Quadruplex encoder and decoder for EDTV system

By employing different independent polarity codes to polarity-modulate respective quads of averaged values in the vertical-temporal plane of luma, chroma, sidepanel and enhanced-luma components in the mid-frequency and/or high-frequency split-bands of a 4.2 MHz baseband television-type signal, the encoded components can be combined into successive composite quads of an encoded single channel, NTSC compatible, enhanced-definition 4.2 Mhz bandwidth television signal. The successive composite quads of the encoded signal can be decoded by a widescreen receiver without crosstalk taking place among the components, while such an encoded signal does not noticeably affect the display of a standard NTSC receiver.

BACKGROUND OF THE INVENTION 
This invention relates to encoders and to decoders for highly-correlated 
information signals and, more particularly, to such encoders and decoders 
for use in connection with a single channel, NTSC-compatible, widescreen 
enhanced-definition television (EDTV) system. 
As is known, an original widescreen signal, comprised of a center panel and 
left and right sidepanels, has its center panel time-expanded and its left 
and right sidepanels time-compressed prior to such signal being broadcast 
as an NTSC compatible 4.2 MHz baseband signal to both widescreen receivers 
and standard NTSC receivers. When received by a widescreen receiver (i.e., 
one displaying a picture having an aspect ratio such as 2:1, 16:9 or 5:3), 
the time-expanded center panel is compressed to its original size and the 
time-compressed sidepanels are expanded to their original size before 
picture display takes place (thereby reproducing the entire original 
widescreen picture on the screen of the widescreen receiver). The use of 
signal compression techniques for the sidepanels of the picture takes 
advantage of the horizontal overscan region of a standard NTSC television 
receiver display, so that such a standard NTSC receiver displays only the 
time-expanded center panel on its standard 4:3 aspect ratio screen (the 
time-compressed sidepanels being hidden due to the horizontal overscan). 
A single channel NTSC compatible, widescreen EDTV television signal 
includes more information than is normally included in a conventional NTSC 
4.2 MHz baseband television signal. A conventional NTSC signal includes 
luma information in a frequency band up to 4.2 MHz and chroma information 
in a more limited band which modulates a 3.58 MHz sub-carrier. A single 
channel, NTSC compatible, widescreen EDTV signal includes both 
high-frequency luma information in a band above 4.2 MHz. and sidepanel 
information, in addition to the luma and chroma information of a 
conventional NTSC signal. Ideally, this additional information should be 
encoded in manner such that it can be decoded at a widescreen receiver 
without any crosstalk taking place between the different types of encoded 
information, and without causing any degradation of the picture displayed 
by a standard NTSC receiver due to the presence of such encoded 
information. 
Reference is now made to co-pending application Ser. No. 07/139,338, filed 
Dec. 29, 1987 by Isnardi et al., and assigned to the same assignee as the 
present application. This application discloses a single channel, NTSC 
compatible, widescreen EDTV system in which the original widescreen signal 
is comprised of high-frequency luma and sidepanel components, in addition 
to a main component comprised of the time-expanded center panel and 
time-compressed sidepanel low frequencies. Each of these three components 
is separately intraframe averaged. Intraframe averaging involves averaging 
the pixels values of each pair of neighboring image pixels in the 
vertical-temporal plane defined by the two interlaced fields of each NTSC 
frame. Such intraframe averaging significantly reduces the image data that 
need be transmitted, without introducing any significant error, since the 
image data defined by such a pair of neighboring pixels is almost nearly 
always highly correlated in any single frame. The intraframe-averaged 
high-frequency sidepanel and luma components quadrature-modulate a 
sub-carrier, which quadrature-modulated sub-carrier is then added to the 
intraframe-averaged main component, thereby providing an NTSC compatible 
4.2 MHz baseband signal. 
The use in the Isnardi et al. application of intraframe averaging allows 
perfect separation (i.e., no crosstalk) in the vertical-temporal plane of 
the main component and each of the two quadrature-modulated components by 
the decoder in the widescreen receiver. However, the main component in 
Isnardi et al. includes both the luma and chroma portions of a standard 
NTSC signal. Intraframe averaging does not allow for separation of luma 
and chroma in the widescreen receiver. They need to be separated therein 
by some other means, such as by linear, time-invariant, vertical-temporal 
filtering of luma and chroma. If such filters were ideal, no crosstalk 
would take place. However, in practice, no such filter is ideal. 
Therefore, significant unwanted crosstalk does take place between the luma 
and chroma portions of the main component and the other additional 
information components. Furthermore, luma, time-invariant, 
vertical-temporal filtering and intraframe averaging do not co-exist 
synergistically: they tend to fight each other. Furthermore, as single 
channel, NTSC compatible, widescreen EDTV system development continues, it 
becomes apparent that more and more additional information components need 
be included in the television signal transmitted to both widescreen 
receivers and standard NTSC receivers. This means that the information 
contained in the luma and chroma must be reduced even more than it is 
reduced by intraframe averaging, but still without any great detriment to 
the picture displayed by either the widescreen receiver or by the standard 
NTSC receiver. The quadruplex encoding and decoding technique of the 
present invention permits a single channel, NTSC compatible, widescreen 
EDTV system to transmit a large number of information components, 
including both luma and chroma, to both widescreen and standard NTSC 
receivers in a manner which permits the information to be separated into 
its various components by the decoder of each widescreen receiver without 
any significant amount of crosstalk between the various information 
components taking place, and without any significant degradation of the 
picture quality displayed by standard NTSC receivers. 
