JPH0678211A - Special image effect device - Google Patents

Abstract

PURPOSE:To perform the reduction processing of an image by hardware without requiring an anti-aliasing filter by performing a band limitation processing and interpolation processing in accordance with an arbitrary reduction ratio on input image sampling data read out from an image memory in which it is stored transiently by an interpolation circuit. CONSTITUTION:This device is equipped with the anti-aliasing filter 11, the image memory 12. the interpolation circuit 13, and a readout address generator 14. When reduction processing is performed, low-pass filter characteristic to perform the band limitation processing required for the prevention of aliasing is supplied in the product of plural filtering characteristics, and the band limitation processing by high-order filtering characteristic is performed by the anti- aliasing filter 11, and the band limitation processing by low-order filtering characteristic is performed by the interpolation circuit 13 also with the interpolation processing. By employing such constitution, the haware equipped with only the high-order filtering characteristic can be used as the anti-aliasing filter 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image special effect device for moving and enlarging / reducing an image by digital image processing.

[0002]

2. Description of the Related Art In an image special effect device for moving, enlarging / reducing an image, etc., the sampling data of an input image cannot always be used as it is as data to be originally output to a sampling grid point on the output side. For example, if the input image is horizontally moved by 1/2 grid, the data to be originally output is T / T which is the sampling period T of the original input image.
It is a sample value obtained by shifting by 2. Therefore, an interpolation circuit for performing interpolation using discrete data held only by the input side grid points is required.

In general, an image special effect device, as shown in FIG. 4, takes in input image data supplied through an anti-aliasing filter 41 into a frame memory 42, and extracts the input image data from this frame memory 42. The interpolation circuit 43 interpolates the data on the grid points (sampling points) of the output image. The read address generator 44 stores the image data used for interpolating the data on the grid points (sampling points) of the output image by the interpolation circuit 44 in the frame memory 42.
A read address for reading from is generated.

In the image special effect device, for example, the input sequence x (n) of the sampling frequency fs is shown as a time waveform in A of FIG. 5 and a frequency spectrum in A of FIG. When the input image is to be reduced by 2/3, the input sequence x (n) is first converted to 2/3 · fs / by the anti-aliasing filter 41.
Band limiting to 2 = fs / 3, the time waveform is shown in B of FIG. 5, and the input image represented by the input sequence x ′ (n) whose frequency spectrum is shown in B of FIG. Take in 42.

Then, in the interpolation circuit 43, the input sequence x'read out from the frame memory 42.
In contrast to (n), as shown in C of FIG. 5, a sequence w (k) is generated by inserting 2-1 = 1 samples having a value of 0 at equal intervals between the samples, and the sequence w (k) is generated. For k), as shown in C of FIG. 6, band limitation processing is performed by an interpolation filter having a low-pass filter characteristic in which f <fs / 2 is a pass band, and a time waveform is shown in D of FIG. Further, an output sequence v (k) whose frequency spectrum is shown in D of FIG. 6 is generated, the output sequence v (k) is thinned to 1 / M, and a time waveform is shown in E of FIG. An output sequence y (m) whose frequency spectrum is shown in E of FIG. 6 is generated.

Generally, in the case of performing L / M reduction (L <M), the input sequence is first band-limited to L / M · fs / 2 by the anti-aliasing filter 41, and then each sample is equally spaced. It is sufficient to insert L-1 samples each having a value of 0 in, to limit the band to f <fs / 2 by the interpolation filter, and thin this out to 1 / M.

In the image special effect device, the reduction ratio (L / M) changes every moment, so it is necessary to change the limiting band of the anti-aliasing filter 41.

Conventionally, the anti-aliasing filter 41 is constructed, for example, by switching the combination of the first to third half band filters 41A, 41B and 41C as shown in FIG. 7 according to the reduction ratio (L / M). The limit band of, was variable.

In the anti-aliasing filter 41 shown in FIG. 7, the first half-band filter 41A is
As shown in FIG. 8, it has a transfer function H ₁ of H ₁ (z) = (1 + 2z ⁻¹ + z ⁻² ) / 4 with fs / 2 as a zero point, and f <fs / 2
Low-pass filter characteristic with pass band | H ₁ (z) |
Present. When the reduction ratio (L / M) is 1, that is, in the non-compression processing, the band of the input image data having the sampling frequency fs is band-limited to f <fs / 2 by the low-pass filter characteristic | H ₁ (z) |.

