JPH05110998A - Scan conversion system - Google Patents

Abstract

PURPOSE:To suppress the degradation of the picture quality for conversion from sequential scanning to interlaced scanning. CONSTITUTION:A picture signal 50 of sequential scanning is inputted to a filter circuit 1 and passes a low pass filter to extract a low band component 51. The low band component 51 is subtracted from the picture signal 50 to generate a high band component 52. The low band component 51 and the high band component 52 are inputted to sequential/interlacing conversion circuits 2, 3 and pass a low pass filter which prevents the turning-back distortion of scanning line thinning, and scanning lines are thinned to obtain a low band interlaced signal 53 and a high band interlaced signal 54. The pass band of the low pass filter by which the high band component 52 passes in the sequential/interlacing conversion circuit 3 is wider than that of the low pass filter by which the low band component passes in the sequential/interlacing conversion circuit 2. Finally, the low band interlaced signal 53 and the high band interlaced signal 54 are added to output an interlaced signal 55.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scan conversion system for image signals.

[0002]

2. Description of the Related Art A conventional scan conversion system will be described with reference to FIG. FIG. 4 is a view of conversion from progressive scanning to interlaced scanning viewed in the vertical / time space. In the figure, the circles represent scanning lines, (a) represents progressive scanning, and (b) represents interlaced scanning image signals. As is clear from the figure, this scan conversion processing is offset subsampling in the vertical / time space, and it is necessary to apply a low-pass filter that prevents aliasing distortion before performing thinning processing. Conventionally, for example, as shown in FIG.
The characteristics shown by the solid line were used. This figure shows the pass band in the vertical-time two-dimensional frequency space (ν-f space), and the square space shown by the broken line shows the frequency band that can be transmitted as the original signal for progressive scanning. The pass band surrounded by the solid line is 1/2 of the square band surrounded by the broken line, and the folded components are prevented from overlapping.

[0003]

In the above-mentioned prior art, a filter having a constant pass band characteristic is applied regardless of the horizontal frequency band for the purpose of preventing aliasing distortion. At this time, when the characteristic of completely removing the aliasing distortion is selected, the image has a blurring feeling, and conversely, when the aliasing distortion is allowed to occur, the image quality deterioration due to this is conspicuous.

An object of the present invention is to provide a scanning conversion system capable of alleviating the drawbacks of the conventional system, preventing the image quality from being deteriorated due to aliasing distortion, and suppressing the blurring of the image.

[0005]

SUMMARY OF THE INVENTION The present invention is a scan conversion method for converting an original image signal of progressive scanning into an interlaced scan, wherein a signal component having a higher frequency in the horizontal direction with respect to the original image signal is more vertical. A low pass filter having a wide pass band in the time-frequency space is applied and then converted to interlaced scanning.

[0006]

In the scanning conversion system of the present invention, a low-pass filter in the vertical / time space is applied so that the folding distortion is sufficiently reduced for the horizontal low frequency component and the folding distortion is permitted for the horizontal high frequency component. Thin scan lines from. That is, although the aliasing distortion of the horizontal low-frequency component largely appears as the image quality deterioration, the horizontal high-frequency component hardly causes the image quality deterioration. Therefore, the image quality deterioration due to the aliasing distortion is prevented by removing only the component that causes the image quality deterioration. It is possible to suppress blurring of the image.

[0007]

Embodiments of the present invention will now be described with reference to FIGS. In the examples shown below, as an example,
The progressive scanning original image signal 50 is divided into two frequency bands in the horizontal direction, and the pass band of the low pass filter for preventing aliasing distortion is made wider for the high band components than for the low band components. The case will be described.

FIG. 1 is a block diagram showing the basic configuration of a circuit that realizes an embodiment of the present invention. The progressive scan image signal 50 is input to the filter circuit 1 and subjected to a horizontal low-pass filter to extract a low-pass component 51. Image signal 50
By subtracting the low frequency component 51 from the high frequency component 52, a high frequency component 52 is generated. The low-frequency component 51 is sequentially input to the interlace conversion circuit 2, a low-pass filter that prevents aliasing of scanning line thinning is applied, and then the scanning lines are thinned to obtain a low-frequency interlace signal 53. At this time, the characteristics of the low-pass filter may be set, for example, as a pass band in the area surrounded by the solid line in FIG.
The high-frequency component 52 is sequentially input to the interlace conversion circuit 3, a low-pass filter corresponding to a horizontal high-frequency component that prevents aliasing of scanning line thinning is applied, and then the scanning lines are thinned out to obtain a high-frequency interlace signal 54. And The characteristic of the low-pass filter at this time may be, for example, a region surrounded by a solid line in FIG. 2 as a pass band. Here, FIG. 2 shows the pass band in the vertical / time frequency space (ν−f space), and the pass band is made wider than the characteristic of FIG. Finally, the low-frequency interlace signal 53 and the high-frequency interlace signal 54 are added and the interlace signal 55 is output.

In this embodiment, the case where the original image signal 50 of progressive scanning is divided into two frequency bands in the horizontal direction has been described, but the number may be more than two.

Further, with respect to the high frequency component in the horizontal direction, even if a low-pass filter for preventing aliasing distortion is not applied, it does not cause a large deterioration.

The sequential / interlace conversion circuit 2 shown in FIG.
By making the memory circuit used for applying the low-pass filter in 3 common, it is possible to reduce the circuit scale.

[0012]

As described above, according to the present invention,
The horizontal low-frequency component is sufficiently suppressed to be aliased, and the horizontal high-frequency component is subjected to a low-pass filter in the vertical / time space to allow the aliased distortion to occur. It is possible to prevent the image quality from deteriorating and suppress the blur feeling of the image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of a circuit that realizes an embodiment of the present invention.

FIG. 2 is a diagram showing a filter characteristic in one embodiment of the present invention.

FIG. 3 is a diagram showing a filter characteristic in one embodiment of the present invention.

FIG. 4 is a diagram illustrating the contents of scan conversion.

[Explanation of symbols]

 1 Filter circuit 2, 3 Sequential / interlace conversion circuit

Claims (1)

[Claims] 1. A scan conversion method for converting an original image signal of progressive scanning into an interlaced scan, wherein a signal component having a higher frequency in the horizontal direction with respect to the original image signal has a wider pass band in a vertical / time frequency space. A scan conversion system characterized by converting to interlaced scanning after applying a low-pass filter having