CA1229160A - Field comb for luminance separation of ntsc signals - Google Patents
Field comb for luminance separation of ntsc signalsInfo
- Publication number
- CA1229160A CA1229160A CA000482084A CA482084A CA1229160A CA 1229160 A CA1229160 A CA 1229160A CA 000482084 A CA000482084 A CA 000482084A CA 482084 A CA482084 A CA 482084A CA 1229160 A CA1229160 A CA 1229160A
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- signal
- chrominance
- combining
- input terminal
- luminance
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/77—Circuits for processing the brightness signal and the chrominance signal relative to each other, e.g. adjusting the phase of the brightness signal relative to the colour signal, correcting differential gain or differential phase
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- Multimedia (AREA)
- Signal Processing (AREA)
- Processing Of Color Television Signals (AREA)
Abstract
Abstract of the Disclosure A field comb filter for separating luminance signal from NTSC composite video includes an adder for additively combining signals separated by 263 horizontal lines. Vertical detail is restored and motion compensation provided by a subtractor for subtractively combining signal separated by 262 horizontal lines and a second adder for adding the difference to the separated luminance signal.
Description
%;~
-1- RCA 80, 9~4 FIELD COMB FOR LUMINANCE SEPARATION OF NTSC SIGNALS
This invention relates to circuitry for separating chrominance and luminance components from composite video signal, and more particularly to a comb filter utilizing a one field delay and incorporating circuitry to compensate for motion induced artifacts.
The use of comb filters for separating luminance and chrominance is well known by those skilled in the art of video processing. Their cost, however, has generally limited their use to relatively simple interline comb filters. A description of an interline comb filter may be found in RCA Review, Vol. 41, No. l, March 1980, pp. 3-28, in the article by DO Pritchard, entitled "A COD Comb Filter for Color TV Receiver Picture Enhancement."
Interline comb filters effectively separate chrominance and luminance components but may produce several undesirable effects. These effects include: loss of diagonal resolution; reduction of vertical resolution;
and the production of "hanging dots" along vertical transitions.
Inter frame comb filters which operate on signals separated by integral video frame intervals separate chrominance and luminance components without any of the foregoing undesirable effects. However, inter frame comb filters may generate extremely annoying artifacts around the edges of moving image objects. To overcome this shortcoming it has been proposed to utilize adaptive comb filters. One such adaptive filter combines a line comb filter with a frame comb filter. In this arrangement, separated luminance and chrominance is acquired from the line comb filter during intervals of inter image motion and from the frame comb filter in the absence of motion.
Adaptive systems, though producing generally improved signals, are relatively expensive and may have compromised performance.
The present invention includes a comb filter system which is generally superior to the interline comb filter or the adaptive inter frame comb filter and requires , PI
- ISLES
-1- RCA 80, 9~4 FIELD COMB FOR LUMINANCE SEPARATION OF NTSC SIGNALS
This invention relates to circuitry for separating chrominance and luminance components from composite video signal, and more particularly to a comb filter utilizing a one field delay and incorporating circuitry to compensate for motion induced artifacts.
The use of comb filters for separating luminance and chrominance is well known by those skilled in the art of video processing. Their cost, however, has generally limited their use to relatively simple interline comb filters. A description of an interline comb filter may be found in RCA Review, Vol. 41, No. l, March 1980, pp. 3-28, in the article by DO Pritchard, entitled "A COD Comb Filter for Color TV Receiver Picture Enhancement."
Interline comb filters effectively separate chrominance and luminance components but may produce several undesirable effects. These effects include: loss of diagonal resolution; reduction of vertical resolution;
and the production of "hanging dots" along vertical transitions.
Inter frame comb filters which operate on signals separated by integral video frame intervals separate chrominance and luminance components without any of the foregoing undesirable effects. However, inter frame comb filters may generate extremely annoying artifacts around the edges of moving image objects. To overcome this shortcoming it has been proposed to utilize adaptive comb filters. One such adaptive filter combines a line comb filter with a frame comb filter. In this arrangement, separated luminance and chrominance is acquired from the line comb filter during intervals of inter image motion and from the frame comb filter in the absence of motion.
Adaptive systems, though producing generally improved signals, are relatively expensive and may have compromised performance.