SUMMARY OF THE INVENTION 
From a broad point of view, the quadruplex.encoder the present invention 
operates on four separate series, in which each series is comprised of 
successive independent values of a parameter. The parameter represented by 
any one series may be different from the respective parameters represented 
by each of the other three series or, alternatively, they may represent 
the same parameter as one or more of the other three series. In any case, 
each of the four series is polarity-modulated by a different predetermined 
polarity code that permit the four polarity-modulated series to be 
combined into a single signal that can be later separated back into the 
original four series by the quadruplex decoder of the present invention. 
While not limited thereto, the quadruplex encoder and quadruplex decoder of 
the present invention are particularly suitable for use in a single 
channel, NTSC compatible, widescreen EDTV system because one of the four 
different predetermined polarity codes corresponds to the polarity coding 
of chroma inherent in the NTSC standard. 
More specifically, the present invention is directed to a quadruplex 
encoder for multiplexing components of a televisiontype signal that 
includes a luma component, a chroma component, and at least one additional 
component. The encoder comprises first means for converting the signal 
into successive sets of four ordinally-arranged information quads, each of 
the quads being comprised of up to four separate values including a single 
chroma component value, at least one luma component value, and one value 
for each additional component included in a quad. The encoder comprises 
second means for polarity-modulating the respective values of chroma the 
component of the four ordinally-arranged quads of each successive set with 
a first specified one of the following three polarity codes which have 
relative polarities of (a) ++-- or, alternatively, --++, (b) +--+ or, 
alternatively, -++-, and (c) +-+- or, alternatively, -+-+, respectively. 
The quadruplex encoder further comprises third means for 
polarity-modulating the respective values of the one additional component 
of four ordinally-arranged quads of each successive set with the second 
specified one of the three codes (a), (b) and (c), respectively. The 
respective values of the luma component of the four ordinally-arranged 
quads of each successive set all have the same polarity, whereby, in 
effect, the respective values of the one luma component are 
polarity-modulated with a fourth polarity code having a relative polarity 
of (d) ++++ or, alternatively, ----. Finally, the quadruplex encoder 
comprises fourth means for separately summing, in order, the 
polarity-modulated values of luma, chroma, and additional components 
included in the quads of the respective first, second, third and fourth of 
the four ordinally-arranged quads of each successive set, thereby deriving 
successive composite quads each of which is comprised of the resulting 
respective four ordinally-arranged summation values of that set. 
The present invention is also directed to a quadruplex decoder for 
demultiplexing successive encoded composite quads supplied thereto. The 
quadruplex decoder comprises first means including at least one matrix 
means responsive to each of the successive composite quads supplied 
thereto for resolving the four values of a composite quad into the 
components thereof. The matrix means derives up to four separate outputs, 
the separate outputs including at least outputs substantially proportional 
to the value of that composite quad's chroma component, an output 
substantially proportional to the value of that composite quad's one 
additional component, and an output substantially proportional to one 
value of that composite quad's luma component. The decoder further 
comprises second means for supplying successive composite quads to the 
first means. 
One important advantage of the quadruplex encoding and decoding technique 
employed by the present invention is that it substantially avoids 
crosstalk among the multiplexed components from taking place.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 diagrammatically illustrates a vertical-temporal image plane of a 
television-type signal in which the occurrence of successive scan lines in 
the vertical image dimension are plotted against the occurrence of 
successive interlaced television fields in the temporal dimension. Thus, 
in FIG. 1, the horizontal image dimension of each scan line is in a 
direction into the paper. It will be noted that the occurrence of image 
information in the vertical-temporal plane is digital in nature (i.e. both 
the scan lines in the vertical dimension and the interlaced fields in the 
temporal dimension occur as image sample values that are discrete and 
countable). However, at the present time, successive image values in the 
horizontal dimension occur in analog form, rather than in digital form. 
While the principle of the present invention could be applied to image 
information in analog form, it is not practical to do so. It is for this 
reason that the following description of the present invention is confined 
to the vertical-temporal plane. However, it should be understood that if 
in the future a completely digital television signal becomes the standard, 
it would be then practical to employ the present invention with digital 
sampled image values in the horizontal-vertical image plane, as well as in 
the vertical-temporal image plane. 
FIG. 1 shows various ways in which image values 100 in the 
vertical-temporal image plane can be organized into information quads, 
each of which is made up of four adjacent image values 100 in the 
vertical-temporal image plane. Because they are adjacent, there is an 
extremely high probability that image information contained in each of the 
four image values of the quad are highly correlated with one another. An 
exception would be the relatively rare case in which an edge intersects a 
particular quad. Specifically, as shown in FIG. 1, the image values 100 of 
the vertical-temporal image plane may be organized into four different 
shapes of quads. A first and second of the four different shape quads are 
comprised of quad 102-u and 102-d, each of which is comprised of scan 
lines from each of four consecutive interlaced fields. The shape of quad 
102-u is designated an up-quad, while the shape of 102-d is designated a 
down-quad. Similarly, quad 104-u is designated an up-quad and 104-d is 
designated a down-quad. However, quads 104-u and 104-d are each comprised 
of two consecutive scan lines from each pair of two consecutive interlaced 
fields. In practice, the vertical-temporal image plane of image value 100 
is organized into a set of successive information quads of the same 
preselected one of the four types of quads shown in FIG. 1. 
