Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
2001-07-30
2004-11-02
Razavi, Michael (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S063000
Reexamination Certificate
active
06812932
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, GB 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 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.
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 technolog
Ishikawa Yuichi
Kasahara Mitsuhiro
Morita Tomoko
Greenblum & Bernstein P.L.C.
Havan Thu-Thao
Razavi Michael
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