SE453246B - DEVICE AND SET FOR PHOTO-TO-IMAGE CAMFILTRATION OF A COMPOSITION TELEVISION SIGNAL - Google Patents

Description

2 a previous line, and the result is that they interleaved the frequency components (eg the chrominance components) are canceled while the non-interleaved frequency components (eg the luminance components) are amplified. By subtracting signals for two consecutive lines (e.g. by inverting the signals for a line and then adding signals for both) the non-interleaved frequencies are canceled the component components while the interleaved frequency components are strengthened. The luminance and chrominance signals can thus mutually combed, whereby they can be separated in a kindly.

The above-mentioned combing process is possible as a result of the built-in high level of signal redundancy from line to line in a typical video image. If you consider a stationary image and a special part in said image it should be emphasized that the redundancy level of the signal representing the relevant batch becomes essentially one hundred percent from image to image picture. Thus, if combing is performed from image to image, more the proportion of residual luminance signal in the combed chrominance signal to be significantly reduced in relation to a signal which is combed from line to line. In a similar way, the proportion comes residual chrominance signal in the combed luminance signal to be reduced to a significant degree in relation to a signal that is combed from line to line.

More specifically, for example, there will be no vertical details accompany the combed chrominance signal. In terms of construction is the chrominance signal of a composite NTSC signal synchronized so that it has an 1800 phase connection from image to image, whereby comb filtration can be done on the basis of the images. Luminance Composites can therefore be taken out by linear addition of the compound the signal from successive images, and the chrominance component the sant can be extracted by linear subtraction of the compound the signal from successive images.

The response response of a comb filter from line to line has zero values or teeth located on the line frequency stand apart, ie they lie at intervals of 15734 kHz, while the filter response from image to image has teeth on interval of 30 Hz. The teeth closer together or 453 246 3 the zero distance in the image comb means that you get one more complete combing process in all room directions than then it applies to the combing between the lines.

In the combing process from frame to frame, non-stationary objects give rise to distortions in the reproduced images.

These distortions are due to an incomplete repeal of the luminance and chrominance components of the combed chrominance components resp. combed the luminance signals (cross components) as well as on a reduction in the effective bandwidth of the luminance signal in the areas where movement occurs. Differences in image content as a result of objects moving and occurring in the time frame of 1/50 second or less is characterized as visible motion see 1 image content.

The distortions generated by motion caused by the combing process from image to image is two-dimensional and depends entirely on movement between the images. Distorted can be observed in both horizontal and vertical directions in the plane of the image, and they manifest themselves as double images or ghosts. images in the reproduced images. The double images are separated to an extent corresponding to the speed of movement, and they can be accompanied by incorrect hue at the edges of the moving the objects.

In contrast to the above, comb filters give off line in line with one-dimensional distortions which vertical constituents 1 an image even if it is tionary. Distortions that accompany the combing process from line to line manifests itself as an effective reduction of the width of the signal representing vertical picture portions and as a softening of the vertical edges of the image content hold.

The object of the present invention is to reduce them undesirable effects obtained as a result of movement in a cam system where one starts from movement from image to image.

A preferred embodiment of the present invention includes a comb filter for processing television signals, which filter includes a delay means for delaying the television signal a picture period. First organs are provided to combine the television signal and the delayed 453 246 4 the vision signal from the delay means to form the sum of which corresponds to a first component of the television the signal. Other means are provided to combine television the signal and the delayed television signal from the delayed to achieve the difference between them corresponding to the they a second component from the television signal. A low-pass file linear phase is provided and has an input socket coupled to said second combining means for receiving it the second component of the television signal. The low-pass filter has an output socket and essentially discards that frequency spectrum which is normally occupied by the other component of the television signal.

Third means are provided, which are connected to said first combining means and to the output socket of the low-pass filter for to combine the first component and the television signal with the low-pass filtered signal to correct the first signal the component component with respect to errors in it depending on movement between the images.