The present invention includes a comb filter system which is generally superior to the interline comb filter or the adaptive inter frame comb filter and requires , PI
- ISLES
-2- RCA 80,984 significantly less hardware than the inter frame comb filter.
The present invention consists of apparatus for separating luminance signal from composite video by using an interfold comb filter and an interline comb filter. A
luminance motion compensation signal may be derived by subtracting in phase composite signals separated by e.g.
262 lines. This compensation signal is combined with comb filtered luminance signal to produce a luminance signal without significant motion induced artifacts and only marginally noticeable hanging dots.
FIGURES lo and lo are schematic representations of a reproduced image and which indicates particular horizontal lines involved in line comb filters and field comb filters, respectively;
FIGURE 2 is a block diagram of an interfold luminance comb filter embodying the present invention.
Referring to FIGURE lay the center portion of the drawing represents the scan lines of an interlaced 20 raster scanned image. The solid horizontal lines are the scan lines of the odd fields and the intervening broken lines represent the scan lines of even fields. At the left edge of the drawing are three columns of numbers designating the scan lines for three successive fields.
25 The (~) sins associated with the line numbers indicate the relative phase of the chrominance signal associated with each line. It will be readily appreciated by those skilled in the art of video systems that one field of conventional NTSC signal includes 262 1~2 lines. Every 30 second field begins with a half line (latter half) while intervening fields end with a half line (beginning half).
Signals delayed by one field period plus or minus a half line period correspond to vertically aligned samples, and are located on adjacent interlaced lines. In the NTSC
- 35 system, signal samples separated by 262 lines have an in phase chrominance sub carrier relationship while signal samples separated by 263 lines have a chrominance sub carrier relationship that is 1~0 degrees out of phase.
TV
I RCA 80,984 To the right of the drawing is a waveform depicting a change in chrominance amplitude meant to illustrate a vertical transition which spans the picture width, i.e. a horizontal color edge in the displayed image. The transition represents the fastest chrominance signal change that can occur due to the effective sampling rate (in the vertical direction of conventional raster scan video cameras.
The curved arrows along the vertical column designated "a" indicate the horizontal lines of signal that are additively combined to produce line comb filtered luminance signal. The curved arrows to the left of column "a" designate the lines in the odd fields that are combined, and the curved arrows to the right of column "a"
indicate the lines that are combined in even fields. For example, in the odd fields, line 1 is added to line 2 to produce luminance signal corresponding to displayed line 2. Line 2 is added to line 3 to produce luminance signal corresponding to displayed line 3, etc.
During vertical chrominance transitions the chrominance signal is not completely canceled from the line comb filtered luminance signal. The residual chrominance signal in the comb filtered luminance generates what is known as "hanging dots" along horizontal edges. Note from FIGURE lo if lines 264 and 265 are averaged the result is YOKE where Y represents luminance signal and I is the change in chrominance signal between lines 26~ and 265. The term ~C/2 is undesired residual chrominance signal. Similarly, if lines 2 and 3 are added and the sum divided by two, the resultant signal is YOKE
where the term I is undesired residual chrominance signal. The residual chrominance values are indicated graphically by the horizontal arrows along the vertical dashed line b. The length of the arrow indicates the I relative amplitude of the residual chrominance associated with the respective line of comb filtered signal.
Ruptured pointing arrows designate residual chrominance having the same relative polarity as the chrominance , . . .
I RCA 80,984 transition, and left ward pointing arrows are of opposite polarity.
Vertical line b' occurs at a point in space corresponding to a half cycle of the chrominance sub carrier from point b. The chrominance signal at point b' is 1~0 degrees out of phase with the chrominance signal at point b. As a consequence, the polarity of residual chrominance in the comb filter luminance signal (for like chrominance transitions) along vertical line b' is opposite to that along dashed line b. Since the residual chrominance linearly adds/subtracts from the luminance signal, it is seen that along a horizontal color image edge, the residual chrominance tends to drive the luminance amplitude alternately toward white and black levels at alternate half cycles of the chrominance signal.
It can also be seen that for a color transition occurring between two lines, residual chrominance is found in -three lines of the line comb filtered luminance signal.
