JP2000156846A - Device and method for converting moving image format - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire an interlaced image that does not have unnaturalness by converting at least either the number of scanning lines or a scanning line structure of an image signal that is subjected to band limitation and obtaining an interlaced image signal. SOLUTION: A moving image signal of a 480 (p) format supplied from a 480 (p) image input terminal 1 is given to a variable band vertical low-pass filter(VLPF) 2 and a motion vector(MV) detector 5. A filter in which a pass- band is changed by an image part is applied to the variable band VLPF 2, and a scanning line thinning device 3 to which the 480 (p) dynamic signal whose frequency characteristic is changed thins a scanning line while making a scanning line to be thinned reverse with even number frames and odd number frames and forms an interlaced signal. An MV detector 5 detects an MV from a supplied image in every block of 16×16 pixels or 8×8 pixels. A vertical motion deciding device 6 obtains a vertical motion coefficient (k) from MV vertical components and gives it to the variable band VLPF 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts a moving image signal into a different moving image format when transmitting, storing, and displaying the image signal, and particularly converts the moving image signal from a progressive image signal to an interlaced image signal or from an interlaced image signal. That converts the number of scanning lines into an interlaced image signal.

[0002]

2. Description of the Related Art <Image format conversion> A moving image signal includes the number of scanning lines, the scanning line structure, the image rate, the number of horizontal pixels,
Several types of formats exist as standards according to the image aspect ratio and the like. Examples are shown in Table 1 below, and the scanning line structure includes an interlaced (interlaced) scanning type and a progressive (sequential) scanning type. The number of scanning lines is 480 lines for the current TV, 720 lines for the HDTV, and 108 lines.
There are 0. The image (frame / field) rate is 60 Hz (59.94 Hz to be exact) for interlacing, but 24 Hz or 30 Hz, which is the same as for film, for progressive scanning.

[0003]

【table 1】

It is necessary to convert image signals between these image formats, where image rate conversion,
The conversion of the scanning line structure, the conversion of the number of scanning lines, and the conversion of the number of horizontal pixels are performed. When converting a progressive image signal into an interlaced image signal, the band is limited in the vertical direction and then the scanning lines are thinned. Since the pass band is suppressed to such an extent that line flicker does not cause a problem, the pass band is set to about 70% of the progressive. Conversion of the number of scanning lines between interlaced image signals may be performed in units of fields or in units of frames. In the processing in units of fields, only the vertical resolution of the field image signal can be obtained. On the other hand, when processing is performed on a frame basis, a good resolution can be obtained when the image is stationary. However, when the image moves, even and odd fields that differ in time overlap with each other, and blurs and double images are generated. This significantly deteriorates image quality.

<Conventional Moving Image Format Converter> FIG. 6 shows an example of a conventional structure of a moving image format converter. This example is a case where a progressive image (480p) having 480 scanning lines is converted into an interlaced image (480i) having 480 scanning lines. 48
The moving image signal of the 480p format supplied from the 0p image input terminal 1 is supplied to a vertical low-pass filter (LPF) 61
The frequency components higher than 180 cph (cycle per height) are suppressed, and are given to the scanning line thinning device 3. The scanning line thinning unit 3 thins out the scanning lines between the even-numbered frames and the odd-numbered frames while reversing the thinned scanning lines to form an interlace signal. 4 obtained in this way
The moving image signal of the 80i format is output from the 480i image output terminal 4.

[0006]

In the conventional moving picture format converter, the scanning lines are thinned out after applying a fixed vertical filter in which aliasing distortion components remain to some extent irrespective of the contents of the image. Therefore, when there is no movement in the vertical direction, the residual aliasing component contributes to the improvement of the resolution, but when the image moves in the vertical direction, the interlacing relationship is visually disrupted, and unnaturalness is a problem. Was. The present invention has been made by focusing on the above points, and when obtaining an interlaced image signal, in a portion where there is movement in the vertical direction,
It is an object of the present invention to provide a moving image format conversion apparatus which narrows a filter pass band to such a degree that aliasing distortion does not remain and produces an interlaced image without unnaturalness.

