DE2462498A1 - COLOR TV SIGNAL ENCODER FOR A LINE SEQUENTIAL COLOR TV SIGNAL - Google Patents

Description

Patent attorneys Dipl.-Ing. H.Wkickmann, Dipl.-Phys. Dr K. Fincke

Dipl.-Ing. RA ₁ VeICKMAn-N, Dipl.-Chem. B. Huber

• 3.

LART

8 MUNICH 86, DEN

PO Box 860 820

MÖHLSTRASSE 22, CALL NUMBER 98 3921/22

Decca Limited

Decca House, 9 Albert Embankment

London, SEI 7SW, England

Parb television signal encoder for a line sequential color television signal

The present invention relates to an encoder for color television systems in which, for each line of a color television signal a luminance signal component is transmitted together with a color signal component which is part of the bandwidth of the luminance signal and which in the line sequence is a succession of different color signal components represents. In a preferred embodiment of the invention, the signal components each comprise one Signal which is the difference between a corresponding chrominance signal (R, G, B - namely red, green and blue) and a represents modified luminance signal M, where M = (R + G + B) / 3. Generally speaking, this means that the size "Color signal component" refers to one component of a series

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from components that make up the low-frequency color content of the image that characterizes the transmitted signal.

The transmission of the luminance signal component and the color signal component a full bandwidth color television signal is often impractical or unnecessary. E.g. the color television signal can be recorded on a mechanically playable or reproducible disk, the reproduction bandwidth of which it is sufficient for the luminance signal, but not for the simultaneous transmission of the entire color information suitable is. It has already been proposed to use only one color signal component at a time in the line follow to transmit and to rebix the color television signal in the receiver by changing the received signal by a sufficient Number of lines delayed, i.e. all color signal components are available simultaneously in one cycle of the sequence power. This method is used, for example, for arrangements such as those given in GB-PS 1 18 "5 197 and in US-PS 3 5βΟ 6 ^ 5 are. If three color signal components are transmitted in this way, the color content of any line in the newly formed one becomes Television picture partly formed from the content of two previous lines. Accordingly, there is necessarily a loss to the resolution of the image in the "vertical" direction. Because the human eye for high frequency color changes is relative is insensitive, you can, as indicated in the aforementioned patents, the resolution of a television picture, whose color content is of low frequency can be improved by adding high frequency luminance signals. This method includes the transmission of a light emitting signal in connection with a color signal component which is of a narrower bandwidth than the luminance signal and which is usually occupies the lower frequency end of the bandwidth permitted for the transmission of the luminance signal. Such a thing combined signal can be transmitted over a channel of the same band

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2482498

wide, as it is for the transmission of a signal containing only the luminance information is required. In the process of recovering the color signal components from such a combined signal e.g. by means of two delay lines which these components at the same time, however, at least part of the signal is averaged over a number of lines to obtain the to form the respective output line of the luminance signal. Accordingly This method results in a considerable loss of vertical image fineness of the luminance signal, since the image fineness is included at least partially at the lower frequency end of the luminance signal.

The invention is primarily relevant to color television systems which improve the vertical resolution of the luminance portion of a television picture signal obtained by decoding a luminance signal component and a line-sequential color signal component of a narrower bandwidth than the luminance signal component. For a better understanding of the properties and the meaning of the invention, the mode of operation of a decoder explained in more detail in German laid-open specification 24 K6 yjS should therefore first be explained briefly. The decoder is designed to compare each line of an input signal with an earlier line of the same chrominance and reduced resolution. It derives signals that indicate vertical transitions in luminance. Averaging the input signal over a plurality of lines can be used to derive low frequency luminance signals in which deficiencies in vertical resolution are compensated for by these aforementioned signals. These derived signals, which are normally in the same frequency range as the color component of the input signal, can be used to recreate a luminance signal with a full bandwidth,

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in spite of the averaging of the part of the bandwidth which contains the sequential Parb components. The sequential Parb parts can thus be recovered from the input signal while preserving the vertical luminance detail.

In a first aspect, the invention is concerned with Countermeasures for a ringing effect that can occur in the system. In the case of the special decoder explained above This ringing effect occurs because the decoder necessarily compares lines that are around a complete Chrominance cycle are spaced apart. The object of the invention is therefore to show a way of how the reverberation can be reduced.

According to the invention, this is achieved by adding each line of the Luminance signal, a signal is added which in detail the difference of at least one complete chrominance cycle the following line and at least one line adjacent to this line following later.