Next consider FIGURE lo which is similar to FIGURE lo except that it depicts using adjacent interlaced lines in a comb filter system. The curved arrows to the left of the dashed vertical "C" indicate the horizontal lines of signal combined during a first field of a field comb filtered luminance signal and the curved arrows to the right of vertical "C" indicate the horizontal lines used in the next successive field of comb filtered signals. The luminance comb filtered samples are the average values of samples from two successive fields.
Spatially the samples are one-half line apart, i.e. they are separated by one-half -the vertical distance that samples combined in a line comb filter are separated.
Due to the inherent bandwidth limitations, the amplitude of chrominance changes are necessarily less than the amplitude of a chrominance transition between lines in a single field. This results in the maximum amplitude of residual chrominance contaminating the comb filtered luminance signal being less for interfold comb filtered I
-5- RCA 80,984 signals than interline comb filtered signals for the same chrominance transition.
The arrows along vertical lines "d" and "d"' represent the residual chrominance signal in a field comb filtered luminance signal for the chrominance signal illustrated at tune right side of the drawing. The occurrence of residual chrominance is restricted to two lines and the maximum amplitude is one-half the maximum amplitude exhibited in the line combed signals. In addition, the polarity of the residual chrominance signal is opposite on adjacent lines. These three features dramatically reduce the observability of "hanging dots" in field combed luminance signals. The one polarity residual chrominance on one line tends to brighten the picture while the opposite polarity residual chrominance on the adjacent interlaced line tends to darken the picture.
The two points are close enough that the eye integrates the brightness over the picture area -tending not to recognize the hanging dot.
As in line comb filters, there is an inherent loss in vertical detail in the field combed luminance signal. That is, for any comb filtered line the luminance signal is the averaged luminance signal over e.g. two lines. Thus, if from line 2 in field l to line 265 in field 2 the luminance signal, Y, changes by an amount MY, the effective change in the field combed luminance signal is JOY. To restore the comb filtered signal a value YO-YO
must be added back to produce the true luminance transition.
Observing the left side of FIGURE lo, and assuming the comb filtered luminance signal is derived from adding lines 2 and 265, over which lines a luminance transition is presumed to have occurred in the vertical direction, it will be noted that the same transition occurs between lines 265 and 527. Lines 265 and 527 have the same phase chrominance signal. Thus, subtracting one from the other will generate a signal corresponding to the luminance transition. Halving this signal produces the ,, I. .
Lo -6- RCA 80,984 desired vertical detail for addition back into the comb filtered luminance signal. Note however, that a system operating simultaneously on lines 2, 265 and 527 to produce a comb filtered signal requires two fields of storage.
In accordance with the principles of the present invention, only one field of storage is required. This is accomplished by combining the closest in-phase lines adjacent the lines utilized in the comb filter. Where lines 2 and 265 are averaged to produce comb filtered luminance, the appropriate in-phase lines for developing a difference signal are lines 265 and 3. If the luminance transition spans several lines and is generally monotonic, this difference signal will be exact, and this is generally the case. Note also that if image motion exists between fields, this motion information will be included in the difference signal. Adding this motion information back into the combed luminance signal tends to correct artifacts occurring in field combed images.
It will be appreciated by those skilled in the art of video comb filters that the difference signal will contain not only luminance vertical detail and luminance motion detail, but also chrominance motion and vertical detail information. It would therefore appear to be desirable to low pass filter the difference signal to eliminate the chrominance components before adding it to the combed luminance signal. In fact, there is a trade off to be made. If the chrominance component is filtered out of the difference signal, the "hanging dots" are less apparent but the edges of objects moving rapidly horizontally are less well defined. Thus, there is a choice between hanging dots or horizontal motion detail.
Referring again to FIGURE lo, the arrows along the vertical line "e" designate the residual chrominance in the comb filtered luminance signal with a wide band difference signal added back. This residual chrominance tends to produce "hanging dots" but they are significantly less apparent than for interline comb filtered signal.
I I RCA 80,984 The residual chrominance is worse only for sharp chrominance transitions. For transitions that span several lines the residual chrominance is in general improved.
FIGURE 2 is a block diagram of circuitry for performing the above-described field comb filtering to produce motion corrected separated luminance signal from composite video. The circuitry may use digital or analog devices depending on the signal to be processed.
