Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-02-21
2002-05-07
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S693000
Reexamination Certificate
active
06384803
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a display apparatus of a plasma display panel (PDP) and digital micromirror device (DMD), and more specifically, to a display apparatus capable of adjusting a subfield number in accordance with brightness.
BACKGROUND 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 1 field is divided into a plurality of differently weighted binary images, and displayed by temporally superimposing these binary images, a subfield is 1 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 SF
1
(FIG.
2
). Collect the second bit from the least significant bit, line them up similarly into a matrix, and let this be subfield SF
2
. Doing this creates subfields SF
1
, SF
2
, SF
3
, SF
4
, SF
5
, SF
6
, SF
7
, SF
8
. Needless to say, subfield SF
8
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 SF
1
, SF
2
, SF
3
, SF
4
, SF
5
, SF
6
, SF
7
, SF
8
in the standard form of a PDP driving signal, and subfields SF
1
through SF
8
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 SF
1
, a write is performed for a pixel represented by “1” in subfield SF
1
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 SF
1
, since weighting is “1,” a brightness level of “1” is achieved. In subfield SF
2
, 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 SF
1
, SF
2
, SF
3
, SF
4
, SF
5
, SF
6
, SF
7
, SF
8
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 SF
1
, SF
2
, SF
3
, SF
4
, SF
5
, SF
6
, SF
7
, but light is not emitted in subfield SF
8
. 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 SF
1
, SF
2
, SF
3
, SF
4
, SF
5
, SF
6
, SF
7
, but light is emitted in subfield SF
8
. Therefore, a brightness level of “128” is achieved.
With the PDP subfield method explained above, to provide an optimum screen display in bright places and dark places, it is necessary to make adjustment in accordance with the brightness of an image.
A PDP display apparatus capable of brightness control is disclosed in the specification of Kokai No. (1996)-286636 (corresponds to specification in U.S. Pat. No. 5,757,343), but here, only light emission frequency and gain control are performed in accordance with brightness, making adequate adjustment impossible.
An object of the present invention is to provide a display apparatus capable of adjusting a subfield number in accordance with brightness, designed to be able to adjust the number of subfields in accordance with the brightness of an image (comprising both a dynamic image and a static image). The average level of brightness, peak level, PDP power consumption, panel temperature, contrast and other factors are used as parameters that represent image brightness.
By increasing the subfield number, it is possible to eliminate pseudo-contour noise, which is explained below, and conversely, by decreasing the subfield number, although there is the likelihood that pseudo-contour noise will occur, it is possible to produce a clearer image.
Pseudo-contour noise is explained below.
Assume that regions A, B, C, D from the state shown in
FIG. 3
have been moved 1 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, 3 vertical pixels in region B (the B
1
portion of
FIG. 3
) will replace 3 vertical pixels in region A (A
1
portion of
FIG. 5
) after 1 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 (01111111) and A
1
region data (10000000), that is (00000000). 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 sum (OR) of A
1
region data (10000000) and B
1
region data (01111111), that is (11111111). 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
Ishikawa Yuichi
Kasahara Mitsuhiro
Morita Tomoko
Eisen Alexander
Greenblum & Bernstein P.L.C.
Hjerpe Richard
Matsushita Electric - Industrial Co., Ltd.
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