JP2517489B2 - Color difference signal demodulation circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color-difference signal demodulation circuit for a sub-sampled video signal which is transmitted line-sequentially and with field-to-field offset sub-sampling of two color-difference signals RY and BY.

More specifically, the present invention relates to a color difference signal demodulation circuit for a MUSE signal that is transmitted after two color difference signals of RY and BY are subjected to line-sequential and inter-field offset and frame-line offset sub-sampling. . In particular, it relates to an inter-field interpolation technique relating to still image processing in color difference signal processing.

[0003]

2. Description of the Related Art A multi-subsample encoding (MUSE) method has been proposed by NHK as a method for band-compressing a high-definition video signal and transmitting it using a broadcasting satellite, and has been used for a prize.

In this system, a high-definition video signal, which is a high-definition video signal, is transmitted by a single channel of satellite broadcasting (bandwidth 27 MHz), and the high-definition signal is compressed by a band-compression encoder by a band-compression signal of 8.1 MHz. (MUSE signal).

The MUSE system is introduced in the following documents.

(A) NHK Technical Research 39th 1987
Volume 2, No. 172, pp. 18 (76) -53 (11)
1) Page, Ninomiya, Otsuka, Izumi, Koshi, Iwadate, "Development of MUSE Method" (b) Magazine "Nikkei Electronics, November 2, 1987, NO.433" published by Nikkei McGraw-Hill Co., Ltd. 1
Pages 89-212, Ninomiya, "Transmission system for high-definition broadcasting using satellites MUSE" Fig. 1 shows an outline of a receiver for this MUSE signal. In FIG. 1, (1) is an input terminal for the MUSE signal, and (2) is A
A / D conversion circuit, and (3) is a de-emphasis circuit.

(4) is a luminance signal still image processing unit, (5) is a luminance signal moving image processing unit, (6) is a color difference signal still image processing unit,
(7) is a color difference signal moving image processing unit.

Reference numerals (8) and (9) denote a mixing circuit for a luminance signal and a color difference signal, respectively, and (10) a motion detection circuit. The mixing ratio of the mixing circuits (8) and (9) is controlled by this motion detection circuit (10).

(11) is a line-sequential synchronizing circuit for color difference signals.

(12) is a matrix circuit, (13) is a monitor gamma correction circuit, (14) is a D / A conversion circuit,
(15) is an R, G, B output terminal.

The luminance signal still image processing unit (4) and the color difference signal still image processing unit (6) utilize the correlation in the time axis direction,
Interpolation processing is performed between fields and frames.
The luminance signal moving image processing unit (5) and the color difference signal moving image processing unit (7) perform interpolation processing in the field by utilizing the correlation in the spatial direction.

The still picture luminance signal and the moving picture luminance signal from the processing sections (4) and (5) are mixed in a pixel unit according to the amount of movement in a mixing circuit (8). This motion amount is obtained by the motion detection circuit (10).

The color difference signals from the processing units (6) and (7) are mixed in the mixing circuit (9).

The processing of the color difference signal, the still image processing, will be described with reference to FIG. The same parts as those in FIG. 1 are designated by the same reference numerals.

(16) is an interframe interpolation circuit.
In order to simplify the explanation, the inter-frame interpolation circuit (16) for the color difference signal is the inter-frame interpolation circuit for the brightness signal built in the brightness signal still image processing unit (4 in FIG. 1). Will be described as a completely different circuit, but it is actually used as well known. (17) is a time axis expansion circuit,
The color difference signal compressed on the time axis is expanded on the time axis and restored.

(18) is an inter-field interpolation circuit.
The inter-field interpolation circuit (18) interpolates the pixels of the color difference signals decimated by the inter-field offset sub-sampling using peripheral pixels.

(19) is a field memory which operates as a field delay element.

(20) is an inter-field interpolation filter.

The operation of this circuit will be described with reference to FIGS. 3 and 4 showing sampling patterns.