[0007]

SUMMARY OF THE INVENTION According to the present invention, when the number of scanning lines or the scanning line structure of a supplied image signal is converted to obtain an interlaced image signal, the amount of vertical movement of the supplied image signal is obtained. And applying a vertical low-pass filter whose pass bandwidth is controlled accordingly to the image signal, and converting at least one of the number of scanning lines of the band-limited image signal and the scanning line structure, A moving image format conversion apparatus and method for obtaining an interlaced image signal.

(Operation) In the present invention, when obtaining an interlaced image signal, the degree of vertical movement is detected for each image portion, and in a portion where there is no vertical movement, aliasing distortion components remain as before. In the case where an interlaced image is obtained by thinning out scanning lines, the resolution is improved. On the other hand, in a part where there is movement in the vertical direction, the filter pass band is narrowed to suppress aliasing components. In this case, if an interlaced image is obtained by thinning out the scanning lines, the image has no aliasing component due to the number of field scanning lines. Therefore, the resolution is equivalent to the number of scanning lines in the field, but no unnaturalness occurs.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment Moving Image Format Converter> A first embodiment of a moving image format converter according to the present invention.
The embodiment will be described below with reference to the drawings. FIG. 1 shows the configuration of the moving picture format conversion apparatus.
The same components as those in the conventional example of FIG. 6 are denoted by the same reference numerals. FIG. 1 includes a variable band vertical low-pass filter (VLPF) 2 instead of the vertical LPF 61 as compared with FIG.
A motion vector (MV) detector 5 and a vertical motion determiner 6 are added. 4 supplied from the 480p image input terminal 1
The 80p format video signal is a variable band VLPF
2 and the MV detector 5. In the variable band VLPF 2, a filter in which a pass band is changed according to an image portion is applied, and a 480p moving image signal whose frequency characteristic is changed is provided to the scanning line thinning device 3.

FIG. 4 shows the configuration of the variable band VLPF 2, but the band can be changed by variably adding the output of the wide band filter and the output of the narrow band filter. The supplied signal is a wideband VL
It is provided to the PF 41 and the narrow band VLPF 44, and is band-limited in the vertical direction by respective characteristics. The specific characteristics are shown in FIG.
A, the transmission characteristic of the vertical frequency (ν) is about -6 dB at 180 cph (cycle per height) in a wide band and about -6 dB at 120 cph in a narrow band. Narrowband VL
The output of the PF 44 is multiplied by a vertical motion coefficient (k) given from the vertical motion determiner 6 by a multiplier 45. Broadband VL
The output of the PF 41 is multiplied by a multiplier 42 by (1−k) given from a subtractor 46. The result of each multiplication is an adder 4
It is added at 3 and output.

In FIG. 1, a scanning line thinning unit 3 thins out scanning lines in an even-numbered frame and an odd-numbered frame while reversing the scanning lines to form an interlace signal, as in the conventional example. The 480i signal obtained is 480
Output from the i-image output terminal. FIG. 7 shows the state of the number of scanning lines by the processing of this embodiment. In FIG. 7, the vertical direction indicates the vertical direction of the image, the horizontal direction indicates time, and ○ indicates each scanning line. On the other hand, the MV detector 5 outputs 1 to the supplied image.
A motion vector (MV) is detected for each block of 6 × 16 pixels to 8 × 8 pixels, and its vertical component is supplied to a vertical motion determiner 6. The vertical motion judging unit 6 obtains a vertical motion coefficient (k) from the vertical component of the MV, and gives it to the variable band VLPF2.

