Apparatus for combining and separating components of a video signal.

DESCRIPTION

This invention concerns an apparatus for encoding video signal components that must be combined, such as the luminance and chrominance components of an NTSC type television signal, to facilitate the separation of such components without intermodulation aberrations.

It is well known that the frequency intercalation of the luminacy and chrominance components of the baseband of an NTSC television signal does not always allow the two components to be separated without intermodulation aberrations such as color crossover abbreviations and luminance crossover . Color crossing aberration results from contamination by chrominance by luminance information, and can be described as a blinking rainbow model in parts of an image where high frequency diagonal luminance information is present, such as in a shirt striped. The luminance crossover aberration is sometimes referred to as a "hanging point" aberration and is visible in a system that uses a luminance / chrominance separator of the comb filter type. The luminance crossing results from the contamination of the luminance by chrominance information, particularly in the vertical image transition regions.

Color crossing and chrominance crossing aberrations are introduced at two locations in the system. First, an imperfect or incorrect separation of luminance / chrominance in a television receiver causes the luminance to be interpreted as chrominance, and vice versa. The second way in which color crossing and chrominance cross aberrations are introduced is in the sodification process itself, which intercalates in frequency the chrominance and luminance components.

Various methods have been proposed to improve the separation of luminance and chrominance components in the receptor by reducing luminance / chrominance intermodulation aberrations. Some of these methods involve treatment schemes at the source and at the receiver that use comb filters of lines, frames and fields, as described by CH Stolle in "Cooperative Processing of Improved NTSC Chrominance / Luminance Separation", SMPTE Journal, August 1986. Another system of prefiltering luminance and chrominance information using multidimensional comb filters, before being combined, is described by Faroudja and others in "Improving NTCS to Achieve Near-RGB Performance ”, SMPTE Journal, August 1987.

The previously proposed methods, which seek to eliminate aberrations of luminance / chrominance intermodulation, suffer from one or more practical problems related to the commutation of aberrations in adaptive movement treatment systems or with the filtration complexity in terms of memory requirements and number of filter sockets, for example. The luminance / chrominance separation system described herein in accordance with the present invention uses a cooperative treatment technique with adapted coding and decoding processes. The system described here has an increased separation of luminance / chrominacy in the vertical and vertical-temporal directions with minimal degradation of the image, and avoids many of the drawbacks of known systems. In addition, the described system is compatible with the existing NTSC system.

In accordance with the principles of the present invention, it is a video signal encoder a signal component is treated to produce a first component with mutually exclusive image pixel groups of identical value within each group and separated by an odd number of lines Image Scan. Likewise, an additional signal component is treated to produce a second component with mutually exclusive image pixel groups of idyllic value within each group and separated by an odd number of image scan lines. The first and second components treated are combined by means of an invertible algorithm. In a decoder the inverse of the combining algorithm is used to separate the combined signal into its constituent parts, that is, the first component treated and the second component treated, without intermodulation of components.

In an illustrated embodiment of the invention, each group comprises a pair of specially correlated and vertically averaged pixels, separated by a horizontal scan line (1H), the luminance information being treated only for frequencies above the vertical detail band. The invertible combiner algorithm involves an additive and subtractive combination of a luminance component with a chrominance component of a chrominance subcarrier. In another illustrated embodiment of the invention, each group comprises a pair of specially correlated averaged pixels, separated 263H.

Figure 1 is an illustration of a luminance / chrominance coding and decoding technique according to an embodiment of the present invention, which uses a coding process with a line interval of 1H;

Figure 2 is a block diagram of an apparatus that implements the technique of Figure 1;

Figures 3 and 4 show aspects of the apparatus of Figure 2 in greater detail;

Figure 5 is an illustration of a luminance / chrominance coding and decoding technique according to another embodiment of the present invention, which uses a coding technique with a field range of 263H;

Figure 6 is a block diagram of an apparatus that implements the technique of Figure 5;

Figures 7 and 8 show aspects of the apparatus of Figure 6 in greater detail; Y

Figure 9 shows a part of the apparatus of Figure 2 in greater detail.

Figure 1 illustrates a process by which the luminance and chrominance components of a

016 186 standard NTSC television signal are encoded in a transmitter and decoded in a receiver. Figure 1 shows how an odd image field has, before being encoded, luminance information (Y) of a narrowed baseband, associated with odd horizontal image scanning lines, designated as Y1, Y3, Y5, Y7, etc., and interwoven baseband chrominance (C) information, associated with odd horizontal image exporation lines, designated C1, C3, C5, C7, etc. Within each odd field (and even fields not shown) of a given frame, non-overlapping, mutually exclusive groups of spatially correlated pairs of image elements (pixels) are treated, separated 1H, averaging pairs of lines vertically and replacing the values ​​of Original pixel by the average values ​​within each group of pixels. This process is performed separately for luminance and chrominance information. The averaging process is performed for all horizontal chrominance frequencies, but is only performed for horizontal luminance frequencies above approximately 1.8 MHz to preserve vertical detail information below approximately

