JP3166240B2 - Scan conversion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal scanning conversion system.

[0002]

2. Description of the Related Art A conventional scan conversion system will be described with reference to FIG. FIG. 4 is a diagram showing the conversion from the sequential scanning to the interlaced scanning as viewed in the vertical / temporal space. In the figure, the circles represent scanning lines, (a) represents an image signal of sequential scanning, and (b) represents an image signal of interlaced scanning. As is apparent from the figure, this scan conversion processing is offset subsampling in the vertical / temporal space, and it is necessary to apply a low-pass filter for preventing aliasing before performing the thinning processing. Conventionally, for example, FIG.
The characteristic shown by the solid line was used. This figure shows a pass band in a two-dimensional vertical / time frequency space (ν-f space), and a square space shown by a broken line shows a frequency band that can be transmitted by an original signal of progressive scanning. The pass band enclosed by the solid line is の of the square band enclosed by the broken line, so that the aliasing components do not overlap.

[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 for completely removing the aliasing distortion is selected, the image is blurred, and conversely, when the aliasing distortion is allowed, the image quality is conspicuously deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a scan conversion system which can alleviate the drawbacks of the conventional system, prevent the image quality from being degraded due to aliasing distortion, and suppress the blurred image.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a scan conversion system for converting an original image signal of a progressive scan into an interlaced scan. Filter circuit to extract the horizontal low-frequency component and apply the horizontal low-frequency component to reduce the horizontal and vertical components.
After applying a band-pass filter, skip the scanning lines and skip
A first sequential / interlacing conversion circuit for converting the image into a scan, and water generated by subtracting the horizontal low-frequency component from the original image signal.
Input the high- frequency component and use the first sequential / interlacing converter.
After applying a low-pass filter in vertical and temporal space with a wide pass band, skip the scanning line and skip
A second sequential / interlaced conversion circuit for converting the
The output of the first sequential / interlaced conversion circuit and the output of the second
By adding the output of the circuit, the output interlaced scan
It is characterized by obtaining a signal .

[0006]

In the scan conversion method of the present invention, a low-pass filter is applied in the vertical and temporal spaces so that aliasing distortion is sufficiently reduced for horizontal low frequency components and aliasing distortion is generated for horizontal high frequency components. Thinning out the scanning lines from. In other words, the aliasing distortion of the horizontal low-frequency component largely appears as image quality deterioration, but the horizontal high-frequency component hardly causes image quality deterioration. It is possible to suppress the blurred image.

[0007]

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

FIG. 1 is a block diagram showing a basic configuration of a circuit for realizing an embodiment of the present invention. The progressive scanning image signal 50 is input to the filter circuit 1 and subjected to a horizontal low-pass filter to extract a low-frequency component 51. Image signal 50
The high-frequency component 52 is generated by subtracting the low-frequency component 51 from. The low-frequency components 51 are sequentially input to the interlace conversion circuit 2, subjected to a low-pass filter for preventing aliasing distortion of the scanning line thinning-out, and then the scanning lines are thinned out to obtain a low-frequency jumping signal 53. The characteristics of the low-pass filter at this time may be, for example, a region surrounded by a solid line in FIG.
The high-frequency component 52 is sequentially input to the interlacing conversion circuit 3 and subjected to a low-pass filter corresponding to a horizontal high-frequency component for preventing aliasing distortion of the thinning of the scanning line. And In this case, the characteristics of the low-pass filter may be, for example, a region surrounded by a solid line in FIG. 2 as a pass band. Here, FIG. 2 shows a pass band in the vertical / time frequency space (ν-f space), and the pass band is widened as compared with the characteristics of FIG. Finally, the low-frequency jump signal 53 and the high-frequency jump signal 54 are added to output a jump signal 55.

In this embodiment, the description has been given of the case where the original image signal 50 for the progressive scanning is divided into two frequency bands in the horizontal direction.

[0010] Even if a low-pass filter for preventing aliasing distortion is not applied to a high frequency component in the horizontal direction, no significant deterioration is caused.

The sequential / interlaced conversion circuit 2 shown in FIG.
By using a common memory circuit for applying the low-pass filter in 3, the circuit scale can be reduced.

[0012]

As described above, according to the present invention,
For the horizontal low-frequency component, the aliasing distortion is sufficiently reduced, and for the horizontal high-frequency component, a low-pass filter is applied in the vertical and temporal space to allow the aliasing to occur, and then the scanning lines are thinned out. It is possible to prevent the image quality from deteriorating and to suppress the blurred image.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating filter characteristics according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating filter characteristics according to an 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 / interlaced conversion circuit

Claims (1)

(57) [Claims] 1. A scanning conversion method for converting an original image signal of progressive scanning into interlaced scanning, wherein the original image signal of progressive scanning is input, and a low-pass filter in the horizontal direction is applied to reduce a horizontal low-frequency component . A filter circuit to be extracted and the horizontal low-frequency component are input, and a low-frequency
After applying the over-type filter, skip the scanning lines and skip
A first sequential-interlaced converter for converting the査, enter the horizontal high-frequency component generated by subtracting the horizontal low-frequency component from the original image signal, skipping the first sequential - of
Vertical and spatio-temporal with a wider passband than the translator
After having been subjected to low-pass filter between, and a second sequential-interlace conversion circuit which converts the thinned by interlaced scanning the scanning lines, an output of the first sequential-interlace conversion circuit, the first 2
Successively by adding the output of the-conversion circuit, Fei output
A scan conversion method characterized by obtaining a skip scan signal .