The vertical motion judging unit 6 needs only the vertical component of the MV. However, in the detection by pattern matching, only the vertical motion cannot be detected.
The detector 5 detects as a vector. The accuracy of the MV to be detected is 1/2 pixel or 1/4 pixel in the vertical direction. Since precision is not required in the horizontal direction, it may be coarse enough to prevent erroneous detection, and one pixel precision is set. Next, the operation of the vertical motion determiner 6 will be described. FIG. 5 shows the internal configuration thereof. The supplied MV vertical component value is made an absolute value by the absolute value converter 51. Next, the limiter 52 keeps the value when the absolute value of the vertical component of the MV is 1 or less, and always sets it to 1 when the absolute value is 1 or more. The value obtained in this way is for each block, but the control signal needs to be changed smoothly in pixel units so that the filter pass band does not change suddenly at the block boundary.

Therefore, a value for each block is assigned to each pixel in the block by a pixel expander 53, and the value is assigned to a space LPF5.
4 to obtain a vertical motion coefficient (k) that changes smoothly in pixel units. The relationship between the vertical motion amount and the filter control will be described with reference to FIG. In a portion where there is no motion in the vertical direction, the vertical motion coefficient (k) is 0, and the filter has a wide band. In this case, as shown in FIG.
Only ph and above are suppressed. Scanning lines are thinned out 480i
Then, the component of 120 cph or more becomes the aliasing distortion component as shown in FIG. 10B, but when interlaced display, a resolution higher than the number of scanning lines of the field is given. Even if the image moves in the horizontal direction due to panning or the like, the interlace relationship is visually maintained if there is no movement in the vertical direction.

The vertical movement is one pixel (1 pixel) per frame.
In the case of (line), the interlaced signal has the same image signal in each field, and the scanning lines visually appear to overlap. In this case, the aliasing component does not contribute to the improvement of the resolution at all, and causes unnaturalness. However, in the present embodiment, since the filter has a narrow band, 12
Frequency components higher than 0 cph are suppressed. Even if the scanning lines are thinned out to 480i, there is no aliasing component as shown in FIG. 10D, and no unnaturalness occurs even in the interlaced display.

When the vertical motion absolute value is an intermediate motion amount larger than 0 and smaller than 1, the filter also has an intermediate band, and some aliasing distortion components remain. When the absolute value of the vertical movement is larger than 1, the aliasing component may contribute to the improvement of the resolution due to the scanning line relationship. However, when the movement in the vertical direction is large, the amount of movement usually changes, and the image quality changes due to the change in the amount of movement, which makes the filter unnatural. This control is determined by the characteristics of the limiter 52, and the characteristics are shown in FIG. In the case where the characteristic A has one or more motions, the band is always narrow. In the case of the characteristic B, the portion where the aliasing distortion component contributes to the improvement of the resolution is the case where the filter band is widened.

<Second Embodiment Moving Image Format Converter> A second embodiment of the moving image format converter of the present invention will be described below. The difference from the first embodiment is in the format conversion relationship. The format conversion is not a simple conversion from a progressive image to an interlaced image, but a conversion from 720p to 1080i. FIG. 2 shows the configuration of the moving picture format conversion apparatus, and the same components as those in the first embodiment of FIG. 1 are denoted by the same reference numerals. In FIG.
Compared to FIG. 1, there are pixel number converters 28 and 29 and a scanning line number converter 27, and other components also operate differently. 720
The 720p format moving image signal supplied from the p image input terminal 21 is supplied to the variable band VLPF 22 and the pixel number converter 29.

In the variable band VLPF 22, a filter whose pass band is changed according to the image portion is applied, and the resultant signal is supplied to the scanning line number converter 27 as a 720p moving image signal whose frequency characteristic is changed. The configuration of the variable band VLPF 22 is the same as that of the variable band VLPF 2 of the first embodiment, but the processing image size and characteristics are different. The characteristics are shown in FIG. 8B, where the wide band has no band limitation and the narrow band has 270 cph.
To have a pass characteristic of about -6 dB. Scanning line number converter 27
Converts 720 lines into 1080 lines by resampling and supplies the converted lines to the scanning line thinning unit 23. The conversion ratio is 2 to 3. Since this process results in oversampling and the resolution remains equivalent to 720 lines, line flicker does not pose a problem even if the wide band characteristics of the variable band VLPF 2 are not band-limited.

