JPH11308577A - Scanning line interpolation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning line interpolation circuit that obtains a scanning line interpolation image with high image quality without causing deterioration in the resolution and interpolation disturbance. SOLUTION: Vertical HPFs 3, 8 generate a field high frequency signal before and after a current field in a vertical direction. A vertical LPF 7 generates a current field low frequency signal in a vertical direction of the current field. A motion direction detection section 4 detects a moving direction value (s) of an image and a moving amount (k). Image shift devices 9, 10 shift a field high frequency signal according to the moving direction value (s). An in-field interpolation device 5 generates an in-field interpolation signal. Adders 13, 14 add the field high frequency signal and the current field low frequency signal to produce a spatiotemporal interpolation signal. Multipliers 13, 14 and an adder 15 mix adaptively the in-field interpolation signal and the time space interpolation signal according to the moving amount (k).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning line interpolation circuit used for converting an interlaced image into a progressive image.

[0002]

2. Description of the Related Art Standard television signals such as NTSC signals and HDTV signals are interlaced (interlaced scanning) signals. FIG. 5 is a diagram showing a scanning line structure,
(A) shows an interlaced signal, (b) shows a progressive (sequential scanning) signal, and (c) shows a signal obtained by converting an interlaced signal into a progressive signal by scanning line interpolation. Note that the progressive signal may be referred to as a non-interlaced signal. In FIG. 5, a circle indicates a scanning line, and a cross indicates an interpolated scanning line.

In FIG. 5, a vertical direction V is a vertical direction of a screen, and a horizontal direction t is a time direction. As shown in FIG. 5A, the interlace signal is composed of two fields in which one frame is shifted in time and in the vertical direction. On the other hand, the progressive signal is shown in FIG.
As shown in (1), there is no shift in the scanning line structure. In the interlaced signal, if the number of high frequency components in the vertical direction of the image increases, interlace interference such as generation of line flicker occurs. On the other hand, in a progressive signal, there is no interlace interference.

Therefore, as shown in FIG. 5 (c), by interpolating the scanning lines of a part thinned out by interlacing with surrounding scanning lines and converting them into progressive signals,
There is a processing method for removing interlace interference. Such a processing method is referred to as progressive scan conversion or double density conversion.

Conventionally, scanning line interpolation for sequential scan conversion and double-density conversion is performed by motion adaptive processing. That is, as shown in FIG. 6, when the image is stationary, a new scan line is generated by performing inter-field interpolation with the average value of the pixels A and B in the preceding and succeeding fields as a new pixel Q indicated by x. I do. If the image is moving, a new scan line is generated by performing intra-field interpolation with a new pixel Q indicated by the average value of the upper and lower pixels C and D.

[0006]

By the way, the progressive scanning conversion by inter-field interpolation or intra-field interpolation can be regarded as a spatio-temporal filter in the time-vertical region for an input signal. Hereinafter, the low-pass filter is abbreviated as LPF), and the intra-field interpolation has characteristics of a vertical LPF.

FIG. 7A shows a spectrum of a still image with respect to a time frequency f and a vertical spatial frequency ν. In a still image, as shown in FIG. 7A, the spectrum of the image exists only on the axis of f = 0. Note that f =
The spectrum that spreads around ● at 60 and −60 (Hz) is an even-order harmonic spectrum. The stopband of inter-field interpolation, which is the interpolation process for still images,
In FIG. 7 (a), the spectrum indicated by the hatched area and the area without the hatched area is the output signal after the sequential scan conversion.

Accordingly, in a still image, by performing inter-field interpolation, the original spectrum including the even-order harmonic spectrum is not impaired, and f = 30, -30 (Hz) indicated by a broken line which causes interlace interference is maintained. It is possible to remove only the odd-order harmonic spectrum spreading around the existing x. As a result, a progressive signal without image quality degradation can be obtained.

On the other hand, FIG. 7B shows a spectrum of a moving image with respect to a time frequency f and a vertical spatial frequency ν. Generally, in a moving image, as shown in FIG. 7B, the inter-field correlation is small, and the spectrum of the image is often spread to a high time region. The reason why inter-field interpolation cannot be used for a moving image can be explained from this. That is, in the inter-field interpolation,
This is because a spectrum in a high time range, which is a great feature of a moving image, is removed.