As known, television conforming to the NTSC standard is comprised of 
successive color frames, each of which color frames is made up of two 
consecutive image frames and each of the two image frames is made up of 
two consecutive interlaced fields. In an NTSC signal, the relative 
polarity of all image values of the luma component is the same, but the 
relative polarity of the image values of the chroma component (i.e., the 
modulated color-carrier) varies during a color frame in a predetermined 
manner. FIG. 2 shows how the relative polarity of the image value of a 
chroma-component quad varies in accordance with (1) the predetermined 
shape of the quad and (2) the relative position of the quad with respect 
to the beginning of a color frame. 
Up-chroma quad 102-u may be positioned in alignment with image frames 1 and 
2 of the same color frame (as indicated by quad 200a) or, alternatively, 
up-chroma 102-u may be positioned in alignment with image frames 2 of one 
color frame and image frame 1 of the immediately following color frame (as 
indicated by 200b). In a similar manner, down-chroma quad 102-d may be 
aligned either like quad 200a or like 200b.(as indicated by quads 202a and 
202b, respectively) 
In the case of up-chroma quad 102-u, the relative polarity code of the four 
chroma values C1 C4 is ++-- (for quad 200a) or, alternatively, --++ (for 
quad 200b). In the case of down chroma quad 102-d, the relative polarity 
code is +--+ (for quad 202a) or, alternatively, -++- (for quad 202b). The 
polarity codes for 200a and 200b are not independent, since one is merely 
the inverted form of the other. For the same reason, polarity codes 202a 
and 202b are not independent. However, the polarity code for either quad 
200a or 200b is independent of the polarity code for either quad 202a or 
200b. Further, aligning the beginning of an up-chroma quad 102-u with the 
second field of either the first or second image frame of a color frame 
results in up-chroma quad 102-u exhibiting one of the non-independent 
polarity codes +--+ or -+ +-. Should the beginning of a down-chroma quad 
102-d be aligned with the second field of image frame 1 or 2 of a color 
frame, the resulting polarity code is either --++ or ++--. Thus, the only 
effect of aligning the beginning of a chroma quad with the second field of 
an image frame, rather than a first field of an image frame, is to 
interchange the polarity codes employed by the respective up and down 
chroma quads 102-u and 102-d. 
Each of chroma quads 104-u and 104-d occupies only an image frame, rather 
than an entire chroma frame. Thus, there are two successive chroma quads 
104 during each color frame. In the respective image frames 1 and 2, 
up-chroma quad 104-u has each of the two alternative non-independent 
polarity codes +-+- (quad 204a) and -+-+ (quad 204b). Down-chroma quad 
104-d has each of the respective alternative non- independent polarity 
codes +--+ (quad 206a) and -++-. Should any of chroma quads 104 begin on 
the second field of either image frame 1 or 2 of a color frame, the result 
would be to interchange the above-described relative polarity codes for up 
and down chroma quads 104-u and 104-d, respectively. 
The following four polarity codes are independent of one another: 
(a) ++-- or, alternatively, --++; 
(b) +--+ or, alternatively, -++-; 
(c) +-+- or, alternatively, -+-+; 
(d) ++++ or, alternatively, ----. 
From the foregoing discussion, it is apparent from the above discussion 
that a chroma quad of an NTSC signal always conforms to a certain 
specified one of polarity codes (a), (b), and (c). It is also apparent 
that a luma quad, corresponding in shape to a chroma quad, conforms to 
polarity code (d). Which one of polarity codes (a), (b) and (c) is the 
specified certain one depends on whether the shape the chroma quad 
conforms to that of up-chroma quad 102-u, down-chroma quad 102-d, 
up-chroma quad 104-u or down-chroma quad 104-d, and also depends on 
whether this chroma quad begins in the first, second, third or fourth of 
the four consecutive fields of a color frame. However, in any event, there 
will always remain two independent ones of polarity codes (a), (b) and 
(c), other than the aforesaid certain specified one thereof, which can 
used to encode up to two additional components of a television-type 
signal. 
More specifically, the present invention makes use of the aforesaid four 
independent polarity codes in a single channel, NTSC compatible, 
widescreen enchanced-definition television system, such as the type of 
system disclosed in the aforesaid co-pending Isnardi et al. application. 
In such a system, an NTSC compatible 4.2 MHz baseband signal is derived 
which includes luma and chroma information in NTSC standard form, and also 
includes additional widescreen side panel information and additional 
chroma information and additional high frequency and additional 
high-frequency luma information above 4.2 MHz. As discussed above, these 
two additional components must be incorporated into the 4.2 MHz baseband 
signal in such a manner that these additional components will be 
substantially unnoticeable to a viewer of a displayed television picture 
on a standard NTSC receiver receiving the aforesaid 4.2 MHz baseband 
signal, although they can be decoded and used by a widescreen enhanced 
definition receiver. 
Referring now into FIG. 3, there is shown a block diagram of one species of 
a quadruplex encoder embodying the present invention for use in a single 
channel, NTSC compatible, widescreen enhanced-definition television 
system. For illustrative purposes, it is assumed that quads conforming in 
shape and color-frame alignment to either up-chroma quad 200a or 
down-chroma quad 202a are utilized by the encoder of FIG. 3. Further, 
while an NTSC compatible signal transmitted to receiver is an analog 
signal, the respective blocks of quadruplex encoder of FIG. 3 may be 
implemented in digital form, in which case a digital-to-analog converter 
may be utilized to change the signal to analog form prior to its 
transmission to a receiver. 
