(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 xe2x80x9c1xe2x80x9d, xe2x80x9c2xe2x80x9d, xe2x80x9c4xe2x80x9d, xe2x80x9c8xe2x80x9d, xe2x80x9c16xe2x80x9d, xe2x80x9c32xe2x80x9d, xe2x80x9c64xe2x80x9d, and xe2x80x9c128xe2x80x9d 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.
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 number of large steps increases, where each step is a gap between the gray-scale level in the input image signal and corresponding gray-scale levels in the display information.
In the above image display apparatus, the conversion of the input image signal may be performed so that bit values of sub-fields to which small luminance weights are assigned become either xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d.
With the above construction, the input image signal is converted so that as a gray-scale level in the input image signal increases, the number of sub-fields with fixed small luminance weights increases. This restricts the power consumption in the address driver when displaying a high-luminance image.
As for a low-luminance part of an image, since the original minute differences between gray-scale levels are maintained, the minute gray-scale levels of the original image are reproduced. In general, low-luminance part of an image consumes little amount of power.
Accordingly, the above-stated construction provides a high-quality image display for a wide range of gray-scale levels ranging from low luminance to high luminance, while reducing the power consumption in the address driver. The above object is also fulfilled by an image display apparatus for displaying gray-scale images by representing each gray-scale level of the images by an ON/OFF pattern of a set of sub-fields constituting one field, the image display apparatus being characterized by converting an input image signal into a piece of display information so that as a gray-scale level in the input image signal increases, the number of serial sub-fields that are all ON or all OFF and are common with an adjacent gray-scale level increases.
With the above construction, it is possible to, for example, write fixed information so that for high gray-scale levels, sub-fields with low luminance weights are all turned ON or all turned OFF. This enables the amount of power consumed in the address driver to be restricted when high gray-scale level part, or high luminance part is displayed. It is also possible with this construction to convert the input image signals so as to reduce the number of sub-fields that are turned OFF commonly between adjacent gray-scale levels in a certain range of highest gray-scale levels. This enables images to be displayed without reduction of peak luminance while reducing the address power as a whole.
The above object is also fulfilled by an image display apparatus for displaying gray-scale images by representing each gray-scale level of the images by an ON/OFF pattern of a set of sub-fields constituting one field, characterized in that (N-M) higher bits of an N-bit input digital image signal are a first signal, lower M bits of the N-bit input digital image signal are a second signal, where M and N are integers satisfying a condition 0xe2x89xa6Mxe2x89xa6N, a calculation using the second signal as an input and including a plurality of delays is performed to obtain a signal, lower M bits of the obtained signal are all changed to xe2x80x9c0xe2x80x9d to generate a third signal, and a signal obtained by adding the third signal to the first signal represents a display gray-scale level.
The above object is also fulfilled by an image display apparatus for displaying gray-scale images by representing each gray-scale level of the images by an ON/OFF pattern of a set of sub-fields constituting one field, characterized in that (N-M) higher bits of an N-bit input digital image signal are a temporary display gray-scale level, where M and N are integers satisfying a condition Mxe2x89xa6N, and an actual display is performed by correcting an error between the N-bit input digital image signal and the temporary display gray-scale level, using an error diffusion method that forms a circular loop by an M-bit line memory.
The above object is also fulfilled by an image display apparatus comprising: means for displaying gray-scale images by representing each gray-scale level of the images by an ON/OFF pattern of a set of sub-fields constituting one field; and means for subjecting an N-bit input digital image signal to an error diffusion process to reduce the number of display bits and displaying the resultant signal, wherein as a gray-scale level in the N-bit input digital image signal increases, the number of display bits to be reduced increases in units of display pixels.
With the above construction, it is possible to respond at high speed to each gray-scale level of pixel in input image signals, calculate the number of effective display bits, and assign different numbers of effective display bits to a low-luminance part and a high-luminance part. As a result of this, the high-luminance part is displayed while the change of the driving waveform supplied to the address electrode is restricted and the amount of power consumed in the address driver is reduced, and the low-luminance part, which allows the address driver to consume little amount of power, is displayed with the original luminance. It should be noted here that xe2x80x9clower bitsxe2x80x9d correspond to part of a set of sub-fields, and that smaller luminance weights are assigned to the lower bits.
Also, in the above construction, even for the high-luminance part where the number of effective bits is reduced, an error between the gray-scale level of the input image signal and the actually displayed gray-scale level is diffused to the periphery. This provides visually sufficient display gray-scale levels. Different from a conventional error diffusion method in which the number of effective display bits is fixed, the image display apparatus of the present invention adds display errors accumulated from peripheral pixels to a focused pixel to the display data by the number of bits that is determined from the gray-scale level of the focused pixel, and at the same time, diffuses newly generated display errors from the focused pixel to peripheral pixels in accordance with the display bits of the focused pixel. This allows the number of effective bit-width to change for each pixel and achieves visually sufficient display gray-scale levels ranging from low to high luminance levels.
In the above image display apparatus, the display gray-scale level may be obtained by adding a signal having an amplitude corresponding to a gray-scale level to the input image signal, either with regular periods or with irregular periods.
In the above image display apparatus, the signal that is added with regular periods may be a signal that is inverted in units of pixels, lines, or fields.
In the above image display apparatus, the signal that is added with irregular periods may be a signal that is inverted at random in units of pixels, lines, or fields.
With the above construction, it is possible to restrict the number of gray-scale levels that are actually used when an image is displayed, and is possible to display the image by increasing the number of gray-scale levels that are visually equal to each other, using the error diffusion method, while preventing a certain image pattern from being recognized by a viewer.
In the above image display apparatus, a display error may be diffused to a peripheral of a focused pixel using the error diffusion method.
With the above construction, it is possible to improve the image quality using a known means for improving the image quality.
