Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-03-27
2004-03-09
Lao, Lun-Yi (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S060000, C345S690000
Reexamination Certificate
active
06703991
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an image display unit for displaying an image on a display device in a plurality of sub-fields, wherein the display device is capable of generating, in each of the sub-fields, a respective illumination level, the image display unit comprising selection means for selecting a first combination of sub-fields for displaying a first color sub-pixel of a particular pixel with a first intensity level, and for selecting a second combination of sub-fields for displaying a second color sub-pixel of the particular pixel with a second intensity level.
The invention further relates to an image display apparatus comprising such an image display unit.
The invention also relates to a method of displaying an image on a display device in a plurality of sub-fields, whereby the display device is capable of generating, in each of the sub-fields, a respective illumination level, the method comprising a step of selecting a first combination of sub-fields for displaying a first color sub-pixel of a particular pixel with a first intensity level, and of selecting a second combination of sub-fields for displaying a second color sub-pixel of the particular pixel with a second intensity level.
2. Description of the Related Art
European Patent Application EP 0 896 317 A2, corresponding to U.S. Pat. Nos. 6,014,258, 6,208,467 and 6,518,977, describes a plasma display panel driven in a plurality of sub-fields. A plasma display panel is made up of a large number of cells that can be switched on and switched off. In the operation of the plasma display panel, three phases can be distinguished. The first phase is the erasure phase, in which the memories of all cells of the panel are erased. The second phase is the addressing phase, in which the cells of the panel that are to be switched on are conditioned by setting appropriate voltages on their electrodes. The third phase is the sustain phase, in which sustain pulses are applied to the cells which cause the addressed cells to emit light for the duration of the sustain phase. The plasma display panel emits light during this sustain phase. The three phases together are called a sub-field period or simply a sub-field. A single image, or frame, is displayed on the panel in a number of successive sub-field periods. A cell may be switched on for zero, one or more of the sub-field periods. The light emitted by a cell in the sub-field periods in which it is switched on, is integrated in the eye of the viewer. In a particular sub-field period, the sustain phase is maintained for a particular time resulting in a particular illumination level of the activated cells. Different sub-fields may have a mutually different or equal duration of their sustain phase. A sub-field is given a coefficient of weight to express its contribution to the light emitted by the panel during the whole frame period. An example is a plasma display panel with 6 sub-fields having coefficients of weight of 1, 2, 4, 8, 16 and 32, respectively. This is a so-called binary distribution. By selecting the appropriate sub-fields in which a cell is switched on, 64 different intensity levels can be realized in displaying an image on this panel. The plasma display panel is then driven by using code words of 6 bits each, whereby a code word indicates, in binary form, which sub-fields are to be switched on, i.e., what the intensity level of a pixel is.
The device described in EP 0 896 317 A2 uses a non-binary distribution of the sub-fields weights. Compared with the binary distribution, the relatively high valued sub-fields of the binary distribution have been split into two lower valued sub-fields. This is at the cost of a reduced number of intensity levels that can be realized with a given number of sub-fields, or at the cost of an increased number of sub-fields for realizing a given number of intensity levels. In the known device, almost every intensity level can be realized by a combination of a high and a low sub-field. In this way, a continuous gradation can be represented with a reduction of false contour interference. In a particular embodiment, the device has two tables, each one of which indicates, for each possible intensity level, the combination of sub-fields realizing that intensity level. For a number of intensity levels, the combination indicated in the one table for a specific intensity level is different from the combination indicated in the other table for that specific intensity level. It is proposed to apply a checkerboard pattern to the image and to use, for a pixel from a white block of the pattern, the combinations from the first table, and for a pixel from a black block of the pattern, the combinations from the second table. This results in a further reduction of false contours.
SUMMARY OF THE INVENTION
It is at object of the invention to provide an image display unit as described in the preamble, with a reduction of flicker. This object is achieved, according to the invention, in a display unit that is characterized in that the selection means is arranged to select that combination as second combination in which the subjective peak in luminance is at a different time position in the frame period compared with the subjective peak in luminance in the first combination. By controlling that the luminance peak from one color sub-pixel falls at a different moment than the luminance peak from the other color sub-pixel, the frequency component of the pixel signal having the frame frequency, usually 50 Hz or 60 Hz, is reduced. By a proper selection of the combination of sub-fields, the peak generated for one color sub-pixel is compensated by a peak in the other color sub-pixel. This is because the two sub-pixels are close together and that, as a consequence thereof, they are perceived as a single light source. It has appeared that when one color is generated at one instant in the frame period and the other color at a later instant in the frame period, the color perception remains unaffected compared with the simultaneous generation of the colors. Hence, one sub-pixel is lit early in the frame period and the other sub-pixel is lit later in the frame period, while the pixel as a whole is still perceived in the desired color. Applicants have realized that it is possible to use this freedom regarding the time of color generation for reducing flicker of the display. In practice, many color intensities will be generated by more than one sub-field, causing that the color will be generated at more than one instant. However, the distribution and weights of the sub-fields are such that there will be a subjective luminance peak in displaying such an intensity, e.g., when the highest sub-field is lit, and the instant of this peak will be perceived as the instant at which the color is generated. The latter is in respect to the perception of flicker and not to the perception of color, since, as described above, the time differences are such that the correct color is perceived.
The known device discloses the possibility of having two tables of different combinations of sub-fields for generating the various intensities. However, the combinations of one table are used for one group of pixels and the combinations of the other table are used for another group of pixels. It is to be noted that for an entire single pixel, always combinations from one of the two tables are used for each of its color sub-pixels. Thus, in the known device, a pixel is treated as one object, i.e., its sub-pixels are treated uniformly, regarding the selection of a combination of sub-fields. This contrasts the current invention, where the individual sub-pixels are individually controlled regarding the selection of sub-fields and the subsequent generation of light.
Furthermore, an embodiment of the known device has combinations of sub-fields that are designed in such a way that for many intensity levels, two emission peaks occur during the field period. This is realized by using a relatively large number of sub-fields and by appropriately positioning the multipl
Salters Bart Andre
Van Dijk Roy
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