In accordance with another feature of the invention is motion detection means connected to the output of the low-pass filter clamp, and they are operable in response to the low-pass filtered the signal to detect the presence of movement between the images. The motion detection means generates a control signal which is operable in response to such a movement. Fourth signal combining means are provided, which have a first input socket connected to said second combining means for receive the other component. Said fourth signal combining ring means has a second input socket and an output socket. If- coupling means are connected to the motion detection means and are controllable in response to the control signal to selectively connect the first component to the second input socket of said fourth signal combining means when movement between na is detected.

In accordance with yet another feature of the invention is one bandpass filter with linear phase connected in series with the output socket of said fourth signal combining means. The bandpass filter is so constructed that it only transmits chrominance signal frequency spectrum.

In the accompanying drawings, Fig. 1 shows a block diagram of 453 246 5 an image known in the art of television signal processing to-image comb filter, Figs. 2a-2d are to the circuit of fi, 1 hearing waves with amplitude plotted against time, while Fig. 2e is a wave which is the result of a modification of the circuit according to Fig. 1, and Fig. 3, which includes Figs. Ba-jc, is a block scheme of one performed in accordance with the present invention image-to-image comb filter.

Fig. 1 shows an image-to-image camera known in the art. For illustrative purposes, the device will be described in connection with the separation of luminance and chrominance signals from a composite television signal. However, the device is not limited to this particular application. For example, devices one according to Fig. 1 is used to comb filter a luminance signal for inserting therein a chrominance signal in the production of a composite video signal.

In Fig. 1, a storage element 10 has the ability to store it electrical expression of an image (eg two sub-images in NTS video format) of a video signal. The storage element 10 receives in sequence the input signal at the input terminal 11 and outputs the ma signal to the output terminal 14 delayed by the duration of a picture period. The element 10 may comprise a digital memory, for example a direct memory (RAM) with suitable support electronics or an analog memory, e.g. a means for transmitting serial charging (CTD), such as a charge-coupled device (CCD) with required support circuits. In principle, it does not matter the element 10 consists of a digital circuit or an analog circuit.

However, it must be assumed that the circuit is digital in nature.

The other circuit elements included will thus be considered be digital in nature in order for digital-analog signal conduction between the circuit elements must be avoidable.

The input signal from the connection ll and the delayed one the signal from the connection 14 is summed in the adder circuit 12.

The luminance component of the signal, which is in phase, is added where the chrominance components, which are 1800 out of phase, cancel each other in phase so as to obtain a substantial chrominance-free luminance signal Y at the connection 15. In- the input signal and the delayed signal are also fed to the sub- cr-anerarxretsen 1,3, 1 which creminanekompäanterna beä de both images are constructively summed up while the luminance 453 246 6 the components cancel each other out so as to obtain an essential luminance-free chrominance signal on the connection 16 (at least when successive image signals are records of the same stationary image).

In Fig. 2, motion effects on the above-described image are to-image cam process graphically illustrated. Fig. 2a represents centers part of the composite signal being fed the clamp ll at any time. Fig. 2b represents the composite video signal from the same image is exactly one image period later in time, whereby some movement has occurred in the picture. In scale 2a it is assumed that the signal component between time T1 and T3 represent an object with the respective luminance and chrominance signal parameters L2 and 02, Föpemálet assumed to be located in an area with uniform image content and with the respective luminance and chrominance signal parameters L1 and Cl.

Between the images, the object moves in the room, which causes that the video signal representation of the object is shifted in time, i.e. falls between the times T2 and T4 in Fig. 2b. Relative- the signal parameters L and C of the luminance and chrominance components the sants of the signal remain unchanged in the waves according to Figs. 2a and 2b, although there is a time shift with respect to on the object represented by L2, C2. Signals: chromic However, the component has a 180 degree phase relationship between waves 2a and 2b (ie between images).