1.8 MHz. The averaged chrominance information modulates a 3.58 MHz chrominance subcarrier that has an opposite phase of alnea line within the field before being combined with the averaged luminance information in a standard way to form a signal of Composite baseband color video. The modulated chrominance signal is then combined with the treated luminance information. The opposite phase of the linear line shown by the chrominance information as a result of the subcarrier modulation process produces additive and subtractive combinations of luminance and chrominance information within each combined luminance / chrominance information group. The additive and subtractive luminance / chrominance combinations associated with the combination process (for example, Y1 + 3 ± 1 + 3) represent an invertible algorithm to facilitate separation of the luminance and chrominance information at the receiver. More specifically, the chrominance subcarrier phase changes so that the phase of the modulated chrominance signal is the same from line to line for separate samples 263H within an image frame, but is the opposite for numbers of number line samples. odd separated 1H within a field and separated 263H within a frame. This phase change from line to line provides the subtractive aspect of an additive-subtractive invertible algorithm.

Decoding in a receiver employs a decoding process of pairs of lines within a field. A received coded composite signal is separated into high and low horizontal frequency bands. Above approximately 2 MHz, mutually exclusive non-overlapping groups containing separate 1H line pairs are added to produce high frequency luminance information, and subtracted to produce modulated chrominance information. The high frequency luminance information is added to the low frequency luminance information, and is subtracted to produce modulated chrominance information. The high frequency luminance information is added to the low frequency luminance information to reconstitute the luminance signal, and the modulated chrominance information is demodulated in the standard manner. The treatment system of separate pairs of lines 1H of Figure 1 shows an improved luminance / chrominance separation in the vertical dimension. The luminance signal produced after decoding pairs of lines (Y1 + 3, Y5 + 7, etc.) does not contain color crossing aberrations, and the chrominance component produced after decoding pairs of lines (C1 + 3, C5 + 7, etc.) lacks luminance cross-firing. The averaging of pairs of lines used in the coding process has a negligible effect on the resolution of the image due to the correlated height of the image information separated a line within the field or separated a field within a frame.

The encoding / decoding process of Figure 1 can be executed, as shown in Figure 2, as follows. In an encoder of a transmitter, a source of color television signals 10, for example, including a color camera, provides a luminance component Y and chroma color I and Q color difference signal components in digital form. The luminance component is filtered by means of a 1.8 MHz horizontal 12 lowpass filter to produce a low frequency YL luminance signal. The YL signal, after its investment by an inverter 14, is combined in an adder 16 with the original luminance signal (Y) to produce a high frequency YH luminance signal. A delay adapter unit 18 matches the transit times of the combined signals in the adder 16 by compensating the delay of the filter 12. The YH signal, which contains luminance frequencies above about 1.8 MHz, is subjected to a process of averaging pairs of lines separated 1H within a field, as discussed in relation to Figure 1, by means of a processor 20. A signal YH 'of the processor 20 is combined in an adder 32 with a low frequency luminance signal YL' coming from the output of a network 21 of separate lane delay 1H.

The color difference signal components I and Q of source 10 are filtered through a 0.5 MHz low pass filter 22 and a 1.3 MHz low pass filter 24, respectively, before being subjected separately to a process of averaging pairs of lines separated 1H in units 26 and 28. Chrominance signals I 'and Q' averaged by pairs of lines of units 26 and 28 are applied to a standard NTSC modulator 30 to quadrature to modulate a 3.58 MHz SC chrominance subcarrier. Included in unit 30 is a delay adapter network to equalize the transit times of the color difference signals of units 26 and 28 before modulating the chrominance subcarrier. A modulated chrominance signal C 'of modulator 30 shows a phase inversion of

016 186 line by line and combined in an adder 33 with a signal Y 'of adder 32 to produce an output NTSC signal that is conducted through a suitable transmission apparatus, for example, which includes RF modulation networks, to A television signal receiver. A line identifier signal FL is provided through a line identifier network 11 to switching control inputs of units 20, 26 and 28. The network 11 responds to the luminance component Y, particularly to the synchronization information of the luminance component Y. Signal F_L, together with a similar signal F_L provided to a receiver network 48 through a receiver line identification network 41 in response to the received NTSC signal, ensures that the coding and decoding processes of lines are synchronized so that they are developed with respect to the same pairs of lines. An apparatus suitable for use as networks 11 and 41 is shown in Figure 9.