The processing content of the scanning line thinning unit 23 is the same as that of the scanning line thinning unit 3 of the first embodiment except that the processing image size is different. In the even-numbered frame and the odd-numbered frame, the scanning lines are thinned while reversing the thinned scanning lines, and the formed interlace signal is supplied to the pixel number converter 28. FIG. 7 shows the state of the scanning line from 720p to 1080i by these processes. The pixel number converter 28 converts the number of horizontal pixels from 1280 pixels to 1920 pixels. The conversion ratio is 2 to 3. This processing results in oversampling, and the resolution remains equivalent to 1280 pixels. The 1080i signal thus obtained is output from the 1080i image output terminal 24.

On the other hand, the supplied image is a pixel number converter 29.
Then, the 720p image is subjected to 1/4 sub-sampling in the horizontal direction, converted from 1280 pixels to 320 pixels, and provided to the MV detector 25. The MV detector 25 is the MV detector of FIG.
Although the basic processing method is the same as that of the detector 5, the block size and the search range are different because MV detection is performed on the subsampled image. The block size is set to 4 (horizontal) × 16 (vertical) pixels in accordance with the subsample. The search range is set to about half that of the MV detector 5 in FIG. 1 according to the number of pixels after the sub-sampling. As a result, the processing amount is reduced to about 1/16 as compared with the case where no sub-sample is performed. The subsample can be 1/8 or the like, and in this case, the processing amount becomes 1/64. However, if the block size is 2
If it is set to × 16, MV detection becomes slightly inaccurate and 4 × 16
If it is left as it is, the control unit becomes slightly coarse. The operation of the vertical motion determiner 26 is the same as that of the vertical motion determiner 6 in FIG. 1, except that the image size is different.

<Third Embodiment Moving Image Format Converter> A third embodiment of the moving image format converter of the present invention will be described below. The difference from the first and second embodiments is in the format conversion relationship from 1080i to 480.
Convert to i. FIG. 3 shows the configuration of the moving picture format conversion apparatus, and the same components as those in the first embodiment of FIG. 1 are denoted by the same reference numerals. 3 includes a pixel number converter 38, an interlace (i) → progressive (p) converter 39, and a scanning line number converter 37 as compared with FIG.
There is no MV detector 5. The other components also operate differently.

A moving image signal of 1080i format supplied from the 1080i image input terminal 31 is supplied to a pixel number converter 38. The pixel number converter 38 converts the number of horizontal pixels from 1920 pixels to 720 pixels, and is provided to the i → p converter 39. The conversion ratio is 8: 3. The i → p converter 39 converts an interlaced image into a progressive image, converts 1080i into 1080p, and supplies the 1080p to a variable band vertical low-pass filter (variable band VLPF) 32. The specific processing contents of the i → p converter 39 are described in
No.-130716, "Scanning Line Interpolation Apparatus and Scanning Line Interpolation Motion Vector Detection Apparatus". There, MV detection is performed, and motion compensation is performed on the preceding and succeeding fields to perform inter-field interpolation. The MV vertical component value obtained at that time is output and given to the vertical motion determiner 36. In this embodiment, since the MV detection result of the i → p converter 39 is used for the vertical motion determination, the MV detector alone is not required.

By such a progressive processing,
The aliasing distortion component that was mixed in due to the scanning line thinning of the interlace signal returned to the original 270 cph or more,
Components below 0 cph are significantly reduced. Variable band VLP
In F32, a filter in which the pass band is changed according to the image portion is applied, and the resultant signal is supplied to the scanning line number converter 37 as a 720p moving image signal whose frequency characteristic is changed. The configuration and the pass band of the variable band VLPF 32 are the same as those of the variable band VLPF 2 of the first embodiment shown in FIG. 1, but the processing image size is different.