Another aspect of the invention relates to reduction the vertical resolution of the color components in order to reduce interference effects that are due to the presence of the derived vertical detail signals decrease. In addition, a reduction in the vertical color resolution is independent of the shape of the decoder is useful, since such a reduction reduces the formation of moving patterns, which are always produced in a final image when high frequency chrominance signals are sampled at a low frequency to generate line-sequential color signal components.

The invention is exemplified below with reference to drawings explained in more detail.

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Fig. 1 shows a color television set.

Fig. 2 and. 3 show two forms of color processing stage

for the coder according to FIG. 1.

4 shows in a diagram the course of the amplitude of a line-sequential color television signal depending on the frequency.

As illustrated in FIG. 4, the color television signal has a luminance signal component Y which is the main part of the for the transmission occupies the available bandwidth W and a color signal component which is limited in bandwidth in such a way that that it occupies the low frequency end of the available bandwidth. The signal component is transmitted in a line sequence: The Color information is not complete for the respective line; rather, it is transmitted in such a way that only a certain Set of color signal components per line is transmitted. Preferably, the color signal components are in the form (R-M), (G-M) and (B-M) are transmitted successively. M is a modified luminance signal, which is of the size (R-i-G + B) / 3 is equivalent to. In contrast to this, the normal luminance signal is defined in a known manner as (0.3R + 0.59G + 0.11B), assuming that the colors red, green and blue the color types are. As a result, the color signal components become different from the normal color difference signals like e.g. (R-Y) transmitted as modified line-sequential color difference signals. However, the present invention could be used for Transmission of such color difference signals or other combinations of color signal or color difference components adapted will.

A suitable decoder is in patent application P 24 46 376 (DT-OS 24 46 376), it works as follows:

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Each line of the input signal D _Q is compared with an earlier signal D ^, the color signal component of which corresponds to that of the input signal. The comparison provides luminance signal components which, in the event that the luminance of the input signal experiences a noticeable transition from one line to the next line, are of sufficiently high frequency to be able to indicate the transition. The decoder has a feedback latch which ensures that these signal components disappear again and that their effect is limited to the region of the transition. The feedback effectively reduces the resolution of the signal being compared to the input signal. The signal components, which are obtained on the basis of the comparison and which define or characterize the transition, are used to regenerate vertical luminance details of the original luminance signal. As indicated in the equation (VTI) below, these signal components are used in particular to obtain the color signal components of corresponding frequencies from the input signal. The lowest frequencies of the luminance signal are obtained in that the mean value Y ^{1 of} the input signal is formed over several lines. These frequencies are also used to recreate the original luminance signal. This is expediently done in that the derived low-frequency signals and marginal indication signals are used to derive the color signal component from the input signal (the color signal component extends over a corresponding frequency range). A comparison of this color signal with the input signal leads to the original luminance signal.

It is now expedient to consider the signals occurring at different points of the decoder at a certain point in time if the input signal has the form (Y ₀ + (RM) ₀ ), for example. The index zero indicates the present point in time; a negative index indicates an earlier one

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Line. The decoder has an adder circuit and a chain of delay lines which provide signals D _Q , D ₁ , D ₂ and D as follows.

D ₀ = l / 2 (Y _o + '(RM) ₀ ) + 1/4 (Y _-5 -t- (RM) _-3 ) +

1/8 (Y _-6 + (RM) _-6 ) -F (I)

D ₁ * 1/2 (Υ_ _χ + (GM) _-1 ) + IA (Y _-4 + (GM) _-4 ) +

1/8 (Y _-7 * -. (GM) _-7 ) ■ + (II)

D ₂ = 1/2 (Y _-2 + (BM) _-2 ) + ■ 1/4 (Y _-5 -I- (BM) _-5 ) +

1/8 (Y _-8 + (BM) _-8 ) +. (III)

D ₃ = 1/2 (Y _-3 +. (RM) _-3 ) + 1/4 (Y _-6 ■ + (RM) _-6 ) +

! / 8 (Y _-9 + (RM) _-9 ) + (IV)

Thus, each of these output signals receives a portion of the Lines of equal parbart, whereby this proportion increases exponentially with age decreases. ITm. To remove the color signal components, a luminance signal of low resolution is formed by averaging three consecutive lines:

Y '= (D ₀ + D ₁ + D ₂ ) / 3 (V)

The result of the three consecutive lines is due the form in which the color components are supplied is essentially a luminance signal, since (R-M) + (G-M) + (B-M) = is.