In the television signal receiver, after RF demodulation and associated conventional input treatment to produce a baseband signal (not shown), the NTSC signal is filtered by means of a 2 MHz low pass filter 40 to produce the YL 'signal of low frequency luminance. The 2 MHz cutoff frequency of filter 40 together with the 1.8 MHz cutoff frequency of decoder filter 12 produces a 200 KHz protection band to reduce horizontal intermodulation. The YL 'signal, after its investment by an inverter 42, is combined with the NTSC signal received from total bandwidth in a combiner 44 to produce a high frequency video signal above 2 MHz. A delay network 46 compensates for the delay exhibited by the filter 40 and equalizes the trip time of the signals combined by the unit 44. The high frequency signal of the combiner 44 is processed by an averaging and differentiation unit 48 that processes pairs of 1H separate lines to divide the input signal into the high frequency luminance and chrominance components YH 'and C'. The high frequency luminance signal YH 'is combined in an adder 52 with the low frequency luminance signal YL' after the signal YL 'is subjected to a delay of lines of 1H through a unit 50, to produce a luminance signal Y 'of total bandwidth.

The modulated chrominance component C 'from unit 48 is conducted to a unit 54 that provides delay adaptation and quadrature demodulation functions to produce color difference signals I' and Q '. The signals I 'and Q' are processed through a chrominance processor 56 that includes gain and offset control circuits, for example, and the luminance signal Y 'is processed by a luminance processor 58 illustratively including control circuits of gain and level shift, before being applied to a matrix 60 to combine the luminance and chrominance signals to produce R, G and B signals representative of red, green and blue image. An exciting display stage 62 amplifies these signals to an appropriate level to drive an image display kinescope 64.

Figure 3 shows an averaging circuit of pairs of lines suitable for use in units 20, 26 and 28 of the coding arrangement of Figure 2. The input signals are filtered through a vertical lowpass filter 70 included to reduce the Vertical spurious aberrations that can occur with certain diagonal scene material. Filter 70 is optional. The filtered input signal is coupled through a 1H line delay unit 72 to an input A of an averaging network 74, and is directly coupled to an input B of the averaging network 74. A signal averaged by lines of the network 74 is directly coupled to an input of a line frequency multiplexer 76 (MUX), and to another input of the MUX 76 through a 1H line delay unit 78. A signal FL of network 11 is applied to a switching control input of MUX 76.

Figure 4 shows details of the line pair averaging / differentiator 48 of Figure 2. A unit 80 receives a delayed version by lines of the input signal at an input A through a 1H line delay unit 82, and receives the input signal itself at an input B. On one output an average signal (A + B) / 2 occurs, and on another output a differentiated signal (AB) / 2 occurs. Versions delayed by lines in 1H and not delayed from the average signal of the unit 80 are driven through a Mux 83 of line frequency and a vertical lowpass filter 84 to an output in which the YH signal is produced. Versions delayed by lines in 1H and not delayed from the differential signal of unit 80 are conducted through a MUX 86 of frequency of lines and a vertical bandpass filter 88 to an outlet in which the chrominance C signal develops. The FL signal is applied to a switching control input of MUX 83 and MUX 86. Output filters 84 and 88 are optional and serve essentially the same purpose as filter 70 in Figure 3.

Figure 5 illustrates another method by which the luminance and chrominance components of a standard NTSC television signal are encoded in a transmitter and decoded in a receiver without luminance / chrominance intermodulation. The method illustrated by Figure 5 is similar to that of Figure 1, except that in Figure 5, treatment of separate pairs of fields 263H is used instead of treatment of pairs of separate lines 1H.

In Figure 5 each odd field includes information of interlaced baseband luminacy associated with odd horizontal lines Y1, Y3, etc. of image exploration and chrominance information C1, C3, etc. of associated interlaced baseband. Each even field includes interlaced baseband luminance information associated with even horizontal lines Y2, Y4, etc. of image exploration and chrominance information C2, C4, etc. of associated interlaced baseband. Within each frame, pairs of separate lines 263H are processed in such a way that mutually exclusive groups not overlapping with separate pixels 263H are averaged vertically4

016 186 mind, replacing the averaged values ​​to the original values ​​within each group. This process is performed separately for luminance and chrominance information. The averaging period is executed for all horizontal chrominance frequencies, but is executed only for horizontal chrominance frequencies above approximately 1.8 MHz to preserve vertical luminance detail information below approximately

1.8 MHz. The averaged chrominance information modulates a 3.58 MHz chrominance subcarrier that has an opposite phase of line to line, before being combined with the averaged luminance information in a standard way to form a video signal. in composite baseband color. The line-to-line phase inversion shown by the modulated chrominance signal as a result of the chrominance modulation process produces additive and subtractive combinations of luminance and chrominance information within each combined luminance / chrominance information group. As in the case of the system of Figure 1, the additive and subtractive combination of luminance / chrominance represents an invertible algorithm to facilitate the separation of luminance / chrominance in the receiver.

