JPH05191722A - Picture magnification device - Google Patents

Abstract

PURPOSE:To magnify a picture with simple circuit configuration by obtaining a required filter coefficient with respect to a conversion ratio of a sampling frequency with interpolation arithmetic operation from discrete data stored in a coefficient memory. CONSTITUTION:An input digital video signal is stored tentatively to a frame memory 1 and a read control means 2 outputs the signal to a digital filter 3 in a rate in response to an output sampling frequency. Then data are stored in a coefficient memory 6 by using a weighted function having a desired frequency characteristic as discrete data for each prescribed interval and a coefficient generating means 4 obtains the weighting coefficient in response to the magnification factor by applying interpolation arithmetic operation to the discrete data of the coefficient memory 6. Then the input digital video signal and the weighting coefficient are subject to produce sum arithmetic operation by a shift register 31 and a multiplier 32. Thus, the picture is magnified with a small capacity memory and simple circuit configuration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image enlarging device,
In particular, it relates to an image enlarging device capable of enlarging a digital image at an arbitrary magnification.

[0002]

2. Description of the Related Art In recent years, image information has been diversified, and in addition to conventional video images, many images such as high-definition television and computer images have been generalized. Since these images have different pixel clock frequencies and number of scanning lines, two-dimensional sampling is required when these images are displayed on a single monitor, for example, a multi-vision system in which multiple NTSC monitors are arranged vertically and horizontally. Frequency conversion must be done.

According to the sampling theorem, the sampling function S (t)
Using, the original signal can be reconstructed by the sampled value according to the following Equation 1.

[0004]

## EQU1 ## g (t) = Σg (iT) S (T-iT)

The case where the sampling frequency fs is converted from 3f to 4f, which corresponds to the case where the image is magnified 4/3 times, will be described as an example.

Now, the sample values before conversion are Q0, Q1, Q2,
..., the converted sample values are P0, P1, P2, .... To obtain the sample values P0, P1, P2, ... After conversion from the sample values Q0, Q1, Q2, ... Before conversion, T = 1 / (3f)
, Q0, Q1, Q2, ... Are g (0), g (T),
g (2T), ..., and substituting this into Equation 1 above, g
(T) may be obtained and the time t of P0, P1, P2, ... May be substituted into it.

This corresponds to interpolating the sampled value Qj by the least common multiple 12f of 3f and 4f, and re-sampling this with 3f to obtain Pi. That is, as shown in FIG. 3A, the sampling function when T = 1 / (4f) is 1
If the values sampled in 2f are S0, S1, S2, ...
The conversion from Qj to Pi in FIG. 3 (b) is obtained by the formulas 2 to 5.

[0008]

[Formula 2] P4k = ΣS41 ・ Q3k + 1

[0009]

[Formula 3] P4k + 1 = ΣS41-3 ・ Q3k + 1

[0010]

[Formula 4] P4k + 2 = ΣS41-6 ・ Q3k + 1

[0011]

[Formula 5] P4k + 3 = ΣS41-9 ・ Q3k + 1

Therefore, in order to convert from Qj to Pi, as shown in FIG. 4, the four kinds of interpolation filters F0 to F3 shown in the equations 2 to 5 are arranged in parallel, and the selector switch S cyclically In addition, the output of each interpolation filter F0 to F3 may be taken out.

In the above equations 2 to 5, if the number of summation terms is set to infinity, correct conversion is performed, but in reality, the number of summation terms must be finite and truncated. As one of the methods, there is a method of approximating the sampling function by a certain approximation function, and one of such approximation functions is Equation 6
There is a Cubic function shown in.

[0014]

[Formula 6]

However, in the method of approximating the sampling function, the frequency characteristic is determined by the approximated function,
It becomes impossible to obtain a desired frequency characteristic.

On the other hand, as a method for setting a desired frequency characteristic, a coefficient memory for individually storing filter coefficients at each sample point for sampling an interpolation function and the number of sample points (for example, sampling frequency from 3f There is a method using a transversal filter having 13 taps in the case of conversion to 4f) and means for calculating the sum of products of the filter coefficient corresponding to the sample point and the input digital video signal at each sample point (special feature). (See Japanese Laid-Open Patent Publication No. 58-97968).