Further, the second half band filter 41B
Has a transfer function H _{2 such} that H ₂ (z) = (1 + 2z ⁻² + z ⁻⁴ ) / 4 with fs / 4 as a zero point, as shown in FIG. By combining them, FIG.
Shows a low-pass filter characteristic | H ₁ (z) | · | H ₂ (z) | with f <fs / 4 as the pass band.
During the compression processing with the reduction ratio (L / M) of 1/2, the band of the input image data with the sampling frequency fs is f <due to this low-pass filter characteristic | H ₁ (z) | · | H ₂ (z) | Band limit to fs / 4.

Further, the third half band filter 41
As shown in FIG. 11, C has a transfer function H ₃ of H ₃ (z) = (1 + 2z ⁻⁴ + z ⁻⁸ ) / 4 with fs / 8 as a zero point, and the first and second half By combining with the band filters 41A and 41B, a low-pass filter characteristic having a pass band of f <fs / 8 as shown in FIG. 12 | H ₁ (z) | · | H
₂ (z) | · | H ₃ (z) | Reduction rate (L /
M) is compressed to 1/4, this low-pass filter characteristic | H ₁ (z) | · | H ₂ (z) | · | H ₃ (z) |
Thus, the band of the input image data whose sampling frequency is fs is band-limited to f <fs / 8.

[0012]

As described above, in the conventional image special effect device, the hardware requires a large-scale anti-aliasing filter in order to perform the band limiting process according to the reduction ratio. There was such a problem.

Therefore, in view of the problems in the conventional image special effect device as described above, an object of the present invention is to perform image reduction processing without requiring a large scale anti-aliasing filter in hardware. An object is to provide an image special effect device that can perform.

[0014]

As described above, in the interpolation circuit in the conventional image special effect device, the interpolation processing is performed by the interpolation filter having the low-pass filter characteristic having the pass band of f <fs / 2. Assuming that the band limiting capability of the interpolation circuit is up to fs / 4, for example, the first transfer function H ₁ (z) and the second transfer function H ₂ (z) are provided on the anti-aliasing filter side. There is no need. Therefore, as shown in FIG. 1, the image special effect device is
An anti-aliasing filter 11 having high-order filter characteristics of only the _third transfer function H ₃ (z), and an image memory 12 for temporarily storing input image sampling data.
With respect to the image data read from the image memory 12, the fs / 4 corresponding to the reduction ratio is obtained by the low-order filter characteristic by the first transfer function H ₁ (z) and the second transfer function H ₂ (z). It can be configured by the interpolating circuit 13 that performs the interpolating process together with the band limiting process up to. Further, when the interpolation circuit 13 has a band limiting processing capability based on a high-order filter characteristic, the anti-aliasing filter is not required in the preceding stage of the image memory.

That is, in order to solve the above-mentioned problems, the image special effect device according to the present invention relates to an image memory for temporarily storing input image sampling data and an input image sampling data read from this image memory.
It is characterized by comprising an interpolating circuit for performing band limiting processing and interpolation processing according to an arbitrary reduction rate. Further, an anti-aliasing filter having a high-order filter characteristic is provided in the preceding stage of the image memory, and input image sampling data is input to the image memory via the anti-aliasing filter. .

[0016]

In the image special effect device according to the present invention, the input image sampling data is temporarily stored in the image memory, and the input image sampling data read out from the image memory is subjected to a band corresponding to an arbitrary reduction ratio by the interpolation circuit. Perform limit processing and interpolation processing. In addition, input image sampling data is input to the image memory through an anti-aliasing filter having a high-order filter characteristic.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image special effect device according to the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 1, an image special effect device according to the present invention is an image special effect device, which is an anti-aliasing filter 11 having only high-order filter characteristics and an image memory for temporarily storing input image sampling data. 1
2 and the image data read from the image memory 12, an interpolation circuit 13 that performs band limitation processing according to the reduction rate by low-order filter characteristics and also performs interpolation processing.
Composed of.

