JP2752287B2 - Video signal processing 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 video signal processing circuit in a video device such as a video camera, and more particularly to a circuit for performing horizontal interpolation and image contour compensation necessary for horizontal zoom processing and the like. Things.

[0002]

2. Description of the Related Art With the digitization of a signal processing circuit of a video camera, adoption of a so-called electronic zoom for electrically performing a zoom process is being studied. In the horizontal zoom process in the electronic zoom, first, a screen area to be zoomed is selected and set, and a video signal on each horizontal scanning line constituting the area is stored in a memory for each pixel. Is extended in the time axis direction and read out discretely, and in order to restore the number of pixels reduced by the expansion of the time axis to a predetermined number of pixels for one horizontal scanning line, interpolation processing based on video signals of two adjacent pixels is performed. Done.

[0003] Linear interpolation is generally used for interpolation processing.
As shown in FIG. 7 , based on video signals D1 and D2 of two pixels adjacent on the same horizontal scanning line (44) and an interpolation coefficient K variably set in accordance with the interpolation position, an interpolation position between these two pixels is determined. Is the weighted average formula D = D1 × (1-K)
It is calculated by + D2 × K.

In a video camera, contour compensation for enhancing the contour of an image is performed. FIG. 2 (a) (b)
(c) shows the principle of horizontal contour compensation. For a luminance signal on one horizontal scanning line, an aperture signal synchronized with the rising and falling points is created, and the aperture signal is added to the luminance signal. As a result, output data in which the horizontal contour is emphasized is obtained.

FIG. 6 shows a conventional circuit for performing horizontal interpolation and contour compensation on a luminance signal. An adder (41) adds an aperture signal obtained by an aperture signal generation BPF (40) to the luminance signal. ), And sends the addition result to the linear interpolation circuit (42). A coefficient generating circuit (43) is connected to the linear interpolation circuit (42), whereby an interpolation coefficient corresponding to the horizontal interpolation position is supplied to the linear interpolation circuit (42).
As a result, output data subjected to contour compensation and interpolation processing is obtained from the linear interpolation circuit (42).

The aperture signal generation BPF (40) is composed of a 3-tap digital interpolation filter, and the linear interpolation circuit (42) is composed of a 2-tap digital interpolation filter.
As shown in FIG. 6 , the impulse response hap of the aperture signal generation BPF (40) is set to (-1, 2, -1).
The impulse response hint of the linear interpolation circuit (42) changes according to the interpolation position. For example, when the interpolation coefficient K = 0, (2, 0), and when K = 0.5, (1, 1) , K = 1.0, they are set to (0, 2). Each coefficient representing these impulse responses is a tap coefficient of each filter.

The impulse response of the entire filter in the circuit configuration of FIG. 6 is obtained. Here, it is considered that a virtual interpolation filter of the impulse response (0, 1, 0) is interposed in the signal line that directly supplies the luminance signal to the adder (41). However, aperture signal creation BPF (40)
Is (-1, 2, -1), the impulse response hth of the virtual interpolation filter is set to (0, 2, 0) in order to match the gain with this.

The impulse response hY before linear interpolation is obtained by adding the impulse response hap and hth, and hY = (− 1, 4, −1). The impulse response of the entire filter is two impulse responses hY and hY.
It can be obtained by convolution operation of int (hereinafter, the operator is represented by *).

For example, the impulse response when the interpolation coefficient K is 0 (hereinafter referred to as H0) is

(Equation 1) Becomes

Similarly, the impulse response H1 when the interpolation coefficient is 0.5 and the impulse response H2 when the interpolation coefficient is 1 are respectively:

(Equation 2)

[0011]

(Equation 3) Becomes

[0012]

However, in the impulse response of the entire circuit described above, the maximum gain and the minimum gain are 8 and -4 in the case of H0 and H2, respectively, while 6 in the case of H1. And -2, and the signal gain is reduced only when the interpolation coefficient is 0.5. As a result,
When the interpolation coefficient is 0.5 or a value near the interpolation coefficient, the signal level is reduced, and there is a problem that the resolution is uneven on the screen and the image quality is deteriorated.