As shown in FIG. 3, four separate information components (comprised of a 
luma component Y, an enhanced-information modulated H carrier component, a 
chroma modulated C carrier component, and a sidepanel modulated S carrier 
component) are applied as inputs to the quadruplex encoder. Specifically, 
the modulated C carrier is applied as an input to quad averager 300, which 
averages the four correlated image values of each successive chroma quad. 
Were the modulated C carrier applied as an input to quad averager 300 in 
conformity with the NTSC polarity standards (shown by the chroma quads of 
FIG. 2), the average value would always be substantially zero because two 
of the four fields of a color frame are of positive polarity and two of 
the fields are of negative.polarity. In order to prevent this, the 
modulated C carrier input to quad averager 300 has the same phase every 
field (i.e., each successive quad of the input has polarity code (d), 
rather than some certain one of polarity codes (a), (b) and (c) in 
accordance with NTSC chroma standards). 
Quad averager 300 includes memory or delay means and summing means for 
deriving an output chroma quad in which all four chroma values thereof are 
the same given proportion of the mean average of th four correlated chroma 
image values in the vertical-temporal plane of each successive input 
chroma quad. Thus, all four values of an output chroma quad from quad 
averager 300 are the same as one another. Each of the successive output 
chroma quads from quad averager 300 are applied as an input to 
polarity-modulator 302. Polarity modulator 302 includes a switch 
responsive to a polarity-pattern pulse for either inverting or not 
inverting the polarity of each chroma value applied as an input thereto. 
The polarity-pattern pulse is generated by a counter and appropriate 
gates, which counter is clocked at the field rate and is reset at the 
color frame rate. Thus, each successive counter cycle is comprised of four 
successive fields. If the chroma quad should conform to up-chroma quad 
200a, polarity-modulator 302 modulates each successive chroma with 
polarity code (a). If the chroma should conform to down chroma 202a, 
polarity 302 modulates each successive chroma quad with polarity code (b). 
The successive polarity-modulated chroma quads are applied as a seperate 
input to adder means 204. 
The successive sidepanel quads which are applied as an input to quad 
averager 306 and the successive enhanced-luma quads which are applied as 
an input to quad averager 308 correspond with the successive chroma quads 
applied as an input to quad averager 300. Further, quad averagers 306 and 
308 are generally similar to quad averager 300 and polarity-modulators 310 
and 312 are generally similar to polarity-modulator 302. However, 
polarity-modulator 310 polarity-modulates the four mean average values of 
each successive sidepanel quad from quad averager 306 with a first 
specified one of polarity code (a), (b) and (c) other than the polarity 
code employed by chroma polarity-modulator 302. In a similar manner, 
polarity-modulator 312 polarity-modulates the four mean average values of 
each successive enhanced-luma quad from quad averager 308 with the 
remaining one of polarity codes (a), (b) and (c) that is not employed by 
either polarity-modulators 302 or 310. The respective outputs of 
polarity-modulators 310 and 312 are applied as separate inputs to adder 
means 304. 
The luma input is split into first and second frequencies respectively 
below and above 1.8 MHz by bandsplit filter 314. The first band below 1.8 
MHz is applied as a separate input to adder means 304. The second band, 
after being intra-framed averaged by intra-frame averager 316, is split 
into third and fourth bands respectively above and below 3.0 MHz by 
bandsplit filter 318. The third band, which comprises frequencies between 
1.8 and 3.0 MHz, is applied a separate input to adder means 304. The 
fourth band above 3.8 MHz, after being extra-framed averaged by 
extra-frame averager 320, is applied as a separate input to adder means 
302. 
Intra-framed averagers, which are disclosed in the aforesaid co-pending 
Isnardi et al. application, average the two values in each image frame. 
This average may be a mean average of the two correlated image values of 
the two interlaced fields of each image frame. However, preferably the 
intra-frame average should be weighted in accordance with detected image 
motion in the temporal dimension. More specifically, in FIG. 3, motion 
detector 322, which is responsive to the respective first-band luma values 
in each successive low-frequency luma quad, computes the value of a 
motion-indicating factor K which controls the weighting of intra-framed 
averager 316 in a manner to be discussed in more detail below. Extra-frame 
averaging consists of averaging the correlated image values of the first 
field and of the second fields. respectively, of the two successive image 
frames making up a color.frame. Thus, the combined effect of intraframed 
averager 316 and extra-framed averager 320 on the luma quad of the first 
frequency band is equivalent to that of a quad averager. If desired, one 
could move intra-frame averager 316 into the third frequency band and 
substitute a quad averager for extra-frame averager 320 in the fourth 
frequency band without affecting the operation of the quadruplex encoder. 
However, this is undesirable because a quad averager operating in the 
vertical-temporal plane requires substantially more memory than does an 
extra-frame operating in the vertical-temporal. 
The video output from adder means 304 is an NTSC compatible 4.2 MHz 
baseband signal comprised of successive composite quads of image 
information. 