Therefore, a vertical filter having a characteristic of a stop band indicated by a hatched portion in FIG. 7B so as not to remove a spectrum in a high time band from a moving image, that is, an intra-field interpolation is required. No. However, in the fixed vertical LPF by the intra-field interpolation, the spectrum in the high time region is preserved, but a part of the original spectrum is lost.
Odd order harmonic spectra are not completely eliminated. Therefore, in the motion adaptation processing by the conventional scanning line interpolation circuit, the resolution deteriorates in the moving part, and interlace interference such as line flicker and jaggies is not completely removed.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem. Even when a moving portion exists in an image during scanning line interpolation, a high-quality image can be obtained without deteriorating resolution or interlace interference. It is an object to provide a scanning line interpolation circuit that can obtain a scanning line interpolation image.

[0012]

In order to solve the above-mentioned problems of the prior art, the present invention provides a scanning line interpolation circuit for interpolating a scanning line of an input image signal. An intra-field interpolation means (5) for generating an intra-field interpolation signal from scanning lines located vertically above and below; and a current-field low-frequency signal for generating a current-field low-frequency signal which is a vertically lower frequency component of the current field. Signal generation means (7); rear-field high-band signal generation means (3) for generating a rear-field high-band signal that is a high-frequency component in the vertical direction after the current field; A front-field high-band signal generation means (8) for generating a front-field high-band signal that is a high frequency component in the vertical direction immediately before with respect to
A moving direction detecting means for detecting a moving direction and a moving amount of an image from a field temporally preceding and following the current field; and the following field height according to the moving direction detected by the moving direction detecting means. First shift means (9) for shifting an area signal, and second shift means (10) for shifting the previous field high-frequency signal in accordance with the movement direction detected by the movement direction detection means.
And a spatio-temporal signal for generating a spatio-temporal interpolation signal by adding the post-field high-frequency signal and the pre-field high-frequency signal shifted by the first and second shift means and the current-field low-frequency signal. Interpolation signal generating means (13, 1)
4) and adaptive mixing means (11, 12, 1) for adaptively mixing the intra-field interpolation signal and the spatiotemporal interpolation signal in accordance with the amount of motion detected by the motion direction detection means.
And 5) providing a scanning line interpolating circuit.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A scanning line interpolation circuit according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of the scanning line interpolation circuit of the present invention, FIG. 2 is a block diagram showing an example of a specific configuration of the motion direction detector 4 in FIG. 1, and FIG. 3 is a scanning line of the present invention. FIG. 4 is a block diagram showing an example in which the interpolation circuit is applied to a motion adaptive interpolation device, FIG. 4 is a block diagram showing an example in which the scanning line interpolation circuit of the present invention is applied to a progressive scan conversion device, and FIG. 8 is a scanning line interpolation circuit of the present invention. FIG. 6 is a diagram showing an image spectrum for explaining the following.

First, the principle of the scanning line interpolation circuit of the present invention will be described with reference to FIG. When an image is translated in the vertical or horizontal direction, the spectrum of the image has a characteristic that it spreads with directionality. For example, when an image has a horizontal movement speed Vx = 0 and a vertical movement speed Vy =
8 when moving at a constant speed in 2 (scanning line / field)
As shown in (1), the spectrum of the image exists only on a fixed straight line indicated by a bold solid line on the f-v plane.

Therefore, in the present invention, the motion direction and the motion amount of the image are detected from a field temporally before and after the current field. This makes it possible to distinguish the spectra of a plurality of characteristic images. Also, based on the detected motion direction, the front and rear field high band signals are spatially shifted up, down, left and right and added to the current field low band signal to obtain a spatiotemporal interpolation signal. This makes it possible to perform an interpolation process having an optimal frequency characteristic on the spectrum of each characteristic image.

For example, with respect to an image having the spectrum shown in FIG. 8, the image is hatched in FIG. 8 (blacked out).
By performing the spatio-temporal interpolation in which a part is a stop band, it is possible to obtain a progressive signal without image quality deterioration.