The sum of resp. the difference between the waves in Figs. 2a and 2b are represented by wave 2c resp. Libra 2d. You see that then in the case of the time segments in which the absolute value of the the vector component between waves 2a and 2b is the same, becomes a virtually complete abolition of chrominance components as a result of the summing of the two waves (Fig. 2c). Equally in this way, the amplitude of the luminance component for the signal is equal in the two waves (2a and 2b) becomes one substantially complete cancellation of the luminance component the consequence of subtracting the two waves (Fig. 2d). The figures 2a, 2b, 20 and 2d represent signals appearing at the respectively the connections 11, 14, 15 and 16 in the circuit according to Fig. 1. 453 246 7 During the time period when movement occurs between the images, ie between the times T1 and T2 and the times Tj and TH, not equal signals are summed differentially, whereby an incomplete constant cancellation of the undesirable component is obtained.

In addition, motion distorts the desired signal. This movement means that the signal is given an average value below the time periods when movement occurs. These average values are in Fig. 2c represented by the signal segments designated (L1 + L2), which is equivalent to (2L1 + 2L2) / 2. Normally weighed the signal from the two images by a factor of 1/2 before combining neras. The amplitude of the combed signal then becomes half the displayed values, and the signal during the operating period becomes (L1 + L2) / 2. The average values (L1 + L2) in the luminance signal show a tendency to mimic the signal transitions so as to holds a double image or ghost image surrounding the moving object sig. The average values (C1 + C2) in the combed chrominance signal during periods when movement occurs between the images, a tendency to distort the hue around the moving object.

If a low-pass filter is provided at the connection 16 in fig The combed chrominance signal in Fig. 2d generates that in Fig. 2e showed the signal. In Fig. 2e, the chrominance signal spectrum has been removed. only the non-canceled luminance component as constitutes the result of movement between the images remains. About signa- the lens of Fig. 2e is added to or subtracted from the signal according to Fig. 2c, the edges of the luminance signal are reset, by obtaining a luminance component equivalent to one that has not been combed. Adding the signal according to Fig. 2e resets the luminance signal of Fig. 2c between the times T1 and T2 to the level 2L2 and reduces the luminance signal between the times T3 and T4 to the value 2L1 as indicated by the dashed lines.

The circuit shown in Fig. 1a is a frame-to-frame comb filter arranged in accordance with the principles of the present invention with the possibility of correcting such distortions as double images or "smearing" that is the result of movement between consecutive images. In Fig. 3, elements such as are marked with the same reference numerals as elements in Fig. 1 identical functions. At connections 15 and 16 in The circuit of Fig. Ba thus generates combed luminance signals. 453 246 8 and combed chrominance signals, said signals contains both cross-components and incompletely combed signal components due to movement between the images.

The combed chrominance signal at connection 16 is is passed to a linear pass low pass filter 27 to remove the chrominance signal spectrum, the non-canceled low frequency the luminance components remain. The low-pass filtered signal from the filter 27 is added in the adder circuit 31 back to it combed the luminance signal from the connection li to obtain holds the corrected luminance signal YC at the connection 32.

The corrected luminance signal is thus formed at the connection in accordance with the principles of the present invention.

The non-canceled residual chrominance component in the combed luminaire The signal from the connection 15 shows a tendency to only form a second order distortion that can not is observed unless one looks very closely at the displayed image.

The low-pass filter 27 must have a linear phase in order to be correct be able to incorporate the movement details into the combed luminance the signal. Transient response is adversely affected if operating details are not introduced correctly due to phase differences between them of the motion affected the segments of the combed luminance signal and the movement details extracted from the combed criminals nalen.

The residual chrominance signal (C2-Cl, C1-C2) in the luminance channel, which is the result of movement between the images, does not entail some major distortions in the reproduced image. However the average signal or transition chrominance signal len (C1 + C2) in the combed chrominance signal component, which the former signal occurs during periods of movement, possibly give rise to undesirable color distortions. Chrominance the signal is a vector quantity. Thus, the vector sum C2 + Cl during periods of movement give rise to colors that differ entirely from the colors represented by one or other of the signals Cl resp. C2. For color purity to retained at the edges of the moving objects, it is often desirable worthy of the chrominance component being corrected for motion-induced errors generated during the comb filtration process.

