Computer graphics processing and selective visual display system – Computer graphics display memory system – Logical operations
Reexamination Certificate
1999-10-26
2002-04-09
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Computer graphics display memory system
Logical operations
C345S690000
Reexamination Certificate
active
06369825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method of converting (or processing) image data that is transferred to a display device. More particularly, the invention relates to an improvement for converting, transferring, and restoring data so that the amount of data change (number of data transitions) is reduced, when gray levels and the like are expressed by a finite number of bits.
2. Description of the Related Art
In cathode-ray tube (CRT) display devices that are computer-related equipments or in liquid crystal displays (LCDs) rapidly spreading in recent years, various methods have been adopted in performing display of gray levels. In displaying gray levels, brightness, for example, is expressed in terms of many intermediate levels between the lightest white and black. Gray levels are represented in image data. In some of the techniques for displaying levels, image data is divided into blocks of a finite number of bits and the gray level of the image data is represented in displayable binary notation by the bits in the block.
For instance, in the case where each data block consists of 4 bits, each bit can express two states with 0 or 1. The 4-bit block can therefore express 16 (2
4
) states, i.e., 16 gray levels. Likewise, in the case where each data block consists of 6 bits, it is able to express 64 (2
6
) states, i.e., 64 gray levels. In general, many drivers use a digital signal by which the number of the output levels are limited to 3 bits (8 gray levels), 4 bits (16 gray levels), 6 bits (64 gray levels), or 8 bits (256 gray levels). In order to convert the output levels representing gray levels to actual brightness, voltage levels respectively required for the gray levels are previously provided so that predetermined levels can be selectively output according to the gray levels.
Such image data of binary notation divided into blocks of a finite number of bits are often transferred in parallel via a plurality of data lines. Even if data that becomes necessary were parallel data bits transferred in parallel at a certain point, in the case where new image data is serially supplied in a time-series manner, as in the case where image data is refreshed, a transition between 0 and 1 will necessarily appear between the previous data and the next data at any of the data lines. Note that the distinction between 0 and 1 can be performed by treating a voltage less than a predetermined voltage as 0 and a voltage greater than the predetermined voltage as 1. This method is obvious to those having skill in this field.
However, in consideration of Electro-Magnetic Interference (EMI), it is preferable that transition should not occur between 0 and 1, if possible. In order to prevent EMI, there is a need to pass an allowable value (standard value) determined in specific groups and countries or throughout the world as a product or an entire system.
Such EMI radiation also arises from internal circuitry wired on a substrate, etc. However, it is often seen that the EMI radiation becomes a problem in the case where it arises from a bus or interface cable that is a set of data lines. The reason is that an interface cable has the property that it serves as an antenna for EMI radiation and increases EMI radiation as it becomes longer. Also, an interface cable or the like is in itself a component for connecting devices separated from each other, so the cable requires a certain degree of length so that it can be widely used.
In addition, there is a relation (general property) that the EMI radiation is proportional to the frequency component of a signal and becomes stronger as the repetition of a signal becomes faster. Here, attention is paid only to a certain specific bit transfered (which means any 1 bit in the 4-bit block), and a time-series change is tracked between data bits, 1 and 0, which are serially transferred. In the case where a digital signal simply repeats a logic high (1), a logic low (0), a logic high (1), and a logic low (0), the strongest EMI radiation arises. Such a state is equivalent to the case where a change in a digital quantity per a certain time period (unit time) in a time-series manner has occurred most frequently. That is, a transition has occurred most frequently between 1 and 0 being transferred adjacently in a time-series manner, and the number of signals repeated, i.e., frequency is high.
The flow of image data in an actual liquid display will be described with reference to FIG.
1
.
FIG. 1
illustrates the constitution of an LCD module
10
, which employs Thin Film Transistors (TFTs) as an example of the LCD. A digital data bus-clock
20
extending from a gate array
11
is elaborately connected to each of an X-driver (also called a data driver or a source driver)
30
and a Y-driver (also called a gate driver)
40
. With this, the TFT on a pixel electrode specified by X and Y can be driven.
The gate array
11
in this example is also called an LCD controller
11
, because it controls the supply of signals to these drivers. The LCD controller and the drivers, as hardware, are realized as internal logic devices internally wired, such as LSI circuits.
In the flow of image data being adopted here, the image data divided into data-bit blocks is serially sent from the source lines to horizontal pixels on a screen, and the gate lines are controlled. In this manner, the image data is displayed on appropriate pixels at predetermined timing. This is what is called scanning of image data. That is, image data is first sent in the horizontal scanning direction. Then, if the sending of the image data in the horizontal direction is completed, the scanning direction will be shifted in the vertical direction and image data will again be sent in the horizontal scanning direction.
FIG. 2
is a schematic diagram showing how image data transferred in a time-series manner via the digital data bus-clock
20
extending from the gate array
11
is taken out as data blocks including a finite number of bits. In data transfer, signals are generally transferred in parallel through parallel data lines from the necessity of processing data in large quantities and at high speeds.
In
FIG. 2
image data is transferred in parallel through 12 data lines (excluding a clock line), which constitute a digital data bus. The 12 data lines are subdivided and exclusively used. For instance, in the case where red (R), green (G), and blue (B) are processed, the 12 data lines are exclusively used for transferring 4 bits for the gray level of red (R), 4 bits for the gray level of green (G), and 4 bits for the gray level of blue (B). Therefore, the image data can easily be taken out as 4-bit blocks.
In order to take out the 4-bit blocks from the 12-bit data transferred in parallel, it is considered that the 4 bits are serially taken out from the most significant bit (MSB) to the least significant bit (LSB), or from LSB to MSB. At this time, the time required for serially taking out data bits and the EMI radiation associated with this are not handled by the present invention, because the associated EMI radiation does not occur through a bus or interface cable that is a set of external data lines.
The 4 bits constituting a data block may be considered as being taken out at substantially the same time, even if they were taken out in a time-series manner. Various methods of taking out data bits which become a data block from the digital data bus-clock
20
is obvious to those having skill in the art, so a description thereof is omitted.
In the case where a gray level has been expressed by a block of a finite number of bits having binary numbers, consider forms of data transfer that will give rise to the problem of EMI. Although it is constant that the total number of transitions arising between the total corresponding bits of blocks to be compared with each other becomes a problem finally, initially there is a necessity of grasping the entire block which is the unit of data transfer.
The necessity of grasping the entire block is also related to how image da
Dinh Duc Q.
Hjerpe Richard
Underweiser Marian
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