JP2008256986A - Image processing method and image display device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform optimum animation correction regardless of the movement of an object without increasing a circuit scale in a display of a subfield light emission type. <P>SOLUTION: A subfield conversion section 22 converts one frame to a subfield light emission pattern corresponding to the luminance level of an input video signal by time-division of the one frame to a plurality of the subfields. A motion vector detection section 24 detects the motion vector of the pixel between the frames with respect to the input video signal. A motion vector correction section 25 attenuates the motion vector to V' by using a coefficient α smaller than 1 when the magnitude of the detected motion vector is smaller than a threshold S. A subfield correction section 23 corrects the light emission position of the subfield light emission pattern according to the motion vector output from the motion vector correction section. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing technique for an image display device that time-divides one frame into a plurality of subfields and emits a subfield corresponding to the luminance level of an input video signal to display a multi-tone image.

  Plasma display panels (PDP) and liquid crystal displays (LCD) are attracting attention as thin and light display devices. The PDP drive system is completely different from the conventional CRT drive system, and is a direct drive system using a digitized input video signal. Therefore, the luminance gradation emitted from the panel surface is determined by the number of bits of the signal to be handled. In the address / display separated driving method, for example, in the case of an 8-bit signal, one frame is composed of eight subfields SF1 to SF8 having a relative luminance ratio of 1, 2, 4, 8, 16, 32, 64, 128. It is possible to display 256 gradations by combining the luminance of 8 subfields.

  When a moving image is displayed on the address / display separation type display device as described above, since the input video signal (original signal) is a discrete signal sampled for each frame, it is visually displayed in the moving direction of the moving image. There is a problem that the image quality deteriorates due to widening of the deviation, or there is a level that does not coincide with the original signal. This phenomenon is called “moving image pseudo contour”, and in order to solve this problem, the following moving image correction method has been proposed.

  That is, the input video signal is corrected by a predetermined moving image correcting means for a moving video signal. However, there is a problem that the optimum conditions for correction differ between a fast-moving moving image portion (rapid moving image portion) and a slow-moving moving image portion (slow moving image portion). Therefore, in Patent Document 1, a motion vector of a pixel between one or a plurality of frames is detected based on an input video signal, and an input video is determined according to whether or not the detected motion vector is larger than a set value S. It is described that a signal obtained by correcting the signal by the rapid moving image correcting means and a signal obtained by correcting the input video signal by the slow moving image correcting means are switched and output to the display device.

  Patent Document 2 describes a method of calculating a pixel motion vector, calculating a drag coordinate of a new subfield codeword of the current pixel, and re-encoding based on the motion vector.

Japanese Patent Laid-Open No. 10-282930 Japanese Patent Laid-Open No. 2002-123211

  In the technique described in Patent Document 1, the rapid moving image correcting unit corrects the lighting position of each subfield, whereas the slow moving image correcting unit corrects the lighting pattern itself, and the correction method is completely different. Different. Therefore, a switching shock may occur when the correction means is switched, resulting in screen distortion. In addition, two different systems of circuits must be provided for the rapid moving image correcting means and the slow moving image correcting means, and there is a problem that the circuit scale increases.

  The technique described in Patent Document 2 corrects the subfield lighting position according to the motion vector, but this method is effective when the object moves rapidly. However, if the movement of the object is slow, correcting the lighting position of the subfield in the same manner will not only reduce the pseudo contour, but also generate a new pseudo contour, which causes a new problem of further degrading the image quality. .

  The present invention has been made in view of the above-described problems. In a subfield light-emitting display, an image capable of performing optimal video correction regardless of the speed of movement of an object without increasing the circuit scale. It is an object of the present invention to provide a processing method and an image display apparatus using the processing method.

  In the image processing method of the present invention, one frame is time-divided into a plurality of subfields, converted to a subfield emission pattern corresponding to the luminance level of the input video signal, and a motion vector of a pixel between frames is detected in the input video signal. Then, the light emission position of the subfield light emission pattern is corrected according to the detected motion vector. If the detected motion vector V is smaller than the threshold value S, the motion vector is attenuated to V ′ using a coefficient α smaller than 1, and the light emission position of the subfield light emission pattern is corrected.

  The image display device of the present invention also includes a subfield conversion unit that time-divides one frame into a plurality of subfields and converts the subframe light emission pattern corresponding to the luminance level of the input video signal, and the input video signal between When the magnitude of the motion vector V detected by the motion vector detection unit that detects the motion vector of the pixel and the motion vector detection unit is smaller than the threshold value S, the motion vector is set to V ′ using a coefficient α smaller than 1. A motion vector correction unit for attenuation and a subfield correction unit for correcting the light emission position of the subfield light emission pattern converted by the subfield conversion unit in accordance with the motion vector output from the motion vector correction unit.