The information needed to correct the combed the chrominance signal is present in the combed luminance signal. This 453 246 9 information can be re-introduced in the same way as in the case to restore the motion details to the combed luminance signal nalen. However, the restitution should not constitute one continuous process, but should only be performed during sequences. The reason for this is the relatively large one the energy density of the luminance signal in comparison with the cross-component santerna in the chrominance signal. Continuous addition of the cam- made the luminance signal to the combed chrominance signal would effectively defeat the combing process. However, the addition of the combed luminance signal to the combed chrominance signal during periods of movement a signal that is preferable in comparison with no chrominance reintroduction taking place.

It is normally necessary to bandpass filter the combed the chrominance signal to eliminate the residual luminance signal, ie the luminance movement details, whereby the to the combed chromium the nance signal added combed the luminance component substantially eliminated from the corrected chrominance signal. Only lumi- the components present in the spectral range of the chrominance signal bands remain in the corrected chrominance signal, and the energy of the luminance signal in this band is relatively low.

The luminance signal is formed by constituents of the chrominance the signal, ie red, blue and green signals, hence the amplitude of the luminance signal is indicative of the amplitude of the chrominance signal. the signal. The ratio of a signal with a value greater than a predetermined value derived from the low pass filter 27 indicates that motion occurs, and the amplitude of this signal indicates the amplitude of the chrominance error. Chrominance signal error that is large enough to cause undesirable distortions In the displayed image can thus be detected by the amplitude of that passed through by the low-pass filter 27 is measured the luminance signal.

In Fig. Ba, one compares to the starting connection of low the pass filter 27 connected to the motion detector 28 the low-pass filtered combed the chrominance signal with a threshold value. The threshold value is set to a level that has been found to give rise to undesirable chrominance distortions. When the low-pass filter the signal from the filter 27 exceeds the threshold value generated the motion detector 28 a control signal which closes the switch 29. 453 246 10 Figs. Jb and 3c show illustrative examples of analogous signal resp. digital signal motion detectors. The analog version 28 'includes a differential amplifier 40 with a large amplifier. and a source 41 for reference potential. The signal from the felt the device 27 is fed to a non-inverting input socket 42 of the the amplifier 40, and the signal from the reference source 41 is supplied the inverting socket of the amplifier 40. When the potential at socket 42 exceeds the reference potential, it becomes the output signal from amplifier 40 high, otherwise it remains low. To the output terminal of the amplifier is a field effect transistor 29 'off n-type coupled, which can be used as the switch 29 in Fig. and. A high potential applied to the control of the transistor (G) closes the switch, while a low potential opens the switch.

In Fig. Jo, the digital version 28 'of motion detection includes a binary reference source 45, a subtractor circuit 43 (comparator rator), a list detector 44 and an on-circuit switch 29 ".

(In the drawing, double lines indicate parallel bit lines.) The subtractor 43 subtracts the reference number (45) from the binary the signal at the output 42 of the filter 27. The difference value is examined of a sign circuit 44 which determines whether it is positioned positive or negative. If the difference is positive, the character circuit a positive output pulse that enables and circuit 29 "to transmit the signal on the data line of the circuit. nings. It should be noted that if the subtractor works with arithmetic of the complement type with two, the sign circuit can be be replaced by an inverting circuit which is directly connected between the most significant bit, i.e. the sign bit, of the subtractor output connections and and-circuit.

The circuits shown in Figs. Bb and 3c are only operable in response to input signals of one polarity. So- which, however, is generally known in the circuit art connect two such circuits in parallel so that they are only in response to signals of both polarities. Alternative The comparator may be of the "door comparator" type.

The switch 29 selectively switches the combed luminance the signal from the connection 15 to one input of the adder circuit 30. A second input to the adder circuit 50 is directly connected to receive the combed chrominance signal 453 246 ll from the connection 16. When movement details that exceed the threshold value is detected, switch n 29 will be closed, at the combed chrominance and luminance components are added in adder circuit 50. When no motion details are detected remains the switch 29 is open, the combed chrominance signal from the connection 16 is passed unchanged by the adder circuit.

