Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
  • G09G3/3611—Control of matrices with row and column drivers
  • G09G3/3622—Control of matrices with row and column drivers using a passive matrix
  • G09G3/3625—Control of matrices with row and column drivers using a passive matrix using active addressing
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
  • G06V10/00—Arrangements for image or video recognition or understanding
  • G06V10/40—Extraction of image or video features

Definitions

• This invention relates in general to data compression techniques, and more specifically to data compression in an active addressed display system.
• a direct multiplexed, rms (root mean square) responding electronic display is the well-known liquid crystal display (LCD).
• LCD liquid crystal display
• a nematic liquid crystal material is positioned between two parallel glass plates having electrodes applied to each surface in contact with the liquid crystal material.
• the electrodes typically are arranged in vertical columns on one plate and horizontal rows on the other plate for driving a picture element (pixel) wherever a column and row electrode overlap.
• the optical state of a pixel is substantially responsive to the square of the voltage applied to the pixel, i.e., the difference in the voltages applied to the electrodes on the opposite sides of the pixel.
• LCDs have an inherent time constant that characterizes the time required for the optical state of a pixel to return to an equilibrium state after the optical state has been modified by changing the voltage applied to the pixel.
• Recent technological advances have produced LCDs with time constants (approximately 16.7 milliseconds) approaching the frame period used in many video displays. Such a short time constant allows the LCD to respond quickly and is especially advantageous for depicting motion without noticeable smearing or flickering of the displayed image.
• the active addressing method continuously drives the row electrodes with signals comprising a train of periodic pulses having a common period T corresponding to the frame period.
• the row signals are independent of the image to be displayed and preferably are orthogonal and normalized, i.e., orthonormal.
• orthogonal denotes that, if the amplitude of a signal applied to one of the rows is multiplied by the amplitude of a signal applied to another one of the rows, the integral of this product over the frame period is zero.
• normalized denotes that all the row signals have the same rms voltage integrated over the frame period T.
• each frame period a plurality of signals for the column electrodes are calculated and generated from the collective state of the pixels in each of the columns.
• the column voltage at any time t during the frame period is proportional to the sum obtained by considering each pixel in the column, multiplying a "pixel value" representing the optical state (either -1 for fully “on”, +1 for fully “off”, or values between -1 and +1 for proportionally corresponding gray shades) of the pixel by the value of that pixel's row signal at time t, and adding the products obtained thereby to the sum.
• active addressing If driven in the active addressing manner described above, it can be shown mathematically that there is applied to each pixel of the display an rms voltage averaged over the frame period, and that the rms voltage is proportional to the pixel value for the frame.
• the advantage of active addressing is that it restores high contrast to the displayed image because, instead of applying a single, high level selection pulse to each pixel during the frame period, active addressing applies a plurality of much lower level (2-5 times the rms voltage) selection pulses spread throughout the frame period. In addition, the much lower level of the selection pulses substantially reduces the probability of alignment instabilities.
• rms-responding displays such as LCDs used in laptop computers, can display image data at video speeds without smearing or flickering.
• LCDs driven with active addressing methods can display image data having multiple shades without the contrast problems present in LCDs driven with conventional multiplexed addressing methods.
• a drawback to utilizing active addressing results from the large number of calculations required to generate column and row signals for driving an rms-responding display. For example, a gray scale display having 480 rows and 640 columns and a frame rate of 60 frames per second requires just under ten billion calculations per second. While it is, of course, possible to perform calculations at this rate, such complex, rapidly performed calculations necessitate a large amount of power consumption. In portable, battery powered devices, such as laptop computers and radio receivers, the power consumption issue is particularly important because battery life is a primary design consideration.
• a method for compressing data in an electronic device having an active-addressed display comprises the step of receiving image data.
• the method further comprises the step of compressing the image data in a two-dimensional transformation utilizing a plurality of orthogonal functions, thereby generating compressed data.
• a set of column values in accordance with active-addressing techniques is generated by performing a one-dimensional transformation of the compressed data utilizing the plurality of orthogonal functions.
• a method for compressing data subsequent to displaying the data in an electronic device having an active-addressed display comprises the steps of receiving image data and generating a set of column values in accordance with active addressing techniques by one-dimensionally transforming the image data utilizing a plurality of orthogonal functions.
• the method further comprises the step of driving columns of the active-addressed display with analog voltages corresponding to the set of column values.
