DE4124008C1 - Filtering video signal in horizontal or vertical direction - delaying input signal by line(s) or image point(s) and forming selection signal from logic coupling for delayed or non-delayed image elements - Google Patents

Abstract

The input video signal for vertical filtering is delayed by one or more lines and that for horizontal filtering is delayed by one or more image points. A comparison is made of a delayed and an undelayed image element, as well as of two delayed picture elements, w.r.t. their amplitudes. The video signal arriving at the input terminal (1) is fed in parallel to a 2-line delay element (10), to the input (31) of a first comparator (30), to the input (51) of a second comparator (50) and to the input (61) of a decoder and multiplexer (60). The output (M) is the filtered, vertically delayed video signal (A) since the two delay elements (10; 20) delay the signal by two TV lines. USE/ADVANTAGE - TV logic filtering without charging function of cascade of comparators and multiplexers, reducing circuitry required and resulting running time.

Description

The invention relates to a method according to the preamble of the claim 1. Such a method is from IEEE Transcations on Consumer Electronics, Vol. 28, No. 3, pp. 157-167.

For vertical or horizontal filtering of video signals are below the Term "logical filter" method known (IEEE-CE, Vol. 28, No. 3, pp. 157-167 and IEEE-CE, Vol. 31, No. 3, pp. 240-254), which in contrast to conventional, non-recursive transversal filters, which as an output signal Calculate the sum of weighted contributions of the multiple delayed input signal, the output signal or contributions to the output signal as a result of cascaded evaluations of the maxima and minima between the delayed Determine input signals. An analogous form of the central functional elements "Minimum formation" and "maximum formation" of such logical filters can be realized by coupling the emitters or collectors of amplifier stages (IEEE-CE, Vol. 28, No. 3, pp. 157-167). In digital version can the minimum and maximum formation by the combination of one Comparators can be achieved with a multiplexer in one stage. For the Form a decision from more than two input signals, for example a minimum of three input values, two such levels must be included  Corresponding circuit complexity can be cascaded. In particular at higher clock frequencies it is necessary to resynchronize the data using Registers between levels required. These measures increase the Running time of the stages and especially require a cascading of several levels in a logical filter further effort for the simultaneous Provision of unprocessed signals. The special property more logical Filters, essential signal components not as a sum, but as a logical decision To determine between the input values of a stage leads to the fact that already determined signal values no longer contribute to the amplitude of the output value deliver.

In contrast, the object of the invention is in a method of A cascading of comparators without changing the function mentioned at the beginning and multiplexers as far as possible and thus the circuitry Reduce effort with the resulting terms.

This object is achieved by the characterizing features of Claim 1 solved.

Advantageous further developments of the method according to the invention result from the subclaims.

In the method according to the invention, after a first comparison, the incoming signal value through a logical combination of all results of this Compare additional information on the delays of the filter existing amplitude pattern generated. Based on this information you can  those input signals that are used exclusively for the further determination of the Output signal and its amplitude value are required, recognized and selected below. In this way, a cascading of Avoid comparators and multiplexers to a large extent.

The invention is described below using an exemplary embodiment in FIGS Drawings explained in more detail. The single figure shows a block diagram of a logical comb filter operating according to the inventive method.

The video signal arriving at input 1 is fed in parallel to input 11 of a 2-line delay element 10 , input 31 of a first comparator 30 , input 51 of a second comparator 50 and input 61 of a decoder and multiplexer 60 . The video signal delayed by the first delay element 10 passes in parallel via its output 12 to the input of a second 2-line delay element 20 , the input 41 of a third comparator 40 , the input 32 of the first comparator 30 and the input 63 of the decoder and multiplexer 60 . The output signal of the second delay element 20 passes through its output 22 in parallel to the input 42 of the third comparator 40 , the input 52 of the second comparator 50 and the input 66 of the decoder and multiplexer 60 . The results of the comparisons (logical yes / no decisions) present at the outputs 33 , 43 , 53 of the comparators 30 , 40 and 50 are fed to the inputs 62 , 65 and 64 of the decoder and multiplexer 60 . The comparison results are decoded by the decoder and multiplexer 60 and the resulting selection signals are processed together with the undelayed video signal at input 61 , the single-delayed signal at input 63 and the double-delayed signal at input 66 in a manner to be explained in more detail.

