Television – Image signal processing circuitry specific to television – Motion vector generation
Reexamination Certificate
1999-09-27
2003-12-09
Saras, Steven (Department: 2675)
Television
Image signal processing circuitry specific to television
Motion vector generation
C348S443000, C348S701000, C345S474000
Reexamination Certificate
active
06661470
ABSTRACT:
TECHNICAL FIELD
The present invention relates to moving picture display method and apparatus for effectively restraining a false contour generated when a moving picture is displayed in a plasma display panel (hereinafter referred to simply as “PDP”).
BACKGROUND ART
Thin typed matrix panels such as a PDP, an EL display device, a fluorescent character display tube, a liquid crystal display device, etc., have begun to be presented in order to respond to the demand of the recent large-sized display device. Particularly, in such thin typed display devices, PDP is largely expected as a direct-viewing-typed display device with a large screen.
As one of PDP halftone display methods, there is an intra-field time division method. In this method, one field comprises N screens (hereinafter referred to as “subfields”) each having a different luminance weight. They are called SF
0
, SF
1
, SF
2
, . . . , SF(N−1) in order of increasing the luminance weight, and luminance weight ratios of the subfields are 2
0
, 2
1
, 2
2
, . . . , 2
N−1
, respectively. A halftone luminance in one field can be controlled by selecting the presence or absence of pixel light-emission in the subfields. The luminance that greets human eyes can be expressed by a total sum of luminance of the pixel light-emission in the respective subfields based on human visual characteristics (persistence characteristics). The number of tone revels, which can be expressed by this display method, is the number of subfields in one field, that is, N power of 2.
FIG. 1
shows a display sequence in one field using the above-mentioned halftone display method. One field comprises eight (N=8) subfields each having a different luminance weight. The respective subfields are called SF
7
, SF
6
, . . . , SF
0
in order of decreasing the luminance weight. Here, SF
7
is called the most significant bit (MSB) side, and SF
0
is called the least significant bit (LSB) side.
With respect to the ratios of the number of pixel light-emission in the subfields, when SF
0
is “1”, SF
1
, SF
2
, . . . , SF
6
, SF
7
are “2”, “4”, . . . , “64”, “128”, respectively. When the number of subfields is 8, it is possible to provide up to 256 tone levels.
The halftone display method using the above-explained subfield method is excellent in the point that multi-levels of tone can be provided even by a binary display device, which can only provide only two tone levels “1” and “0” such as PDP. The driving of PDP using the subfield method can realize the image quality, which is substantially the same as the TV image of a cathode ray tube type.
However, for example, when a moving picture of an object whose contrast is gradually changed is displayed, the so-called false contour, which is peculiar to a PDP image and does not appear on the TV image of the cathode ray tube type, is generated.
The generation of the false contour is a phenomenon, which is caused by human visual characteristics. More specifically, when the image signal level has 256 tone levels, the color, which is different from the color to be originally displayed, appears in a stripe form along a boundary of N power of 2 such as 128, 64, 32, 16 as if the tone was lost. However, when a still image is displayed, an observer does not feel such a false contour. The feature of the false contour is recognized at only a moving portion and the periphery of the above signal levels
The principle of generating the false contour by the subfield half tone display ark method will be explained with reference to FIGS.
2
(
a
) and
2
(
b
). FIG.
2
(
a
) shows a case in which the number of subfields in a field is 8 and they are arranged in order of increasing the luminance weight, that is, SF
0
, SF
1
, SF
2
, . . . , SF
7
. It is assumed that a moving picture is moved three pixels in one filed when the signal level at a certain pixel position changes from
127
to
128
. FIG.
2
(
b
) shows a change of luminance, which the observer receives when the observer watches the moving picture on the screen.
Thus, in the case that the signal level
127
(pixel light-emission from SF
0
to SF
6
) and the signal level
128
(pixel light-emission in only SF
7
) are adjacent to each other, a tone difference is 1 LSB (1/256). A value of pixel light-emission that the observer feels on the eye's retina is an integral value of the number of the pixels when the image is shifted by a nonuniform pixel light-emission time. In other words, the pixel light-emission in the respective subfields to be produced at the same pixel position is generated at the different pixel position in the moving picture. Therefore, the halftone luminance of the pixels cannot be expressed simply by the total sum of the respective subfields, and this is the reason why the observer feels the image as a false contour in one's eyes.
As shown in FIG.
2
(
b
), when the moving picture is scrolled from the left side of the display screen to the right side, the observer feels the boundary portion between the above signal levels as a light line. Conversely, when the moving picture is scrolled from the right side to the left side, the observer feels the signal level boundary portion as a dark line by a spatial separation of the subfields.
On the other hand, in the display method in which the subfields are arranged in order of decreasing the luminance weight, that is, SF
7
, SF
6
, SF
5
, . . . , SF
0
, when the moving picture is scrolled from the left side of the display screen to the right side, the observer feels the signal level boundary portion as a dark line. Conversely, when the moving picture is scrolled from the right side to the left side, the observer feels the signal level boundary portion as a light line. Namely, the appearance of the false contour differs, depending on the moved direction of the moving picture on the display screen.
Moreover, the generation of the false contour also depends on the motion velocity of the moving picture. The faster the motion velocity, the larger the range where the false contour is generated becomes. For example, in a case of the moving picture in which ten pixels are shifted in one field, the false contour extends to ten pixels.
Conventionally, various kinds of proposals are disclosed as measurements against the false contour. Japanese Unexamined Patent Publication No. 7-271325 discloses a technique in which the display order of the subfields is rearranged in order such that the false contour becomes inconspicuous instead of the order of simple increasing a pulse number ratio such as, 1, 2, 4, 8, 32, 64, 128. For example, the subfields are displayed in order such that the subfield having the longest display period in the subfields is arranged at the center of the field. Or, the display order of the subfields is changed for each field.
However, the advantages obtainable from the rearrangement of the subfields and the change of the light-emission sequence in the subfields for each field are extremely limited, and these measurements cannot deal with the false contour in the moving picture whose motion velocity is fast.
Japanese Unexamined Patent Publication No. 8-123355 discloses a technique of restraining the false contour using the motion detection. More specifically, an amount of motion and a direction are detected from two continuous moving picture in the field and an image corresponding to a background. Then, an amount of motion correction is obtained based on the detected value and a time divisional ratio in a unit time of each subfield, and the light-emitting pattern of the corresponding subfield is shifted by the amount of correction.
In Japanese Unexamined Patent Publication No. 8-211848, the following technique is disclosed. Specifically, a motion vector is detected for each pixel block by display data between the fields, and a head subfield in the field displays data corresponding to input data. Then, the subsequent subfields move display data so as to display an image by use of a value obtained by multiplying the motion vector by a value, which is obtained by dividing delay time from each h
Fukushima Hiroaki
Kawakami Hidehiko
Kawamura Hideaki
Tokoi Masaki
Tomida Kazuo
Anyaso Uchendu O.
Greenblum & Bernstein P.L.C.
Saras Steven
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