JP2001189850A - Device and method for converting resolution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a circuit by using a single interpolation circuit and to use a high-level interpolating method in a resolution converter. SOLUTION: The resolution converter in a picture processor for converting the resolution of a picture is provided with a picture property detection circuit for discriminating characters or a natural picture from video signals in which characters and a natural picture coexist, an interpolation function generating circuit for generating an interpolation function by a cubic convolution system based on the discrimination of the character or the natural picture, and a resolution converting circuit for performing resolution conversion of contracting or magnifying to the video signal based on the interpolation function outputted from the interpolation function generating circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a resolution conversion apparatus and method for an image processing apparatus, and more particularly to a resolution conversion apparatus and method for performing resolution conversion for reducing or enlarging an input video signal.

[0002]

2. Description of the Related Art Hitherto, a resolution conversion device in an image processing apparatus has been used to display various input signals particularly in a fixed pixel display device such as a liquid crystal display (hereinafter, LCD) or a plasma display (hereinafter, PDP). It is used as a circuit.

[0003] Such a resolution conversion device has become popular, but in recent years it has been required to improve the image quality. In addition, LCDs and PDPs are often used as monitors for personal computers, and video outputs of personal computers are often used. Recently, many personal computers have a DVD-ROM drive or a TV tuner, and some computer images are output. The part may display a moving image of a natural image in a window display.

In this case, a video signal is a mixture of text characters and graphics of a computer and a natural moving image, and it is also required to display all the images with high image quality.

In order to meet this demand, for example, as disclosed in Japanese Patent Application Laid-Open No. H11-055503, it has been proposed to adaptively switch between natural images and characters by using an interpolation circuit.

According to the publication, when converting the resolution of a digital image, even if the image is a mixture of characters and a natural image, the sharpness of the character and the gradation of the natural image are not lost. Assuming that the resolution conversion ratio is an integer ratio M: N, the original image is divided into M × M pixel subdivision regions. If the image processing of the linear interpolation circuit is determined to be an image, and if the image processing is equal to or less than the threshold value, the image of the adaptive thinning circuit according to the correlation coefficient for each of the M × M pixel regions determined to be a character image if determined to be a character image. In an image processing apparatus that performs processing and reduces the size to N × N pixels,
The reduction process for each subdivided image region is a process of thinning out MN lines in both the row and column directions.
It also describes that lines to be thinned are determined for each subdivided image area.

[0007]

The technique disclosed in the publication requires two types of interpolation circuits and the interpolation circuit is composed of a linear interpolation circuit and an adaptive thinning circuit. There is a problem that cannot be met.

The main object of the present invention is to provide a single interpolation circuit.
By simplifying the circuit and using advanced interpolation methods,
An object of the present invention is to provide an optimum interpolation circuit for each image by the coefficient control.

[0009]

According to the present invention, a circuit for detecting the characteristics of an image and a characteristic of an interpolation function of the resolution conversion circuit are changed on the basis of the detection result in a resolution conversion device in the image processing device. The circuit is provided.

The present invention also relates to a resolution conversion device in an image processing device for converting the resolution of an image, wherein an image property detection circuit for determining whether a character or a natural image is present from a video signal in which a character and a natural image are mixed, An interpolation function generating circuit that generates an interpolation function by a cubic convolution method based on whether the image signal is a natural image or not, and performs resolution conversion for reducing or enlarging the video signal based on the interpolation function output from the interpolation function generation circuit. A resolution conversion circuit.

The present invention also relates to a resolution conversion method in an image processing apparatus for converting the resolution of an image, wherein a character or a CG image is converted for each block or pixel from a video signal in which a character or a CG image and a natural image are mixed. Determine whether the image is a natural image, generate an interpolation function by a cubic convolution method based on the determination of the character or the CG image or the natural image, and perform resolution conversion for reducing or enlarging the video signal based on the interpolation function. It is characterized by performing.
The image processing apparatus according to the present invention, which will be described with reference to FIG. 1, includes an image property detecting circuit 3 and an interpolation function generating circuit 4 according to the present invention, in addition to the configuration of the resolution converting circuit 2.