However, in this method, the number of filter coefficients required for the interpolation calculation differs depending on the conversion ratio of the sampling frequency. Therefore, if the conversion ratio can be set arbitrarily, all the conversion ratios required can be set. It is necessary to selectively read the filter coefficient from the memory.

Therefore, if the conversion ratio can be arbitrarily set in this method, a large-scale memory capable of storing a large amount of filter coefficients is required.
A large-scale circuit configuration is required to selectively read out the required filter coefficient from a large-scale memory.

It is an object of the present invention to provide an image enlarging device capable of realizing conversion of sampling frequency in which a conversion ratio and its frequency characteristic can be arbitrarily set with a memory having a relatively small capacity and a simple circuit configuration.

[0020]

An image enlarging device according to the present invention is an image enlarging device for obtaining an enlarged image by interpolating an input digital video signal, and a weighting function having a desired frequency characteristic is set at regular intervals. A coefficient memory for storing as discrete data, a coefficient generating means for obtaining a weighting coefficient corresponding to an enlargement ratio from the discrete data stored in the coefficient memory by an interpolation operation, and a means for multiplying and adding the input digital video signal and the weighting coefficient. It is characterized by including.

[0021]

In the present invention, the filter coefficient required for the conversion ratio of the sampling frequency arbitrarily set is obtained from the discrete data of the weighting function stored in the coefficient memory for each point interval by interpolation calculation.

[0022]

FIG. 1 shows an image enlarging device according to an embodiment of the present invention.
The following is a specific description with reference to FIG.

As shown in the block diagram of FIG. 1, the image enlarging apparatus includes a frame memory 1, a read control unit 2, a digital filter 3, a coefficient generating means 4 and a coefficient memory 5.
Equipped with.

The frame memory 1 temporarily stores the input digital video signal, and the read control means 2 outputs the input digital video signal from the frame memory 1 to the digital filter 3 at a rate according to the output sampling frequency.

The digital filter 3 has a predetermined number of taps,
For example, a shift register 31 from which 4 taps are derived
And the data taken out from each tap and the coefficient generating means 4
It is composed of, for example, four multipliers 32 for multiplying the output of each of the outputs and the adder 33 for generating the sum of the outputs of the respective multipliers 32 as an output digital video signal.

Tap of shift register 31 and multiplier 3
The number of 2 is not particularly limited, but the number of 3 or less is
It is not preferable because the interpolation accuracy required for practical use cannot be secured. By using the four taps and the multiplier 32, it is possible to obtain high interpolation accuracy to the extent that there is practically no problem in spite of a relatively small-scale circuit configuration and obtain a good result. A larger number of taps and multipliers 32 may be provided to improve the accuracy of interpolation, but the number of taps and multipliers 32 of the shift register 31 should be 4 because the circuit configuration tends to be complicated. Is recommended.

The coefficient memory 5 stores a weighting function corresponding to an interpolation operation determined from a predetermined frequency characteristic as discrete data at regular intervals.

The number of discrete data stored in the coefficient memory 5 depends on the size of the coefficient memory 5 and is an integer n of the number of taps.
Double plus one, that is, in this embodiment, (4 × n +
1) Discrete data are stored. For example, if the integer n is 8 due to the capacity of the coefficient memory 5,
(4 × 8 + 1) = 33 pieces of discrete data are stored. If the coefficient memory 5 having a large capacity is used, the integer n is 9, 1
Discrete data represented by 0 can be stored.

Note that the design method of the FIR digital filter can be applied as it is to the method of obtaining these 33 discrete data, and for example, the desired frequency characteristic can be obtained by using the frequency sampling method [(33-1) / 2] + 1 = If 17 frequency sample points are given, 33 discrete data including the sample are obtained by the discrete inverse Fourier transform.