The decoder generates another low-resolution luminance signal:

Y "= (D ₁ + D ₂ + D ₃ ) / 3 (VI)

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The two derived luminance signals are compared with the Input signal summarized according to the following equation:

_ 4y »_ (Y ₊ (RM)) = e - (RM), = (VII) _: where e represents a luminance error signal.

The method of operation described leads to a chrominance signal which is combined with some interfering flanic signals. The subtraction of the two luminance ^{signals (5Y!} -4y ") leads to a luminance signal which is similar in vertical sharpness to the input signal, but which, as explained above, is derived from the input signal and a number of previous lines of the derived luminance signal and the input signal according to equation (VIl) is limited in bandwidth by a low-pass filter; it is combined with the input signal in an adder to:

Y + (R-M) + (e - (R-M)) - Y + e '(VIII)

The result of this summary is that the color component in the input signal is canceled out by the derived chrominance signal becomes, and the input luminance signal more complete Bandwidth is reclaimed, however, along with some interfering, bandwidth-limited signals that hit a sharp Vertical luminance transition in an image obtained in the receiver cause an overshoot or an oscillation can. In practice, a viewer will see ghost lines spaced at three line intervals from the vertical transition are. The occurrence of overshoots can be reduced by reducing the attenuation of the signal which is fed back from the output of the chain of delay lines. However, this comes at the expense of a certain amount

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Deterioration in the appearance of any vertical edge in the image.

In practice, the formation of the vertical detail signal (5Y ¹ - - ² IY ") can be simplified, since both components of this signal _{contain the signals D. and D 2.} Accordingly, it is easier to treat the following equation:

5Y '- 4Y "= ((5D ₀ + D ₁ + D ₂ ) - 4D ₃ ) / 3 (IX)

This equation shows more clearly the formation of a detail signal from the difference between the two signals D and D ^ _{5 of the} same type and the formation of an averaging signal (D + D, + D ,,) which does not contain any color signal component.

The chrominance signals which, as previously indicated, are separated in a known manner by three separated by two delay lines Points obtainable are affected by the feedback that increases the vertical resolution of the chrominance signals that received from the delay lines. This is accompanied by an effective delay of about three television lines. Because each transition is due to exponential signals is displayed, there is some asymmetry in the representation of any vertical color transition. These However, asymmetry is masked out to a large extent by the resolution of the chrominance signals by means of a coder is decreased.

For a better understanding of an encoder that sends a signal in a for processing by the decoder described above suitable form, a few disturbing effects should first be mentioned, to a greater or lesser extent based on the coding method of the television signal. Most color television coders generate some unwanted annoyance

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Information that depends on the content of the television picture can lead to a reduction in the quality of the image. The present system gets some unwanted interfering signals in images that have sharp vertical luminance or color transitions. The concerned unwanted annoying Signals can generally be viewed as falling into three categories, namely luminance / chrominance crosstalk, a chrominance / luminance crosstalk and a luminance overshoot.

The color channel crosstalk (luminance on chroma) is one of the viewers of NTSC, PAL or SECAM color television signals familiar effect; the luminance detail is reproduced in the image as color information. In these systems, however, causes the horizontal luminance detail the unwanted, disturbing color, while in the system described here the vertical Luminance detail brings with it a color takeover in the image. The level of the offending or unwanted color in the Image can be changed if, during encoding and decoding, the chrominance levels differ from those described so far Is changed from the unity gain states shown in equations. During the coding, the composite signal can be used the luminance signal and the proportion of the sequential color signal components can be set. Any change in this The proportion can be compensated again by suitable amplification in the color part of the decoder. The greater the amplitude of the The lower the color channel crosstalk in the final image.

The color channel crosstalk (color type on luminance) describes the formation of a disturbing luminance detail through vertical ones Color transitions, i.e. where the image e.g. two adjacent horizontal bands of different colors, but which are almost the same luminance. To train the

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To minimize disturbing details, the vertical resolution should be used of the color signal component can be reduced during coding. In addition, there is a reduction in the encoder color signal gain this type of color channel crosstalk too. In practice there must be a subjective balance between the two types of color channel crosstalk can be found.

The luminance overshoot describes the effect of the feedback the delay lines of the decoder. The arrangement of the delay lines includes a trap filter, which to a takeover of the overshoot after vertical transitions, as has been described above. A certain Compensation and thus a reduction in the visibility of the Effect can be made during coding. For example, two periods of an operation are introduced, which is a pre-overshoot as a result, by a certain amount Phase correction with respect to the overshoot pattern together with some reduction in the amplitude of this pattern.