In FIGURE 2, base band composite video is applied to input terminal 10 from which it is routed to the input ports of a 262 line delay element 20, a signal adder 40 and a signal subtracter 50. Delay element 20 delays signal applied thereto by 262 horizontal video line periods. The delayed signal from delay element 20 is applied to a further delay element 30 which delays signal by one horizontal video line period. The delayed signal from element 20 is also applied to respective input ports of signal subtracter 50 and a second subtracter 60.
20 Delayed signal from delay element 30 is applied to respective input ports of signal adder 40 and signal subtracter 60. Finally the signal sums from adder 40 and the signal differences from subtracter 50 are applied to respective input ports of a signal adder 70. The output, 80, of adder 70 is comb filtered, motion corrected luminance signal. The OlltpUt, 90, of subtracter 60 is line combed chrominance signal.
Consider that signal from horizontal line n is present a-t the output of delay element 30. The signal at the input to element 30 therefore corresponds to line nil.
Lines n and nil being successive lines, their chrominance components are 180 degrees out of phase. wine n being subtracted from line nil in subtracter 60 cancels the luminance component of the applied video signal and produces a chrominance signal of twice amplitude which will be subsequently halved for further chrominance processing.
~2;2';~6~
I RCA 80, 984 If the output signal from delay element 20 is line no then the input to element 20 is line n+263.
Lines n from delay element 30 and n+263 are summed in adder 40. Note that if n is an odd number, then n~263 is 5 an even number. For NTSC signal, odd numbered lines all have the same phase chrominance sub carrier and even numbered lines have the opposite phase sub carrier. Lines n and n+263 are separated by 263 lines or one field period plus a half line period (for NTSC signal). Adding the 10 even and odd numbered lines in adder 40 cancels the chrominance component and produces separated luminance signal. This luminance signal contains residual chrominance at chrominance transitions, lacks a portion of vertical luminance detail, and includes artifacts due to 15 - interfold motion.
Lines no from delay element 20 and n+263 are applied to subtracter 50. These lines are either both odd or both even, thus they have the same chrominance phase.
These lines are separated by a full field period less 20 half line period. Line no is subtracted from line n-l-263 to generate a difference signal which includes vertical detail and motion information. This difference signal is applied to one input of adder 70 where it is combined with the separated luminance signal from adder 40 to reinsert US the vertical detail and motion information therein.
With respect to the luminance signal the algorithm performed by the FIGURE 2 circuit may be described by the equation:
y = Sn,~,263-~Sn+ Sn+263-sn+l ) ( 1 ) 30 where is the signal produced at output port 80 and Sun is signal from line n where "n" is an integer.
As indicated before, it may be preferred to low pass filter the difference signal before reinsertion into the luminance signal. This is indicated by the element US 100 in phantom coupled between elements 50 and 70. If such an element 100 is incorporated in the circuitry, then it may be required to insert a delay element between -9- RCA 80,984 elements 40 and 70 to compensate for inherent signal delays in element 100.
For convenience, the interline chrominance comb filter is shown utilizing the one line delay element 30.
An alternative chrominance comb filter is shown in phantom including the subtracter 110. In this alternative, signal delayed by one line is tapped from delay element 20 and subtracted in subtracter 110 from signal applied at input terminal 10. Note that when this alternative chrominance kamikaze used, the comb filtered luminance, the difference signal and the comb filtered chrominance all have contributions from line n+263.
. :
The present invention consists of apparatus for separating luminance signal from composite video by using an interfold comb filter and an interline comb filter. A
luminance motion compensation signal may be derived by subtracting in phase composite signals separated by e.g.
262 lines. This compensation signal is combined with comb filtered luminance signal to produce a luminance signal without significant motion induced artifacts and only marginally noticeable hanging dots.
FIGURES lo and lo are schematic representations of a reproduced image and which indicates particular horizontal lines involved in line comb filters and field comb filters, respectively;
FIGURE 2 is a block diagram of an interfold luminance comb filter embodying the present invention.
Referring to FIGURE lay the center portion of the drawing represents the scan lines of an interlaced 20 raster scanned image. The solid horizontal lines are the scan lines of the odd fields and the intervening broken lines represent the scan lines of even fields. At the left edge of the drawing are three columns of numbers designating the scan lines for three successive fields.
