DE2462498C3 - Color encoder for processing a line-sequential color television signal - Google Patents

Description

The present invention relates to a color encoder for processing a line sequential Color television signal in which each signal corresponding to one line has a wide-banded luminance signal component and in each case a color signal component · τ> from a cyclically repeating sequence of Color signal components of different chrominance (chrominance cycle) and smaller bandwidth than those of the Having luminance signal component.

The color signal components comprise this forthcoming v) Trains t in each case a signal representing the difference between a corresponding chrominance signal (/ ?, G, B - namely, red, green and blue group) and a modified luminance signal M, where M = (R + G + B ) / 3 is. In general terms, the "color signal" component refers to a component made up of a series of components that represent the low-frequency color content of the image that characterizes the transmitted signal.

From DE-OS 19 35 213 is a color television system «ι known, in which the luminance signal is transmitted in each line with full bandwidth, no chrominance signal is added in the first line of each three-line cycle, while in the second and color difference signals are added to the third line. The color difference signal of the second line exists from the difference in the chrominance signal of the basic color blue minus a low-frequency luminance signal component, while the color difference signal of the third line by the difference in the chrominance signal of the Basic color red minus the low-frequency luminance signal component is formed. This signal format facilitates the regression of the composite signal in the decoder. But it is only one of the possible Formats of a line-sequential color television signal.

The transmission of the luminance signal component and the color signal component of a color television signal having full bandwidth is often impractical or unnecessary. So z. B. the color television signal be recorded on a mechanically playable or reproducible disk, the playback bandwidth Sufficient for the luminance signal for the simultaneous transmission of the entire color information however, is not suitable. It has already been proposed to use only one color signal component to transmit the respective point in time in the line sequence and the color television signal in the receiver thereby new to form that the received signal is delayed by a sufficient number of lines, so makes all color signal components available simultaneously in a cycle of the sequence. After this Process work z. B. Arrangements as given in GB-PS 11 85 197 and in US-PS 35 60 635 are.

From DE-OS 21 61 106 another format for color difference signals is known. Here the luminance signal component is transmitted with the full bandwidth, with a component of a "modified color difference signal" also occurring in each line of the line sequence. The advantage of this format, known per se, in which a modified luminance signal M (designated Y _m in DE-OS 21 61 106) is that the simple sum of the three color difference signals provides the luminance signal.

If three color signal components are transmitted in this way, the color content of any line in the newly formed television picture partly formed from the content of two previous lines. Accordingly occurs necessarily a loss of resolution of the image in the "vertical" direction. Because the human eye is relatively insensitive to high-frequency color changes, what is known per se is the resolution of a television picture, the color content of which is of low frequency, can be improved by using high-frequency Adds luminance signals. This method involves transmitting a luminance signal in Connection to a color signal component which is of a lower bandwidth than the luminance signal and which are usually the lower frequency end of those permitted for the transmission of the luminance signal Occupies bandwidth. Such a combined signal can have the same bandwidth over a channel be transmitted as it is for the transmission of a containing only the luminance information Signal is required. In the course of recovery the color signal components from such a combined signal e.g. B. by means of two delay lines that these components are available at the same time make, however, at least part of the signal is averaged over a number of lines to produce the respective Form output line of the luminance signal. Accordingly, this method results in a significant one Loss of vertical image fineness of the light-emitting signal, since the image fineness is at least partially at the bottom

Frequency end of the luminance signal is included.

A decoder, with the help of which the vertical resolution of the luminance component of a television picture signal, the by decoding a luminance signal component and a line-sequential color signal component lower bandwidth than the luminance signal component obtained can be improved, is shown in the DE-PS 24 46 376 described. This decoder is designed in such a way that it can handle every line of an input signal compares an earlier line of the same chromaticity and reduced resolution. He derives signals, the vertical ones Designate luminance transitions. The averaging of the input signal over a large number of lines can be are used to derive low frequency luminance signals in which deficiencies of the vertical Resolution are compensated by these aforementioned signals. These derived signals that usually in the same frequency range as the color component of the input signal, can also can be used to re-create a luminance signal of full bandwidth, despite the Averaging of the part of the bandwidth that contains the sequential color components. The sequential color components can thus be recovered from the input signal while the vertical luminance detail preserved.