An object of the present invention is to provide a video signal processing circuit capable of obtaining a uniform gain irrespective of an interpolation position, thereby obtaining an image having a uniform resolution.

[0014]

As shown in FIG. 1, a video signal processing circuit according to the present invention performs horizontal contour compensation and horizontal interpolation processing on an input video signal, and outputs the resulting video signal. In the processing circuit, 4
A contour compensating circuit comprising interpolation filter among performing a weighted average in accordance with the tap coefficients, respectively the video signal of the pixel, is connected in parallel to the contour compensating circuit, two pixels in the center in the 4 pixels a linear interpolation circuit composed weighted average of interpolation filter among performing in accordance with the tap coefficients, respectively the video signal, the horizontal interpolation position at least before
When the position overlaps the position of two pixels, a predetermined reference value is
If the interpolation position is an intermediate position between the two pixels,
Double the value obtained by linear interpolation from the quasi-value,
Generation of coefficients to be supplied to the contour compensation circuit as tap coefficients
And comprising a circuit, and the contour compensating circuit and the adding circuit that adds the output signal of the line form interpolation circuit.

[0015]

The impulse response gap of the interpolation filter of the contour compensation circuit (1), that is, the tap coefficient, is changed by the coefficient generation circuit (4) according to the horizontal interpolation position.
It is variably set so as to obtain a constant gain.

For example, when the interpolation coefficient is 0, the impulse response gap of the contour compensation circuit 1 is (-1, 2, -1, -1).
0), obtained by linear interpolation when the interpolation coefficient is 0.5
Double the value (-1, 1, 1, -1), interpolation coefficient is 1
Is set to (0, -1, 2, -1). Also,
The impulse response gint of the linear interpolation circuit 2 is a value (0, 1, 1, 0) obtained by linear interpolation when the interpolation coefficient is 0 (0, 2, 0, 0), and when the interpolation coefficient is 0.5. ), When the interpolation coefficient is 1, it is set to (0, 0, 2, 0).

In this case, the impulse responses G0, G1, and G2 of the entire circuit when the interpolation coefficient is 0, 0.5, and 1 are obtained as follows by adding the impulse responses gap and gint.

[0018]

(Equation 4)

[0019]

(Equation 5)

[0020]

(Equation 6)

Therefore, the maximum gain and the minimum gain of the impulse response are constant values of 4 and -2, respectively, when the interpolation coefficient is 0, 0.5, or 1. Similarly, by giving an appropriate impulse response to other interpolation coefficients, the maximum gain and the minimum gain can be set to constant values.

[0022]

According to the video signal processing circuit of the present invention, in the horizontal interpolation processing indispensable for the electronic zoom, the gain of the signal becomes a constant value irrespective of the interpolation coefficient. An image is obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method of calculating an impulse response according to an interpolation position for an aperture signal generation BPF constituting the contour compensation circuit (1) shown in FIG. 1 will be described.

FIG. 5 (a) (b) (c) are each interpolation coefficient (interpolation position) indicates an impulse response of the BPF when the 0, 0.5, and 1. These impulse response waveforms are the same, and their time axes are merely shifted from each other by a time corresponding to a half of the pixel pitch. The impulse response waveform is obtained by first determining a desired frequency characteristic to be realized by the filter, and then converting the characteristic on a time axis.

[0025] Then, FIG impulse response (-1,2 when the as shown interpolation position from (a) is 0, -1,
0) is determined, the impulse response (1,1,1 when the interpolation position from FIG. 5 (b) is 1/2, -1) is determined, the interpolation position from further FIG 5 (c) The impulse response (0, -1, 2, -1) at 1 is determined.

As described above, by shifting the impulse response in accordance with the interpolation position, the frequency characteristics of the filter become constant regardless of the interpolation position.

[0027] The coefficients D1, D2, D3, D4 of the impulse response to be set for each interpolation position shown in Figure 4 (a).
Where each coefficient when the interpolation position HK 0, 1/2 and 1 are those determined by the impulse response of FIG. The other interpolation positions 1/4 and 3/4 are determined by linear interpolation of the interpolation positions 0 and 1/2 or 1/2 and 1 in consideration of simplification of the circuit configuration.

