Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-08-15
2004-09-14
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, C345S204000
Reexamination Certificate
active
06791515
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a display apparatus such as a plasma display. More particularly, the present invention relates to an image display apparatus for writing display information with reduced power consumption.
(2) Description of the Related Art
Typically, when a display apparatus such as a plasma display which displays images based on a two-value display method is used to display images, the display apparatus displays gray-scale images by dividing one field in the time domain into a plurality of sub-fields to which luminance weights are assigned, and controlling ON/OFF of light emission for each sub-field. For example, to display images with 256 gray-scale levels, one field is divided into 8 sub-fields, and assigns luminance weights “1”, “2”, “4”, “8”, “16”, “32”, “64”, and “128” to the 8 sub-fields in the order of time. The display apparatus receives an input digital signal that contains a set of 8 bits that correspond to the above sequence of sub-fields, in the reversed order of the bit sequence (i.e., the lowest bit corresponds to the lowest luminance weight).
FIG. 24
shows relationships between input gray-scale levels contained the input image signals and display gray-scale levels, and the luminance weights assigned to the sub-fields.
FIG. 25
is a plot, based on the data shown in
FIG. 24
, of display gray-scale levels on the vertical axis vs. input gray-scale levels on the horizontal axis. The sub-field information shown in the drawings is written into display cells as the display information by applying voltage to the display cells via the address electrode.
The address electrodes have capacitances for other driving electrodes. Capacitances are also disposed between adjacent address electrodes. When the voltage waveform of the voltage applied to the address electrode changes greatly, a great amount of power is consumed for charging or discharging the capacitances. The amount of power consumed in the address driver also increases as the number of pixels to be displayed on the display apparatus increases, or as the driving voltage required for the addressing increases.
As a solution to the above problems, Japanese Laid-Open Patent Application No. 10-187093 discloses a technique that is equivalent to the one shown in FIG.
26
. This technique intends to reduce the amount of power consumed in the address driver by shifting the timing of the driving waveform, removing the high-frequency component from the spatial frequency component of the input signal in accordance with the expected values of the amount of power consumed in the data driver, or omitting to display lower bits of the display signal in accordance with the expected values of power consumption amount.
Japanese Laid-Open Patent Application No. 2000-66638 (P2000-66638A) discloses a technique that intends to reduce the gray-scale levels of display images using a method in which data for sub-fields with smaller luminance weights is prevented from being written or changed, in accordance with the expected values of amount lost in the driver that are obtained from the display data changing patterns.
However, the conventional method of shifting the timing of the address driving waveform have a defect that it needs to secure a time for shifting the address driving waveform, and as a result, needs to lengthen the period of the address driving waveform. That is to say, the time required for the address driving over the whole period of one field is proportionate to the number of lines on the display apparatus. The time required for the address driving occupies relatively a large portion of the field cycle. As a result, if the time required for the address driving increases slightly, the time that can be used for light emission greatly decreases. This makes it difficult to maintain the luminance.
The other method of restricting the number of display bits or display gray-scale levels in accordance with the expected values of power consumption amount also has a defect that to accurately expect the amount of heat generated in the driving device, it is required to add up a great amount of image information in the time and space domain. This increases the scale of circuits such as a memory device.
When, as is the case with the above conventional technique, the number of bits for the display image is changed only in accordance with the expected values of power consumption amount, the reduction of the number of bits or gray-scale levels may be noticed as image deterioration depending on the display images. This method also has a problem that a certain pattern in the whole image may be displayed as a different image depending on the position of the pattern in the whole image or depending on a combination with another pattern, or that an image that should move smoothly in time may move discontinuously. These phenomena allow viewers to feel unnaturalness.
SUMMARY OF THE INVENTION
The object of the present invention accordingly is to provide an image display apparatus that is practical and effective in reducing the power consumption when image display information is written.
The above object is fulfilled by an image display apparatus for displaying gray-scale images by writing display information to an image display area of a panel, the display information including values of a plurality of sub-fields constituting a field, the image display apparatus being characterized by converting an input image signal into a piece of display information so that a difference between sub-fields in correspondence with each other in adjacent high gray-scale levels becomes less, and displaying a gray-scale image in accordance with the piece of display information.
With the above-described construction, in the display information converted from the input image signal, high gray-scale levels, which have high luminance weights, may have common sub-field values. When this happens, even if gray-scale levels in a certain range in input image signals change frequently, the frequency of change in the waveform of voltage applied to the address electrode decreases. This reduces power consumption in the address driver.
The low luminance levels in input image signals may be faithfully reflected in the display information. In general, low luminance part of an image can be reproduced by turning ON a small number of sub-fields, and writing a small number of sub-fields into the panel. This allows the driver to consume a little amount of power. As a result, even if low luminance levels in input image signals are reflected faithfully in the display information, the amount of power consumed in the address driver does not change much.
On the contrary, in general, high-luminance part of an image is reproduced by switching between ON and OFF a large number of sub-fields. The high luminance part therefore has a high probability that the amount of power consumed in the address driver increases. As a result, the effect of restricting the power consumption in the address driver is expected more by allowing the higher-luminance part to have a more amount of common writing information.
In the above-stated construction, even if the input image signal is converted so that high gray-scale levels have lower sub-field values in common, the difference generated by this is relatively small. As a result, if the number of gray-scale levels is restricted in this way, viewers do not recognize it as an image quality degradation. The image display apparatus, therefore, can display images with the luminance ranging from low to high levels, without allowing the viewers to notice an image quality degradation.
In the above image display apparatus, the conversion of the input image signal may be performed so that as a gray-scale level in the input image signal increases, the number of sub-field values that are common with an adjacent gray-scale level increases.
In the above image display apparatus, the conversion of the input image signal may be performed so that as a gray-scale level in the input image signal increases, the numbe
Kawahaea Isao
Sekimoto Kunio
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