• the image data is then compressed by using a compression method in which the set of column values is one-dimensionally transformed utilizing the plurality of orthogonal functions, wherein the compression method results in compressed data which is subsequently stored.
• an electronic device for driving an active-addressed display comprises a data port for receiving image data and compressing circuitry coupled to the data port for generating compressed data by compressing the image data using a method in which the image data is two-dimensionally transformed utilizing a plurality of orthogonal functions.
• the electronic device further comprises transforming circuitry coupled to the compressing circuitry for performing a one-dimensional transformation of the compressed data utilizing the plurality of orthogonal functions to generate a set of column values.
• Column drivers coupled to the transforming circuitry and the active-addressed display drive columns of the active-addressed display with a first set of analog voltages corresponding to the set of column values.
• FIG. 1 is a front orthographic view of a portion of a conventional liquid crystal display.
• FIG. 2 is an orthographic cross-section view along line 2-2 of FIG. 1 of the conventional liquid crystal display.
• FIG. 3 is a matrix of Walsh functions in accordance with the present invention.
• FIG. 4 depicts Walsh functions in accordance with the present invention.
• FIG. 5 is an electrical block diagram of an electronic device for generating signals to active-address the liquid crystal display of FIG. 1 in accordance with the present invention.
• FIG. 6 is a flowchart depicting the operation of a controller included in the electronic device of FIG. 5 in accordance with the present invention. Description of a Preferred Embodiment
• orthographic front and cross-section views of a portion of a conventional liquid crystal display (LCD) 100 depict first and second transparent substrates 102, 206 having a space therebetween filled with a layer of liquid crystal material 202.
• a perimeter seal 204 prevents the liquid crystal material from escaping from the LCD 100.
• the LCD 100 further includes a plurality of transparent electrodes comprising row electrodes 106 positioned on the second transparent substrate 206 and column electrodes 104 positioned on the first transparent substrate 102.
• a column electrode 104 overlaps a row electrode 106, such as the overlap 108
• voltages applied to the overlapping electrodes 104, 106 can control the optical state of the liquid crystal material 202 therebetween, thus forming a controllable picture element, hereafter referred to as a "pixel".
• pixel a controllable picture element
• an LCD is the preferred display element in accordance with the preferred embodiment of the present invention, it will be appreciated that other types of display elements may be used as well, provided that such other types of display elements exhibit optical characteristics responsive to the square of the voltage applied to each pixel, similar to the root mean square (rms) response of an LCD.
• FIGs. 3 and 4 depict an eight-by-eight (third order) matrix of Walsh functions 300 and the corresponding Walsh waves 400 in accordance with the preferred embodiment of the present invention.
• Walsh functions are both orthogonal and normalized, i.e., orthonormal, and are therefore preferable for use in an active-addressed display system, as briefly discussed in the Background of the Invention herein above. It may be appreciated by one of ordinary skill in the art that other classes of functions, such as Pseudo Random Binary Sequence (PRBS) functions or Direct Cosine Transform (DCT) functions, may also be utilized in active- addressed display systems.
• PRBS Pseudo Random Binary Sequence
• DCT Direct Cosine Transform
• Walsh functions When Walsh functions are used in an active-addressed display system, voltages having levels represented by the Walsh waves 400 are uniquely applied to a selected plurality of electrodes of the LCD 100.
• the Walsh waves 404, 406, and 408 could be applied to the first (uppermost), second and third row electrodes 106, respectively, and so on. In this manner, each of the Walsh waves 400 would be applied uniquely to a corresponding one of the row electrodes 106. It is preferable not to use the Walsh wave 402 in an LCD application because the Walsh wave 402 would bias the LCD 100 with an undesirable DC voltage.
• the values of the Walsh waves 400 are constant during each time slot t.
• the duration of the time slot t for the eight Walsh waves 400 is one-eighth of the duration of one complete cycle of Walsh waves 400 from start 410 to finish 412.
• the duration of one complete cycle of the Walsh waves 400 is set equal to the frame duration, i.e., the time to receive one complete set of data for controlling all the pixels 108 of the
• the eight Walsh waves 400 are capable of uniquely driving up to eight row electrodes 106 (seven if the Walsh wave 402 is not used). It will be appreciated that a practical display has many more rows. For example, displays having four-hundred-eight rows and six-hundred-forty columns are widely used today in laptop computers. Because Walsh function matrices are available in complete sets determined by powers of two, and because the orthonormality requirement for active addressing does not allow more than one electrode to be driven from each Walsh wave, a five- hundred-twelve by five-hundred-twelve (2 9 x 2 9 ) Walsh function matrix would be required to drive a display having four-hundred-eighty row electrodes 106.