The above object is also fulfilled by an image display apparatus for displaying gray-scale images by representing each gray-scale level of the images by an ON/OFF pattern of a set of sub-fields constituting a field in the time domain, characterized in that an area composed of a plurality of adjacent pixels is set in response to an input image signal, then a plurality of pieces of display information having, in common, sub-fields with a same pattern between adjacent pixels are generated, and the gray-scale images are displayed in accordance with the plurality of pieces of display information.
With the above construction, it is possible to generate the display information in accordance with a rule set for a certain range of gray-scale levels in the input image signals, and restrict the amount of power consumed when data is written, by allowing adjacent pixels to have common sub-field values. It is important especially that the writing information is generated not in accordance with a certain rule for the whole screen, but in accordance with the rule set for a certain range of gray-scale levels in the input image signals. This enables the display information to be generated so as to increase the effect of reducing the amount of writing power consumed in the address driver, while restricting the image quality degradation.
In the above image display apparatus, a piece of display information corresponding to the smallest change of an average gray-scale level in the area maybe selectively used.
With the above construction, in addition to the effect of restricting the amount of power consumed when data is written, by allowing adjacent pixels to have common sub-field values, it is possible to prevent an image quality change from being noticed, by restricting the change of the average luminance value due to replacement of writing information and restricting the change of luminance and color tone.
In the above image display apparatus, a standard pixel may be set in the area, and gray-scale levels of pixels excluding at least the standard pixel in the area are changed so that the plurality of pieces of display information have, in common, sub-fields having a same pattern between adjacent pixels.
With the above construction, it is possible to restrict signal change between the standard pixel and the other pixels and reduce the amount of power consumed in the address driver, while maintaining the original value of the standard pixel. This prevents the image information from noticeably changing and restricts the image quality degradation.
In the above image display apparatus, a standard pixel may be set in the area, and when a difference between a gray-scale level of a pixel in the area and that of the standard pixel is lower than a value that is determined in accordance with a gray-scale level of the standard pixel indicated in an input image signal, the gray-scale level of the pixel in the area and the gray-scale level of the standard pixel are adjusted to be equal to each other.
With the above construction, pixels with luminance levels being little different from the luminance of the standard pixel are each replaced with the same signal as that of the standard pixel. This replacement does not cause a viewer to recognize an image quality degradation. Since the signal of the standard pixel completely matches the signal of each of the peripheral pixels, the change between signals of the standard pixel and the peripheral pixels is eliminated. This reduces the amount of writing power consumed in the address driver.
In the above image display apparatus, the sub-fields commonly contained in the plurality of pieces of display information may be lower sub-fields among all sub-fields.
With the above construction, adjacent pixels have common lower sub-field values with low luminance. This restricts the amount of power consumed in the address driver when data is written, and also prevents the image quality from deteriorating greatly.
In the above image display apparatus, the area may be composed of two adjacent lines.
With the above construction, the signals in the area have a value in common. However, this arrangement does not cause the image quality to deteriorate greatly since the lines in a pair inherently show a strong correlation with each other. Accordingly, this restricts the amount of power consumed in the address driver when data is written.
In the above image display apparatus, the area changes regularly or irregularly in units of pixels.
With the above construction, in the case of an area that changes regularly in units of pixels (e.g., an area representing a title pattern such as a checkered pattern), it is possible to restrict the frequency of signal change between adjacent pixels while attaching importance to the average luminance or color tone of the entire pattern area rather than to the gray-scale level of each pixel constituting the pattern. This restricts the amount of power consumed in the address driver when data is written, while restricting the image quality degradation. In the case of an area that changes irregularly in units of pixels, representing details of a complicated image such as xe2x80x9chairxe2x80x9d or xe2x80x9ctexturexe2x80x9d and tending to be recognized by a viewer as an image quality degradation when the high-frequency component is removed from the spatial frequency component, it is possible to allow a plurality of sub-fields to have a common value while maintaining the contrast between each pixel of the original image. This restricts the amount of power consumed in the address driver when data is written, and also prevents the image quality from deteriorating greatly.
The above object is also fulfilled by an image display apparatus for displaying gray-scale images by representing each gray-scale level of the images by an ON/OFF pattern of a set of sub-fields constituting a field in the time domain, characterized in that an area composed of a plurality of adjacent pixels is set in response to an input image signal, then a signal level of the area is changed, and a luminance difference between main gray-scale levels in the area is changed to be no less than a certain value that is determined in accordance with the luminance difference between the main gray-scale levels.
With the above construction, it is possible to restrict the signal change between pixels and restrict the amount of power consumed in the address driver when data is written, while maintaining the contrast of the image.
In the above image display apparatus, the main gray-scale levels in the area may form a regular pattern in units of pixels (for example, a checkered pattern).
In the above image display apparatus, the main gray-scale levels in the area may be two or less gray-scale levels for each display color, and form a regular pattern in units of pixels for each display color. More particularly, the pattern may be a checkered pattern or a tile pattern, for example.
The above object is also fulfilled by an image display apparatus for displaying gray-scale images by representing each gray-scale level of the images by an ON/OFF pattern of a set of sub-fields constituting a field in the time domain, characterized in that an area composed of a plurality of adjacent pixels is set in response to an input image signal, a standard pixel is set in the area, then gray-scale levels of pixels excluding at least the standard pixel in the area are changed so that the number of sub-fields that are different between the standard pixel and pixels adjacent to the standard pixel is restricted, and so that a luminance difference between main gray-scale levels in the area is changed to be no less than a certain value that is determined in accordance with the luminance difference between the main gray-scale levels.
With the above construction, it is possible to restrict the signal change between pixels and restrict the amount of power consumed in the address driver when data is written, while maintaining the contrast of the image.