In the following discussion of the operation of the quadruplex encoder 
shown in FIG. 3, it is assumed that the luma input is a 4.2 MHz baseband 
signal; the spectrum of the modulated C carrier, which is comprised of a 
1.5 MHz in-phase component" and a 0.5 MHz quadrature-phase component, lies 
entirely in a band between 1.8 and 4.2 MHz; the 2.0 MHz bandwidth spectrum 
of the modulated S carrier also lies entirely in a band between 1.8 and 
4.2 MHz; and the 1.0 MHz bandwidth spectrum of the modulated H carrier, 
which defines enhanced luma information between 4.2 and 5.2 MHz, lies in a 
band between 3.0 and 4.2 MHz. It is further assumed that intra-frame 
averager 316 can read out from memory each of the two intra-frame averaged 
luma values, computed for each of the two consecutive image frames of a 
color frame, in any one or more of the four ordinally-arranged quad 
positions of each successive luma quad input to bandsplit filter 318. It 
is first assumed that the vertical-temporal plane has been organized into 
up-chroma quads 200a, so that the C component is polarity-modulated with 
polarity code (a); that polarity code (b) is specified for the S component 
and polarity code (c) is specified for the H component. In accordance with 
this first assumption, the following equations define the respective four 
values L1, L2, L3 and L4 of each successive ordinally-arranged composite 
quad output from adder means 304 for the high-frequency band above 3.0 
MHz, for the mid-frequency band between 1.8 and 3.0 MHz, and for the 
low-frequency band below 1.8 MHz, respectively. More specifically, the 
equations for the high-frequency band are: 
EQU L1=Y+C+S+H 
EQU L2=+C-S-H 
EQU L3=Y-C-S+H 
EQU L4=Y-C+S-H 
where Y, C, S and H are the quad-averaged values of each of these 
respective components employed for each successive composite quad. 
The equations for the mid frequency band are: 
EQU L1=Ya+C+S 
EQU L2=Yb+C-S 
EQU L3=Ya-C-S 
EQU L4=Yb-C+S 
where Ya and Yb, respectively, are the computed averages by intra-frame 
averager 316 for the first and second image frames of a color frame, 
respectively. The H component does not appear in the mid-frequency band 
equations because its frequency spectrum is confined solely to the 
high-frequency band. 
The equations for the low-frequency band are: 
EQU L1=Y1 
EQU L2=Y2 
EQU L3=Y3 
EQU L4=Y4 
where Y1, Y2, Y3 and Y4 are the four independent ordinally-arranged values 
of the luma component Y in the low-frequency band. The C and S components 
do not appear in the low band equations because the frequency spectra 
thereof are confined solely to the mid-frequency and high-frequency bands. 
In each of the high-frequency, mid-frequency, and low-frequency bands the 
set of the four equations L1, L2, L3 and L4 are independent of one 
another. This independence makes it possible to separate the luma Y, 
chroma C, sidepanel S and enhanced-luma H components from one another 
without any crosstalk therebetween by the quadruplex decoder incorporated 
in a widescreen enhanced-definition television receiver, while permitting 
a standard NTSC receiver to properly display the luma and chroma 
components. In this regard, the fact that the mid-frequency band is 
comprised of only three of the four components and contains two 
independent values of the luma places certain constraints on the set of 
equations for the up-quad pattern (i.e., in which chroma component C must 
be polarity-modulated with polarity code (a) ). First, it is essential 
that each of the two independent luma component values Ya and Yb be 
associated with both of opposite-polarity chroma component values C in 
order that NTSC compatibility be achieved. Second, in order to attain 
independence, it is essential that the respective polarities of both 
chroma C and sidepanel S components associated with one of the Ya luma 
component values be opposite to the polarities of the chroma C and 
sidepanel S components associated with the other Ya luma component value 
(and similarly for the Yb luma component values). In order to meet this 
latter constraint for the up-quad pattern the sidepanel component must be 
polarity-modulated by polarity code (c), as was assumed above. Thus, the 
set of equations for L1, L2, L3 and L4 set forth above for the up-quad 
pattern is the only set of equations that can be employed for the up-quad 
pattern. 
In a down-quad pattern, the chroma component must be polarity modulated by 
polarity code (b), as indicated by down-chroma quad 202a, in order to 
conform to the NTSC standard. Polarity modulating the chroma quad with 
polarity code (b) permits two different sets of equations for L1,L2 L3, 
and L4, both of which conform to the above-discussed constraints on the 
set of equations for the mid-frequency band. 
In a first of these two sets of equations, the respective values of L1, L2, 
L3 and L4 for the mid-frequency band are: 
EQU L1=Ya+C+S 
EQU L2=Yb-C+S 
EQU L3=Ya-C-S 
EQU L4=Yb+C-S 
Therefore, L1, L2, L3 and L4 for the high-frequency band of this first set 
of equations are: 
EQU L1=Y+C+S+H 
EQU L2=Y-C+S-H 
EQU L3=Y-C-S+H 
EQU L4=Y+C-S-H 
It will be noted that in this first set of equations for a down pattern, 
the sidepanel S component is polarity-modulated with polarity code (a) and 
the enhanced-luma H component is polarity-modulated with polarity code 
(c). 
In a second set of equations for L1, L2, L3 and L4 for the down pattern, 
the sidepanel S component is polarity-modulated with polarity code (c) and 
the enhanced-luma H component is polarity-modulated with polarity code 
(a). Specifically, L1, L2, L3 and L4 of the mid-frequency band of the 
second set of equations for the down quad are: 
EQU L1=Ya+C+S 
EQU L2=Ya-C-S 
EQU L3=Yb-C+S 
EQU L4=Yb+C-S 
Therefore, L1, L2, L3 and L4 for the high-frequency band of the second set 
of equations of the down pattern are: 
EQU L1=Y+C+S+H 
EQU L2=Y-C-S-H 
EQU L3=Y-C+S-H 
EQU L4=Y+C-S+H 
The respective values of L1, L2, L3 and L4 for the low-band of both the 
first and second sets of equations of the down pattern are identical to 
those described above for the up pattern. 