The output signal from the adder circuit 50 is connected to one linear phase bandpass filter 34, said bandpass filter only transmits the chrominance signal frequency spectrum at its output socket 35.

The circuit elements 31 and 30 can be either adder or subtractor circuits, as indicated by the sign T at their input socket in fig. yes. However, they must be circuits of the same type, ie both adders or both subtractors. It because- the fact that they are adders or subtractors determines how the leading or lagging motion-distorted signal the segments are restored resp. repealed.

Claims (10)

453 246. 12 Patent claims A comb filter for processing television signals, the filter including a delay means (10) for delaying said television signal a picture period, first means (12) for combining said television signal and the delayed television signal from said delay means to form their sum corresponding to a first component (Y) in said television signal and second means (13) for combining said television signal and the delayed television signal from said delay means to form their difference corresponding to a second component (C) in said television signal, said comb filter being k characterized by a linear phase low-pass filter @ P (27) and having an input terminal coupled to said second combining means (13) for receiving said second component in the television signal and having an output terminal, said low-pass filter substantially discarding the frequency spectrum as normal occupied by said second component, and third means (31) cow applied to said first combining means (12) and to said output socket of said low-pass filter to combine the first signal component with the low-pass filtered signal to correct the first signal component for errors in the same due to movement between images. Comb filter according to claim 1, characterized by motion detection means (28) coupled to said output socket of said low-pass filter (27) and actuable in response to said low-pass filtered signal to detect the occurrence of movement between images and to, depending on such motion see generating a control signal, fourth signal combining means (30) having an input socket connected to said second combining means (13) for receiving said second component, said fourth signal combining means having a second input socket and an output socket, and switching means (29) connected to said motion detecting means and operable in dependence on said control signal to selectively couple said first component to said second input socket of said fourth signal combining means when movement between images is detected. Comb filter according to claim 2, characterized in that said television signal is a composite signal 453 246 13 which includes chrominance and luminance components, said first component (Y) corresponding to the luminance signal, said second component (C ) corresponds to the chrominance signal and that said delay means comprises a memory means (10) for storing at least one image of the video signal. 4. A comb filter according to claim 3, characterized by a linear phase bandpass filter connected in series with said output socket of said fourth signal combining means, said bandpass filter being designed so as to transmit only the chrominance signal frequency spectrum. Cam filter according to claim 2, characterized in that said motion detecting means includes said low-pass filter (27), a reference (41; 45), and comparison means (28 '; 28 ") for comparing a pass-through filter with said low-pass filter. and for generating said control signal whenever the low-pass filtered signal differs from the reference by a predetermined amount. Cam filter according to claim 2, characterized in that said third combining means and / or said fourth combining means is a signal adder circuit. 7. A comb filter according to claim 2, characterized in that said third combining means and / or said fourth combining means is a signal subtractor circuit. A method of comb-filtering television signals using the device according to claim 1 for separating chrominance and luminance components, characterized in that the television signal is delayed by the duration of an information image, that delayed and non-delayed television signals are subtractively combined to provide a comb-filtered chrominance component, that delayed and non-delayed television signals are additively combined to produce a comb-filtered luminance signal, that said combed chrominance component is low-pass filtered by means of a linear phase filter to substantially eliminate the chrominance signal passed therefrom, and combed chrominance signal is combined with said combed luminance signal during times when movement occurs between images to produce a combed luminance signal which is substantially free of distortions due to movement between images. [55 I '. p ». -. f J »'3" H4 ". "Om p¿, ¿, _u, s IV 3 ,. fl wfm or fi g: dthq 9 t,, Kq¿, ¿/; LMM; .f (g 5,,. /, N. Fmrv, v .ffxwu _, f 'mu | 1' 453 246 14 9. A method according to claim 8, wherein the occurrence of movement between images is detected, that in dependence on such movement a control signal is generated and that said cam-filtered chrominance signal is combined with said cam-filtered luminance signal in response to said control signal . 10. A method according to claim 9, characterized in that said combined chrominance and comb filtered luminance signals are bandpass filtered so that only the chrominance spectrum is transmitted.