25 The (~) sins associated with the line numbers indicate the relative phase of the chrominance signal associated with each line. It will be readily appreciated by those skilled in the art of video systems that one field of conventional NTSC signal includes 262 1~2 lines. Every 30 second field begins with a half line (latter half) while intervening fields end with a half line (beginning half).
Signals delayed by one field period plus or minus a half line period correspond to vertically aligned samples, and are located on adjacent interlaced lines. In the NTSC
- 35 system, signal samples separated by 262 lines have an in phase chrominance sub carrier relationship while signal samples separated by 263 lines have a chrominance sub carrier relationship that is 1~0 degrees out of phase.
TV
I RCA 80,984 To the right of the drawing is a waveform depicting a change in chrominance amplitude meant to illustrate a vertical transition which spans the picture width, i.e. a horizontal color edge in the displayed image. The transition represents the fastest chrominance signal change that can occur due to the effective sampling rate (in the vertical direction of conventional raster scan video cameras.
The curved arrows along the vertical column designated "a" indicate the horizontal lines of signal that are additively combined to produce line comb filtered luminance signal. The curved arrows to the left of column "a" designate the lines in the odd fields that are combined, and the curved arrows to the right of column "a"
indicate the lines that are combined in even fields. For example, in the odd fields, line 1 is added to line 2 to produce luminance signal corresponding to displayed line 2. Line 2 is added to line 3 to produce luminance signal corresponding to displayed line 3, etc.
During vertical chrominance transitions the chrominance signal is not completely canceled from the line comb filtered luminance signal. The residual chrominance signal in the comb filtered luminance generates what is known as "hanging dots" along horizontal edges. Note from FIGURE lo if lines 264 and 265 are averaged the result is YOKE where Y represents luminance signal and I is the change in chrominance signal between lines 26~ and 265. The term ~C/2 is undesired residual chrominance signal. Similarly, if lines 2 and 3 are added and the sum divided by two, the resultant signal is YOKE
where the term I is undesired residual chrominance signal. The residual chrominance values are indicated graphically by the horizontal arrows along the vertical dashed line b. The length of the arrow indicates the I relative amplitude of the residual chrominance associated with the respective line of comb filtered signal.
Ruptured pointing arrows designate residual chrominance having the same relative polarity as the chrominance , . . .
I RCA 80,984 transition, and left ward pointing arrows are of opposite polarity.
Vertical line b' occurs at a point in space corresponding to a half cycle of the chrominance sub carrier from point b. The chrominance signal at point b' is 1~0 degrees out of phase with the chrominance signal at point b. As a consequence, the polarity of residual chrominance in the comb filter luminance signal (for like chrominance transitions) along vertical line b' is opposite to that along dashed line b. Since the residual chrominance linearly adds/subtracts from the luminance signal, it is seen that along a horizontal color image edge, the residual chrominance tends to drive the luminance amplitude alternately toward white and black levels at alternate half cycles of the chrominance signal.
It can also be seen that for a color transition occurring between two lines, residual chrominance is found in -three lines of the line comb filtered luminance signal.
Next consider FIGURE lo which is similar to FIGURE lo except that it depicts using adjacent interlaced lines in a comb filter system. The curved arrows to the left of the dashed vertical "C" indicate the horizontal lines of signal combined during a first field of a field comb filtered luminance signal and the curved arrows to the right of vertical "C" indicate the horizontal lines used in the next successive field of comb filtered signals. The luminance comb filtered samples are the average values of samples from two successive fields.
Spatially the samples are one-half line apart, i.e. they are separated by one-half -the vertical distance that samples combined in a line comb filter are separated.
Due to the inherent bandwidth limitations, the amplitude of chrominance changes are necessarily less than the amplitude of a chrominance transition between lines in a single field. This results in the maximum amplitude of residual chrominance contaminating the comb filtered luminance signal being less for interfold comb filtered I
-5- RCA 80,984 signals than interline comb filtered signals for the same chrominance transition.
The arrows along vertical lines "d" and "d"' represent the residual chrominance signal in a field comb filtered luminance signal for the chrominance signal illustrated at tune right side of the drawing. The occurrence of residual chrominance is restricted to two lines and the maximum amplitude is one-half the maximum amplitude exhibited in the line combed signals. In addition, the polarity of the residual chrominance signal is opposite on adjacent lines. These three features dramatically reduce the observability of "hanging dots" in field combed luminance signals. The one polarity residual chrominance on one line tends to brighten the picture while the opposite polarity residual chrominance on the adjacent interlaced line tends to darken the picture.