The image property detection circuit 3 determines whether the video signal input 1 is a natural image input by a camera or the like, a text character or a CG image generated by a computer or the like, on a pixel-by-pixel basis or in an appropriate block unit. Judgment is made and the information is output to the interpolation function generation circuit 4. The interpolation function generation circuit 4 generates an optimum interpolation function for each image based on the information, and the resolution conversion circuit 2 executes an operation called resolution conversion for reduction or enlargement based on the interpolation function.

Therefore, an effect is obtained that the resolution conversion process can be performed with characteristics optimal for the characteristics of each image.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described.
This will be described in detail with reference to the drawings.

(1) Description of Configuration Referring to FIG. 1, there is shown an image processing apparatus as one embodiment of the present invention. This image processing apparatus includes a resolution conversion circuit 2, an image property detection circuit 3, an interpolation function generation circuit 4,
And a resolution setting circuit 6. The image property detection circuit 3 determines whether the input video signal is a natural image, a text character generated by a computer or the like, or a CG image for each pixel or in an appropriate block. In the image property detection circuit 3, a high-pass filter and a comparator are provided, and the output of the high-pass filter is input to the comparator, and is compared with a predetermined threshold value. If the threshold value is larger, it is determined that there are many high-frequency components. , A text character or a CG image, and if it is smaller than the threshold value, it is determined to be a natural image. The result is
It is supplied to an interpolation function generating circuit 4 for generating an interpolation function by cubic convolution, and a coefficient for determining the interpolation function is output. The output is input to a resolution conversion circuit 2, and a resolution conversion process is performed by using the interpolation coefficient.

The interpolation function generating circuit 4 is a constant a for controlling interpolation characteristics by a cubic convolution method using hardware by a dedicated DSP (Digital Signal Processor) for generating functions or software by a program having storage means. And the interpolation function h according to the resolution setting that will change the interpolation position.
(T) is calculated and output to the resolution conversion circuit 2. The interpolation function h (t) calculates and outputs a luminance or a hue for resolution conversion of a target block or a target pixel from a 4 × 4 block unit or from a 4 × 4 dot in the horizontal and vertical directions.

The resolution setting circuit 6 is a setting means for setting the resolution of an input video signal by input means such as a keyboard and a mouse, and outputs a signal corresponding to the interpolation function generating circuit 4 and the resolution converting circuit 2 to each. I do.

In the image property detecting circuit 3, a method of discriminating between a text character or a CG image and a natural image can also be judged based on the difference between the maximum density and the minimum density near the target image. If the density difference is larger than a predetermined value, it is determined to be a text character or a CG image, and if the density difference is smaller than a predetermined value, it is determined to be a natural image. This discrimination method is complicated in configuration in order to detect the density difference between the maximum density and the minimum density, but may be used in the present embodiment.

(2) Description of Operation Hereinafter, the operation of this embodiment will be described.

In FIG. 1, a video signal input 1 is input to a resolution conversion circuit 2 and an image property detection circuit 3.
The image property detection circuit 3 detects a high-frequency component of the input video signal. If the high-frequency component is higher than a certain threshold value, it is determined to be a text character or a CG image generated by a computer or the like. It is determined that the input image is a natural image input. Image property detection circuit 3
Sets the value of the constant a for controlling the interpolation characteristics.

The result is input to the interpolation function generating circuit 4. The interpolation function generation circuit 4 generates an interpolation function called cubic convolution, as shown in FIG. The cubic convolution means that an interpolation value of a new sample point P (X, Y) at the time of reduction or enlargement is added to each data of 16 points around P (X, Y), as shown in FIG. This is a method of generating by multiplying an interpolation function.