Specifically, as shown in FIG. 2, the anti-aliasing filter 11 connected to the input terminal 10 is connected.
The image memory 12 to which the input image sampling data x (n) is supplied from the input terminal 10 via the anti-aliasing filter 11 and the input image sampling data x (n) read from the image memory 12 An interpolation circuit 13 for performing band limitation processing and interpolation processing according to the reduction ratio, and a read address generator 14 for giving a read address to the image memory 12 and the interpolation circuit 13 are provided.

In this image special effect device, a low-pass filter characteristic for performing band limiting processing required to prevent aliasing during reduction processing is given by a product of a plurality of filter characteristics, and the high-order filter characteristic thereof is given. The band limiting process by the antialiasing filter 11 is performed, and the band limiting process by the low-order filter characteristic is performed by the interpolation circuit 13 together with the interpolation process.

For example, in the image special effect device of this embodiment,
It is assumed that the reduction processing with a reduction ratio L / M of up to 1/4 is performed.
To prevent aliasing during 1/4 reduction processing
For the input image data whose sampling frequency is fs
If the band is limited to f <fs / 8, fs / 8 is
H for zero₃(Z) = (1 + 2z^-Four+ Z^-8) / 4
Transfer function H₃The band due to the higher-order filter characteristics given by
The band limiting process is applied to the anti-aliasing filter 11 described above.
H, with fs / 2 as the zero point₁(Z) = (1 + 2
z^-1+ Z^-2) / 4 first transfer function H₁And fs / 4
H with zero as the zero point ₂(Z) = (1 + 2z^-2+ Z^-Four) / 4
Second transfer function H₂A low order given by the product of and
Filter characteristics ｜ H₁(Z) ｜ ・ ｜ H₂(Z) | Band
The restriction processing is performed by the interpolation circuit 13 together with the interpolation processing.
The low pass with f <fs / 8 as the pass band
Filter characteristics | H₁(Z) ｜ ・ ｜ H₂(Z) ｜ ・ ｜ H₃
(Z) | is obtained.

As described above, as the anti-aliasing filter 11, a simple hardware having only high-order filter characteristics can be used.

It should be noted that the interpolation circuit 13 has a sufficiently high band limiting capability, and a low-pass filter characteristic | H ₁ (z) | · | H ₂ (z) | ・ in which the pass band is f <fs / 8. | H
_{If the} band limitation by ₃ (z) | can be performed together with the interpolation processing in the interpolation circuit 4, the anti-aliasing filter 11 is not necessary.

The image memory 12 includes N memories M _{1 to} M each having a storage capacity of frame / N.
Consist _N, the input image sampling data x supplied through an anti-aliasing filter 2 from the input terminal 1 '(n) is written are sequentially distributed to the N memory M ₁ ~M _N. That is, the N adjacent input data x ′ (k) to x ′ (k + N) are stored in different memories M.
Written from _{1 to MN} .

Although the image memory 12 stores image data for one frame, it actually has a storage capacity for two frames, and while writing to one frame memory. Then, reading is performed from the other frame memory.

The reading of the image data from the image memory 12 is performed according to the read address given by the read address generator 14.

Here, the image data taken into the image memory 12 is sampled discrete image data, and the data on the grid points (sampling points) on the output image are on the grid points of the input image. Since this is not always the case, the read address provided by the read address generator 5 has an integer part and a decimal part. For example,
As shown in FIG. 3, when the image data to be read (x mark) is located at the center of the grid point (⊚ point) of the input image, the read address of the memory is given by the values x + 0.5 and y + 0.5. .

Then, the image memory 12 uses N integers of image data x '(k) to x' (k + N) required for N tap interpolation processing by the integer part of the read address given by the read address generator 14. ) Is the above N memories M
_It is read in parallel from _{1 to MN} . N pieces of image data x ′ (k) to x ′ read in parallel in this way
(K + N) is supplied to the interpolation circuit 13.

[0029] The interpolation circuit 13 includes N multipliers MUL ₁ ~MUL _N of the N image data x '(k) ~x' ( k + N) is supplied, said N multipliers MUL ₁ ~
It is composed of a coefficient generator CFG that gives filter coefficients a _{1 to} a _N to MUL _N , and an adder ADD that calculates the sum of the multiplication outputs of the _N multipliers MUL _{1 to} MUL _N.

