JP2611211B2 - Two-dimensional filter device - Google Patents

Description

Description: A. INDUSTRIAL APPLICATION FIELD The present invention relates to a two-dimensional filter device, and in particular, performs filtering according to a deformation direction of an image when an input image is deformed to obtain an output image. Two-dimensional filter device for

B. Summary of the Invention The present invention relates to a two-dimensional filter device that performs filtering when an input image is geometrically deformed to be an output image. By performing filtering in a direction inclined by the constant angles θ and −θ, an output image that is effective for any deformation and has high image quality can be obtained.

C. Conventional technology Generally, in the creation of special effects and animations for broadcasting, image conversion such as rotating, enlarging, reducing, or adding a more complicated geometric change to an input image and outputting the image. Is applied. When such image conversion is performed, a two-dimensional band-limited filtering process is required to remove so-called aliasing noise (aliasing noise) particularly when the image is reduced.

In this case, as a filtering process for so-called anti-aliasing, when performing a filter operation on each pixel on an image, a method of performing the operation at once using each image information of pixels surrounding a target pixel, There is known a method of performing each of the filter operations in the X-axis direction and the Y-axis direction, which are the coordinate axis directions of the screen, twice.

D. Problems to be Solved by the Invention Among the above-mentioned methods, the former method can obtain a good anti-aliasing characteristic, but needs to calculate many pieces of image information at a time, and the apparatus is complicated. And it becomes large and expensive.

In the latter method, the filtering process in the X-axis direction and the filtering process in the Y-axis direction are performed separately, so that the configuration is relatively simple. However, the image quality is deteriorated when the image is reduced in the oblique direction. There is a problem that it is large.

Further, as the direction of the reduction accompanying the image conversion,
For example, when a reduction occurs in the 45 ° direction from the upper right to the lower left on the screen, if filtering is performed such that substantially the same amount of band limitation is performed in the vertical and horizontal directions (XY directions), the upper left and the lower right will be used. Since the band of the direction component is also limited, it is desired to perform filtering only in the direction in which the deformation occurs.

The present invention has been made in view of such circumstances, and when reduced not only vertically and horizontally but also diagonally, filtering can be performed only in the deformed direction to prevent deterioration of image quality, and It is an object of the present invention to provide a two-dimensional filter device in which the calculation for the filter processing is simple.

E. Means for Solving the Problems The two-dimensional filter device according to the present invention, in order to solve the above problems, when converting the input image into an output image that is geometrically deformed, In a two-dimensional filter device for performing filtering in accordance with
A first filter circuit system for performing filtering in the XY-axis direction corresponding to the coordinate axis direction of the screen using a first band-limiting filter for filtering in the axial direction and a second band-limiting filter for filtering in the X-axis direction; A third band-limiting filter that filters in a direction inclined by a non-zero angle θ with respect to the Y axis, and a fourth band-limiting filter that filters in a direction inclined by a non-zero angle −θ with respect to the Y axis. A second filter circuit system that performs filtering in each direction having the angles θ and −θ with respect to the Y axis, a signal from the first filter circuit system, and a signal from the second filter circuit system. And a weighting addition circuit for controlling the weighted addition coefficient of the addition circuit in accordance with the direction of the deformation, The method is characterized in that filtering is performed only in the direction of the deformation by controlling the band limiting amounts of the first to fourth band limiting filters according to the case.

F. Operation A first filter circuit system for filtering in the vertical and horizontal directions (XY axis) and a second filter circuit system for filtering in an oblique direction (inclined by an angle θ and −θ with respect to the Y axis) , It can exhibit good aliasing removal effect even when reduction deformation is made in almost any direction,
An output image with little image quality degradation can be obtained.

G. Examples Hereinafter, examples of the present invention will be described with reference to the drawings.

For example, when an input planar image is geometrically deformed and pasted on a three-dimensional curved surface such as a sphere or a polyhedron and converted into an output image, the image is locally enlarged or reduced. When this image reduction deformation is performed, image quality degradation due to so-called aliasing occurs. Therefore, a band limiting filter (for so-called anti-aliasing) is required to prevent this. One embodiment of such a two-dimensional band limiting filter device for anti-aliasing is shown in FIG.

In FIG. 1, an input terminal 1 is supplied with, for example, an image information signal that has been subjected to the image conversion processing. This input image information signal has a first filter circuit system 10 for filtering in the direction of the XY coordinate axis of the screen and an inclination θ and an inclination of −θ (θ is a non-zero predetermined value, for example, 45 °) with respect to the Y axis. And a second filter circuit system 20 for filtering in each direction.
Each output signal from 0 and 20 is weighted and added by the addition circuit 30 and is taken out from the output terminal 2.