• the duration of the time slot t is 1/512 of the frame duration.
• Four-hundred-eight Walsh waves would be used to drive the four-hundred-eighty row electrodes 106, while the remaining thirty- two, preferably including the first Walsh wave 402 having a DC bias, would be unused.
• the electronic device 500 e.g., a portable laptop computer or a paging receiver, comprises a data port 505 for receiving image data from a video source (not shown).
• the data port 505 may be, for example, a communication bus, a floppy drive for reading image data from diskettes, or, in the case of a paging receiver, receiving circuitry for recovering image data from a radio frequency (RF) signal.
• RF radio frequency
• the electronic device 500 further comprises an analog-to-digital (A/D) converter 510 for converting the analog image data values to digital image data values, which are provided to a controller 515 for transforming the image data into another domain, as will be explained in greater detail below.
• A/D converter 510 is determined by the desired image to be displayed on the LCD 100. For instance, if the pixels 108 of the LCD 100 are to be either fully “on” or fully “off", the A/D converter 510 may convert the image data to binary data, wherein -1 represents a fully on pixel and +1 represents a fully off pixel. 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 the gray shades. It will be recognized that the A/D converter 510 may not be necessary if digital image data is received by the data port 505. Coupled to the controller 515 is an orthonormal function database
• the orthonormal matrix may be, for example, the Walsh function matrix 300 (FIG. 3), although matrices of other orthonormal functions, such as DCT or PRBS functions, may be used as well.
• the orthonormal matrix is utilized by the controller 515 in transforming the image data upon reception.
• the controller 515 performs a two-dimensional transformation of the image data utilizing the orthonormal matrix to result in two-dimensionally transformed image data.
• the two-dimensional transformation can be accomplished utilizing a Fast Fourier Transform algorithm, or modification thereof, or a Fast Walsh Transform, although many other fast, efficient algorithms can be alternatively utilized.
• One such algorithm involves the use of matrix multiplication and can be represented by the following equation:
• I 2D OM * I * OM, wherein ⁇ 2D represents the two-dimensionally transformed image data, I represents the image data, and OM represents the orthonormal matrix stored in the orthonormal function database 520. It will be appreciated that, when matrix multiplication is utilized, the order of the terms in the above-recited equation cannot be varied.
• the electronic device 500 further includes a memory device, such as a random access memory (RAM) 535, for storing the compressed data.
• RAM random access memory
• the electronic device 500 further comprises, in addition to the RAM 535, a read only memory (ROM) 540, which stores subroutines executed by the controller 515 during operation of the electronic device 500, and a clock 545, which generates timing signals for use in system timing.
• ROM read only memory
• a data entry device 550 may be coupled to the controller 515.
• the data entry device 550 may comprise a keyboard, whereas, when the electronic device 500 is a paging receiver, user-accessible controls, rather than a keyboard, may be coupled to the controller 515.
• the image data can be displayed automatically, or the data entry device 550 can be used to input commands directing the controller 515 to present the image data.
• the controller 515 operates on the compressed data to generate signals suitable for active-addressing the LCD 100. More specifically, an entropy decoder 555 is employed to decode the compressed data, resulting in the two-dimensionally transformed image data which has been previously quantized.
• This data can be easily and quickly transformed into signals for active-addressing columns of the LCD 100 by performing a one- dimensional inverse transformation of the data.
• an orthonormal matrix i.e., a separable and symmetric matrix
• OM 1/OM. Therefore, because the orthonormal matrix stored in the orthonormal function database 520 was previously utilized in the data compression process, the same orthonormal matrix can be utilized by the controller 515 to perform a one-dimensional transformation, e.g., a Walsh Transform, rather than a one-dimensional inverse transformation.
• this process is illustrated by the following equation:
• I 2 D is the two-dimensionally transformed image data that has been quantized
• OM is the orthonormal matrix
• IID is the resulting one-dimensionally transformed image data, which is equivalent to column values (CV) suitable for active-addressing the columns of the LCD 100.