The coefficient generator CFG has a filter characteristic of a filter characteristic (a ₀ shown as a product of a transfer function H _O giving a low pass filter characteristic for band limitation and a transfer function H _IP giving a low pass filter characteristic for interpolation processing. , A _{L
·· a (N-1) L} ), (a 1, a L + 1 ··· a (N-1) L + 1)
... (a _L-1 , a _2L-1 ... a _NL-1 ) are recorded in the read-only memory.

For band limiting in the interpolation circuit 13
As for the low-pass filter characteristic of,
Let H₁(Z) = (1 + 2z^-1+ Z^-2) / 4 first
Transfer function H of₁Filter characteristic given by | H₁|
H with fs / 4 as the zero point₂(Z) = (1 + 2z^-2+
z^-Four) / 4 second transfer function H₂The first transfer function
H ₁Filter characteristic given by the product of₁(Z) ｜ ・
| H₂(Z) | is adopted.

The N image data x '(k) to x'
For (k + N), the set of filter coefficients to be operated is selected by the position of the data desired to be obtained as an interpolation point, that is, the decimal part of the read address, and the coefficient generator 1 is operated.
4 to the N multipliers MUL _{1 to} MUL _N.

The N multipliers MUL _{1 to} MU
L _N is the N image data x ′ (k) to x ′ (k +
N) and the filter coefficient a _{n- k} given from the coefficient generator 14 are multiplied. Furthermore, the adder ADD, each multiplication output a _nk · the N multipliers MUL ₁ ~MUL _N
The sum of x '(k) is calculated and output as interpolation image data.

[0034]

As is apparent from the above description, in the image special effect device according to the present invention, the input image sampling data is temporarily stored in the image memory, and the input image sampling data read from the image memory is interpolated. Since the circuit performs the band limiting process and the interpolation process according to an arbitrary reduction ratio, the image reducing process can be performed without requiring a large scale anti-aliasing filter in hardware. Further, by providing the anti-aliasing filter in the preceding stage of the image memory with only the high-order filter characteristic required when performing interpolation processing with a large reduction rate by the interpolation circuit, the hardware of the anti-aliasing filter is It can be small.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of an image special effect device according to the present invention.

FIG. 2 is a block diagram showing a specific configuration of the image special effect device according to the present invention.

FIG. 3 is a diagram showing an example of a relationship between grid points (sampling points) of an input image and grid points (sampling points) of an output image in the image special effect apparatus.

FIG. 4 is a block diagram showing a configuration of a conventional image special effect device.

FIG. 5 is a waveform diagram for explaining an operation principle of image reduction processing in the image special effect device.

FIG. 6 is a diagram showing a frequency spectrum for explaining an operation principle of image reduction processing in the image special effect apparatus.

FIG. 7 is a block diagram showing a configuration of an anti-aliasing filter in a conventional image special effect device.

FIG. 8 is a diagram showing frequency characteristics of a first half-band filter which constitutes the anti-aliasing filter.

FIG. 9 is a diagram showing frequency characteristics of a second half-band filter which constitutes the anti-aliasing filter.

FIG. 10 is a diagram showing low-pass filter characteristics obtained by combining the frequency characteristics of the first and second half-band filters in the anti-aliasing filter.

FIG. 11 is a diagram showing frequency characteristics of a third half-band filter which constitutes the anti-aliasing filter.

FIG. 12 is a diagram showing low-pass filter characteristics obtained by combining the frequency characteristics of the first to third half-band filters in the anti-aliasing filter.

[Explanation of symbols]

Input terminal 11 Anti-aliasing filter 12 Image memory 13 · interpolation circuit 14 .......... read address generator M ₁ ~M _N ······· memory MUL ₁ ~MUL _N ··· multiplier CFG ········・ CFG ADD ・ ・ ・ ・ ・ ・ ・ ・ ADD

Claims (2)

[Claims] 1. An image memory for temporarily storing input image sampling data, and an interpolation circuit for performing band limiting processing and interpolation processing according to an arbitrary reduction rate on the input image sampling data read from the image memory. An image special effect device provided. 2. An anti-aliasing filter having a high-order filter characteristic is provided in the preceding stage of the image memory, and input image sampling data is input to the image memory via the anti-aliasing filter. The image special effect device according to claim 1.