A preferred encoder according to the invention is designed so that it combines a luminance signal of high resolution with a chrominance signal of low resolution. The coded signal has the form Y + K (color signal component) for the respective line, where K is usually in the range from 0.5 to 1.0 and where the color signal component is a line sequence of (R-M), (G-M) and (B-M). The chromaticity sequence is preferred chosen so that an interlaced field with a continuous sequence of red, green and blue is obtained, as indicated in the table below:

7 09 a T7 / 0 38 7

Line field 1 field 2

1 Y + (R-M)

2 Y + (G-M)

3 Y + (B-M)

4 Y + (R-M)

5 Y + (G-M)

β 'Y + (B-M)

7 Y + (R-M)

8 ■ Y + (G-M) ... etc.

The LED signal is related to the color signal component delayed by three lines for the same line. A compensation for the overshoot and a reduction the vertical resolution in the chrominance signal are also performed.

In Fig. 1, an encoder is shown schematically. The input signals of the encoder include a luminance signal of an understandable bandwidth and a chrominance signal. Each line of the chrominance signal corresponds to the line of the luminance signal that occurs at the same time; it can either be from a camera or composite signals can be obtained in any of a number of known ways. The luminance signal is subject to a delay of six lines, i.e. a delay of three lines more than the chrominance signal which is transmitted over a processor or a processing device 30 is directed, which delays it by three lines and by means of an adder summarized with the luminance signal.

The encoder includes six delay lines 31 to 3β for two drel line compensation periods for the compensation of the Overshoot that occurs after a vertical transition due to interfering signals that are not eliminated by the decoder.

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can be ned. Accordingly, to the luminance signal that passes through the chain of six delay lines, two signals are added, each in a similar manner from a corresponding row of three delay lines are derived and which are the difference in detail between firstly the average luminance of two consecutive Lines and secondly the luminance of an immediately following line. The signals at the inputs of the delay lines Occurring 34 through 36 are the next three Lines after the line subject to treatment, and the signals at the inputs of the delay lines 31 to 33 are the fourth to sixth lines after the line subject to treatment. Regarding the series of the three delay lines 31 to 33, the input signal for the first delay line becomes 31 inverted by means of an inverter 37 and combined with an averaged signal by means of an adder 38, which is formed by an adder 41. This adder 41 is at the inputs of the two following Delay lines 32 and 33 connected. The proportionality of the input resistance 42 for the inverter 37 and the input resistances 4-3 and 44 for the adder 41 is chosen so that the output from adder 38 is zero when there is no difference in luminance between three consecutive ones Lines of the input signal is present. As a result, the three lines of the luminance signal become in the proportions (-2, +1, +1) combined. The previous three lines of the luminance signal are treated in the same way; an exception, however, is the fact that the gain in the difference signal obtained therefrom is twice the The gain of the difference signal is that of the fourth through sixth lines after the line under treatment is obtained. Otherwise the stages 37a to 4la correspond to the stages 37 to 41. An adder 45 collects the difference signals

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from the adders 38 and 38a together with the output luminance signal which is a line-sequential chrominance signal is added by the color processing stage 30 (chroma processor) by means of an adder 47. The chrominance signal arrives normally through a low pass filter 46 to remove the color signal component of the output signal to e.g. 500 kHz.

The color signal component of a signal used to transmit an input image by a system comprising an encoder and a decoder as described here should ideally have a low vertical resolution so that no interference signals are generated when the relatively low sampling frequency of one third of the line frequency is used. If there is a high-frequency color component in the original signal, then so the scanning required to form a line-sequential signal results in moving color patterns in the Final image. The formation of such patterns can be reduced by reducing the vertical resolution of the chrominance signal will. This is important to the decoder described earlier since it is desirable to have high frequency chrominance signals in the final output signal to avoid. However, the following chroma processing can improve the appearance of the final image even when the transmitted signal is processed without the decoder described above.

An embodiment of the Chx'oma processor according to Flg. 1 is in Fig. 2 illustrates. In this case it is assumed that the input signal to the processing stage modified two at the same time Color difference signals include, for example, (R-M) and (B-M). These two signals are generated by corresponding modulators 50 and 51 with a 90 phase shift to a subcarrier frequency modulated by a source 52 and by a series of

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six delay lines 53 to 58 passed through with a delay duration of one line each. That the delay lines supplied input signal and the output signal emitted by each delay line is via input counter tähde fed to a Suramier amplifier 59, which is a Output signal to each of two demodulators 60 and 6l emits. These demodulators come with a 90 phase shift Subcarrier frequency signals from source 62 (the may be formed or replaced by the source 52). The two chrominance signals are then in a matrix 63 under Formation of the chrominance signals (R-M), (B-M) and - Q R-M) + (B-M) J = (G-M) matriculated. These signals are then sequentially using a sampling switch 64 switched through to the output, the works with the line frequency. In this embodiment each chrominance signal in vertical resolution through its combination reduced with proportions of other chrominance lines. The relevant shares are determined by the input resistances of the Amplifier 59 determined ;: they can be chosen so that subjectively the optimal effect in a reproduced image caused will.