The decoding in a receiver is essentially the same as that studied in relation to the arrangement of Figure 1, except that the arrangement of Figure 5 employs a process of decoding pairs of fields at 263H within a frame. The field pair treatment system of Figure 5 shows an improved separation of luminance-chrominance in the vertical-temporal dimension without aberrations of color crossing or luminance crossing.

The coding / decoding process of Figure 5 can be implemented as shown in Figure 6. The arrangement of Figure 6 is similar to that of Figure 2, except that Figure 6 uses networks 120, 121, 126, 128 , 148 and 150 of field treatment at 263H instead of line treatment networks at 1H, and field identification networks instead of lines to produce FF and FL signal field identifiers.

Figure 7 shows a 263H field pair averaging network suitable for use in the field pair averaging networks 120, 126 and 128 of the encoder of Figure 6. Figure 8 shows a field pair averaging / differentiator suitable for use in the decoding network 148 of Figure 6. The devices of figures 7 and 8 are similar to the devices of figures 3 and 4, except that the devices of figures 7 and 8 employ field pair treatment units at 263H instead of pair treatment units of lines at 1H.

Figure 9 shows devices suitable for use as networks 11 and 41 of Figure 2. An input signal, such as the luminance component Y in the case of a generator 11, is applied to a synchronism separator and signal generator of time 160. The generator 160 includes a synchronization signal separator and sensor circuits and counter circuits to produce a horizontal beam suppression interval signal that is applied to a clock input (CLK) of a line counter 165, and to produce a signal of vertical beam suppression interval that is applied to a RESET input (reset) of line counter 165. The counter 165 is reset at the end of each vertical beam suppression input signal and then begins a horizontal line count process in response to the clock input beam suppression signal. The OUTPUT signal is obtained by perceiving the least significant bit of the line count to produce a low logic level for even lines and a high logic level for odd lines, for example. Apparatus suitable for use as the field identification networks shown in Figure 6 for producing signals F_F and F_F/ field identifiers can be easily developed in the manner explained, for example, in the “CIRCUIT CONCEPTS” text by Gerald A. Eastman, pages 88-92, available from Tektronix, Inc., Beaverton, Oregon, USA.

The principles of the present invention can be used to code, combining and separating then signals other than the luminance and chrominance components described. In such a case, one of the signals that will be combined must show a phase change from line to line (that is, it has a substantial negative correlation) within a field or within a frame in order to develop an invertible algorithm. , such as the illustrated algorithm that uses a combination of additive and subtractive signal. The required phase change may be inherent in the nature of such a signal, or it may be produced by external means, such as a modulation process.

The principles of the present invention can also be used to develop an encoder / decoder arrangement of a cooperating frame processor, where the elements to be grouped are separated 525H, that is, separated from a frame, instead of 1H 0 263H as He has illustrated.

Explanation of symbols of the figures

<td colspan="2">Fig. 1</td>

<td>CI =</td><td>odd fields before coding;</td>

<td>PPL =</td><td>averaging of pairs of lines (above 1.8 MHz for luminance)</td>

<td>CO =</td><td>combination</td>

<td>DPL =</td><td>decoding of pairs of lines</td>

<td>LUM =</td><td>luminance (no color crossing)</td>

<td>CRO =</td><td>chrominance (no luminance crossing)</td>

<td colspan="2">Fig. 2 and 6</td>

<td>TRA</td><td>= transmitter</td>

<td>REC</td><td>= receiver</td>

S NTSC = NTSC signal Fig. 3

Line pair averaging in the encoder

016 186

E = input S = output

Fig. 4

Averaging / differentiating pairs of lines in the decoder

E = input; S YH = YH signal output; SC = signal output C; RL = line delay

<td colspan="2">Fig. 5</td>

<td>PC</td><td>= pairs of fields before</td>

<td>PPC</td><td>dify = peer averaging</td>

<td>CO</td><td>of fields (above 1.8 MHz for luminance) = combination</td>

<td>DFP</td><td>= decoding pairs of</td>

<td>Lum</td><td>fields = luminance (no color crossing</td>

<td>CRO</td><td>= chrominance (no luc crossing</td>

<td>Fig. 7</td><td>minancia)</td>

Averaging pairs of fields in the encoder

Symbols 170 ... 178 are equivalent to those in Figure 3 (70 ... 78) replacing lines with fields.

E = input; S = output Fig. 8

Averaging / differentiating field pairs in the decoder

The symbols 180 ... 188 are equivalent to those in Figure 4 (80 ... 88) replacing lines with fields.

E = input; S YH '= signal output YH'; SC '= = signal output C'; RC = field delay

Fig. 9

E = input

S = output

SH = horizontal beam suppression

SV = vertical beam suppression

CLK = clock

RESET = reposition

016 186