JPH04263593A - Subsample prefilter between moving vector correction frames - Google Patents

Abstract

PURPOSE:To reduce the deterioration of resolution and the generation of loop back distortion by constituting a temporal filter where a frame memory controlling the readout of a temporarily written sample picture signal by the moving vector is taken as a delay circuit. CONSTITUTION:The moving vector detected by a moving detection circuit 6 is supplied to a intra-frame prefilter 1, and the filter is controlled according to the magnitude of the moving vector. The moving vector is also supplied to a moving detection circuit 4 and controlled according to the magnitude of the moving vector. In this case, the moving vector represents the moving of the picture of the picture signal sampling the picture element located differently between alternate frames, and the filter 1 prevents the generation of the loop back distortion accompanied by subsample. The picture signal is transferred with the information on the moving vector, and the picture element is interpolated between frames so as to be reproduced. At this point, a temporal filter where a frame memory 16 controlling the readout of the temporarily written sample picture signal with the moving vector is taken as the delay circuit is adopted so as to reduce the deterioration of resolution.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to motion vector correction interframe sub-sampled image signal transmission suitable for narrowband transmission of high-definition television such as the so-called MUSE method.
Motion vector correction to prevent aliasing distortion due to subsamples Regarding the pre-filter for subsamples between frames, we have corrected the resolution loss that occurs when playing back motion images of the entire screen due to panning, tilting, etc. of the camera. It is designed to be preventable.

0002

BACKGROUND OF THE INVENTION Conventionally, the above-mentioned type of prefilter for motion vector correction interframe subsamples performs temporal filter processing on the high-frequency components of an image signal where aliasing distortion occurs due to the subsamples, and Among the three types of signals: the input signal, the output signal, and the average of both, the one with the minimum absolute value of the signal amplitude is selected, and the absolute value is further determined according to the signal amplitude of the high frequency component of the image signal. A device that performs prefilter processing by selectively outputting either the minimum image signal or the image signal output from a temporal filter has been used.

According to the above-mentioned prefilter processing,
Sufficient prefilter processing is applied to image signals in areas where the signal amplitude of high frequency components is large, such as moving edges in the image, and although the signal amplitude of the edge area itself is fine, the signal amplitude of the edge area itself is smaller than that of the area. Sufficient prefilter processing will not be performed on the image signal. However, if aliasing distortion is allowed to some extent due to such insufficient prefiltering, it is possible to prevent a decrease in resolution due to a decrease in high frequency components due to the prefiltering.

0004

[Problems to be Solved by the Invention] On the other hand, motion vector correction in inter-frame subsample transmission of image signals is normally performed when the entire image is moving uniformly and slowly, and the visual sense can follow that movement, so The purpose of this is to improve resolution deterioration caused by prefiltering a motion image signal that needs to be processed in the same way as an image signal. However, when the conventional pre-filtering process described above is applied to such a moving image signal, even if motion vector correction is applied to a moving image signal in which the entire screen is moving uniformly, both resolution degradation and aliasing distortion occur. This has the drawback that the effect of motion vector correction is halved, and the elimination of such a drawback has been a problem that has conventionally been desired to be solved.

[0005]

[Means for Solving the Problems] An object of the present invention is to solve the above-mentioned conventional problems, and to sufficiently reduce resolution deterioration by motion vector correction even for motion image signals of the entire screen due to panning, tilting, etc. An object of the present invention is to provide a prefilter for motion vector correction inter-frame subsamples configured to obtain a dynamic vector correction.

That is, the motion vector correction inter-frame subsampling prefilter of the present invention subsamples an image signal obtained by subsampling pixels at different positions between alternate frames through a prefilter that prevents the occurrence of aliasing distortion caused by subsamples. motion vector correction interframe sub-sampled image signal transmission for transmitting the image signal along with information on a motion vector representing the motion of the image, and at least when restoring the motion image, interpolating pixels between frames according to the motion vector to reproduce the image signal. The prefilter is characterized in that it is constituted by a temporal filter whose delay circuit is a frame memory capable of controlling readout of sub-sampled image signals once written using a motion vector.

[0007]

[Operation] Therefore, according to the present invention, a moving image signal in which the entire screen moves uniformly and slowly is processed as a still image signal, so that the resolution does not deteriorate and the motion vector correction can be applied sufficiently effectively. Moreover, the effect of the prefilter processing can be sufficiently obtained for the motion image signal representing the movement of the image in the small and medium portions of the screen.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings.

First, FIG. 1 shows an example of a schematic configuration of a transmission system for motion vector correction interframe sub-sampled image transmission when the present invention is applied to so-called MUSE type high-quality television narrowband transmission. In the illustrated transmission system, conventionally, an input image signal is supplied to a still image processing circuit 2 via an interframe prefilter 1 and also directly to a moving image processing circuit 3 and a motion detection circuit 4. The moving image processing circuit 3 is controlled according to the detected image movement, and the processed still image signal and moving image signal are supplied to the mixer 5, and the input image signal is further supplied to the motion vector detection circuit 6 for detection. The mixer 5 is controlled by the motion vector to mix the processed still image signal and the moving image signal at a ratio according to the magnitude of the motion vector,
The mixed output image signal is sent to the inter-frame sub-sampling circuit 7.
However, when the present invention is applied, the signals are connected by dotted lines as shown in the figure.
The motion vector detected by the motion vector detection circuit 6 is supplied to the interframe prefilter 1, and as described later, the filtering action of the prefilter 1 is controlled by the magnitude of the motion vector, and the motion vector is also supplied to the motion detection circuit 4. The motion detection effect is controlled by the magnitude of the motion vector.