Here, the configuration and operation of the scanning line interpolation circuit of the present invention will be specifically described. In FIG. 1, an interlaced image signal input from an input terminal 1 is input to a field delay unit 2, a vertical high-pass filter (hereinafter, high-pass filter is abbreviated to HPF) 3, and a motion direction detection unit 4.

The field delay unit 2 delays the input image signal by a time corresponding to one field, and inputs the delayed image signal to the intra-field interpolator 5, field delay unit 6, and vertical LPF 7. The field delay unit 6 delays the input image signal by a time corresponding to one field, and inputs the delayed image signal to the motion direction detection unit 4 and the vertical HPF 8. Therefore, the vertical HPF 3, the intra-field interpolator 5 and the vertical LPF 7, and the vertical HPF 8 each have 1
Different image signals are input for each field. The image signal output from the field delay unit 2 is defined as a current field.

The vertical HPF 3 extracts a high-frequency signal of a field temporally subsequent to the current field, which is the field to be interpolated, and inputs the signal to the image shifter 9. Similarly, the vertical HPF 8 extracts a high-frequency signal of a field temporally before the current field that is the interpolated field,
Input to the image shifter 10. That is, the vertical HPF 3
A post-field high-band signal generating means for generating a post-field high-band signal which is a high-frequency component in the vertical direction after the current field. This is a front field high band signal generation means for generating a front field high band signal which is a high frequency component in the vertical direction.

The moving direction detecting section 4 indicates a value (hereinafter referred to as a moving direction value) s indicating a moving direction of an image between two fields (one frame) and a moving amount of the image by a configuration and a method described later. A value (motion amount value) k is obtained, the motion direction value s of the image is input to the image shifters 9 and 10, and the motion amount value k of the image is input to the multipliers 11 and 12. That is, the movement direction detection unit 4 is a movement direction detection unit that detects a movement direction and a movement amount of an image from a field temporally before and after the current field.

The image shifter 9 and the image shifter 10 are
The input high-frequency signal is spatially moved according to the motion direction value s, and is input to the adder 13. The image shifter 9
And the field that moves spatially by the image shifter 10 have a reverse time relationship with respect to the current field that is the field to be interpolated, so that the moving directions are also reversed. The adder 13 adds the spatially shifted high-frequency signals of the preceding and succeeding fields, and inputs the sum to the adder 14.

The vertical LPF 7 takes out the low-frequency signal of the current field and inputs it to the adder 14. Note that the vertical LPF 7
Is a current field low band signal generating means for generating a current field low band signal which is a low frequency component in the vertical direction of the current field. The adder 14 adds the result of addition of the high-frequency signals of the preceding and succeeding fields input from the adder 13 and the low-frequency signal of the current field input from the vertical LPF 7 to generate a spatiotemporal interpolation signal. That is, the adder 13 and the adder 14
Is a spatio-temporal interpolation signal generating means for generating a spatio-temporal interpolation signal by adding the rear field high band signal, the previous field high band signal and the current field low band signal. This spatiotemporal interpolation signal is input to the multiplier 11.

Further, the intra-field interpolator 5 adds the scanning lines located above and below the interpolated scanning line spatially to generate an intra-field interpolation signal. In the intra-field interpolator 5, a delay equivalent to the delay generated when the spatio-temporal interpolation signal is generated is made, and the intra-field interpolation signal synchronized with the spatio-temporal interpolation signal is input to the multiplier 12.

As described above, the motion amount k is input from the motion direction detector 4 to the multipliers 11 and 12.
The multiplier 11 multiplies the input spatio-temporal interpolation signal by (1−k), the multiplier 12 multiplies the input intra-field interpolation signal by k, and inputs each multiplication result to the adder 15. The adder 15 adds the spatio-temporal interpolation signal weighted by the motion amount value k and the intra-field interpolation signal, and outputs a final interpolation signal from an output terminal 16. Note that the multipliers 11 and 12 and the adder 15 are provided in the motion direction detecting unit 4.
Adaptive mixing means for adaptively mixing the intra-field interpolation signal and the spatio-temporal interpolation signal in accordance with the motion amount value k detected by the method.