The mid-band frequency luma component value Ya and Yb are two computed 
values derived by intraframe averager 316. Usually Ya is a mean average or 
other averaging function of Y1 and Y2 of each successive 
ordinally-arranged luma quad, and Yb is usually the mean average or other 
averaging function of Y3 and Y4 of each successive ordinally-arranged.luma 
quad. However, in principal, this need not be the case. For example, Ya 
could be the mean average of Y1 and Y3 and Yb could be the mean average of 
Y2 and Y4 (which amounts to extra-frame averaging), but with Ya still 
being derived in the Y2 ordinal position within a luma quad, and with Yb 
still being derived in the Y3 ordinal position in a luma quad. This would 
be equivalent to a swapping lines L2 and L3 in the first set of the down 
pattern. 
Line-swapping is a tempting approach, especially when motion- adaptation 
becomes important, because re-arranging values of +C's and -C's would 
cause grossly incorrect colors, while swapping temporarily adjacent lines 
is relatively benign. However, this line-swapping technique has inherent 
difficulties when only a portion of the band is swapped. Because of 
non-ideal horizontal filtering around the 1.8 MHz point, some signal 
elements in the transition band will not be correctly swapped back into 
place by the widescreen enhanced-definition television receiver, while 
some that should not be swapped will be swapped by the receiver. If one 
could lower the frequency from 1.8 MHz all the way to zero, the 
line-swapping technique would work for the widescreen receiver, but, even 
then a standard NTSC receiver display would look terrible whenever 
something in the displayed picture moves. 
It has been found that a desirable way to provide for motion adaptation in 
the computation of respective luma values for Ya and Yb in intra-frame 
averager 316 is to employ the following averaging functions: 
EQU Ya =K(Y1+Y2)/2+(1-K) (Y1) 
EQU Yb=K(Y3+Y4)/2+(1-K) (Y4) 
where K is a motion-indicating factor having a fractional value between 
zero and unity, in which zero represents absence of motion in the temporal 
dimension and unity represent maximum motion in the temporal.dimension. 
Motion detector 322, which is responsive to the four independent values Y1, 
Y2, Y3 and Y4 of each ordinally-arranged quad of the low-frequency luma 
component, computes the value of the motion-indicating factor K in 
accordance with the following equations: 
EQU .DELTA.T=.vertline.(Y1+Y2)-(Y3+Y4).vertline. 
EQU .DELTA.V=.vertline.(Y1+Y3)-(Y2+Y4).vertline. 
EQU and 
EQU K=.DELTA.T/(.DELTA.T+.DELTA.V) 
A widescreen enhanced-definition television receiver includes a quadruplex 
decoder for separating the 4.2 MHz baseband signal comprised of successive 
composite quads back into its constituent components. The quadruplex 
decoder shown in FIG. 4 cooperates with the quadruplex encoder shown in 
FIG. 3. 
Referring to FIG. 4, bandsplit filter 400 splits the successive composite 
quads of the baseband signal applied as an input thereto into first and 
second frequency bands respectively below and above 2.0 MHz. The 2.0 MHz 
employed by bandsplit filter 400 provides a 0.2 MHz guard band with 
respect to the 1.8 MHz employed by bandsplit filter 314 of the quadruplex 
encoder of FIG. 3. This guard band is desirable, although not essential, 
because it guards against crosstalk in the horizontal dimension of the 
image display. 
The low-frequency first band is applied as an input to motion detector 402 
and is also applied as one input to adder means 404. The second frequency 
band from filter 400 is applied as an input to first matrix means 406. 
First matrix means 406, described below, which operates on the frequency 
band of each successive composite quad extending from 2.0 to 4.2 MHz, 
derives Y, chroma C and sidepanel S and H' outputs. The H' output includes 
the enhanced-luma H component in the high-frequency band above 3.0 MHz and 
also includes a luma-difference component proportional to the difference 
between Ya and Yb in the mid-frequency band below 3.0 MHz. Bandsplit 
filter 408, which splits the H' output into third and fourth bands 
respectively below and above 3.0 MHz, separates the enhanced-luma H 
component in the high-frequency fourth band from the luma-difference 
component in the mid-frequency third band. This luma-difference component 
from bandsplit filter 408 and the luma component from first matrix means 
406 are applied as respective first and second inputs to second matrix 
means 410, described below. The output from second matrix means 410 is 
applied as a first input to motion decoder 412, which has the 
motion-indicating factor K applied as a second input thereto from motion 
detector 402. The output from motion decoder 412 is applied as a second 
separate input to adder means 404. The output from adder means 404 
comprises the luma component over its entire 4.2 MHz baseband frequency 
range. 
First matrix means 406, which is preferably implemented in digital form, 
comprises memory delay means sufficient to permit the respective values of 
L1, L2, L3 and L4 of each successive composite quad applied as an input 
thereto to be derived simultaneously. This permits the matrixing of the 
four respective values of L1,L2, L3 and L4 as a predetermined algebraic 
sum thereof. Matrix means 406 includes two such matrices, one for 
resolving the value of the chroma C component and another for resolving 
the value of the sidepanel S component of each successive composite quad. 
The resolved chroma C and sidepanel S components are then applied as 
respective outputs from first matrix means 406 to appropriate 
chroma-carrier and sidepanel-carrier decoders. 
The Y and H' components are not resolved by first matrix means 406. 
