Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-09-22
2003-04-29
Chow, Dennis-Doon (Department: 2675)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S589000, C382S252000
Reexamination Certificate
active
06556214
ABSTRACT:
This application is based on an application No. H10-267896 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display method for displaying a multilevel image based on a digital image input signal, and reduces the deterioration that occurs in image quality where there are insufficient display levels.
2. Description of the Prior Art
When displaying a multilevel image using a digital display apparatus such as a PDP (Plasma Display Panel), limitations on the number of colors that can be displayed by the display apparatus mean that smooth gradations between light and dark parts of an image cannot be displayed. As a result, brightness changes in steps, creating patterns composed of lines of equal brightness that spoil the displayed image.
One method for preventing such decreases in image quality is called error diffusion. In this method, limitations in the ability to display certain shades are compensated for by diffusion the difference (“display error”) between a value in the image signal that should be reproduced and the actual color used to display this value among the pixel values of the surrounding pixels. As one example, when an 8-bit (256-color) display is used to display an image expressed using 12 bits (4096 colors) per pixel, the lower four bits of each pixel value is set as the display error. As shown in
FIG. 49
, 7/16 of this display error is added to the pixel on the right, 3/16 of this display error is added to the pixel below and to the left, 5/16 of this display error is added to the pixel below, and 1/16 of this display error is added to the pixel below and to the right. The color used to display each pixel is then calculated according to the total of the input image signal that corresponds to the pixel and display errors that are added to this pixel due to the surrounding pixels.
This calculation is performed using the circuit shown in FIG.
50
. Numeral
2001
in
FIG. 50
represents the 12-bit input image signal, numeral
2002
represents the upper 8 bits of the output of the adder
2012
, numeral
2003
represents the lower 4 bits of the output of the adder
2012
, numerals
2004
-
2007
are multiplication units that multiply the display errors by the stipulated weightings, and numerals
2008
-
2011
are delay units for appropriately delaying the inputted display errors so that the display errors are diffused into the surrounding pixels. The adder
2012
adds the various values produced by the multiplication units
2004
-
2007
to the input image signal.
In this error diffusion process, the illustrated circuit calculates the sum of the original digital data (the input image signal) and the errors for four of the surrounding pixels that are inputted into the adder
2012
by the multiplication units
2004
-
2007
. The upper 8 bits of this sum are outputted to the display apparatus and the lower 4 bits are diffused into the pixel values of the surrounding pixels.
In recent years, however, improvements in the performance of display apparatuses have led to increases in the frequency of image signals, so that the above calculation method is not fast enough to perform error diffusion processing for a modern display apparatus.
One potential solution to this problem would be to reduce the display frequency by using a shift register or the like to convert a serial input image signal into a multiphase signal so that digital data corresponding to a plurality of pixels that are adjacent in the scanning direction is input in parallel. Conventional error diffusion methods diffuse the display error of the pixel to the left of the target pixel into the pixel value of the target pixel. With such method, however, there is the drawback that several data cycles (a data cycle being the time taken to input the input image signal for one pixel into the circuits that perform the processing) would be required to determine the pixel values that should be displayed for all of the pixels in one set of multiphase data. This means that it would not be possible to output data as multiphase data (not that the concept of “multiphase data” is explained in detail in the Embodiments section of this specification).
SUMMARY OF THE INVENTION
The present invention was developed after an extension review of the problems stated above and has an object of providing a multilevel image display method that can perform error diffusion even when data is inputted as multiphase data.
The stated object is achieved by a multilevel image display method for a multilevel image display apparatus, the multilevel image display apparatus processing digital values corresponding to a plurality of pixels, which are adjacent in a scanning direction, in parallel as a data block and converting the digital values corresponding to each pixel in a data block into multilevel values that are used when displaying an image, the multilevel image display method including: an error calculation process for calculating a display error from a digital value that corresponds to a target pixel; and an error diffusion process for diffusing the display error calculated for the target pixel into digital values corresponding to pixels included in at least one data block that follows a data block including the target pixel.
With the stated construction, an image with what appear to be a large number of colors can be displayed due to error diffusion even when digital image data is inputted as multiphase data where pixel values for a plurality of pixels that are adjacent in the scanning direction are inputted in parallel. While the conventional method basically only diffuses the display error of the target pixel into a digital value of a pixel that is adjacent to the target pixel on the same scanning line, the present invention diffuses the display error of the target pixel into digital values of pixels in data blocks that are inputted after the data block that includes the target pixel. While conventional methods are incapable of diffusing errors for all pixels when data is inputted as multiphase data, the present invention is capable of such processing. In short, amended data can be outputted with the same number of phases as the input multiphase data. The diffusion of errors into digital values corresponding to pixels in data blocks that are inputted after the data block including the target pixel can be performed according to the techniques described below.
Here, the error diffusion process may diffuse the calculated display error into digital values corresponding to pixels that lie on scanning lines which are below a scanning line that includes the target pixel.
With the above technique, more time is available for the calculations for error diffusion that needed to be performed within one data cycle in conventional error diffusion methods. This means that the error diffusion processing can be performed by relatively low-speed circuitry.
Here, the error diffusion process may diffuse the calculated display error into digital values of pixels in data blocks that come after the data block including the target pixel, said pixels having a same position (hereafter, “phase”) in a data block as the target pixel.
With the above technique, error diffusion processing is performed separately for the data in each phase of the multiphase input signal, so that the construction of the circuitry can be simplified.
Here, when error diffusion process diffuses the calculated display error into digital values of pixels on a same scanning line as the target pixel, the display error may be diffused into pixels that have a same phase within a data block as the target pixel, and when the error diffusion process diffuses the calculated display error into digital values of pixels on a lower scanning line, the display error may be diffused into pixels that are adjacent to the target pixel.
If display errors are only diffused into digital values of pixels with the same phase, the pixels that are affected by a target pixel will be spatially separated from the ta
Kawahara Isao
Yamada Kazuhiro
Chow Dennis-Doon
Matsushita Electric - Industrial Co., Ltd.
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