In the coefficient generating means 4, the weighting coefficient corresponding to the enlargement ratio set from the discrete data of the weighting function stored in the coefficient memory 5 is obtained by a generally known interpolation operation such as linear interpolation or Cubic interpolation.

For example, the coefficient memory 5 stores discrete data of 33 weighting functions, and the sampling frequency is, for example, 7
In the case of transforming to / 5 times, as shown in FIG. 2, from the 33 discrete data stored in the coefficient memory 5, (4
× 7 + 1) = 29 coefficients are obtained by interpolation calculation. In FIG. 2, since 0 to 1 / f and 0 to -1 / f are symmetric, only 0 to 1 / f is shown.

Here, 17 black circles in FIG. 2 indicate the discrete data stored in the coefficient memory 5, that is, the weighting function of the desired frequency characteristic for each fixed interval, 12
Each white circle indicates a weighting function obtained from 17 discrete data by an interpolation operation such as linear interpolation.

The 29 weighting functions thus obtained are cyclically used as filter coefficients in the digital filter 3
Of the digital video data and is used for interpolation calculation of digital video data.

In this embodiment, when the conversion to 8/5 times is performed, the data stored in the coefficient memory 5 is (4 × 8 +).
1) = 33 coefficients are calculated by interpolation using 33 discrete data coefficients, and in the case of converting to 9/5 times, the 33 discrete data stored in the coefficient memory 5 Using the coefficients, (4 × 9 + 1) = 37 coefficients are calculated by interpolation calculation.

In the above embodiment, the shift register 31 is provided in the digital filter 3 so that interpolation for horizontal direction, that is, sampling frequency conversion can be performed. However, the shift register 31 is used instead. By substituting the line delay element, the interpolation for the vertical direction, that is, the conversion for the number of scanning lines can be performed.

[0036]

As described above, according to the image enlarging apparatus of the present invention, the weighting function of the desired frequency characteristic for each constant interval is stored in the coefficient memory as discrete data, and the discrete data is enlarged by the coefficient generating means. Since the weighting function corresponding to the rate is obtained by the interpolation calculation, a desired frequency characteristic can be obtained even if the enlargement rate is different. In other words,
Even if the change ratio is arbitrarily set, the input digital video signal can be interpolated with the arbitrarily set frequency characteristic.

In addition, since the weighting function corresponding to the enlargement factor is obtained by the interpolating calculation in the coefficient generating means from the discrete data stored in the coefficient memory, the coefficient memory has a capacity for storing the discrete data of the frequency characteristic set arbitrarily. Therefore, a large-capacity memory for storing all weighting functions corresponding to each enlargement factor is unnecessary, and the capacity of the coefficient memory for storing the weighting functions can be reduced.

Further, since the capacity of the coefficient memory can be made small, the circuit configuration for cyclically reading the weighting function from the coefficient memory can be made small.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an image enlarging apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a method for obtaining a weighting coefficient from discrete data in a coefficient memory.

FIG. 3 is an explanatory diagram showing a method of enlarging an image by a factor of 4/3 using a sampling frequency.

FIG. 4 is a block diagram of an interpolation filter that enlarges an image 4/3 times.

[Explanation of symbols]

 3 Digital Filter 31 Shift Register 32 Multiplier 33 Adder 4 Coefficient Generating Means 5 Coefficient Memory

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuaki Uwa 2-18 Keihan Hondori, Moriguchi City Sanyo Electric Co., Ltd. (72) Inventor Ichika Mizukami 2-18 Keihan Hondori, Moriguchi City Sanyo Electric Co., Ltd. Within

Claims (1)

[Claims] 1. An image enlarging apparatus for obtaining an enlarged image by interpolating an input digital video signal, a coefficient memory for storing a weighting function having a desired frequency characteristic as discrete data at regular intervals, and An image enlarging apparatus comprising: a coefficient generating unit that obtains a weighting coefficient from the discrete data stored in the coefficient memory by interpolation calculation; and a unit that calculates the sum of products of the input digital video signal and the weighting coefficient. ..