The output pattern of the time axis expansion circuit (17) is shown in FIG. The RY signal (□) is multiplexed on the odd line and the RY signal (◯) is multiplexed on the even line. In Figure 3 (x)
Marks are pixels thinned by the inter-field offset sub-sampling process on the transmission side. Incidentally, A2 and A6 in FIG. 3 are data received in the same field. A4
Is 2 fields (1 frame) with A2 and A6
Data received in distant fields, interpolated. The inter-field interpolation filter (20) is shown in FIG.
As shown in, the thinned pixels (x) are inserted as they are in the pixels of the same color difference signal line immediately below the previous field. That is, in FIG. 4, the pixel level of A1 is directly substituted into B1 and the pixel level of C1 is directly substituted into D1.

In this example, since the same color difference signal line is directly below, the signal level of the line directly below is substituted as it is, but if the field is different, the same color difference signal line is immediately above. Therefore, in different fields, the signal level of the line immediately above is directly substituted. That is, a switching means for switching the line to be substituted by the field is substantially required, but the description is omitted.

By the way, as described above, in the method of directly substituting the level of the same color difference signal line immediately below or above, the image quality deterioration such as dot interference occurs at the edge portion of the screen extending in the horizontal direction.

An example of this dot interference will be described with reference to FIG. Incidentally, FIG. 5 shows only the RY signal. Then, the high-level RY signal is marked with □, and the low-level RY signal is
The Y signal is represented by a black square with a black square. And FIG.
It is assumed that there is a color edge having an RY signal component at the position E in (a).

FIG. 5A shows a sampling pattern of the RY signal after the time axis expansion.

FIG. 5B shows RY after inter-field interpolation.
3 shows a sampling pattern of a signal.

FIG. 5C shows a sampling pattern of the RY signal after line-sequential synchronization. This line-sequential synchronization is
Interpolation using the color difference signals of the upper and lower lines,
This interpolation filter is a vertical 3-tap filter. Incidentally, in FIG. 5C, a signal in which half of the square mark is black indicates an intermediate level RY signal.

As shown in FIG. 5C, dot interference occurs near the color edge E.

In order to reduce this dot interference, the inter-field interpolation circuit does not simply interpolate the thinned pixels by substituting the pixels immediately above or below them, but instead of interpolating the pixels horizontally or vertically. Can be interpolated into

As this two-dimensional filter, it is conceivable to use a symmetrical two-dimensional filter having vertical 3 taps and horizontal 5 taps for inter-field interpolation. This 3x
Each tap gain of 5 taps is shown in FIG. k ₀₀ ~
k ₁₂ is a tap gain, and the same symbols have the same values.
That is, the vertical and horizontal directions are symmetrical with respect to the horizontal line and the vertical line including k ₀₀ .

However, as described above, in the MUSE signal, the line of the same color difference signal is one line immediately above or below,
One line apart in time. Then, except for this line, at least three lines are separated.
That is, in the vertical direction, filtering is performed using signals of two lines, that is, the current line of the current field and the same color difference signal line immediately above or below the previous field.
This is appropriate from the circuit scale.

An example of such a vertical 2-tap configuration will be shown. The tap coefficient at this time is the value shown in FIG.
That is, the value obtained by adding the tap coefficients of the upper and lower lines in FIG. 6A is used as the tap coefficient immediately above or immediately below the previous field.

FIG. 7 shows an inter-field interpolation filter of this tap coefficient. (21) is an input terminal of the current field pixel, and (22) is an input terminal of the previous field pixel.
A delay switching circuit (23) switches the delay amount of the previous field pixel for each field so that the same color difference signal as that of the current field pixel is output.

(24) is a parallel-serial conversion circuit. This parallel-serial conversion circuit (24) has f _ck
Two inputs are selectively output according to the signal level of SS.
Note that f _ck is a sampling clock before inter-field interpolation. The polarity of f _ck SS is inverted at each frequency f _ck in each field. (25) to (29) are delay elements, which delay the signal for 1/2 f _ck period. (30) ~ (3
1) is an adder.

Numerals (32) to (37) are multipliers for multiplying filter coefficients. This multiplier is composed of a ROM memory and is composed of a look-up table memory that outputs a predetermined value according to the input data value. (3
8) to (41) are adders.

(42) is a selection output circuit, and f _ck SS
Controlled by signals. (43) is an output terminal.

Among the multipliers (32) to (37), the multipliers (32), (33) and (34) are for sample pixels, and the multipliers (35), (36) and (37) are interpolation insertion. For non-sampled pixels.