In decoders of the type explained above, in which around a complete line sequence cycle Lines spaced apart from each other are compared with occurring color types, ringing effects can occur occur which are expressed as ghost images in the television image.

The object of the invention is to show a color encoder which largely reduces ringing effects as they occur in a color decoder which compares ^{lines 1 * spaced apart by a complete line sequence cycle of occurring colors (chrominance cycle).}

According dei invention this is achieved in that, for Leuchtdi ^ 'Uesignalkomponentc the EIT to be processed row ¹ signal is added to the difference between einVr to at least one complete Farbartzyklu? later following line and at least one line adjacent to this later following line corresponds. Dtf ^ luminance signal of each line is increased by a correction signal, which corresponds to the subsequent luminance transition and reduces the luminance oscillation generated by the color decoder.

An exemplary embodiment of the invention is explained in more detail below with the aid of drawings will. It shows

F i g. 1 shows a diagram of the time profile of the amplitude of a line-sequential color television signal depending on the frequency and

F i g. 2 is a block diagram of the color coder.

The color television signal has, as shown in FIG. 1 illustrates a luminance signal component Y which takes up the main part of the bandwidth W available for transmission> ηύ .'a color signal component which is limited in bandwidth in such a way that it takes up the low-frequency end of the available bandwidth. The signal component is transmitted in a line sequence: The color information is not for the respective line

Completely; rather, it is transmitted in that only a specific set of color signal components is transmitted per line. The color signal components are preferably in the form (RM). (GM) and (B-M) transmitted successively. M is a modified luminance signal which corresponds to the quantity (R + G + B) / i. In contrast to this, the ordinary light-emitting signal is defined in a known manner as (0.3 /? + 0.596 "+ 9.1 \ B), on the assumption that the colors red, green and blue are the types of color. As a result, the color signal components are transmitted contrast to the normal color difference signals such. B. (R-Y) as a modified line-sequential color difference signals. However, the present invention could be adapted ZjR transmission of such color difference signals or other combinations of color signal or color difference components.

A suitable decoder is described in DE-PS 24 46 376, it works as follows:

Each line of an input signal D ₀ is compared with an earlier signal Di , the color signal component of which corresponds to that of the input signal. The comparison yields 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 circuit 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 equation (VII) 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 '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 specific point in time, if the input signal has the form (Yo + (R - M}>) , for example. The index zero here indicates the present point in time; a negative index indicates one The decoder has an adder circuit and an iCette of delay lines which provide signals Do, Di, D ₂ and D ₃ as follows.

D ₀ = 1/2 (V ₀ + (R- M) ₀ ) + 1/4 (y_., + (R- M).,) + 1/8 (K_ ₍ , + (R- M) _ ₆ ) + (I) D ₁ = 1/2 (y_, + (G - M) _,) + 1/4 (K-4 + (G - M) _ ₄ ) + 1/8 (Y_ ₇ + (G- M) _ ₇ ) + (II)

D ₂ = 1/2 (V_ ₂ + <ß - M) _,) + | .4 (V. ₅ + Iß - Λ /) s) + I / 8 (V_ "+ (ß - M).«) +

(III) (IV)

Each of these output signals thus receives a proportion of the lines of the same color bar, this proportion mi decreases exponentially with age. To remove the color signal components, a luminance signal is used low resolution formed by averaging three consecutive lines:

V "= (D _n + D,

(V!

The result of the three consecutive lines is essentially a luminance signal due to the form in which the color components are supplied, there

The decoder generates another low-resolution luminance signal:

Y " = (D ₁ + D ₂ + D ₃ ) 3.

