KR100203319B1 - Method and apparatus for storing compressed data for subsequent presentation on an active addressed display - Google Patents

Abstract

An electronic device 55 for driving an active-addressed display 100 is coupled to a data port 505 for receiving image data and to the data port 505, so that a plurality of normal orthogonal functions, i. And a compression circuit 530 for generating the compressed data by compressing the image data using a method in which the image data is converted two-dimensionally using normalized functions.

The electronic device 500 is coupled to the compression circuit 530 and has a conversion circuit 515 for performing one-dimensional transform on the compressed data using the normal orthogonal functions to generate a set of column values. More included.

Column drivers 565 coupled to the conversion circuit 515 and to the active-addressed display 100 are connected to the active-addressed display 100 with an analog voltage corresponding to the set of column values. Drive the columns.

Description

[Name of invention]

Method and apparatus for storing and displaying compressed data on an active addressed display

[Field of Invention]

The present invention relates generally to data compression techniques, and more particularly to data compression in an active addressed display system.

[Background of invention]

Liquid crystal displays (LCDs) are well known as an example of a direct multiplexed rms responding electronic display.

In such a display, a nematic liquid crystal material is located between two parallel glass plates, which have electrodes on each surface in contact with the liquid crystal material.

These electrodes are arranged in vertical columns on one plate and horizontal rows on the other to drive a picture element (pixel) wherever the column and row electrodes overlap. Are arranged.

In an rms-responsive display, the optical state of the pixel substantially responds to the square of the voltage applied to the pixel, i.e. the difference in voltage applied to the electrodes on opposite sides of the pixel.

LCDs have a unique time constant that represents the time required for the optical state of the pixel to return to equilibrium stste after the pixel's optical state is changed by varying the voltage applied to the pixel.

Recent technological advances have led to the production of LCDs with time constants (approximately 16.7 ms) close to the frame period used in many video displays.

This short time constant allows the LCD to respond quickly and is particularly advantageous for displaying movement without smearing or flickering noticeably occurring in the displayed image.

Conventional direct multiplexed addressing methods for LCDs face problems when the display time constant approaches the frame period.

This problem arises because conventional direct multiplexed addressing methods apply a short duration selection pulse to each pixel once per frame.

The voltage level of the select pulse is typically 7-13 times higher than the rms voltage averaged over the frame period.

The optical state of pixels in LCDs with short time constants tends to return to equilibrium between select pulses, and the human eye combines changes in brightness to a sensed intermediate level, resulting in image contrast. contrast is lowered.

In addition, alignment instabilities may occur in some types of LCDs due to the high level of the selection pulse.

To overcome these problems, an active addressing method has been developed for driving rms responsive electronic displays.

This active addressing method continuously drives the row electrodes by signals composed of a train of periodic pulses having a common period T corresponding to the frame period.

The low signals are independent of the picture to be displayed and are preferably orthogonal and normalized signals.

That is, orthonormal.

The term orthogonal multiplies the magnitude of the signal applied to one of the rows by the magnitude of the signal applied to the other of the rows, indicating that the integration of this product during the frame period is zero.

The term normal indicates that all row signals have the same rms voltage integrated over frame period T.

During each frame period a plurality of signals for the column electrodes is calculated and generated from the collective state of the pixels in each column.

During the frame period, the column voltage at any time t takes into account each pixel in the column, giving a pixel value representing the optical state of the pixel (-1 for fully on, +! For fully off, or gray). Multiply the value of the row signal of the pixel at time t by the shade, which is proportional to the gray shade, and is proportional to the sum obtained by adding the products thus obtained. .

Driving with the active addressing method, it can be mathematically shown that each pixel of the display is subjected to an average rms voltage during a frame period, which is proportional to the pixel value for that frame.

The advantage of active addressing is that it does not apply one high level select pulse to each pixel during the frame period, but a plurality of much lower level (2-5 times the rms voltage) select pulses scattered throughout the frame period. The reason for this is that high contrast can be restored to the displayed image.

In addition, the possibility of alignment instability is reduced because of the much lower level of select pulses.

As a result, using rms-responsive displays and active addressing methods such as LCDs used in laptop computers, image data can be displayed at video speed without smearing or flickering.