That is, the description will be made with reference to the example of FIG.

[0038] a) the sample points A4, as a result of the filtering process, the A _'4 obtained by the following equation.

A ′ ₄ = 2k ₀₀ × A ₄ + 4k ₁₁ × (A ₃ + A ₅ ) + 2k ₀₂ × (A ₂ + A ₆ ) b) The non-sampling point B4 is obtained by the following equation.

B ₄ = 2k ₁₀ × A ₄ + 2k ₁₀ × (A ₃ + A ₅ ) + 4k ₁₂ × (A ₂ + A ₆ ) Each tap gain is doubled because the DC gain is 1.

FIG. 8 shows waveforms at various portions a to f of the circuit shown in FIG.

In the figure, the notation of coefficients is simplified as follows.

K ₀ = 2k ₀₀ , k 1 = 4k ₁₁ , k ₂ = 2
k ₀₂ , k ₃ = 4k ₁₀ , k ₄ = 2k ₀₁ , k ₅ = 4k ₁₂ , and the parallel-serial conversion circuit (24) is f _ck SS
The signal (b) of the previous field is selectively output at the timing of "L" (low level), and the signal (a) of the current field is selectively output at the timing of "H" (high level).

The selective output circuit (42) selectively outputs the signals (d) and (e) at the timings of "L" and "H" of f _ck SS. If a two-dimensional filter is used in this way,
The signal corresponding to is as shown in FIG. 9, and dot interference can be prevented.

[0045]

As described above, in order to prevent the dot interference caused by the field interpolation of the color difference signals, the inter-field interpolation filter (20) shown in FIG.
The two-dimensional filter may be used.

However, this two-dimensional filter has a multiplier (3
2) to (37). The multipliers (32) to (3
7) is constituted by a look-up table type ROM memory, and the capacity becomes large and the circuit scale also becomes large when the circuit is integrated (IC, LSI).

According to the present invention, the multipliers (32) to (37) are used.
It is intended to reduce the capacity used and prevent an increase in the circuit scale as much as possible.

[0048]

According to the present invention, a subsample video signal in which two types of color difference signals are line-sequential and inter-field offset subsampled is received, and the color difference signal in the received subsample video signal is output. Inter-field offset sub-sampling color difference signal output means (1
6), an inter-field interpolating processing circuit (18) for inter-field interpolating the output of the inter-field offset sub-sampling color difference signal output means (16), and a signal from the inter-field interpolating processing circuit (18). In the chrominance signal demodulation circuit for sub-sampled video signals, the inter-field interpolation circuit includes a line-sequential synchronism circuit (11) for generating RY color difference signals and BY color difference signals which are line-sequentially synchronized. The inter-field offset sub-sampling color difference signal output means (16) provided in the processing circuit (18)
Is provided in the inter-field interpolation processing circuit (18) and the insertion circuit (24) that alternately outputs the color difference signal of a certain field from the color difference signal and the color difference signal of the same color difference that is apart from this color difference signal by about one field period. The insertion circuit (24)
The vertical spatial frequency characteristic is 1125.
And a horizontal-vertical two-dimensional filter circuit (20) in which the tap coefficient is set to be 0 at / 2.

Further, according to the present invention, an inter-frame interpolation processing circuit (16) for inter-frame interpolating a color difference signal in an input MUSE signal and an output of the inter-frame interpolation processing circuit (16) are inter-field interpolated. Inter-field interpolation processing circuit (18) to be processed and this inter-field interpolation processing circuit (18)
In the chrominance signal demodulation circuit for MUSE signals, which includes a line-sequential synchronization circuit (11) for generating line-sequentially RY color-difference signals and BY signals from the signals from A color difference signal of a certain field which is provided in a processing circuit (18) and which has been subjected to interframe interpolation processing;
An insertion circuit (24) for alternately inserting a color difference signal having the same color difference, which is separated from the color difference signal by about one field period, and an inter-field interpolation processing circuit (18) are provided from the insertion circuit (24). A two-dimensional filter circuit (20) in which the tap coefficient is set so that the vertical spatial frequency characteristic becomes 0 at 1125/2.