(Vl)

.'ο

The two derived luminance signals are combined with the input signal according to the following equation summarized:

5 Y '- 4 V "- (Y + (R - M)) = <■ - (R - M) . (VII)

where e represents a luminance error signal.

The method of operation described leads to a chrominance signal which is combined with some disruptive edge signals. The subtraction of the two luminance signals (5 V-4 Y ") results in 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 Comparison of the derived luminance signal and the input signal obtained according to equation (VII) is limited in bandwidth by a low-pass filter; it is combined in an adder with the input signal as:

y + (R - M) + (e - (R - M)) = Y + c. (VIII)

The result of this summary is. that the color component in the input signal is derived by the Chrominance signal is canceled and the full bandwidth input luminance signal is recovered is, however, together with some interfering, bandwidth-limited signals, which on a sharp Vertical luminance transition in an image obtained in the receiver, a harmonic or an oscillation can evoke. In practice, a viewer will see ghost lines that occur at intervals of three Lines are removed from the vertical transition. This can reduce the occurrence of overshoots be that the attenuation of the signal is reduced, which is from the output of the chain of Delay lines is returned. However, this comes at the cost of some deterioration in the Appearance of any vertical edge in the picture.

In practice, the formation of the vertical detail signal (5 V-4 Y ") can be simplified since both

Components of this signal contain the signals D \ and U,. Accordingly, it is easier to treat the following equation:

5>"- 4 Y" = ((5D ₀ + D ₁

D ₂ ) -4 D,) 3

(IX)

This equation shows more clearly the formation of a detail signal from the difference between the two signals D ₀ and Ds of the same chrominance and the formation of a mid-king signal (Da + D <+ D ·). which does not contain any color signal component.

The chrominance signals, which, as indicated above, are known from three by two delay lines separate points are available, are influenced by the feedback that the vertical on Resolution of the chrominance signals obtained from the delay lines decreases. This is accompanied an effective delay of about three television lines. Since every transition through exponentialc Signals displayed is a certain asymmetry in the representation of any vertical color transition; available. However, this asymmetry is masked out to a large extent by the fact that by means of a: Color coders the resolution of the chrominance signals is reduced.

For a better understanding of a color code, the eir signal in a for processing by the zuvoi provides a suitable form described decoder, it should first be mentioned some disturbing effects that ir be based to a greater or lesser extent on the manner in which the television signal is encoded. Most of the color coded generate a certain unwanted, disruptive informa tion that depends on the content of the television picture; The present system gets some unwanted Disturbing signals emerge in images that have sharp vertical luminance or color transitions. These unwanted, interfering signals can generally be divided into three categories, namely crosstalk Luminance on chrominance, a crosstalk chrominance on luminance and a luminance overshoot.

The invention is concerned with the effect of luminance overshoot. The luminance overshoot describes the effect of the feedback of the decoder's performance lines. Whose Delay lines include a trap filter, which causes overshoot after vertical transitions leads, as has been described above, a certain compensation and thus a reduction the visibility of the effect can be made during coding. So z. B. two Periods of a process are introduced, the result of which is a pre-overshoot, by a certain amount Phase correction for the overshoot pattern along with some reduction in the Amplitude of this pattern.

In a preferred embodiment of the color coder according to the invention is designed so that it sums up a luminance signal of high resolution with a chrominance signal of low resolution, the encoded signal having for each line in the form Y + K (color signal component), where K is typically in the range of 0.5 to 1.0 and where the color signal

component has a line sequence of (RM), (G-M) and (BM) . The chromaticity sequence is preferably selected in such a way that an interwoven field with a continuous sequence of red, green and blue is obtained, as shown in the table below:

row Field I Field 2 . etc. 1 Y + (R-M) 2 Y + (G-M) 3 Y + (B-M) 4th Y + (R-M) 5 Y + (G-M) 6th Y + (B-M) 7th Y + (R-M) 8th Y + (G-M) ..