Specifically, both the Y and H' outputs from first matrix means 406 are 
still comprised of the four separate values L1, L2, L3 and L4 from each 
successive composite quad. However, in the case of the Y component output, 
all the four separate values have the same polarity as one another; while, 
in the case of the H' output, the four separate values have a set of 
predetermined polarities which are not the same as one another. The 
luma-difference component, applied as the first input to second matrix 
means 410, has the same predetermined polarities as the H' output from 
first matrix means 406. 
The Y input to second matrix means 410 is proportional to a fully 
quad-averaged value of Y in both the mid-frequency band and the 
high-frequency band, while the luma-differnce input to second matrix means 
410 is proportional to the difference of Ya-Yb in only the mid-frequency 
band. Second matrix means 410 includes first and second matrices, both of 
which are responsive to the luma-difference (Ya-Yb) and Y inputs applied 
thereto, for respectively resolving the value Ya in the first matrix and 
resolving the value of Yb in the second matrix. Further, second means 410 
includes an appropriate memory or delay means for restoring the relative 
position of the restored values of Ya and Yb, respectively, to the first 
and to the second image frames of each successive quad. Therefore, the 
output from second matrix means 410 is comprised of respective values of 
Ya and Yb in the mid-frequency band of the luma component and a fully 
quad-averaged value of Y in the high-frequency band of the luma component. 
In the previous discussion, it was stated that the chroma C and sidepanel S 
outputs from first matrix means 406 are each a predetermined algebraic sum 
of the respective values of L1, L2, L3 and L4, and that the H' output is 
comprised of four values of L1, L2, L3 and L4 having predetermined 
polarities. Both the predetermined algebraic sums of the chroma C and 
sidepanel S outputs and the predetermined polarities of the H' output 
depend upon whether the decoding of each successive composite quad by the 
quadruplex encoder of FIG. 3 employed an up-pattern, a first down-pattern 
or a second down-pattern. More specifically, in case of an up-pattern, the 
predetermined algebraic sums for C and S and the relationships for Y and 
H' are: 
EQU 4C=L1+L2-L3-L4 
EQU 4S=L1-L2-L3+L4 
EQU 4Y=L1+L2+L3+L4 
EQU 4H'=L1-L2+L3-L4 
In the case of the down-pattern: 
EQU 4C=L1-L2-L3+L4 
EQU 4S=L1+L2-L3-L4 
EQU 4Y=L1+L2+L3+L4 
EQU 4H'=L1-l2+L3-L4 
In the case the second down-pattern: 
EQU 4C=L1-L2-L3+L4 
EQU 4S=L1-L2+L3-L4 
EQU 4Y=L1+L2+L3+L4 
EQU 4H'=L1-L2-L3+L4 
It is apparent that the mid-frequency band portion of the fully 
quad-averaged 4 Y signal is equal to the sum of 2 Ya and 2 Yb, while the 
mid-frequency band portion of the 4 H' signal is equal to the difference 
between 2 Ya and 2 Yb. Therefore second matrix means 410, by appropriately 
adding and subtracting the first and second inputs thereto, is able to 
solve the simultaneous equations to thereby resolve the respective values 
of Ya and Yb. The addition and subtraction can take place in many 
different ways. In general, the resolved values of Ya and Yb will not 
occur in the proper ordinal positions within a quad. Therefore, in 
general, second matrix means 410 requires memory means or delay means for 
restoring the resolved values of Ya and Yb to their respective proper 
positions within a quad, as discussed above in the description of second 
matrix means 410. However, the need for such memory or delay means in 
second matrix 410 can be eliminated by adhering to the following approach 
for combining the respective first and second inputs to second matrix 
means 410. First, the algebraic sum of the values of L1, L2, L3 and L4 
comprising the luma-difference (Ya-Yb) input to second matrix means 410 is 
computed. Then, the value of this computed algebraic sum is added to each 
of those two values L1, L2, L3 and L4 of the Y input to second matrix 
means 410 which are associated with positive polarity L1, L2, L3 and L4 
values of H', and is subtracted from each of the two remaining L1, L2, L3 
and L4 values of the Y input to second matrix means 410. This results in 
each of Ya and Yb being restored to their proper ordinal positions in a 
luma quad without requiring additional memory or delay means. 
Each successive quad of the low-frequency first band from filter 400 is 
comprised of four independent luma-component values in this low-frequency 
band. Motion detector 402, which is identical in structure and function to 
motion detector 322 described above, derives the motion-indicating factor 
K applied to motion decoder 412. Motion decoder 412 converts the 
respective the values of Ya and Yb into a luma quad comprised of 
ordinally-arranged luma values Y1', Y2', Y3', and Y4', wherein: 
EQU Y1'=Ya 
EQU Y2'=KYa+(1-K)Yb 
EQU Y3'=KYb+(1-K) Ya 
EQU Y4'=Yb 
It should be understood that adder means 404 may contain any delay means 
required to insure that the corresponding quad values of its two inputs 
occur in time coincidence with one another when they are added together. 
The high-frequency fourth band output from filter 408, which is comprised 
of the enhanced-luma H modulated-carrier component, is applied to an 
appropriate H decoder. 
Referring to FIG. 5, there is shown an alternative embodiment of the 
quadruplex encoder. In FIG. 5, blocks 500, 502, 504, 506, 510, 512, 514, 
516, 518 and 520, respectively, are structurally and functionally 
equivalent to corresponding blocks 300, 302, 304, 306, 310, 312, 314, 316, 
318 and 320, respectively, of FIG. 3, described above. Further, although 
FIG. 5 does not show a motion detector, motion adaptation similar to that 
described in connection with FIG. 3 could be employed in FIG. 5, if 
desired. 