[0050]

In order to simplify the explanation, first, the coefficients of the actual multiplier according to the filter characteristic of the present invention will be shown. That is, according to the present invention, in FIG. 7, k ₀₀ = 2k ₁₀ , k ₀₁ = 2k ₁₁ , k ₀₂ = 2k ₁₂ (1) Equation (1) is obtained, and the multipliers (32) and (35) , (33) and (3
6), (34) and (37) can be shared.

It will be described that the filter characteristic satisfying the expression (1) is the present invention.

First, general matters will be discussed.

The tap coefficients (a ₀₀ , a
Consider a horizontal 7-tap, vertical 5-tap symmetric digital filter with ₀₁ , ... The transfer function of the filter is

[0054]

[Equation 1]

It is expressed by the equation (2).

Here, Z ^-1 is a horizontal unit delay operator, and W ^-1 is a vertical unit delay element.

The frequency characteristics of the filter are as follows: Z = exp (2πjμξo) W = exp (2πjνηo) (3) Formula μ: horizontal frequency, 1 / ξo: horizontal sampling frequency ν: vertical frequency, 1 / ηo: Substitute vertical sampling frequency,

[0058]

[Equation 2]

Is given by For simplicity, when the multiplicity is included in the coefficient, the equation (4) becomes the following equation.

[0060]

(Equation 3)

B ₀₀ = a ₀₀ , b ₀₁ = 2a ₀₁ , etc. This is applied to a color difference signal filter and reduced to 3 × 5 taps.

Bmn (m = 0, 1, n = 0, 1, 2) The frequency characteristic value point gain (F1, ..., F6) at 6 points is given in order to determine the six unconstant (bmn). And the above formula

[0063]

[Equation 4]

Then, this is solved for bmn.

Let us consider what kind of spatial frequency characteristics the filter can be constructed.

For simplicity, a symmetrical two-dimensional filter having horizontal 5 taps and vertical 3 taps is used. The tap coefficient is shown in Figs.
The point gain in the dimensional space area is shown in FIG. There is the following relationship between the tap coefficient and the point gain.

[0067]

(Equation 5)

To construct the filter, 2b ₁₀ =
Since b ₀₀ , 2b ₁₁ = b ₀₁ , 2b ₁₂ = b ₀₂ should be satisfied,

[0069]

(Equation 6)

From the equations (6), (7) and (8), F ₄ = F ₅ =
F ₆ = 0.

As described above, the point gains on the spatial frequency when the tap coefficients of the two-dimensional filter are obtained are selected at equal intervals as shown in FIG. In order to satisfy the tap coefficient, F ₁₀ = F ₁₁ = F ₁₂ = 0.

[0072]

EXAMPLE One example of the present invention will be described with reference to FIG.

In FIG. 12, the same parts as those in FIG. 7 are designated by the same reference numerals.

In FIG. 12, the multipliers (35) (3) shown in FIG.
6) (37) adder (40) (41) selection output circuit (4
2) can also be omitted.

The multipliers (32) and (33) in this embodiment
FIG. 13A shows k ₀₀ k ₀₁ k ₁₂ which is the basis of the coefficient of (34).
Shown in 13B shows the point gain on the spatial frequency at that time. In FIG. 12, k ₀₀ = 2k ₁₀ = 0.3325 k ₀₁ = 2k ₁₁ = 0.25 k ₀₂ = 2k ₁₂ = −0.0825.

[0076]

As described above, according to the present invention, the circuit scale of the inter-field interpolation circuit for color difference signals can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram for explaining signal processing of a conventional MUSE decoder.

FIG. 2 is a diagram for explaining conventional still image processing of color difference signals.

FIG. 3 is a diagram showing a sub-sampling pattern of a color difference signal.

FIG. 4 is a diagram showing a sampling pattern of color difference signals for explaining inter-field insertion.

FIG. 5 is a diagram showing a sampling pattern for explaining the operation of the circuit.

FIG. 6 is a diagram for explaining tap coefficients.

FIG. 7 is a diagram showing an inter-field interpolation filter for color difference signals.

FIG. 8 is a diagram showing the timing of each part of FIG.

FIG. 9 is a diagram showing a sampling pattern.

FIG. 10 is a diagram of tap coefficients.

FIG. 11 is a diagram of a point gain on a spatial frequency.

