Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-08-05
2002-07-02
Luu, Matthew (Department: 2672)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S060000, C345S182000
Reexamination Certificate
active
06414657
ABSTRACT:
BACKGROUND OF THE INVENTION
1. (Field of the Invention)
The present invention is related to a display apparatus such as a plasma display panel (PDP) and digital micromirror device (DMD), and more specifically, to a display apparatus achieving gradation display by using a plurality of subfield images.
2. (Related Art)
A display apparatus of a PDP and a DMD makes use of a subfield method, which has binary memory, and which displays a dynamic image possessing half tones by temporally superimposing a plurality of binary images that have each been weighted. The following explanation deals with PDP, but applies equally to DMD as well.
A PDP subfield method is explained using
FIGS. 1
,
2
and
3
.
Now, consider a PDP with pixels lined up 10 across and 4 vertically, as shown in FIG.
3
. Let the respective R,G,B of each pixel be 8 bits, assume that the brightness thereof is rendered, and that a brightness rendering of 256 gradations (256 gray scales) is possible. The following explanation, unless otherwise stated, deals with a G signal, but the explanation applies equally to R, B as well.
The portion indicated by A in
FIG. 3
has a signal level of brightness of 128. If this is displayed in binary, a (1000 0000) signal level is added to each pixel in the portion indicated by A. Similarly, the portion indicated by B has a brightness of 127, and a (0111 1111) signal level is added to each pixel. The portion indicated by C has a brightness of 126, and a (0111 1110) signal level is added to each pixel. The portion indicated by D has a brightness of 125, and a (0111 1101) signal level is added to each pixel. The portion indicated by E has a brightness of 0, and a (0000 0000) signal level is added to each pixel. Lining up an 8-bit signal for each pixel perpendicularly in the location of each pixel, and horizontally slicing it bit-by-bit produces a subfield. That is, in an image display method, which utilizes the so-called subfield method, by which one field is divided into a plurality of differently weighted binary images, and displayed by temporally superimposing these binary images, a subfield is one of the divided binary images.
Since each pixel is displayed using 8 bits, as shown in
FIG. 2
, 8 subfields can be achieved. Collect the least significant bit of the 8-bit signal of each pixel, line them up in a 10×4 matrix, and let that be subfield SF1 (FIG.
2
). Collect the second bit from the least significant bit, line them up similarly into a matrix, and let this be subfield SF2. Doing this creates subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8. Needless to say, subfield SF8 is formed by collecting and lining up the most significant bits.
FIG. 4
shows the standard form of a 1 field PDP driving signal. As shown in
FIG. 4
, there are 8 subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 in the standard form of a PDP driving signal, and subfields SF1 through SF8 are processed in order, and all processing is performed within 1 field time. The processing of each subfield is explained using FIG.
4
. The processing of each subfield constitutes setup period P
1
, write period P
2
and sustain period P
3
. At setup period P
1
, a single pulse is applied to a sustaining electrode, and a single pulse is also applied to each scanning electrode (There are only up to 4 scanning electrodes indicated in
FIG. 4
because there are only 4 scanning lines shown in the example in
FIG. 3
, but in reality, there are a plurality of scanning electrodes, 480, for example.). In accordance with this, preliminary discharge is performed.
At write period P
2
, a horizontal-direction scanning electrodes scans sequentially, and a predetermined write is performed only to a pixel that received a pulse from a data electrode. For example, when processing subfield SF1, a write is performed for a pixel represented by “1” in subfield SF1 depicted in
FIG. 2
, and a write is not performed for a pixel represented by “0.”
At sustain period P
3
, a sustaining pulse (driving pulse) is outputted in accordance with the weighted value of each subfield. For a written pixel represented by “1,” a plasma discharge is performed for each sustaining pulse, and the brightness of a predetermined pixel is achieved with one plasma discharge. In subfield SF1, since weighting is “1,” a brightness level of “1” is achieved. In subfield SF2, since weighting is “2,” a brightness level of “2” is achieved. That is, write period P
2
is the time when a pixel which is to emit light is selected, and sustain period P
3
is the time when light is emitted a number of times that accords with the weighting quantity.
As shown in
FIG. 4
, subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 are weighted at 1, 2, 4, 8, 16, 32, 64, 128,respectively. Therefore, the brightness level of each pixel can be adjusted using 256 gradations, from 0 to 255.
In the B region of
FIG. 3
, light is emitted in subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, but light is not emitted in subfield SF8. Therefore, a brightness level of “127” (=1+2+4+8+16+32+64) is achieved.
And in the A region of
FIG. 3
, light is not emitted in subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, but light is emitted in subfield SF8. Therefore, a brightness level of “128” is achieved.
A display apparatus as described above which displays image with gradations by using a plurality of subfields has a problem that pseudo-contour noise appears while displaying a motion picture. Pseudo-contour noise is noise that occurs from the human visual characteristics. It appears due to the human visual characteristics and a characteristics of subfield display in a display apparatus which displays image with gradations by using the subfield method. That is, it is a phenomenon, whereby, when a person moves his eyes, a subfield that differs from an original gradation is projected on a retina, and therefore the original gradation is misperceived. Pseudo-contour noise is explained below.
Assume that regions A, B, C, D from the state shown in
FIG. 3
have been moved one pixel width to the right as shown in FIG.
5
. Thereupon, the viewpoint of the eye of a person looking at the screen also moves to the right so as to follow regions A, B, C, D. Thereupon, three vertical pixels in region B (the B
1
portion of
FIG. 3
) will replace three vertical pixels in region A (A
1
portion of
FIG. 5
) after one field. Then, at the point in time when the displayed image changes from
FIG. 3
to
FIG. 5
, the eye of a human being is cognizant of region B
1
, which takes the form of a logical product (AND) of B
1
region data (0111 1111) and A
1
region data (1000 0000), that is (0000 0000). That is, the B
1
region is not displayed at the original 127 level of brightness, but rather, is displayed at a brightness level of 0. Thereupon, an apparent dark borderline appears in region B
1
. If an apparent change from “1” to “0” is applied to an upper bit like this, an apparent dark borderline appears.
Conversely, when an image changes from
FIG. 5
to
FIG. 3
, at the point in time when it changes to
FIG. 3
, a viewer is cognizant of region A
1
, which takes the form of a logical add (OR) of A
1
region data (1000 0000) and B
1
region data (0111 1111), that is (1111 1111). That is, the most significant bit is forcibly changed from “0” to “1,” and in accordance with this, the A
1
region is not displayed at the original 128 level of brightness, but rather, is displayed at a roughly 2-fold brightness level of 255. Thereupon, an apparent bright borderline appears in region A
1
. If an apparent change from “0” to “1” is applied to an upper bit like this, an apparent bright borderline appears.
In the case of a dynamic image only, a borderline such as this that appears on a screen is called pseudo-contour noise (“pseudo-contour noise seen in a pulse width modulated motion picture display”: Television Society Technical Report, Vol.19, No.2, IDY95-21, pp.61-66), causing degradation of image quality.
As technology for reducing this pseudo-contour noise, there is a display apparatus disclosed in Japanese Paten
Ishikawa Yuichi
Kasahara Mitsuhiro
Morita Tomoko
Chung Daniel J
Greenblum & Bernstein P.L.C.
Luu Matthew
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