Here, the mathematical formula of FIG. 2 will be described.
The interpolation function h (t) is

(Equation 1) ・ ・ (1) Where a is a constant for controlling the interpolation characteristics, P
The interpolation value Q of (X, Y) is given by: Q = ΣΣP (k, l) · h (X_k−X) · h (Y_k−Y)... (2) Also, t is the interpolation pixel P (X, Y) to be obtained.
And the other reference points (16 points) in the X and Y directions
Separated. That is, X_k-X, Y_kThis corresponds to -Y. One pixel
The minute distance is one.

Therefore, h (t) is 16 in the x direction, y
There are 16 in the direction, 32 of these interpolated values and P (k,
The convolution of l) becomes the value of P (X, Y). X is the x coordinate of the interpolation pixel, and Y is the y coordinate of the interpolation pixel.

K and l represent the x coordinate of the reference point. For example, the tenth or 150th number counted from the left. It is used to generally represent the coordinates of a reference pixel. Similarly, 1 is the coordinate of the reference point in the y direction.

For example, if P (k, l) is the 100th pixel from the left and the 50th pixel from the top, P (k, l) becomes
P (100, 50). Similarly, P (k-1,1-
1) = P (99,49). Then P
If (X, Y) is 100.75 from the left and 50.25 from the top, P (100.75, 50.25).

Next, P (k-1, l-1) = P
The interpolated value of P (X, Y) for (99,49) is obtained as follows.

T = Xk−X = 99−100.7 in the x direction
5 = −1.75 Since the absolute value of t is 1 or more, h (t) is obtained from the equation (1).
Uses the second expression.

H (t) = h (-1.75) = a│-1.
75│^Three-5a│-1.75│^Two + 8a | -1.75 |-
4a to obtain an interpolation function. Here, since a is a constant, h
(T) can be obtained. This h (t) and P (k−
1,1,1) (assuming the result is R),
Next, calculation in the Y direction is performed.

T = Yk-Y = 49-50.25 in the y direction
= −1.25 and the absolute value of t is 1 or more, so h (t) uses the second equation.

H (t) = h (-1.25) = a│-1.
25│^Three−5a | −1.25 |^Two + 8a│-1.25│-
From 4a, an interpolation function in the y direction is obtained. This h (t) and earlier
Multiply the obtained R to obtain the interpolated value of P (k-1, l-1)
Confuse. Similarly, calculate the other 15 points and add all the results.
Together, the value Q of P (X, Y) is obtained. This is the supplement
It becomes the value of the inter-pixel. That is, this calculation is: Q = ΣΣP (k, l) · h (X_k−X) · h (Y_k−Y), and becomes the interpolation value Q.

In this case, the interpolation characteristic controls the interpolation characteristic.
It can be changed by the determined constant a. FIG. 3 shows a change in the interpolation characteristic when the constant a is changed. FIG. 3 shows the result of equation (1) of the interpolation function h (t). The horizontal axis is the interval t. That is, the distance between the interpolation pixel and the reference pixel in the X and Y directions. In the example described above, the value of h (t) at t = -1.75 or t = -1.25 can be read.

For example, when the value of a is -2, the interpolation curve becomes steep, and the interpolation characteristic has an effect of increasing sharpness, and is suitable for interpolation of a text character or a CG image. A text character or CG image often changes in luminance and hue with a steep change with respect to a background image, often has a high frequency component in terms of frequency, and is determined to be a text character or CG image. Then, an interpolation function h (t) is calculated by setting a = −2.0.
The correction coefficient based on the interpolation function h (t) is supplied to the resolution conversion circuit 2.

On the other hand, when the value of a is -0.5, the interpolation curve becomes gentle, and the interpolation characteristic becomes that of a general natural image. In other words, in the case of a natural image, in general, there are few sudden changes in luminance and hue due to changes in man-made objects such as buildings and overpasses in nature. Is small, the constant a for controlling and determining the interpolation characteristic is set to a small value, and the interpolation function h
(T) is calculated and supplied to the resolution conversion circuit 2.