  According to the present invention, in a subfield light emitting display, it is possible to provide good image quality regardless of the speed of movement of an object without increasing the circuit scale.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of an image display apparatus according to the present invention. A video signal transmitted via a broadcast wave (radio wave) or a network or the like is received by the video signal receiving unit 1 to select a desired channel. The compression-coded video signal and the like are subjected to decoding processing (decompression decoding) into a video signal as necessary. The image processing unit 2 converts the video signal into a subfield video signal for displaying a multi-tone image, and performs moving image correction for pseudo contour removal described later. The subfield video signal is supplied to the display unit 3 such as a PDP to display an image.

FIG. 2 is a diagram showing an example of the internal configuration of the image processing unit 2 in FIG. A video signal from the video signal receiving unit 1 is input to the terminal 21.
The subfield conversion unit 22 converts the video signal into a subfield light emission pattern suitable for displaying a multi-tone image on the subfield light emission type display unit 3 such as a PDP. For example, as shown in FIG. 5, an 8-bit signal causes one screen (frame) to be divided into eight subfields SF1 to SF8 having a relative luminance ratio of 1, 2, 4, 8, 16, 32, 64, and 128. Time-division is performed, and 256 gradations are displayed by combining the luminances of the eight divided screens.

  The motion vector detection unit 24 detects a motion vector for each pixel or each block from the input video signal. From this motion vector, information on the speed and direction of movement of the object can be obtained. Regarding the motion detection technique and the motion estimation technique for detecting the motion vector, since a well-known technique used in the MPEG encoding process or the like can be applied, description thereof is omitted here.

  The motion vector correction unit 25 compares the motion vector detected by the motion vector detection unit 24 with a preset threshold value (threshold value) S, and corrects the motion vector according to the magnitude. This threshold value S can be given from the terminal 26.

  The subfield correction unit 23 corrects the subfield lighting position using the information on the motion vector corrected by the motion vector correction unit 25. By this correction, the pseudo contour at the time of moving image display can be removed. The corrected video signal (subfield data) is output from the terminal 27 to the display unit 3.

  FIG. 6 is a diagram schematically illustrating a subfield lighting position correction method performed by the subfield correction unit 23. Here, for simplicity, one screen (frame) is composed of four subfields (SF1 to SF4), and one screen is turned on in the order of SF4 → SF3 → SF2 → SF1. The horizontal axis represents time, and the vertical axis represents the screen position. In this figure, it is assumed that the object of interest moves to screen position 00 in the first frame, screen position 05 in the second frame, and screen position 10 in the third frame. In the subfield signal output from the subfield conversion unit 22, the lighting position of each subfield is the same within each frame period (filled portion in the figure). As a result, when an object moving through successive frames is viewed, a display displacement width Z0 is generated, which causes a pseudo contour. In such a case, in this embodiment, the lighting position of each subfield is corrected so as to be arranged in accordance with an oblique straight line (movement straight line, line of sight path) indicating the movement of the object (shaded portion in the figure). As a result, the display deviation width Z0 can be reduced to Z1, and the pseudo contour can be suppressed. Then, by determining the gradient of the moving straight line as a reference for the arrangement in accordance with the speed of motion of the object, that is, the detected motion vector, the display deviation width can be minimized.

  The present embodiment is characterized in that the motion vector correction unit 25 corrects the motion vector detected by the motion vector detection unit 24 and supplies it to the subfield correction unit 23. Further, the correction method performed by the subfield correction unit 23 is a single method for correcting the subfield lighting position, and thus the circuit configuration is simplified.

  FIG. 3 is a diagram showing an internal configuration of the motion vector correction unit 25 in FIG. In this embodiment, when the detected motion vector is equal to or smaller than the threshold value (threshold value) S, correction for attenuating the magnitude of the motion vector is performed.

  The motion vector magnitude calculation unit 32 converts the motion vector V (reference numeral 31) detected by the motion vector detection unit 24 into a vector magnitude signal | V |. The comparison correction unit 33 compares the magnitude | V | of the motion vector with the threshold value S. When the magnitude of the motion vector | V | is less than or equal to the threshold value S, the magnitude of the motion vector is attenuated to αV using a coefficient α smaller than 1, and the motion vector V ′ (reference numeral 34) thus corrected is sub- Output to the field correction unit 23. When the magnitude | V | of the motion vector is larger than the threshold value S, the input motion vector V is output as V ′ as it is.