The first filter circuit system 10 includes a band-limiting filter (a so-called vertical filter) 11 for filtering in the Y-axis direction (vertical direction) of the XY coordinate axis of the screen, and a band-limiting filter for filtering in the X-axis direction (horizontal direction). Horizontal filter)
At least 12. Where the vertical filter
Numeral 11 denotes an arithmetic processing using each image information of a plurality of pixels arranged in a vertical direction (Y-axis direction, downward in the figure) among the pixels in the screen S as shown by an arrow in FIG. 2, for example. The horizontal filter 12 performs a calculation process of image information between pixels in the horizontal direction (X-axis direction) of the screen, as shown by an arrow in FIG. 3, for example. It is to filter. These filters 11 and 12 are connected in series together with image memories 13, 14 and 15, and the image memory 13 is provided between the input terminal 1 and the vertical filter 11.
12 and an image memory 15 between the horizontal filter 12 and the output terminal 2, respectively. Next, the second filter circuit system 20 performs filtering in a direction inclined at a fixed angle θ, for example, clockwise with respect to the Y axis (see FIG. 4). Filter in a direction inclined at a fixed angle θ in a direction opposite to the clockwise direction with respect to the Y axis, that is, in a direction inclined at an angle −θ in the clockwise direction (see FIG. 5). 22), and filtering is performed in each direction having the angles θ and −θ with respect to the Y axis. These diagonal filters 2
Like the first filter circuit system 10, the first and 22 are connected in series with the image memories 23, 24, 25, etc., to form a second filter circuit system 20.

By the way, each of the filters 11, 12, 21 and 22 is virtually considered as a digital filter having a configuration as shown in FIG. 6, for example. The digital filter includes a plurality of delay circuits 4... 4 connected in series from an input terminal 3, a coefficient multiplier 5... 5 connected to the input side (or output side) of these delay circuits 4. And an adder 6 for adding the output signals from the coefficient multipliers 5...
Is output from the terminal 7. By setting the delay amount D of each of the delay circuits 4... 4 of the digital filter to a predetermined time, filters in the above-described directions can be configured.

For example, FIG. 7 shows a plurality of pixels p arranged on the screen.
... p is indicated, and the image information signal is represented by XY on this screen.
This is obtained by sequentially scanning each pixel in the X-axis direction and the Y-axis direction of the coordinates. For example, in a normal raster scan image signal, scanning in the X-axis direction (so-called horizontal direction) is performed. Each time the scanning is performed, the scanning position moves one line at a time in the Y-axis direction (so-called vertical direction), thereby scanning the entire two-dimensional plane. In this case, the interval between adjacent pixels in the X-axis direction corresponds to the sampling clock cycle τ _X of the input signal, and the pixel interval in the Y-axis direction corresponds to the one-line scanning cycle (so-called horizontal scanning cycle) τ _Y. Yes, it is.

Therefore, when performing the Y-axis direction of the filtering as described above longitudinal filter 11, since operations between pixels adjacent in the vertical direction as the pixels p _B for the pixel p _A of FIG. 7 is a basic , The delay circuit 4 having the filter configuration of FIG.
4 is equal to the horizontal scanning period τ _Y (D =
By setting τ _Y ), an operation for band-limited filtering processing in the vertical direction (Y-axis direction) can be performed based on the pixel information of a plurality of pixels arranged in the vertical direction. For the horizontal filter 12 that performs filtering in the X-axis direction, the delay amount D inside the filter is set to be equal to the sampling clock period τ _X (D = τ _X ), so that the pixel p _{A in} FIG. , An X-axis band-limited filtering can be performed by performing an operation based on the pixel information of a plurality of pixels arranged in the horizontal direction, such as the pixel p _{C corresponding} to. Next, when setting the direction of the filtering in the oblique lower left direction filter 21, for example, in the direction from the pixel p _A of Figure 7 to a pixel p _D, the delay amount D as a reference, from one line cycle tau _Y 1 By setting (D = τ _Y −τ _X ) equal to a time shorter by the clock period τ _X , each image information of a plurality of pixels arranged in a diagonally lower left direction from the pixels p _A to p _D is used. By performing a filter operation, band-limited filtering in the same direction can be performed. Similarly, the oblique when the direction of the filtering in the lower right direction filter 21 sets the pixel p _A in a direction toward the pixel p _E, the reference amount of delay D time plus the clock period tau _X line period tau _Y (D = Τ _Y -τ _X ).