Further, according to the LCD driven by the active addressing method, it is possible to display image data having a plurality of shades without the contrast problem present in the LCD driven by the conventional multiplexed addressing method.

The disadvantage of using active addressing is that a large amount of computation is required to generate column and row signals to drive the rms-responsive display.

For example, a gray scale display with 480 rows and 640 columns and a frame rate of 60 frames per second requires nearly 10 billion calculations per second.

Of course, it is possible to make calculations at this rate, but doing such complex and fast calculations leads to large power consumption.

In portable, battery powered devices such as laptop computers and radio receivers, the power dissipation issue is particularly important as the processing life is an important consideration in design.

Thus, there is a need for a method and apparatus for minimizing the power consumption required to display image data on an active-addressed display.

[Summary of invention]

According to one aspect of the invention, a method of compressing data in an electronic device having an active-addressed display comprises receiving image data.

The method further includes compressing the image data by two-dimensional transformation using a plurality of orthogonal functions to generate the compressed data.

Subsequently, a set of column values according to the active-addressing technique is generated by performing a one-dimensional transformation on the compressed data using a plurality of orthogonal functions.

According to another feature of the invention, a method of compressing data after displaying data in an electronic device having an active-addressed display comprises the steps of receiving image data and using a plurality of orthogonal functions to perform one-dimensional image data. Generating a set of column values in accordance with an active addressing technique by one-dimensionally transforming.

The method further includes driving the columns of the active-addressed display with analog voltages corresponding to the set of column values.

Then, image data is compressed using a compression method in which a set of column values are converted into one dimension using a plurality of orthogonal functions, and as a result, compressed data that is subsequently stored by this compression method is generated.

According to another particular aspect of the present invention, an electronic device for driving an active-addressed display comprises a data port for receiving image data and a plurality of orthogonal functions coupled to the data port; Compression circuitry for forming the compressed data by compressing the image data using a method in which the image data is two-dimensionally transformed using < RTI ID = 0.0 >

The electronic device is coupled to the compression circuitry and is for transforming circuitry for performing one-dimensional transformation on the compressed data using a plurality of orthogonal functions to generate a set of column values. It further includes.

Column drivers coupled to the conversion circuit and the active-addressed display drive the columns of the active-addressed display with the first set of analog voltages corresponding to the set of column values.

[Brief Description of Drawings]

1 is a front orthographic view of a portion of a conventional liquid crystal display.

2 is a cross-sectional view of a conventional liquid crystal display based on line 2-2 of FIG.

3 shows a matrix of Walsh functions in accordance with the present invention.

4 illustrates Walsh functions in accordance with the present invention.

5 is an electrical block diagram of an electronic device for generating signals for active addressing the liquid crystal display of FIG. 1 in accordance with the present invention.

6 is a flow chart illustrating operation of a controller included in the electronic device of FIG. 5, in accordance with the present invention.

Detailed description of the invention

1 and 2, a front view and a cross-sectional view of a portion of a conventional liquid crystal display (LCD) 100 includes a space filled with a layer of liquid crystal material 202 therebetween. The first and second transparent substrates 102, 206 are shown.

A circumferential seal 204 prevents liquid crystal material from escaping from the LCD 100.

The LCD 100 includes a plurality of transparent electrodes including row electrodes 106 positioned on the second transparent substrate 206 and column electrodes 104 positioned on the first transparent substrate 102. tranparent electrodes).

At each point where the column electrode 104 overlaps the row electrode 106, such as the overlap 108, the voltage applied to the overlapping electrodes 104, 106 is the optical state of the liquid crystal material 202 therebetween. Can be controlled, thus forming a controllable picture element, which will be referred to as a pixel.

LCD is a preferred display element in accordance with a preferred embodiment of the present invention, but if other kinds of display elements have optical properties responsive to the square of the voltage applied to each pixel, similar to the rms response of the LCD, It will be appreciated that these other kinds of display elements may also be used.

3 and 4 show an 8x8 (third order) matrix of Walsh functions 300 and their corresponding Walsh waves 400, according to a preferred embodiment of the present invention. .

Walsh functions are orthogonal and normalized, i.e., normal orthogonal, and are therefore preferred for use in active addressed display systems as described briefly in the background of the invention.