The scanning line number converter 37 outputs 10
The 80 lines are converted into 480 lines, and the obtained 480p image is given to the scanning line thinning device 3. The conversion ratio is 9: 4. The scanning line thinning unit 3, as in FIG. 1, thins out the scanning lines in the even-numbered frames and the odd-numbered frames while reversing the thinning-out scanning lines to obtain a formed interlace signal. The 480i signal thus obtained is output from the 480i image output terminal 4. The vertical motion determiner 36 calculates i → p
Receives the vertical component value of MV from the converter 39 and calculates the vertical motion coefficient.
(k) is output. The operation of the vertical motion determiner 36 is the same as that of the vertical motion determiner 6 in FIG. 1, except that the image size is different.

[0024]

According to the present invention, when an interlaced image signal is obtained, the degree of vertical movement is detected for each image portion, and in a portion where there is no vertical movement, aliasing distortion components remain as in the past, and scanning is performed. When an interlaced image is formed by line thinning, the resolution is improved. On the other hand, in a part where there is movement in the vertical direction, the filter pass band is narrowed to suppress aliasing components. In this case, if an interlaced image is obtained by thinning out the scanning lines, the image has no aliasing component due to the number of field scanning lines. Therefore, the resolution is equivalent to the number of scanning lines in the field, but no unnaturalness occurs. As a result, it is possible to convert to a high-quality interlaced image signal with less unnaturalness while maintaining the resolution.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a moving image format conversion apparatus according to the present invention.

FIG. 2 is a diagram showing a configuration of a second embodiment of the moving picture format conversion apparatus of the present invention.

FIG. 3 is a diagram showing a configuration of a third embodiment of the moving picture format conversion apparatus of the present invention.

FIG. 4 is a diagram illustrating a configuration example of a variable band vertical low-pass filter (VLPF).

FIG. 5 is a diagram illustrating a configuration example of a vertical motion determiner.

FIG. 6 is a diagram illustrating a configuration example of a conventional moving image format conversion device.

FIG. 7 is a diagram showing a state of an image format.

FIG. 8 is a diagram illustrating frequency characteristics of a vertical low-pass filter (VLPF).

FIG. 9 is a diagram illustrating conversion characteristics of a limiter.

FIG. 10 is a diagram showing a state of a vertical spectrum.

[Explanation of symbols]

1: 480 interlaced (i) image input terminals, 2, 2
2, 32 ... variable band vertical low-pass filter (VLPF),
3, 23 ... scanning line thinning device, 4 ... 480 interlace
(i) Image output terminal, 5, 25 ... MV detector, 6, 26,
36: Vertical motion determiner, 21: 720 progressive
(p) Image input terminal, 24 ... 1080 interlace (i)
Image output terminals, 27, 37 ... scanning line number converter, 28,
38: pixel number converter, 39: interlace (i) → progressive (p) converter, 41: wideband vertical low-pass filter (VLPF), 42, 45: multiplier, 43: adder,
44 ... narrow band vertical low pass filter (VLPF), 46 ...
Subtracter, 51: absolute valuer, 52: limiter, 53: pixel expander, 54: spatial LPF, 61: vertical low-pass filter (LPF), k: vertical motion coefficient

Claims (2)

[Claims] 1. A moving image format conversion apparatus for converting at least one of the number of scanning lines and a scanning line structure of a supplied image signal to obtain an interlaced image signal, comprising: Motion amount detecting means for detecting an amount, and applying a vertical low-pass filter whose pass band width is controlled in accordance with the vertical motion amount to the supplied image signal, to thereby perform a band-limited image. A moving image, comprising: a filter unit for obtaining a signal; and a scanning line thinning unit for converting at least one of the number of scanning lines and the scanning line structure of the band-limited image signal to obtain an interlaced image signal. Image format converter. 2. A moving image format conversion method for converting at least one of the number of scanning lines and a scanning line structure of a supplied image signal to obtain an interlaced image signal, comprising: Detect the amount, on the supplied image signal, a vertical low-pass filter whose pass bandwidth is controlled according to the amount of vertical movement, to obtain a band-limited image signal, A moving image format conversion method, wherein at least one of the number of scanning lines and the scanning line structure of the band-limited image signal is converted to obtain an interlaced image signal.