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

In Fig. 2 a color encoder is shown schematically. the Input signals to the color coder include a full bandwidth luminance signal and a chrominance signal. Each line of the chrominance signal corresponds to the simultaneously occurring line of the luminance signal; it can be obtained either from a camera or a composite signal, on either one Path of a variety of well-known paths. The luminance signal is a delay of six Subject to lines, d. H. a delay of three lines more than the chrominance signal, which is via a Processor or a processing device 30 is directed, which delays it by three lines and means an adder with the luminance signal.

The color encoder contains six delay lines 31 to 36 for two three-line compensation periods to compensate for the overshoot that occurs after a vertical transition due to interfering signals occurs that cannot be eliminated by the decoder. Accordingly, to the luminance signal, that passes through the chain of six delay lines adds two signals to each are derived in a similar manner from a corresponding series of three delay lines and which the Difference in detail between firstly the average luminance of two consecutive lines and second, the luminance of an immediately following line. The signals at the inputs of the

Delay lines 34 through 36 occur are the next three lines after the treatment underlying line, and the signals at the inputs of the delay lines 31 to 33 are the fourth to sixth line after the line subject to treatment. Regarding the series of the three delay lines 31 to 33, the input signal for the first becomes Delay line 31 inverted by means of an inverter 37 and by means of an adder 38 with a summarized averaged signal, which is formed by an adder 41. This adder 41 is connected to the inputs of the two subsequent delay lines 32 and 33. The proportionality of the input resistor 42 for the inverter 37 and the input resistors 43 and 44 for the Adder 41 is chosen so that the output from adder 38 is zero when none. Difference in the luminance is present between three consecutive lines of the input signal. Consequently the three lines of the luminance signal are combined in the ratios (-2, +1, +1). the previous three lines of the luminance signal are treated in the same way; an exception however, the fact that the gain in the difference signal obtained therefrom is twice that of The gain of the difference signal is that of the fourth to sixth lines after the treatment underlying line is obtained. Otherwise, steps 37a to 4a correspond to steps 37 to 41. On Adder 45 combines the difference signals from adders 38 and 38a with the output luminance signal, which is a line-sequential chrominance signal from the color processing stage 30 by means of an adder 47 is added. The chrominance signal normally passes through a low pass filter 46 to the color signal component of the output signal to z. B. to limit 500 kHz.

The color signal component of a signal for the transmission of an input image by a system comprising a Color encoders and a decoder as described here should ideally have a low vertical resolution so that no spurious signals are generated when the relatively low sampling frequency of one third of the line frequency is used. Is a high frequency color guide in the original signal present, the sampling required to form a line sequential signal results in itself moving color patterns in the final image. The formation of such patterns can be reduced by

so that the vertical resolution of the chrominance signal is reduced. This is for the decoder described earlier is significant as it is desirable to avoid high frequency chrominance signals in the final output signal.

For this purpose 2 sheets of drawings

Claims (3)

Palent claims: 1. Color encoder for processing a line-sequential color television signal in which each line -. corresponding signal a broadband luminance signal component and a color signal component each from a cyclically repeating sequence of different color signal components Chroma (chrominance cycle) and a smaller band width than that of the luminance signal component , characterized in that for the luminance signal component of the to be processed Line a signal is added which is the difference between one by at least one i ~> complete chrominance cycle later following line Mnd at least one of this later following line the adjacent line. 2. Color encoder according to claim 1, characterized by a chain of one line each: o delaying delay stages (31-36) which are a sequence of lines of the luminance signal component simultaneously make available and a combining network (37a, 38a, 41a, 42a, 43a, 44a, 45) connected to the line to be processed one of the difference (37a, 38a, 2i 42a ^ between the line mentioned later and a mean value (41a, 43a, 44a,) of the two lines preceding this line Signal added (45). 3. Color encoder according to claim 1 or 2, characterized in that the difference signal for both each line following the line to be processed by one complete chrominance cycle as well as for each line r> that follows the line to be processed by two complete chrominance cycles is formed and added to the line to be processed.