One of ordinary skill in the art would be to display active systems with other kinds of functions, such as Pseudo Random Binary Sequence (PRBS) functions or Direct Dosine Transform functions. You can understand that it can be used in.

When used in an active-addressed display system, the Walsh functions apply one voltage to a plurality of selected electrodes of the LCD 100 that have the levels represented by the Walsh wave 400.

For example, the Walsh waves 404, 406, and 408 can be applied to the first (topmost), second and third row electrodes 106, etc., respectively.

In this way, each Walsh wave 400 will be applied one to the corresponding one of the row electrodes 106.

Since the Walsh wave 402 biases the LCD 100 to an unwanted DC voltage, it is desirable to not use the Walsh wave 402 in the LCD.

It will be interesting to note that the values of the Walsh wave 400 are constant during each type slot t.

The duration of time slot t for eight Walsh waves 400 is equal to eight minutes of the duration of one complete cycle of Walsh waves 400 from start point 410 to end point 412. 1

When using a Walsh wave to active address a display, the duration of one complete cycle of the Walsh wave 400 is the frame duration, i.e. one complete data for controlling all pixels 108 of the LCD 100. It is set equal to the time at which the set (one complete set of data) is received.

The eight Walsh waves 400 may drive the eight row electrodes 106 (seven if the Walsh waves 402 are not used) one by one.

It will be appreciated that the actual display has much more rows.

For example, displays with 408 rows and 640 columns are nowadays widely used in laptop computers.

Walsh function matrices are available in complete sets, determined by powers of two, and since active addressing requires normal orthogonality, it does not allow more than one electrode from each Walsh wave to be driven. To drive a display with 480 row electrodes 106, a Walsh function matrix of 512 × 512 (2 ⁹ × 2 ⁹ ) would be needed.

In this case, the duration of time slot t is 1/512 of the frame duration.

408 Walsh waves will be used to drive the 480 row electrodes 106, while the remaining 32 Walsh waves, preferably including the first Walsh wave 402 with DC bias, will not be used.

It will be appreciated that driving a display, such as LCD 100 (FIG. 1), requires a large number of calculations to be performed quickly according to the active-addressing technique, and thus consumes a lot of power.

In portable devices powered by a battery, power consumption becomes a very important issue due to the limited capacity of the battery.

Next, referring to FIG. 5, an electrical block diagram of an electronic device 500 including an active-addressed display such as LCD 100 is shown.

An electronic device 500, such as a portable laptop computer or a paging receiver, for example, is a data port 505 for receiving image data from a video source (not shown). It includes.

The data port 505 recovers image data from, for example, a communication bus, a floppy drive for reading image data from a diskette or a radio frequency (RF) signal in the case of a paging receiver. It may be a receiving circuit.

The electronic device 500 further includes an analog to digital (A / D) converter 510 for converting analog image data values into digital image data values, which are described below. As will be explained in more detail, it is provided to the controller 515 for converting image data into another domain.

The resolution and range of the A / D converter 510 are determined by the image to be displayed on the LCD 100.

For example, if the pixels 108 of the LCD 100 are all on or all off, the A / D 510 may display pixels with -1 fully on and +1 fully off. Image data can be converted into binary data.

If gray shades are also to be displayed on the LCD 100, the A / D converter 510 may generate values between -1 and +1 for gray shades.

It will be appreciated that the A / D converter 510 is unnecessary if receiving digital image data at the data port 505.

The controller 515 is coupled to a regular function database 520 for storing a plurality of orthogonal and preferably normalized functions in the form of a normal orthogonal matrix, wherein the number of rows of this normal orthogonal matrix is the LCD 100. It may be more than or equal to the number of rows included in the.

Matrices of other normal orthogonal functions, such as DCT or PRBS function, may also be used, but the normal orthogonal matrix may be, for example, a Walsh function matrix (300, FIG. 3).

According to the present invention, a normal orthogonal matrix is used by the controller 515 to convert the image data upon receipt.

Upon receiving the image data, the controller 515 performs a two-dimensional transformation on the image data using a normal orthogonal matrix, resulting in image data converted in two dimensions.

This two-dimensional transform may use many other fast and efficient algorithms, but can be done using, for example, the Fast Fourier Transform algorithm or its transform or Fast Walsh transform.