Next, the detailed configuration and operation of the movement direction detecting section 4 in FIG. 1 will be described. 2, the input interlaced image signal is input to an image shifter 17, and the image signal output from the field delay 6 is input to an image shifter 18. The image shift setting device 19
Image shift values are sequentially generated according to a preset search range, and input to the image shifter 17, the image shifter 18, and the motion direction determiner 23. Note that the search range means a range in which an input signal is shifted in order to detect a moving direction and a moving amount of an image signal.

For example, assuming that the search range is ± 1 in the scanning line unit in the vertical direction and ± 2 in the pixel unit in the horizontal direction, the image shift setting unit 19 sets 15 × 3 (vertical × horizontal) image shifts. The values will be generated sequentially. Image shifter 17
The image shifter 18 spatially shifts the input image signal according to the image shift value, and inputs the image signal to the subtracter 20. Note that the field spatially moved by the image shifter 17 and the field spatially moved by the image shifter 18 have the opposite time relationship with respect to the current field, which is the interpolated field, so that the moving directions are also opposite. To

The subtractor 20 subtracts the output of the image shifter 17 from the output of the image shifter 18 to obtain an inter-frame difference, and inputs the difference signal (inter-frame difference value) to the absolute value converter 21. I do. The absolute value converter 21 converts the input difference value between frames into an absolute value and inputs the absolute value to the spatial LPF 22. The spatial LPF 22 smoothes a spatial change by applying a spatial low-pass filter to the absolute value of the inter-frame difference value, and inputs the result to the motion direction determiner 23. As described above, each image shift value is input to the motion direction determiner 23 from the image shift setting unit 19, and the motion direction determiner 23 calculates an inter-frame difference value of each image shift value input from the spatial LPF 22. Compare.

The motion direction determiner 23 outputs to the output terminal 24 the image shift value that minimizes the inter-frame difference value as a result of the comparison between the inter-frame difference values, as the motion direction value s of the image. This movement direction value s is input to the image shifters 9 and 10 in FIG. 1 as described above. Further, the motion direction determiner 23 converts the minimum inter-frame difference value into the non-linear converter 2.
Enter 5 The non-linear converter 25 non-linearly converts the input inter-frame difference value and outputs the result as a motion amount value k of the image. That is, 0 is set when the input inter-frame difference value is equal to or lower than the noise level, and 1 when the input frame difference value is equal to or higher than the predetermined level.
And linearly convert between them.

The predetermined level is such that the intra-field interpolation signal obtained by the intra-field interpolator 5 in FIG. 1 is more appropriate than the spatio-temporal interpolation signal obtained by the processing up to the adder 14. Set to the level you want. The motion amount value k thus obtained is output from the output terminal 26. This motion amount value k is input to the multipliers 11 and 12 in FIG. 1 as described above.

The scanning line interpolation circuit of the present invention is configured as described above. The scanning line interpolation circuit of the present invention is used as a scanning line interpolation circuit of a motion adaptive interpolation device as shown in FIG. 3, and as a scanning line interpolation circuit of a sequential scanning line conversion device as shown in FIG. Can be

First, in FIG. 3, an image signal input from the input terminal 1 is input to a scanning line interpolation circuit 30, an inter-field interpolator 31, and a motion detector 33. The scanning line interpolation circuit 30 is the scanning line interpolation circuit according to the present invention shown in FIG. The scanning line interpolation circuit 30 generates a motion interpolation signal,
Input to the adaptive mixer 32. Inter-field interpolator 31
Generates the average value of the pixels A and B in the temporally preceding and succeeding fields of the interpolated field as a stationary interpolation signal as described with reference to FIG. The motion detector 33 detects the motion of the image. The adaptive mixer 32 adaptively mixes the motion interpolation signal and the stationary interpolation signal according to the magnitude of the motion detected by the motion detector 33, and outputs a final interpolation signal from an output terminal 34.

Next, in FIG. 4, the input interlaced image signal is input to the scanning line interpolation circuit 40 and the field delay unit 41. The scanning line interpolation circuit 40 is the scanning line interpolation circuit according to the present invention shown in FIG. The interpolation signal generated by the scanning line interpolation circuit 40 is input to the line buffer 42. The field delay unit 41 delays the input image signal by the same amount as the delay generated by the scanning line interpolation circuit 40 and inputs the same to the line buffer 43. The line buffer 42 and the line buffer 43 hold one line's worth of signal and read it out at twice the speed of the input signal. The outputs of the line buffers 42 and 43 are input to a switch 44, and are alternately selected by the switch 44 to become a sequential scanning signal, which is output from an output terminal 45.