As mentioned above, FIG. 2 shows an example of the configuration of the interframe prefilter 1 in which the filtering action can be controlled by the motion vector detection output according to the present invention. In the interframe prefilter having the illustrated configuration, conventionally, an input image signal is guided to a subtracter 12 via a low-pass filter 11, and a high-frequency component of the input image signal is obtained as a difference from the input image signal. The high frequency image signal component is sent to the subtracter 13, coefficient unit 14, adder 15 and frame memory 1.
6, which is configured to add the inter-frame difference at a predetermined ratio, to the adder 17, where it is added to the low-pass image signal component from the low-pass filter 11, and then folded back during sub-sampling processing. An image signal from which high-frequency components that may cause distortion have been removed is extracted, but when the present invention is applied, the motion vector detection output described above with respect to FIG. The read address of the storage signal in the frame memory 16, which is supplied to the memory 16 and constitutes a temporal filter, is controlled by the motion vector.

[0011] However, in the interframe subsample transmission of high-definition television signals such as the MUSE system, the aliasing distortion accompanying the interframe subsample is 4MHz.
Since the occurrence of aliasing distortion occurs in the high frequency range above, the temporal filter constituting the pre-filter for preventing aliasing distortion is designed to perform a filtering action only on high frequency signal components of 4MHz or above. In order to control the motion vector according to the present invention, the read address of the frame memory constituting the temporal filter is controlled according to the motion vector, as described above. Therefore, there is a strong mutual correlation between the image signal input to the temporal filter and the frame memory controlled by the motion vector detected from the image signal, and if the motion vector is perfectly detected, the entire screen will be uniformly slow. For a moving image signal that moves rapidly, the above-mentioned correlation becomes 1 and the input of the coefficient unit 14 constituting the temporal filter becomes 0, as in the case of a still image signal. In reality, the motion vector of the detection result includes a detection error, and the input of the coefficient unit 14 is not truly zero, but the error component also falls within the passband of the temporal filter and is automatically be compensated.

[0012] Furthermore, if the entire background on the screen is moving uniformly and slowly, and there is a stationary foreground part in the background, the stationary foreground part may be moved at the same time as the moving background. When motion vector correction is applied, an inter-frame difference that did not exist before the correction will occur in the static foreground part, and then it will be attenuated by the action of the temporal filter, returning to the original state before the correction. I will do it. However, in conventional sub-sampled image transmission between motion vector correction frames such as the Muse method, the moving image signal of the entire screen in such a case is once processed as a moving image signal. There is no possibility that new image quality deterioration as described above will occur due to the prefilter processing.

[0013]

Effects of the Invention As is clear from the above description, in conventional motion vector corrected interframe subsample image signal transmission such as the Muse method, generation of aliasing distortion due to interframe subsamples can be suppressed by interframe prefiltering. Because of the suppression, high frequency signal components are lost due to prefilter processing in moving image signals where the entire screen moves uniformly, even though they require the same resolution as still images. As a result, the motion vector correction was unable to exhibit sufficient image quality improvement effects.

However, the decrease in resolution in moving images, where the entire screen moves uniformly and slowly, such as when panning and tilting a camera, and the visual sense can follow the movement, is similar to the same decrease in resolution in still images. According to the method, an equivalent image quality deterioration occurs, and such resolution reduction due to motion vector correction of moving images has conventionally been considered a weak point of motion vector correction frame-to-frame sub-sampled image signal transmission such as the Muse method, but with the present invention, the filter By introducing an interframe prefilter whose effect is controlled according to the motion vector detection results, it can be used even for the above-mentioned types of moving image signals.
A remarkable effect can be achieved in that the motion vector correction acts sufficiently effectively without causing a decrease in resolution, and the deterioration in image quality that was conventionally unavoidable in such cases can be improved.

[0015]

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of a transmission system when the present invention is applied to motion vector correction interframe sub-sample image signal transmission.

FIG. 2 is a block diagram showing an example of the configuration of an interframe prefilter in the transmission system shown in the first diagram when the present invention is applied;

[Explanation of symbols]

1 Inter-frame prefilter 2 Still image processing circuit 3 Moving image processing circuit 4 Motion detection circuit 5 Mixer 6 Motion vector detection circuit 7 Inter-frame sub-sampling circuit 11 Low-pass filter (LPF) 12, 13
Subtractor 14 Coefficient units 15, 17 Adder 16 Frame memory

Claims (1)

[Claims] 1. An image signal obtained by subsampling pixels at different positions between alternate frames is transmitted together with information on a motion vector representing the motion of the image through a prefilter that prevents the occurrence of aliasing distortion due to subsampling, At least when restoring a motion image, the once-written subsample image signal is used as the prefilter in motion vector correction interframe subsample image signal transmission that reproduces the image signal by interpolating pixels between frames according to the motion vector. 1. A prefilter for motion vector correction interframe subsamples, characterized in that the prefilter is constructed of a temporal filter using a frame memory as a delay circuit, the readout of which can be controlled by motion vectors.