One such algorithm uses matrix multiplication and can be represented by the following formula.

I _2D = OM * I * OM

[Where I _2D is the two-dimensional transformed image data, I is the image data, and OM represents a normal orthogonal matrix stored in the normal orthogonal function database 520.] When performing matrix multiplication, the terms of the terms It will be appreciated that orders cannot be changed.

The controller 515 is further coupled to a quantizer 525 that quantizes two-dimensionally converted image data to a level closest to several predetermined levels by conventional methods.

The entropy encoder 530 coupled to the controller 515 uses one of several well-known entropy encoding methods, such as Huffman encoding, which encodes according to the probability that the values of the quantized data occur. Used to compress the quantized data.

According to the present invention, the electronic device 500 further includes a memory device such as random access memory (RAM) for storing compressed data.

In this way, image data received by the electronic device 500 is compressed before being stored, thus taking up less memory space.

According to the trend of the market, portable devices that are mainly carried by the user should be designed as small and light as possible, so that storing the compressed image data without storing the image data itself is an electronic device 500 such as a laptop computer. It is particularly advantageous when it is a portable device.

Thus, with this goal in mind, the size of components such as memory included in portable devices is also limited.

Preferably, the electronic device 500, in addition to the RAM 535, stores subroutines executed by the controller 515 during the operation of the electronic device 500. ROM 540 and a clock 545 for generating timing signals for use in system timing.

In addition, the data input device 550 can be coupled to the controller 515.

For example, if the electronic device 500 is a laptop computer, the data input device 550 may include a keyboard, whereas if the electronic device 500 is a paging receiver, control means accessible to a user rather than a keyboard. (user-accesible controls) can be coupled to the controller 515.

According to the present invention, the image data may be displayed automatically or the image data may be displayed by inputting commands for instructing the controller 515 using the data input device 550.

Instructed in that manner, the controller 515 processes the compressed data to generate signals suitable for active addressing the LCD 100.

More specifically, an entropy decoder 555 is used to decode the compressed data, resulting in two-dimensionally transformed image data that was previously quantized.

By performing a one-dimensional inverse transformation on this data, this data can be easily and quickly converted into signals for active-addressing the columns of the LCD 100.

If one of ordinary skill in the art knows that a normal orthogonal matrix, i.e. a separable and symmetric matrix, is equal to its inverse, i.e., OM = 1 / OM You'll understand that it's a lot simpler.

Thus, a normal orthogonal matrix stored in a normal orthogonal function database 520 was previously used in a data compression process, and thus not a one-dimensional inverse transform, but a one-dimensional transform such as, for example, a Walsh transform. The controller 515 may use the same normal orthogonal matrix to perform.

If matrix multiplication is used, this process is described by the following formula.

CV = I _1D = I _2D * OM

[Where, I _2D is the quantized, two-dimensionally transformed image data, OM is a normal orthogonal matrix, and I _1D is the resulting one-dimensionally transformed image data, which is used to active-address the columns of the LCD 100. Same values as the appropriate column values (CV).]

As briefly described in the background of the invention, the row signals for driving the rows of the LCD 100 are signals obtained from normal orthogonal functions independently of image data.

The column signals for driving the columns of the LCD 100 are a linear combination of all the low signals and the image data, i.e. analog voltages corresponding to the column values, and one-dimensionally the image data using normal orthogonal functions. Can be generated by converting.

Thus, it will be appreciated that the column values generated by transforming the quantized data into one dimension are already in a form suitable for active-addressing the columns of the LCD.

As a result, the electronic device 500 does not need to decompress previously compressed stored data for convenient storage.

The electronic device 500 does not need to generate column values directly from the image data each time the image data is displayed.

Instead, the electronic device 500 simply performs one-dimensional transformation on the compressed data when it is about to be displayed.

On the other hand, in the conventional apparatus, the data compressed and stored in the memory must be decompressed, which requires a lot of calculation before display.

In addition, to active-address the display in the device, the device also generates column signals for driving the columns of the display by conventional methods.

As a result, conventional devices must contain many complex circuits that require a lot of current to operate.

Thus, conventional compression, decompression methods and subsequent display of image data may not be suitable for use in portable devices, typically powered by a small capacity battery.