[0028] In a further embodiment, in order to hardware the generation of the respective coefficient, expressed in 2 bits interpolation position HK as shown in FIG. 4 (b), BPF in order to reduce the calculation error
Are all represented by integers. That is,
Each coefficient in FIG. 4 (b) is twice the corresponding coefficient in FIG. 4 (a). 4 (b), the positive sum of the coefficients at each interpolation position (maximum gain) and negative total value (minimum gain) and respectively 4 and -4, almost a <br/> value regardless of the interpolation position It has become.

The aperture signal generation BPF (1) shown in FIG.
And a linear interpolation circuit (2), except that these circuits are connected in parallel with each other, and that the above-described tap coefficient corresponding to the horizontal interpolation position is supplied from the coefficient generation circuit (4).
As a single circuit configuration, it is possible to adopt the same configuration as the conventional one.

On the other hand, FIG. 3 shows an example in which the aperture signal generation BPF (1) and some of the circuit elements of the linear interpolation circuit (2) are shared, and the aperture signal generation BPF (1) is connected in series. Connected first to fourth D-FFs (5) (6) (7)
(8) and a multiplier (9) (1) that multiplies the output signal of each D-FF by predetermined coefficients K3, K4, K5, and K6 according to the interpolation position.
0) (11) (12) and an adder that adds the outputs of these multipliers
(13).

On the other hand, the linear interpolation circuit (2) includes the second and third DFs constituting the aperture signal generation BPF (1).
F (6) and F (7), multipliers (14) and (15) which multiply output signals of these D-FFs by predetermined coefficients K1 and K2 according to interpolation positions, Adder (1
6).

According to the circuit, the circuit configuration is simplified by using the D-FFs (6) and (7).

The description of the above embodiments is for the purpose of illustrating the present invention, and should not be construed as limiting the invention described in the appended claims or reducing the scope thereof. Further, the configuration of each part of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made within the technical scope described in the claims.

For example, in the above embodiment, the coefficient generating circuit
The tap coefficient in (4) is determined from the impulse response for the three cases where the interpolation positions HK are 0, 2, and 4,
Although the tap coefficients at other positions are determined by linear interpolation, it is also possible to determine the tap coefficients so that the frequency characteristics are the same for all positions without performing any linear interpolation.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a video signal processing circuit according to the present invention.

FIG. 2 is a waveform diagram illustrating the principle of contour compensation.

FIG. 3 is a block diagram specifically showing another embodiment of the video signal processing circuit according to the present invention.

FIG. 4 is a table showing values of tap coefficients according to interpolation positions;
It is.

FIG. 5 is an impulse response waveform diagram at each interpolation position.
You.

FIG. 6 is a block diagram of a conventional circuit.

FIG. 7 is a diagram illustrating the principle of linear interpolation.

[Explanation of symbols]

 (1) Aperture signal creation BPF (2) Linear interpolation circuit (3) Adder (4) Coefficient generation circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masao Takuma 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Seiji Kawakami 2--18 Keihanhondori, Moriguchi-shi, Osaka (56) References JP-A-2-131679 (JP, A) JP-A-4-10783 (JP, A) JP-A-5-284388 (JP, A)

Claims (1)

(57) [Claims] 1. A video signal processing circuit which performs horizontal contour compensation and horizontal interpolation processing on an input video signal and outputs the result, wherein tap coefficients are respectively applied to video signals of four pixels arranged in a horizontal direction. a contour compensating circuit comprising interpolation filter among performing a weighted average in accordance with, this is connected to the contour compensation circuit in parallel, each tap coefficient with respect to the video signal of the middle two pixels in the four pixels A linear interpolation circuit composed of an interpolation filter for performing a weighted average according to the linear interpolation circuit, and a horizontal interpolation position overlapping at least the position of the two pixels.
When the horizontal interpolation position is between the two pixels
When the position is between, obtained by linear interpolation from the reference value
The values obtained by doubling the values are used as tap coefficients, respectively,
A coefficient generation circuit for supplying to the compensation circuit, the contour compensating circuit and a video signal processing circuit, characterized in that it comprises an adding circuit for adding and outputting the output signal of the linear interpolation circuit.