FIG. 4 is a diagram illustrating an example of input / output characteristics of the motion vector correction unit 25. The horizontal axis represents the magnitude of the input motion vector | V |, and the vertical axis represents the magnitude of the output motion vector | V ′ |. When the magnitude | V | of the motion vector is less than or equal to the threshold value S, the attenuation coefficient is α (0 <α <1), and the line-shaped attenuation intersects at the intercept (1-α) S on the horizontal axis. Characteristics are shown as an example. At that time, the output characteristics in each region are expressed by the following equations.
When V <(1-α) S, V ′ = 0
When (1-α) S ≦ V ≦ S, V ′ = (1 / α) V− (1 / α−1) S
When V> S, V ′ = V
Of course, the attenuation characteristic of FIG. 4 is an example, and it may be a smooth curve in the attenuation region.

Here, the operation and effects of the present embodiment will be described in detail.
As shown in FIG. 6, in the correction for shifting the subfield lighting position in accordance with the movement of the object (moving straight line), the lighting is performed so that the display deviation width Z is sufficiently small (ideally, one pixel interval). Shift position. However, whether this correction can be effectively realized depends on the magnitude of the movement of the object.

FIG. 7 is a diagram comparing the correction of the subfield lighting position during the rapid movement and the slow movement.
(A) is a correction at the time of rapid movement, and the lighting position of each subfield can be arranged almost faithfully on the line-of-sight path (straight line). That is, the display deviation width is small, and multiple gradations can be expressed correctly.

  (B) is correction at the time of slow movement. Since the amount of shift of the lighting position is the smallest unit of the pixel interval, the lighting position of each subfield can be faithfully arranged on the line-of-sight path when the movement of the object becomes small and the gradient of the moving line becomes gentle. It becomes difficult. As a result, the display deviation width becomes large. In other words, shifting the lighting position during slow movement has the opposite effect, and a new pseudo contour is generated, which may deteriorate the image quality before correction. The reason for this is that, even when moving slowly, the human visual resolution is high, and even a small deviation is easily recognized.

  (C) shows generation | occurrence | production of a pseudo contour combining said phenomenon. (1) is a case where the lighting pattern is not shifted with respect to the moving image. Naturally, the pseudo contour generated by the gaze direction integration increases as the moving speed increases. (2) is a case where the lighting pattern is shifted, and the pseudo contour is decreased in a region having a high speed, but the pseudo contour is increased in a region having a low speed.

  Therefore, at the time of rapid movement, the detected motion vector may be sent to the subfield correction unit 23 as it is. During slow movement, the detected motion vector is attenuated and sent to the subfield correction unit 23 to limit the correction of the lighting position. As a result, the occurrence of a pseudo contour can be suppressed regardless of the amount of movement of the object.

The threshold value (threshold value) S of the motion vector V in this case is a correction limit determined from the geometrical relationship between the pixel interval and the number of subfields in FIG. 6, that is, the moving straight line for the display displacement width Z to be one pixel interval. It is determined from the condition of the gentlest slope. In other words, the threshold value S is the minimum value of the amount of motion that can be corrected with the display deviation width Z as one pixel interval.
The attenuation coefficient α is suitably set to a value other than 0, for example, about 0.5 in order to smoothly switch the output V ′ of the motion vector with the threshold value S as a boundary.

  FIG. 8 is a diagram for explaining the effect of the attenuation coefficient α. It shows how the lighting patterns P1 to P4 (P1 'to P4') change according to the amount of movement. (A) is a case where α = 0, and the pattern changes rapidly between P3 and P4 with the threshold value S as a boundary. As a result, a pattern switching shock appears on the display screen. On the other hand, (b) shows a case where α> 0, the pattern gradually changes, and the patterns P3 'and P4' do not change suddenly on either side of the threshold value S. Thus, by setting the α value, it is possible to provide a buffer region and prevent the image from being disturbed by the switching shock.

  FIG. 9 is a diagram illustrating another configuration example of the image processing unit 2 in FIG. The configuration is such that a threshold value setting unit (threshold setting unit) 28 is added to the configuration of the image processing unit 2 of the first embodiment (FIG. 2), and resolution information 29 of the display unit 3 is input thereto. The point is different. In this example, the threshold value S of the motion vector that is the determination criterion in the motion vector correction unit 25 is changed according to the resolution of the screen of the display unit 3.

  FIG. 10 is a diagram showing the relationship between the resolution and the threshold value S. As shown in FIG. Thus, when the resolution is high, the threshold value S is also changed to a large value and set. The reason will be explained.