One designates the undelayed video signal at input 61 with "A", the comparison result at input 62 with "f", the simply delayed video signal at input 63 with "C", the comparison result at input 64 with "g", the comparison result at input 65 with "h" and the twice-delayed teletext signal at input 66 with "B", a minimum signal M is obtained at the output 67 of the decoder and multiplexer 60 through the logical combination of the functions

f = (C <A)
g = (B <A)
H = (C <B)

according to the table

fgf MXY
000 BAC
001 CCC
010 ABC
101 ABC
110 CCC
111 BAC

The output signal M represents the video signal A filtered in the vertical direction, since the two delay elements 10 and 20 each delay by two television lines. In order to achieve filtering in the horizontal direction, the delay elements 10 and 20 would have to be designed in such a way that they delay by multiples of the pixel distance.

In order to separate the luminance and chrominance information from one another in PAL-coded video signals, the decoder and multiplexer 60 additionally generates signals X and Y at its outputs 68 and 69 , which signals are obtained by logically combining the comparison results f, g and h according to the above Table can be determined. The signals X and Y are fed to the inputs 71 and 72 of an adder 70 , which is the normalized sum of the signals X and Y according to the equation

S = (X + Y) / 2

forms. The output signal S at the output 73 of the adder 70 is fed in parallel to the input 82 of a fourth comparator 80 and the input 93 of a further decoder and multiplexer 90 . Furthermore, the signal M is fed in parallel to the input 81 of the fourth comparator 80 and the input 91 of the decoder and multiplexer 90 . The result of the comparison at the output 83 of the fourth comparator 80 reaches the input 92 of the decoder and multiplexer 90 . The signals f, g and h from the outputs 33 , 53 and 43 of the other comparators 30 , 50 and 40 are also fed to the decoder and multiplexer 90 at its inputs 94 , 95 , 96 . The signal Z is generated at the output 97 of the decoder and multiplexer and is fed to the filter output 2 .

If the result of the comparison carried out in comparator 80 is referred to as "i" (logical yes / no signal), the output signal Z is determined in accordance with the following table:

fghi Z
0000 B
0001 AC
001- C
0100 A.
0101 BC
1010 BC
1011 A.
110- C
1110 AC
1111 B

The filtering in the output signal Z is carried out in the same way as for the signal M in the vertical direction, provided that the delay elements 10 , 20 each delay by two lines, while filtering is carried out in the horizontal direction, if the delay elements 10 and 20 by a multiple of the pixel -Delay distance. It goes without saying that instead of a delay by two lines, a delay by a multiple of the line length is also possible for vertical filtering. Furthermore, temporal filtering of the video signal A is possible if the delay elements 10 and 20 delay essentially by a multiple of the field duration.

The filter of the type described above sets one without changing the function cost-effective implementation of logical filters with largely avoidance a cascading of minimum and maximum formations.  

Logical filters have, for example, a low-pass character for input signals essentially consist of high-frequency signal components (fine structures in video images) while high-frequency signal components are connected with certain low-frequency signal components (e.g. on the edges of flat Picture elements) are not filtered. In contrast, transversal filters lead by filtering high-frequency signal components even at edges to one Sanding these edges. An application of logical filters for the Pre-filtering or separation of chrominance and luminance components in PAL-coded Video signals therefore allow, for example, high-frequency suppression vertical components (of the color carrier), while also high-frequency Signal components at vertical color transitions are not affected. In this way, the vertical resolution of the decoded video image compared to a chrominance-luminance separation by means of transversal filters and the dot structures on vertical color transitions known from this filter avoided.

Claims (3)

1. A method for filtering a video signal in the horizontal or vertical direction, in which the incoming video signal is delayed by one or more lines for vertical filtering or by one or more pixels for horizontal filtering, a delayed and a non-delayed in a first comparison Delayed picture element and two delayed picture elements are compared with one another with regard to their amplitude, characterized in that a logic signal is used to form a selection signal and one of the delayed or non-delayed picture elements is selected as an outgoing video signal with the aid of this selection signal . 2. Video filter according to claim 1, in which a non-delayed and two delayed signals are used, and from these three input signals the outgoing video signal (M) is determined, which together with  a standardized first sum from the undelayed video signal and the simply delayed video signal and a standardized second Sum of the single delayed video signal and the double delayed video signal is processed into an output signal (Z), characterized in that by further logical links of the Results of the first comparison formed two further selection signals and with the help of these two further selection signals one or two of the Input signals are selected that the selected input signals are added and normalized so that in a second comparison the normalized Sum of the selected input signals with the outgoing Video signal (M) is compared, and that by logical combination the result of the second comparison with the results of the first Comparative, a fourth selection signal is formed, and that with the help of the fourth selection signal either the normalized sum or the outgoing video signal (M) is selected as output signal (Z). 3. The method according to claim 1 or 2, characterized in that a temporal filtering by delaying the incoming video signal essentially performed one or more fields or frames becomes.