FIG. 12 is a diagram showing an embodiment to which the present invention is applied.

13 is a diagram illustrating the tap coefficient and the spatial frequency point gain of FIG. 12;

FIG. 14 is a diagram for explaining tap coefficients.

FIG. 15 is a diagram for explaining a point gain of a spatial frequency.

[Explanation of symbols]

16 Interframe Interpolation Circuit (Interfield Offset Subsampling Color Difference Signal Output Means, Interframe Interpolation Processing Circuit) 18 Interfield Interpolation Circuit (Interfield Interpolation Processing Circuit) 11 Line Sequential Synchronization Circuit 24 Parallel-Serial Conversion Circuit (Insertion circuit) Interpolation filter between 20 fields (horizontal-vertical two-dimensional filter circuit)

Claims (4)

(57) [Claims] 1. An inter-field offset sub-sampling color difference signal for receiving a sub-sampling video signal in which two types of color-difference signals are line-sequential and inter-field offset sub-sampling and outputting the color-difference signal in the received sub-sampling video signal. Output means (16) and this inter-field offset sub-sampling color difference signal output means (16)
Inter-field interpolation processing circuit (18) for inter-field interpolating the output of
8), a line-sequential synchronization circuit (1) for creating line-sequentially synchronized RY color difference signals and BY color difference signals.
In the color difference signal demodulation circuit for sub-sampled video signals, the inter-field interpolation processing circuit (18)
And an interposing circuit for alternately outputting a color difference signal of a certain field from the inter-field offset sub-sampling color difference signal output means (16) and a color difference signal of the same color difference separated by about one field period from the color difference signal. (24) and the inter-field interpolation processing circuit (18), the signal from the insertion circuit (24) is input, and the tap coefficient is set so that the vertical spatial frequency characteristic becomes 0 at 1125/2. Horizontal-vertical two-dimensional filter circuit (20), and a color difference signal demodulation circuit for sub-sampled video signals. 2. An inter-field offset sub-sampling chrominance signal for receiving a sub-sampled video signal in which two kinds of chrominance signals are line-sequential and inter-field offset sub-sampled, and outputting the chrominance signal in the received sub-sampled video signal. Output means (16) and this inter-field offset sub-sampling color difference signal output means (16)
Inter-field interpolation processing circuit (18) for inter-field interpolating the output of
8), a line-sequential synchronization circuit (1) for creating line-sequentially synchronized RY color difference signals and BY color difference signals.
In the color difference signal demodulation circuit for sub-sampled video signals, the inter-field interpolation processing circuit (18)
And an insertion circuit for alternately outputting the color difference signal of the current field from the inter-field offset sub-sampling color difference signal output means (16) and the color difference signal of the same color difference of the previous field separated by about 1 field period ( Two
4) and the inter-field interpolation processing circuit (18), the signal from the insertion circuit (24) is input, and the tap coefficient is set so that the vertical spatial frequency characteristic becomes 0 at 1125/2. Horizontal-vertical two-dimensional filter circuit (2
0) and a color difference signal demodulation circuit for sub-sampled video signals. 3. An interframe interpolation processing circuit (16) for interframe interpolating a color difference signal in an input MUSE signal,
Inter-field interpolation processing circuit (18) for inter-field interpolation processing the output of this inter-frame interpolation processing circuit (16)
And a line-sequential synchronization circuit (11) for producing line-sequentially synchronized RY color difference signals and BY color difference signals from the signal from the inter-field interpolation processing circuit (18). In the signal color difference signal demodulation circuit, the color difference signal of a certain field, which is provided in the inter-field interpolation processing circuit (18) and subjected to the inter-frame interpolation processing, and the same color difference separated from this color difference signal by about one field period. An insertion circuit (24) for alternately inserting a color difference signal and an inter-field interpolation processing circuit (18) are provided. The signal from the insertion circuit (24) is input to the vertical spatial frequency characteristic of 1125 / A color difference signal demodulation circuit for a MUSE signal, comprising: a two-dimensional filter circuit (20) in which a tap coefficient is set so as to be 0 when 2. 4. The color difference signal demodulation circuit for MUSE signals according to claim 1, wherein the two-dimensional filter circuit (20) is a horizontal symmetrical filter.