  As described with reference to FIG. 7, the display deviation width Z changes according to the amount of movement. If the amount of movement is large to some extent, the display deviation width Z becomes a constant value regardless of the amount of movement, but if the amount of movement is small, the display deviation width Z becomes unstable. This can be understood from the fact that when the gradient of the moving straight line is gentle in FIG. 6, the arrangement of the lighting positions becomes unstable when the gradient value is changed. That is, the display deviation width Z is close to one pixel interval or considerably larger than one pixel interval, and has a property of vibrating with respect to the amount of movement. This is visually unsightly, especially on high-resolution screens. Therefore, it is preferable that the threshold value S is set to a large value on a screen having a high resolution so as to suppress the variation in the display deviation width Z.

  FIG. 11 is a block diagram showing another embodiment of the image display apparatus according to the present invention. The configuration is obtained by adding a frame rate conversion unit 4 to the configuration of the image display apparatus of the first embodiment (FIG. 1). The frame rate conversion unit 4 is a circuit that converts the frame rate of the video signal received by the video signal reception unit 1 and has a function of converting, for example, 60 Hz to 120 Hz. At that time, the frame rate conversion unit 4 creates an interpolated video frame corresponding to the motion between the video frames, and thus includes a process of calculating motion vector information in the process.

  In this embodiment, the image processing unit 2 performs moving image correction using the motion vector information calculated by the frame rate conversion unit 4. That is, the motion vector detection unit 24 in the first embodiment (FIG. 2) is not necessary, and the configuration of the entire image display apparatus is simplified.

1 is a block diagram showing an embodiment of an image display device according to the present invention. The figure which shows an example of an internal structure of the image process part 2 in FIG. The figure which shows the internal structure of the motion vector correction | amendment part 25 in FIG. FIG. 6 is a diagram illustrating an example of input / output characteristics of a motion vector correction unit 25. The figure which shows conversion to the subfield light emission pattern for a display of a multi-tone image. The figure which showed typically the correction method of a subfield lighting position. The figure which compared the correction | amendment of the lighting position at the time of rapid movement and slow movement. The figure explaining the effect of attenuation coefficient (alpha). The figure which shows the other structural example of the image process part 2 in FIG. The figure which shows the relationship between the resolution and the threshold value S. The block diagram which shows the other Example of the image display apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Video signal receiving part 2 ... Image processing part 3 ... Display part 4 ... Frame rate conversion part 22 ... Subfield conversion part 23 ... Subfield correction part 24 ... Motion vector detection part 25 ... Motion vector correction part 28 ... Threshold value setting Unit 32 ... Motion vector magnitude calculation unit 33 ... Comparison correction unit.

Claims (6)

In an image processing method for displaying a multi-tone image on a subfield light emission type display unit,
One frame is time-divided into a plurality of subfields, converted into a subfield emission pattern corresponding to the luminance level of the input video signal,
Detecting a motion vector of a pixel between frames for the input video signal,
The light emission position of the subfield light emission pattern is corrected according to the detected motion vector,
When the magnitude of the detected motion vector V is smaller than the threshold value S, the motion vector is attenuated to V ′ using a coefficient α smaller than 1, and then the light emission position of the subfield light emission pattern is corrected. A featured image processing method. The image processing method according to claim 1,
The image processing method according to claim 1, wherein the threshold value S is a minimum value of a motion amount obtained from a condition that an object display deviation width is an interval of one pixel by correcting a light emission position of the subfield light emission pattern. The image processing method according to claim 1 or 2,
The threshold value S is set by changing to a large value when the resolution of the display screen is high. In an image display device that displays a multi-tone image on a subfield light emitting display unit,
A sub-field conversion unit that time-divides one frame into a plurality of sub-fields and converts the frame into a sub-field emission pattern corresponding to the luminance level of the input video signal
A motion vector detection unit for detecting a motion vector of a pixel between frames for the input video signal;
A motion vector correction unit that attenuates the motion vector to V ′ using a coefficient α smaller than 1 when the magnitude of the motion vector V detected by the motion vector detection unit is smaller than the threshold S;
A subfield correction unit that corrects the light emission position of the subfield light emission pattern converted by the subfield conversion unit according to the motion vector output from the motion vector correction unit;
An image display device, characterized in that a subfield emission pattern corrected by the subfield correction unit is supplied to the display unit. The image display device according to claim 4.
A threshold setting unit that sets the threshold S used in the motion vector correction unit according to the resolution of the display unit;
The threshold value setting unit changes and sets the threshold value S to a large value when the resolution is high. The image display device according to claim 4 or 5,
A frame rate conversion unit for converting a frame rate of the input video signal;
The image display apparatus, wherein the motion vector detection unit uses the motion vector information calculated by the frame rate conversion unit.

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