Those skilled in the art will appreciate that the electronic device 500 according to the present invention uses similarities between data compression and active addressing to reduce the number and complexity of calculations for displaying compressed image data. It will be appreciated that less power consumption is required than conventional devices.

As a result, the battery life of the electronic device 500 may be longer than that of a battery that powers conventional devices that display compressed data using active addressing techniques.

As shown in FIG. 5, the electronic device 500 is a digital-to analog (D / A) converter 560 coupled to the controller 515 for converting column values into analog voltages. And column drivers 565 coupled to the D / A converter 560 for driving the columns of the LCD 100 with these analog voltages, ie, column signals.

In addition, the row drivers 570 are used to drive the rows of the LCD 100 with analog voltages corresponding to regular orthogonal functions, that is, row signals.

Controller 515, ROM 540, RAM 535, and clock 545 may use other integrated or hard-wired circuitry that can perform the same operation, but Schaumburg, Ill. It can be built using a properly programmed digital signal processor (DSP), such as the DSP56000 from Motorola Inc. of the company. A / D converter 510, orthogonal function database 520, entropy decoder 530, entropy decoder 555, and quantizer 525 are C-Cube Systems of San Jose, CA. Image compression / decompression chips, such as the Model No. CL550-30 chip manufactured by Microsoft Corporation). In addition, the D / A converter 560, column drivers 565, row drivers 570 can be made using the following conventional components.

If one of ordinary skill in the art wants to display gray scale or color images, the electronic device 500 may calculate the rms correction calculated for each column of image data, if necessary. The method may further comprise means for calculating rms correction factors.

Once calculated from the image data, the rms correction element can be stored in RAM 535 as additional information associated with the compressed image data, restored when the image data is displayed, and added to the columns of the matrix formed from the column values. do.

This process will result in a matrix of corrected column values, which are then provided to column drivers 565 as described above.

Circuits and techniques for performing rms correction factor calculations have been assigned to this assignee and are incorporated herein by reference, the method and apparatus of which the name of the invention drives an electronic display (Method and Apparatus for Driving an Electronic Display). See Herold's US patent application (Attorney's Docket No. PT00843U).

6 is a flowchart illustrating the operation of a controller 515 (FIG. 5) according to the present invention.

As described above, upon receiving the image data from the A / D converter 510 in step 605, the controller in step 610 uses the normal orthogonal functions stored in the normal orthogonal function database 520 to access the image data. Perform a two-dimensional transform on

This transformation can be performed using, for example, a matrix multiplication or a Fast Walsh Transform.

This two-dimensionally converted image data is then provided to a quantizer 525 in step 615 for processing.

After receiving the quantized data in step 620, the controller 515 provides the quantized data to the entry-e encoder 530 in step 625.

Entropy encoder 530 processes the quantized data to generate compressed image data, which is passed to controller 515 in step 630 and stored in RAM 535 in step 635. .

Subsequently, if an image is to be displayed in step 640, the controller 515 retrieves the compressed data in step 645 and passes it to entropy decoder 555 (FIG. 5) in step 650.

This entropy decoder 555 decodes the compressed data to recover the quantized data, which is returned to the controller 515 at step 655.

Subsequently, in step 660, the controller 515 performs one-dimensional transformation on the quantized data using normal orthogonal functions to convert one-dimensionally equivalent image to column values used for active addressing of columns of the LCD 100. Generate data.

The column values are provided to the D / A converter 560 at step 665, as described above, and the D / A converter 560 then provides analog column values to the column drivers 565.

The controller 515 also provides normal orthogonal functions to the row drivers 570 at step 670.

In accordance with the active-addressing technique, column drivers 565 drive the columns of LCD 100, and row drivers 570 drive the rows of LCD 100 at about the same time.

In accordance with the present invention, one would contemplate another embodiment in which an image defined by image data is displayed by the LCD 100 prior to storage.

In this case, rather than using a two-dimensional transform to compress the image data as soon as it is received, the image data is transformed into a one-dimensional transform using normal orthogonal functions stored in a normal orthogonal function database 520 (FIG. 5).

As described above, the column values thus generated are used to drive the columns of the LCD 100, and normal orthogonal functions are used to drive the rows of the LCD 100.