The two points are close enough that the eye integrates the brightness over the picture area -tending not to recognize the hanging dot.
As in line comb filters, there is an inherent loss in vertical detail in the field combed luminance signal. That is, for any comb filtered line the luminance signal is the averaged luminance signal over e.g. two lines. Thus, if from line 2 in field l to line 265 in field 2 the luminance signal, Y, changes by an amount MY, the effective change in the field combed luminance signal is JOY. To restore the comb filtered signal a value YO-YO
must be added back to produce the true luminance transition.
Observing the left side of FIGURE lo, and assuming the comb filtered luminance signal is derived from adding lines 2 and 265, over which lines a luminance transition is presumed to have occurred in the vertical direction, it will be noted that the same transition occurs between lines 265 and 527. Lines 265 and 527 have the same phase chrominance signal. Thus, subtracting one from the other will generate a signal corresponding to the luminance transition. Halving this signal produces the ,, I. .
Lo -6- RCA 80,984 desired vertical detail for addition back into the comb filtered luminance signal. Note however, that a system operating simultaneously on lines 2, 265 and 527 to produce a comb filtered signal requires two fields of storage.
In accordance with the principles of the present invention, only one field of storage is required. This is accomplished by combining the closest in-phase lines adjacent the lines utilized in the comb filter. Where lines 2 and 265 are averaged to produce comb filtered luminance, the appropriate in-phase lines for developing a difference signal are lines 265 and 3. If the luminance transition spans several lines and is generally monotonic, this difference signal will be exact, and this is generally the case. Note also that if image motion exists between fields, this motion information will be included in the difference signal. Adding this motion information back into the combed luminance signal tends to correct artifacts occurring in field combed images.
It will be appreciated by those skilled in the art of video comb filters that the difference signal will contain not only luminance vertical detail and luminance motion detail, but also chrominance motion and vertical detail information. It would therefore appear to be desirable to low pass filter the difference signal to eliminate the chrominance components before adding it to the combed luminance signal. In fact, there is a trade off to be made. If the chrominance component is filtered out of the difference signal, the "hanging dots" are less apparent but the edges of objects moving rapidly horizontally are less well defined. Thus, there is a choice between hanging dots or horizontal motion detail.
Referring again to FIGURE lo, the arrows along the vertical line "e" designate the residual chrominance in the comb filtered luminance signal with a wide band difference signal added back. This residual chrominance tends to produce "hanging dots" but they are significantly less apparent than for interline comb filtered signal.
I I RCA 80,984 The residual chrominance is worse only for sharp chrominance transitions. For transitions that span several lines the residual chrominance is in general improved.
FIGURE 2 is a block diagram of circuitry for performing the above-described field comb filtering to produce motion corrected separated luminance signal from composite video. The circuitry may use digital or analog devices depending on the signal to be processed.
In FIGURE 2, base band composite video is applied to input terminal 10 from which it is routed to the input ports of a 262 line delay element 20, a signal adder 40 and a signal subtracter 50. Delay element 20 delays signal applied thereto by 262 horizontal video line periods. The delayed signal from delay element 20 is applied to a further delay element 30 which delays signal by one horizontal video line period. The delayed signal from element 20 is also applied to respective input ports of signal subtracter 50 and a second subtracter 60.
20 Delayed signal from delay element 30 is applied to respective input ports of signal adder 40 and signal subtracter 60. Finally the signal sums from adder 40 and the signal differences from subtracter 50 are applied to respective input ports of a signal adder 70. The output, 80, of adder 70 is comb filtered, motion corrected luminance signal. The OlltpUt, 90, of subtracter 60 is line combed chrominance signal.
Consider that signal from horizontal line n is present a-t the output of delay element 30. The signal at the input to element 30 therefore corresponds to line nil.
Lines n and nil being successive lines, their chrominance components are 180 degrees out of phase. wine n being subtracted from line nil in subtracter 60 cancels the luminance component of the applied video signal and produces a chrominance signal of twice amplitude which will be subsequently halved for further chrominance processing.