As described above, the scanning line interpolation circuit of the present invention can detect the moving direction and size of an image and change the characteristics of the spatio-temporal interpolation filter to the optimum spectrum for the image at that time. Therefore, in scanning line interpolation such as sequential scan conversion and double-density conversion, resolution does not deteriorate, and interlace interference such as line flicker and jagging does not occur.

[0034]

As described in detail above, the scanning line interpolation circuit of the present invention generates an intra-field interpolation signal from scanning lines spatially above and below a current field to be interpolated. Means, a current field low band signal generating means for generating a current field low band signal which is a vertical low frequency component of the current field, and a vertical high frequency component which is temporally behind the current field. A post-field high-frequency signal generating means for generating a field high-frequency signal, and a front-field high-frequency signal generating means for generating a front-field high-frequency signal that is a vertically high frequency component temporally before the current field. A moving direction detecting means for detecting a moving direction and a moving amount of an image from a field temporally before and after the current field, and a moving direction detecting means. Accordance with the detected motion direction Te, a first shifting means for shifting the rear field high frequency signal,
Second shifting means for shifting the previous field high frequency signal in accordance with the motion direction detected by the motion direction detecting means, and the rear field high frequency signal and the previous field high frequency signal shifted by the first and second shifting means. A spatio-temporal interpolation signal generating means for generating a spatio-temporal interpolation signal by adding the current field low-frequency signal, and an intra-field interpolation signal and a spatio-temporal interpolation signal according to the amount of motion detected by the motion direction detecting means. Since it is configured with an adaptive mixing means for performing adaptive mixing, even if there is a moving portion in the image when performing scanning line interpolation, a high-quality scanning line interpolation image can be generated without deterioration in resolution or interlace interference. Obtainable.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a specific configuration of a motion direction detector 4 in FIG.

FIG. 3 is a block diagram showing an example in which the present invention is applied to a motion adaptive interpolation device.

FIG. 4 is a block diagram showing an example in which the present invention is applied to a progressive scan conversion device.

FIG. 5 is a diagram showing various scanning line structures.

FIG. 6 is a diagram showing inter-field interpolation and intra-field interpolation.

FIG. 7 is a diagram showing a spectrum of an image of inter-field interpolation and intra-field interpolation for explaining a conventional problem.

FIG. 8 is a diagram showing an image spectrum for explaining the present invention.

[Explanation of symbols]

 2,6 field delay device 3,8 vertical high-pass filter 4 motion direction detector 5 intra-field interpolator 7 vertical low-pass filter 9,10 image shifter 11,12 multiplier 13,14,15 adder

Claims (1)

[Claims] A scanning line interpolation circuit for interpolating a scanning line of an input image signal, wherein an intra-field interpolation signal for generating an intra-field interpolation signal from scanning lines spatially located above and below a current field to be interpolated. Means, a current-field low-frequency signal generating means for generating a current-field low-frequency signal that is a low-frequency component in the vertical direction of the current field; and A rear-field high-band signal generating means for generating a certain rear-field high-band signal; and a front-field high-band signal for generating a front-field high-band signal which is a vertically high frequency component temporally before the current field. Generating means for detecting a motion direction and a motion amount of an image from a field temporally before and after the current field; First shift means for shifting the rear field high frequency signal according to the motion direction detected by the motion direction detection means; and the front field high frequency signal according to the motion direction detected by the motion direction detection means. Second shifting means for shifting the high-frequency signal after addition of the rear-field high-frequency signal and the previous-field high-frequency signal shifted by the first and second shifting means, and the current-field low-frequency signal. A spatio-temporal interpolation signal generating means for generating a spatial interpolation signal; and an adaptive mixing means for adaptively mixing the intra-field interpolation signal and the spatio-temporal interpolation signal according to a motion amount detected by the motion direction detecting means. A scanning line interpolation circuit characterized in that it is configured.