P (X, Y) shown in FIG. 2 is a pixel that does not exist at the current sample point, and indicates a pixel newly generated when the resolution is converted. Also, blocks around P (X, Y), for example, P (k, l) and P (k + 1,
The blocks surrounded by l), P (k + 1, l + 1), and P (k, l + 1) are used when obtaining the properties of the image. When the interpolation coefficient is switched in the block unit determination, the switching conversion is performed by determining the block in which P (X, Y) exists.

The interpolation value Q obtained as described above becomes a pixel value newly generated when the resolution is converted. This interpolation value Q is the output itself of the resolution conversion circuit. This set of Qs becomes a video signal after resolution conversion.
Further, the position of the image is changed according to the resolution setting signal from the resolution setting circuit 6.

Here, a constant a for generating characteristics suitable for interpolation for text characters or CG images in advance
And a constant a for generating a characteristic suitable for interpolation of a general natural image is prepared, and the interpolation function generation circuit 4 generates the image property detection circuit 3 based on the determination result for each pixel or in an appropriate block unit. , An interpolation function optimal for each image is generated and input to the resolution conversion circuit 2.

The resolution conversion circuit 2 obtains an interpolation value Q based on the input interpolation function, performs resolution conversion for reduction or enlargement, and outputs the result to the video output 5.

The details of the resolution conversion circuit 2 are shown in FIG.
The operation will be described. The video signal input 1 is first input to a FIFO (First In First Out) 20 which is a first-in first-out buffer by a vertical resolution converter, and absorbs a change in the time axis due to the vertical resolution conversion. The output is input to line memories 21, 22, and 23,
In addition to the output of O20, data for four lines is prepared. The respective outputs are input to coefficient units 24, 25, 26, 27. On the other hand, the interpolation value Q from the interpolation coefficient generation circuit 4
Is input to a coefficient generation circuit 12, and based on the data and actual image position information, coefficient units 24 to 27 are output.
Generate a coefficient to input to. The coefficient generating circuit 12 generates an interpolation coefficient based on the constant a, the reduction ratio / enlargement ratio, and the position information in the X and Y directions according to the determination result of the image property detection circuit. It is provided as an LUT (lookup table) using a ROM / RAM that receives the above as input and outputs an interpolation coefficient. Further, a setting signal 13 corresponding to the setting of the resolution from a keyboard or the like is input to the coefficient generation circuit 12, and a lookup table in the coefficient generation circuit 12, for example, is set by the setting signal. A coefficient corresponding to the interpolation value Q is generated. Coefficient generation circuit 12
Then, a digital signal of a coefficient value input to the coefficient unit is output serially in timing.

In the coefficient units 24, 25, 26, and 27, the above coefficients are multiplied by the input signals,
The outputs of 5, 26 and 27 are h (−1−y),
h (0-y), h (1-y), h (2-y), and the adders 28, 29, 30 add up the respective results.
In that case, the result of the adder 28 is h (−1−y) + h (0
−y), and the result of the adder 29 is h (1−y) + h
(2-y), and the output of the adder 30 is h (-1-y).
+ H (0-y) + h (1-y) + h (2-y).

The output of the adder 30 is then subjected to a horizontal resolution conversion unit to perform resolution conversion processing on adjacent pixels in the horizontal direction of the cubic convolution. In FIG. 3, the output of the adder 30 is input to one-dot delay units 31, 32, and 33 that delay one pixel, and together with the output of the adder 30, prepares data for four pixels. Each output is
The coefficients are input to coefficient units 34, 35, 36, and 37. On the other hand, the data 11 from the interpolation coefficient generation circuit 4
2 and generates coefficients to be input to coefficient units 34 to 37 based on the data and the actual image position information.

In the coefficient units 34, 35, 36, and 37, the above coefficients are multiplied by the input signal, and the outputs of the coefficient units 34 to 37 are h (−1−x), h (0−x), h ( (1
−x), h (2-x), and the adders 38, 39, 40
Then, add each result. In that case, the adder 38
Is h (-1-x) + h (0-x), the result of the adder 39 is h (1-x) + h (2-x), and the output of the adder 40 is h (-1-x) ) + H (0-x) + h (1
−x) + h (2-x).