~2;2';~6~
I RCA 80, 984 If the output signal from delay element 20 is line no then the input to element 20 is line n+263.
Lines n from delay element 30 and n+263 are summed in adder 40. Note that if n is an odd number, then n~263 is 5 an even number. For NTSC signal, odd numbered lines all have the same phase chrominance sub carrier and even numbered lines have the opposite phase sub carrier. Lines n and n+263 are separated by 263 lines or one field period plus a half line period (for NTSC signal). Adding the 10 even and odd numbered lines in adder 40 cancels the chrominance component and produces separated luminance signal. This luminance signal contains residual chrominance at chrominance transitions, lacks a portion of vertical luminance detail, and includes artifacts due to 15 - interfold motion.
Lines no from delay element 20 and n+263 are applied to subtracter 50. These lines are either both odd or both even, thus they have the same chrominance phase.
These lines are separated by a full field period less 20 half line period. Line no is subtracted from line n-l-263 to generate a difference signal which includes vertical detail and motion information. This difference signal is applied to one input of adder 70 where it is combined with the separated luminance signal from adder 40 to reinsert US the vertical detail and motion information therein.
With respect to the luminance signal the algorithm performed by the FIGURE 2 circuit may be described by the equation:
y = Sn,~,263-~Sn+ Sn+263-sn+l ) ( 1 ) 30 where is the signal produced at output port 80 and Sun is signal from line n where "n" is an integer.
As indicated before, it may be preferred to low pass filter the difference signal before reinsertion into the luminance signal. This is indicated by the element US 100 in phantom coupled between elements 50 and 70. If such an element 100 is incorporated in the circuitry, then it may be required to insert a delay element between -9- RCA 80,984 elements 40 and 70 to compensate for inherent signal delays in element 100.
For convenience, the interline chrominance comb filter is shown utilizing the one line delay element 30.
An alternative chrominance comb filter is shown in phantom including the subtracter 110. In this alternative, signal delayed by one line is tapped from delay element 20 and subtracted in subtracter 110 from signal applied at input terminal 10. Note that when this alternative chrominance kamikaze used, the comb filtered luminance, the difference signal and the comb filtered chrominance all have contributions from line n+263.
. :
Claims (7)
1. Apparatus for separating luminance signal from composite video signal including chrominance and luminance signal components, comprising:
an input terminal for applying composite video signal;
signal delaying means having an input port coupled to said input terminal and having first and second output taps at which signals delayed by substantially one field period and one horizontal line period less than said substantially one field period are provided;
first signal combining means having first and second input ports coupled to said input terminal and said first tap respectively for additively combining signals applied thereto;
second signal combining means having first and second input ports coupled to said input terminal and said second tap for subtractively combining signals applied thereto; and third signal combining means having first and second input ports respectively coupled to said first and second signal combining means for additively combining signals produced thereby, and having an output port at which said luminance signal is produced.
an input terminal for applying composite video signal;
signal delaying means having an input port coupled to said input terminal and having first and second output taps at which signals delayed by substantially one field period and one horizontal line period less than said substantially one field period are provided;
first signal combining means having first and second input ports coupled to said input terminal and said first tap respectively for additively combining signals applied thereto;
second signal combining means having first and second input ports coupled to said input terminal and said second tap for subtractively combining signals applied thereto; and third signal combining means having first and second input ports respectively coupled to said first and second signal combining means for additively combining signals produced thereby, and having an output port at which said luminance signal is produced.
2. The apparatus set forth in claim 1 wherein said third signal combining means is coupled to said second combining means through a filter having a transfer response which rejects chrominance signal frequencies.
3. The apparatus set forth in claim 1 further including means for separating chrominance signal from said composite signal, comprising:
fourth signal combining means, having first and second input ports coupled to said first and second taps, for subtractively combining signals applied thereto, and having an output port at which separated chrominance signal is produced.
fourth signal combining means, having first and second input ports coupled to said first and second taps, for subtractively combining signals applied thereto, and having an output port at which separated chrominance signal is produced.