Then, if the image data is to be stored, the compression process is completed by performing one-dimensional transformation on the column values to obtain the data converted in two dimensions.

Following quantization and entropy encoding, the resulting compressed data is stored to take up less space in RAM 535.

In summary, the electronic device described above uses the similarity between data compression and active-addressing to reduce the complexity of the required circuitry and the number of calculations performed thereby, allowing the electronic device to consume less power.

More specifically, the electronic device compresses the transform into two-dimensional transform using normal orthogonal functions after receiving the image data and before storing the image data.

In this way, the compressed data is advantageous because it takes up less storage space than the image data itself.

Then, to display the image data, the electronic device decodes the compressed data and then performs one-dimensional transformation on the compressed data using normal orthogonal functions, resulting in active-column columns of the rms-responsive display such as an LCD. This results in column values that are already in a form suitable for addressing.

This electronic device does not perform complex decompression calculations or subsequent complex column value calculations, resulting in longer battery life than conventional devices for compressing image data and continuing to display it in an active-addressing display.

It will be appreciated that a method and apparatus are provided to minimize the power consumption required to display image data on an active-addressed display.

Claims (10)

An electronic device for driving an active-addressed display, comprising: receiving means for receiving image data; Compressing means, coupled to the receiving means, for compressing the image data to generate compressed data; Transformation means coupled to the compression means for performing one-dimensional transformation on the compressed data using the plurality of orthogonal functions to generate a set of column values; transforming means); And a first set of analog voltages coupled to the converting means and to the active-addressed display, corresponding to the set of column values without the need to completely decompress the compressed data. And column driving means for driving the columns of the active-addressed display. The electronic device of claim 1, further comprising a memory for storing the compressed data. 2. The row drive of claim 1, coupled to the compression means and the active-addressed display to drive rows of the active-addressed display with a set of second analog voltages corresponding to the plurality of orthogonal functions. An electronic device, further comprising row driving means. The image data of claim 1, wherein the image data is transformed in two dimensions using a two-dimensional Walsh transform, and the one-dimensional transform on the compressed data is a one-dimensional Walsh transform. Electronic device. The method of claim 1, wherein the compression means comprises means for converting the image data into two dimensions using a matrix multiplication technique, wherein the one-dimensional transformation on the compressed data is performed using a matrix multiplication technique. Electronic device. 2. The method of claim 1, wherein the column drive means comprises column drivers for driving columns of the active-addressed display with the first set of analog voltages corresponding to the set of column values. Characterized by an electronic device. The apparatus of claim 1, wherein the means for compressing comprises: a database for storing a plurality of regular orthogonal functions; A controller coupled to the database for performing two-dimensional transformation on the image data to generate two-dimensionally converted image data; A quantizer coupled to the controller for quantizing the two-dimensionally transformed image data to generate quantized data; And an entropy encoder coupled to the quantizer for entropy encoding the quantized data to generate the compressed data. 8. The apparatus of claim 7, wherein the means for converting comprises: an entropy decoder coupled to the entropy encoder and the controller to entropy decode the compressed data to obtain the quantized data; And a controller that performs the one-dimensional transformation to generate the set of column values. An electronic device for driving an active-addressed display, comprising: a data port for receiving image data; A database coupled to the data port for storing a plurality of orthogonal functions; First transforming means coupled to the database and the data port for transforming the image data in two dimensions using the plurality of orthogonal functions to generate image data converted in two dimensions; A quantizer coupled to the first conversion means for quantizing the two-dimensionally transformed image data to generate quantized data; An entropy encoder coupled to the quantizer for entropy encoding the quantized data to produce compressed data; A memory coupled to the entropy encoder for storing the compressed data; An entropy decoder coupled to the memory for entropy decoding the compressed data to obtain the quantized data; Second transforming means coupled to the entropy decoder for transforming the quantized data in one dimension using the plurality of orthogonal functions to generate a set of column values; And column drivers coupled to the second conversion means for driving the columns of the active-addressed display with a set of first analog voltages corresponding to the set of column values. Electronic device. 10. The row driver of claim 9, coupled to the database and the active-addressed display to drive rows of the active-addressed display with a set of second analog voltages corresponding to the plurality of orthogonal functions. Electronic devices further comprising row drivers.