Figure 3 illustrates the reduction in color vertical resolution after scanning. This is a little easier to achieve because only one signal needs to be processed. A sequential input signal, i.e. (R-M), (G-M) and (B-M), which can be obtained by means of a sampling switch connected to the output of a matrix representing the three signals Delivering at the same time is a chain of delay lines 71 to 76 supplied. The operation of those shown in FIG Circuit arrangement is easier to understand using the example given below. When the input signal is given by (R-M), then a summary of the second to last line (-2) and the fourth to last line (-4) given with (G-M) + (B-M) = - (R-M). As a result, from

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five lines of the sequential chrominance signal. Output of the same color component can be obtained.

Referring to Fig. 3, an adder 77 summarizes one through the resistor 78 specified portion of the output signal of the sixth delay line with one through resistors 79 and 80 specified portion of the input signal or the output signal of the third delay line together. All of these signals are signals of the corresponding chrominance. The output signals of the second and fourth delay lines are selected in Components which are determined by resistors oil and 82 are added by means of an adder 83 and by means of an inverter 84 inverted. The output signals of the first and fifth Delay lines are combined in components determined by resistors 85 and 86 by means of an adder 85 and inverted by means of an inverter 88. The inverters 84 and 88 lead the adder 77 signals of corresponding chrominance to. The various resistances determine the proportions of the lines that form the low-resolution chrominance signal be summarized; they determine the vertical resolution of the relevant signal. The proportions can be set in this way that subjectively the best final appearance of an image is achieved. Both in this embodiment and in the In the embodiment shown in FIG. 2, the average delay of the exne chrominance signal has the duration of three lines.

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Claims (6)

Patent to sayings 1, color television signal encoder for generating a line sequential Color television signal each corresponding to a line Signal a broadband luminance signal component and each a color signal component from a cyclic see repeating sequence of color signal components of different Chroma and a smaller bandwidth than that of the luminance signal component , characterized in that the encoder for the luminance signal component of the to be processed Line adds a signal that is the difference of at least one a complete cycle of the line sequence of the color types later following line and at least one of these later following line Row corresponds to adjacent cell. 2. Encoder according to claim 1, characterized by a chain of delay stages (31-36), each delaying one line, which make a sequence of lines of the luminance signal component available simultaneously and through a combining network (37a, 38a, 41a, 42a, 43a, 44 _a , 45) which adds to the line to be processed a signal corresponding to the difference between the said later following line and an average value of the two lines preceding this line. 3 · Encoder according to Claim 1 or 2, characterized in that it the difference signal for each line following the line to be processed by a complete cycle of the color types later and for each line that follows the line to be processed by two complete cycles of the types of color and forms in each case added to the line to be processed. 7098 17/0387 4. Encoder for generating a color television signal with a luminance signal component and a line-sequential one Color signal component, in particular according to one of the preceding claims, characterized by a vertical resolution at least one of the color signal components at the same point in time reducing color processing stage with this one color signal component recording chain of delay stages each delaying by one line (53-58; 7I-76) and with one the output signals of the delay stages (53-58; 71-76) with different, constant weights adding to each other adding stage (59; 77, 78) which emits a color signal, in which each line of this one color signal component is combined with parts of other lines of the same color type. 5. Encoder according to claim 4, the color processing stage of which Takes up color signal components in their line sequence, characterized in that the adder (77, 78) each line of the color signal formed from these components with at least one chrominance cycle from the previous line by at least one separated later line as well as a line resulting from the combination of two other lines of different colors same chromaticity as the previous line combined (Fig. 5). 6. Encoder according to claim 4, the color processing stage of which takes two of the color signal components simultaneously, characterized in that the color processing stage has a modulation stage (5Ο-52) which the two color signal components for passage through the delay stages (53-58) with 90 ⁰ phase shift on a Modulated on the carrier signal, a demodulator (6Ο-62) which separates the color signal components from the combined output signal of the delay stages (53-58) and a sampling switch (64) which connects the color signal components to an output one after the other (Fig. 4) . 709817/0387