The only significant difference between the respective embodiments of the 
quadruplex encoder shown in FIGS. 3 and 5 is the way that the 
enhanced-luma component is handled. In the embodiment of FIG. 5, the luma 
component input to bandsplit filter 514 is a baseband signal which 
includes an enhanced-luma band extending from 4.2 to 5.2 MHz, rather that 
extending only to 4.2 MHz. This differs from the FIG. 3 encoder 
embodiment, wherein the enhanced-luma component is a separate modulated 
carrier and the baseband luma component extends only to 4.2 MHz. 
In the quadruplex encoder embodiment of FIG. 5, the high-frequency fourth 
band luma output from extra-frame averager 520 is supplied as an input to 
low-pass filter 524 having a 5.2 MHz cut-off frequency. The output from 
low-pass filter 524 is applied as one input to frequency converter 526. 
This first input to frequency converter 526 is comprised of both the 
high-frequency band of the regular luma component extending from 3.0 to 
4.2 MHz and the enhanced-luma component extending from 4.2 to 5.2 MHz. An 
8.4 MHz continuous-wave folding-carrier, after being polarity-modulated by 
enhanced-luma polarity modulator 512, is applied as a second input to 
frequency converter 526. Frequency converter 526 is designed to pass to 
its output only frequencies up to 4.2 MHz and reject from its output all 
frequency above 4.2 MHz. Thus, the output from frequency converter 526 
will include both the high-frequency band portion of the regular luma 
component extending from 3.0 to 4.2 MHz applied to its first input, which 
is forwarded directly without frequency conversion to its output, and the 
polarity-modulated, frequency-converted enhanced-luma component, which now 
occupies a frequency band extending from 3.2 to 4.2 MHz in the output from 
frequency converter 526. This output from frequency converter 526 is 
applied as one of the separate inputs to adder means 504. Therefore, just 
as in the quadruplex encoder embodiment of FIG. 3, the output from adder 
means 504 is a 4.2 MHz baseband signal comprised of successive composite 
quads. 
The quadruplex decoder shown in FIG. 6 cooperates with the quadruplex 
encoder shown in FIG. 5. In FIG. 6, each of blocks 600, 604, 606, 608 and 
610, respectively, are similar in structure and function to corresponding 
blocks 400, 404, 406, 408 and 410 of FIG. 4. Further, while no motion 
detector or motion decoder are shown in FIG. 6, if the quadruplex encoder 
of FIG. 5 employs motion adaptation, a motion detector and motion decoder 
corresponding respectively to motion detector 402 and 412 would be 
employed in the quadruplex decoder of FIG. 6. 
In FIG. 6, the high-frequency fourth band output from filter 608 is applied 
as a first input to frequency converter 614 and an 8.4 MHz continuous-wave 
unfolding carrier is applied as a second input to frequency converter 614. 
Frequency converter 614 is designed to pass to its output all frequencies 
up 5.2 MHz and to reject all frequencies above 5.2 MHz. The frequency band 
between 3.0 and 4.2 MHz applied to the first input of frequency converter 
614 includes the 3.2 to 4.2 MHz band occupied by the quadruplex-encoded 
enhanced-luma component. After being frequency converted by the 8.4 MHz 
unfolding carrier, the enhanced-luma component will be restored to it 
original 4.2 to 5.2 MHz band in the output from frequency converter 6.14. 
This output from frequency converter 614 is applied as one the separate 
inputs to adder means 604. Thus, the output from adder means 604 will be a 
luma baseband signal extending up to 5.2 MHz. 
In the description of the quadruplex encoders of FIGS. 3 and 5 and the 
quadruplex decoders of FIGS. 4 and 6, it was assumed for illustrative 
purposes that the vertical-temporal plane was organized into quads, such 
as chroma quads 200a and 200b, comprised of a single scan line from each 
of the four consecutive fields of a color frame. However, it is apparent 
that the vertical-temporal plane may be organized into quads, such as 
chroma quads 204a and 206a, comprised of two consecutive scan lines from 
each of the two interlaced fields making up each of the two images frames 
of a color frame. In this latter case, each of the quad averagers of the 
quadruplex encoders of FIGS. 3 and 5 would be organized to average the 
four correlated image values which correspond to each of these latter 
quads. However, it is apparent from FIG. 2 that, in this latter case, the 
respective polarities of these image values of the second frame of a color 
frame are inverted with respect to the polarities of the first image frame 
of a color frame. Therefore, for this second frame of a color frame, the 
proper alternative specified one of the three polarity codes (a), (b) (c), 
set forth above, should be employed. Further, intra-frame averaging in 
this latter case need not be motion-adapted, since the image information 
is updated every image frame. Further, the intra-frame averager of a 
quadruplex encoder, in this latter case, will be employed to intra-frame 
average either the correlated luma-component image values of each pair of 
corresponding scan lines of the two fields of an image frame, or, instead, 
the two correlated image values of each pair of consecutive scan lines of 
each of the two interlaced fields of an image frame. 
In general, polarity codes may be used to provide 2.sup.n independent 
values, in a manner which permits these independent values to be decoded 
without any resulting crosstalk therebetween. In the case of the 
quadruplex encoders and decoders disclosed herein, the value of n happens 
to be equal to two. However, the principles of the present invention could 
be extended to cases in which the value of n is greater than two. 
Further, the principles of the present invention may be applied to signals 
other than a television-type signal, although the present invention is 
particularly suitable for use with a television-type signal.