The above operation corresponds to the resolution conversion processing in the vertical direction, and the resolution conversion processing in the horizontal direction in the subsequent stage is also performed together with the resolution conversion processing by cubic convolution. In the horizontal resolution conversion process, only the line memory unit is replaced by a one-dot delay, and the difference in configuration is small. After the horizontal resolution conversion process, the FIFO 41 corrects the time axis and outputs the video signal as the video signal output 5.

[0043]

As described above, according to the present invention, the image property detecting device determines whether a natural image input by a camera or the like, a text character or a CG image generated by a computer or the like is pixel by pixel or an appropriate block. Judgment is made in units, based on the information, an optimal interpolation function is generated for each image, and resolution conversion is performed. Therefore, an effect that resolution conversion processing having characteristics optimal for the properties of each image can be performed can be performed. can get.

The interpolation circuit employs cubic convolution, which enables high-precision interpolation, and performs interpolation by changing only the coefficients with one interpolation circuit. The effect that the scale can be reduced can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a resolution conversion circuit of an image processing device according to the present invention.

FIG. 2 is an explanatory diagram of cubic convolution of the image processing device according to the present invention.

FIG. 3 is a characteristic diagram of an interpolation function of a cubic convolution of the image processing apparatus according to the present invention.

FIG. 4 is a specific circuit diagram of a resolution conversion circuit of the image processing device according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 video signal input 2 resolution conversion circuit 3 image property detection circuit 4 interpolation function generation circuit 5 video signal output 11 interpolation function generation circuit output signal 12 coefficient generation circuit 20, 41 FIFO 21 to 23 1 line memory 24 to 27, 34 to 37 Coefficient multiplier 31-33 1 dot delay unit 28-30, 38-40 Adder

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Claims (6)

[Claims] 1. A resolution conversion device in an image processing device for converting the resolution of an image, comprising: an image property detection circuit for determining whether a character or a natural image is present from a video signal in which a character and a natural image are mixed; An interpolation function generation circuit that generates an interpolation function based on the determination of the cubic convolution method, and a resolution conversion circuit that performs resolution conversion for reducing or enlarging the video signal based on the interpolation function output from the interpolation function generation circuit. A resolution conversion device comprising: 2. The image property detecting device includes a high-pass filter for detecting a high-frequency component from the video signal, and a comparator for comparing an output of the high-pass filter with a predetermined value. The resolution conversion apparatus according to claim 1, wherein a determination signal for determining whether the image is a character or a natural image is output in units. 3. The interpolation function generation circuit according to claim 1, wherein the interpolation function generation circuit generates an interpolation function by the cubic convolution using a constant a for controlling and determining an interpolation characteristic from the image property detection circuit. Resolution converter. 4. The resolution conversion circuit receives the video signal by FIFO, and comprises a plurality of line memories, an equal number + 1 coefficient multipliers, and an adder for adding respective outputs of the same number + 1 coefficient multipliers. Vertical resolution conversion unit, a plurality of 1-dot delay units, and the same number + 1 coefficient multipliers and the same number +
A horizontal resolution conversion unit comprising an adder for adding each output of one coefficient multiplier; a FIFO receiving an output of the horizontal resolution conversion unit; and each coefficient from an interpolation function from the interpolation function generation circuit. 2. The resolution conversion apparatus according to claim 1, further comprising a coefficient generation circuit for generating a coefficient of the multiplier. 5. A resolution conversion method in an image processing apparatus for converting the resolution of an image, wherein the character or CG image or the natural image is obtained for each block or pixel from a video signal in which a character or a CG image and a natural image are mixed. And generating an interpolation function by a cubic convolution method based on the determination of the character or the CG image or the natural image, and performing resolution conversion of reduction or enlargement of the video signal based on the interpolation function. Characteristic resolution conversion method. 6. The resolution conversion method according to claim 1, wherein the determination as to whether the image is a character or a CG image or a natural image is made by determining a high-frequency component for each block or each pixel according to an output level.