Referring again to FIG. 1, the signal from the first filter circuit system 10 is sent to the coefficient multiplier 31 of the adder circuit 30, and the signal from the second filter circuit system 20 is sent to the coefficient multiplier 32. After being weighted by the coefficient multipliers 31 and 32, they are added by the adder 33 and sent to the output terminal 2.

Here, each band limiting filter 11, 12, 21 and 22 in each of these filter circuit systems 10 and 20 is a control terminal.
Each filter characteristic (particularly, the amount of band limitation) changes according to the control signal supplied to 16, 17, 26, and 27, respectively. Further, each coefficient multiplier 31, 32 of the addition circuit 30
The multiplication coefficient changes according to the control signals supplied to the control terminals 34 and 35, and the weight (addition coefficient) of each signal at the time of addition changes. Then, an adding circuit 30 is provided in accordance with the direction (particularly, the reduction direction) of the deformation accompanying the image conversion.
And the band-limiting filters 11, 12, and 13 according to the degree of the deformation (reduction ratio).
By controlling the above-mentioned band limiting amounts of 21 and 22, optimal filtering is performed.

For example, a specific example in the case of the above θ = 45 ° will be described. In the case where a reduction occurs in the 45 ° direction from the upper right to the lower left on the screen, in the related art, the bandwidth is limited by approximately the same amount in the vertical and horizontal directions (XY directions). Is performed, but this limits the band of the 45 ° direction component from the upper left to the lower right, whereas according to the above embodiment of the present invention, the second filter circuit system The filter characteristics are controlled so that the band limiting amount of the band limiting filter 21 becomes maximum and the band limiting by the filter 22 does not occur.
By minimizing the multiplication coefficient of the coefficient multiplier 31 and maximizing the multiplication coefficient of the coefficient multiplier 32, the band limitation is caused only for the 45 ° component from the upper right to the lower left on the screen. Since there is no band limitation for other components in the XY direction or the 45 ° direction from the upper left to the lower right on the screen, image quality degradation can be minimized.

Note that the present invention is not limited to only the above-described embodiment. For example, the angle θ is not limited to 45 degrees and can be set to an arbitrary angle. May be weighted and added. In addition, various changes can be made without departing from the spirit of the present invention.

H. Effects of the Invention According to the two-dimensional filter device of the present invention, when an input image is deformed to obtain an output image, good aliasing elimination (anti-aliasing) can be performed regardless of the reduction deformation in any direction. -Aliasing) effect can be exhibited, and the filter operation is relatively simple, and an output image with little image quality degradation can be obtained by a simple configuration and operation processing.
Moreover, since filtering can be performed only in the direction in which the deformation occurs, and unnecessary filtering can be prevented in the direction in which the deformation does not occur, deterioration of the image quality can be effectively suppressed.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a schematic configuration of a two-dimensional filter device according to one embodiment of the present invention, and FIGS. 2 to 5 are diagrams showing four band-limited filters used in the embodiment. FIG. 6 is a schematic plan view showing each filtering direction, FIG. 6 is a block diagram showing a general digital filter configuration, and FIG. 7 is a schematic plan view for explaining the relationship between a two-dimensional filter operation and each pixel on the screen. is there. DESCRIPTION OF SYMBOLS 1 ... Input terminal 2 ... Output terminal 10 ... 1st filter circuit system 11, 12, 21, 22 ... Band limiting filter 20 ... 2nd filter circuit system 30 ... Addition circuit

Claims (1)

(57) [Claims] 1. A two-dimensional filter device for filtering an input signal representing an input image according to the deformation when converting the input image into an output image that has been geometrically deformed. A first band-pass filter that filters in the Y-axis direction and a second band-pass filter that filters in the X-axis direction
Equivalent to the screen coordinate axis direction by the band-limiting filter of
A first filter circuit for filtering in the XY-axis direction; a third band-limiting filter for filtering the input signal in a direction inclined by a non-zero angle θ with respect to the Y-axis; and a non-zero filter for the Y-axis. A second filter circuit system for performing filtering in each direction having the inclinations of the angles θ and −θ with respect to the Y axis by using a fourth band limiting filter that performs filtering in a direction inclined by the angle −θ, An adder circuit for weighting and adding the signal from the first filter circuit system and the signal from the second filter circuit system, and controlling a weighted addition coefficient of the adder circuit according to the direction of the deformation. By controlling the band limiting amount of the first to fourth band limiting filters according to the degree of the deformation, the filtering is performed only in the direction of the deformation. A two-dimensional filter circuit.