4. The apparatus set forth in claim 1 further including means for separating chrominance signal from said composite signal, comprising:
a third output tap on said delaying means at which signals delayed by one horizontal line period are provided;
a fourth signal combining means having first and second input ports respectively coupled to said input terminal and said third output tap, for subtractively combining signals applied thereto, and having an output port at which separated chrominance signal is produced.
a third output tap on said delaying means at which signals delayed by one horizontal line period are provided;
a fourth signal combining means having first and second input ports respectively coupled to said input terminal and said third output tap, for subtractively combining signals applied thereto, and having an output port at which separated chrominance signal is produced.
5. A field comb filter for producing motion compensated luminance signal from composite video signal, comprising:
means for combining said composite video and composite video signal delayed by substantially one field period to produce comb filtered luminance;
means for subtractively combining said composite video signal and composite video signal delayed by a period one horizontal line period less than said substantially one field period to produce a difference signal; and means for additively combining said difference signal and said comb filtered luminance to produce at an output thereof said motion compensated luminance signal.
means for combining said composite video and composite video signal delayed by substantially one field period to produce comb filtered luminance;
means for subtractively combining said composite video signal and composite video signal delayed by a period one horizontal line period less than said substantially one field period to produce a difference signal; and means for additively combining said difference signal and said comb filtered luminance to produce at an output thereof said motion compensated luminance signal.
6. The field comb filter set forth in claim 5 wherein said substantially one field period is the duration of one field period plus the duration of one half one horizontal line.
7. Comb filter apparatus for separating luminance information from a video signal provided in field format so that image lines of each successive field are displayed interlaced with image lines from the preceding field, said comb filter comprising:
an input terminal for applying said video signal;
means coupled to said input terminal and having first and second output ports for providing respective signals separated by one horizontal line period and corresponding to lines of signal delayed substantially by one field period from signal applied to said input terminal, said signals from said first and second output ports corresponding to the interlace lines immediately preceding and following the signal corresponding to the image line applied to said input terminal, chrominance components of video signal from said first and second output ports being 180 degrees out of phase and the chrominance component from one of said first and second output ports being in phase with a chrominance component at said input terminal;
first means for additively combining video signal from said input terminal and delayed signal from one of said first and second output ports having a chrominance component with a 180 degree phase relationship with video signal applied to said input terminal;
second means for subtractively combining video signal from said input terminal and delayed signal from the other of said first and second output ports, having a chrominance component of like phase with video signal applied to said input terminal; and means for additively combining signals produced by said first and second means to produce a luminance component of said video signal.
an input terminal for applying said video signal;
means coupled to said input terminal and having first and second output ports for providing respective signals separated by one horizontal line period and corresponding to lines of signal delayed substantially by one field period from signal applied to said input terminal, said signals from said first and second output ports corresponding to the interlace lines immediately preceding and following the signal corresponding to the image line applied to said input terminal, chrominance components of video signal from said first and second output ports being 180 degrees out of phase and the chrominance component from one of said first and second output ports being in phase with a chrominance component at said input terminal;
first means for additively combining video signal from said input terminal and delayed signal from one of said first and second output ports having a chrominance component with a 180 degree phase relationship with video signal applied to said input terminal;
second means for subtractively combining video signal from said input terminal and delayed signal from the other of said first and second output ports, having a chrominance component of like phase with video signal applied to said input terminal; and means for additively combining signals produced by said first and second means to produce a luminance component of said video signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US61554484A | 1984-05-31 | 1984-05-31 | |
| US615,544 | 1984-05-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1229160A true CA1229160A (en) | 1987-11-10 |
Family
ID=24465848
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000482084A Expired CA1229160A (en) | 1984-05-31 | 1985-05-22 | Field comb for luminance separation of ntsc signals |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS60263593A (en) |
| KR (1) | KR930002126B1 (en) |
| CA (1) | CA1229160A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100808187B1 (en) | 2006-03-21 | 2008-02-29 | 엘지전자 주식회사 | Scanning display apparatus |
-
1985
- 1985-05-22 CA CA000482084A patent/CA1229160A/en not_active Expired
- 1985-05-30 KR KR1019850003746A patent/KR930002126B1/en not_active IP Right Cessation
- 1985-05-30 JP JP60118686A patent/JPS60263593A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| KR930002126B1 (en) | 1993-03-26 |
| KR850008087A (en) | 1985-12-11 |
| JPS60263593A (en) | 1985-12-27 |
| JPH03836B2 (en) | 1991-01-09 |
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