in that the TV signal is a complete signal including chrominance and luminance components, the first component (Y) corresponding to the luminance signal and the second component (C) corresponding to the chrominance signal. and the delay means comprises a storage means (10) for storing at least one total picture of the video signal. A comb filter according to claim 3, characterized by a linear phase bandpass filter which is connected in series with the output terminal of the fourth signal combining means, which bandpass filter is adapted to pass the chrominance signal frequency spectrum only. A comb filter according to claim 2, characterized in that the motion detection means includes: a) low pass filters (27), b) a reference (41; 45), and c) comparing means (28 '; 28 ") to compare the signal, which the low pass filter has passed, with the reference, and generates the control signal each time the low pass filtered signal deviates from the reference with a predetermined value. Comb filter according to claim 2, characterized in that the third combining means and / or the fourth combining means is a signal adding circuit. Comb filter according to claim 2, characterized in that the third combining means and / or the fourth combining means is a signal subtraction circuit. A method of comb filtering TV signals using the comb filter of claim 1 to separate chrominance and luminance components, characterized in the following 15 DK 167420 B1 steps: a) delaying the TV signal by a time interval of an information total picture, b) subtracting combining the delayed and the delayed TV signal to produce a comb-filtered chrominance component c) additive combining the delayed and the d) low pass filtering of the combed chrominance component with a linear phase filter to substantially eliminate the chrominance signal therefrom and e) combining the low pass filtered combed chrominance signal with the core signal periods 15 of movement from one total frame to the next to produce a warped luminance signal which is essentially free of distortion due to scene movement from one frame to the next. Method according to claim 8, characterized by a) detecting the occurrence of scene noise from one total image to the next, b) generating a control signal in response to such a movement, and c) combining the comb filtered chrominance signal with the comb filtered luminance signal. in response to the control signal. A method according to claim 9, characterized by bandpass filtering of the combined, comb filtered chrominance signal and the comb filtered luminance signal to pass the chrominance spectrum only. 35