• the row signals for driving the rows of the LCD 100 are signals derived from orthonormal functions independent of the image data.
• the column signals, i.e., analog voltages corresponding to the column values, for driving the columns of the LCD 100 are linear combinations of all row signals and the image data and can be generated by one-dimensionally transforming the image data utilizing the orthonormal functions.
• the electronic device 500 conveniently avoids having to decompress the stored data, which has been previously compressed for storage.
• the electronic device 500 further avoids the necessity of generating column values directly from the image data each time the image data is to be displayed. Instead, the electronic device 500 simply performs the one-dimensional transform on the compressed data when it is to be displayed.
• the electronic device 500 exploits the similarities between data compression and active addressing to reduce the number and complexity of calculations for displaying compressed image data, thereby necessitating a smaller amount of power consumption than conventional devices. As a result, the battery life of the electronic device 500 may be longer than that of a battery powering a conventional device which displays compressed data utilizing active addressing techniques.
• the electronic device 500 further comprises a digital-to-analog (D/A) converter 560 coupled to the controller 515 for converting the column values to analog voltages and column drivers 565 coupled to the D/A converter 560 for driving the columns of the LCD 100 with the analog voltages, i.e., column signals.
• row drivers 570 are employed to drive the rows of the LCD 100 with analog voltages, i.e. row signals, corresponding to the orthonormal functions.
• the controller 515, the ROM 540, the RAM 535, and the clock 545 can be implemented by using a suitably programmed digital signal processor (DSP), such as the DSP 56000 manufactured by Motorola, Inc. of Schaumburg, Illinois, although other integrated or hard-wired circuitry that is capable of performing equivalent operations may be alternatively utilized.
• DSP digital signal processor
• the A/D converter 510, the orthonormal function database 520, the entropy decoder 530, the entropy decoder 555, and the quantizer 525 can be implemented using an image compression /decompression chip, such as the model no. CL550-30 chip manufactured by C-Cube Microsystems of San Jose, California.
• the D/A converter 560, the column drivers 565, and the row drivers 570 can be implemented using the following conventional elements:
• D/A converter 560 CXD1178Q Sony Corporation column drivers 565 SED1779D0A Seiko Epson Corp. row drivers 570 SED1704 Seiko Epson Corp.
• the electronic device 500 may, when necessary, further include means for calculating rms correction factors, which are calculated for each column of image data.
• the rms correction factors once calculated from the image data, could be stored in the RAM 535 as additional information associated with the compressed image data, recovered when the compressed image data is to be displayed, and added to the columns of a matrix formed from the column values. This process would yield a matrix of "corrected" column values, which would thereafter be provided to the column drivers 565 as described above. Circuits and techniques for performing rms correction factor calculations are taught in the U.S.
• FIG. 6 is a flowchart depicting the operation of the controller 515
• the controller 515 when the image data is received, at step 605, from the A/D converter 510, the controller 515 performs, at step 610, a two-dimensional transformation of the image data utilizing the orthonormal functions stored in the orthonormal function database 520.
• the transformation may be performed, for example, by using matrix multiplication or by using a Fast Walsh Transform.
• the two-dimensionally transformed image data is provided, at step 615, to the quantizer 525 for processing thereby.
• the controller 515 provides, at step 625, the quantized data to the entropy encoder 530.
• the entropy encoder 530 processes the quantized data to generate compressed image data, which is transmitted, at step 630, to the controller 515 for storage, at step 635, in the RAM 535.
• the controller 515 retrieves, at step 645, the compressed data for transmission, at step 650, to the entropy decoder 555 (FIG. 5).
• the entropy decoder 555 decodes the compressed data to recover the quantized data, which is returned, at step 655, to the controller 515.
• the controller 515 performs, at step 660, a one-dimensional transformation of the quantized data utilizing the orthonormal functions, thereby generating one- dimensional transformed image data which is equivalent to the column values used for active addressing the columns of the LCD 100.
• the column values are, as described above, provided, at step 665, to the D/A converter 560, which subsequently provides analog column values to the column drivers 565. Additionally, the controller 515 provides, at step 670, the orthonormal functions to the row drivers 570. In accordance with active-addressing techniques, the column drivers 565 drive the columns of the LCD 100 and the row drivers 570 drive the rows of the LCD 100 at approximately the same time.
• the image defined by the image data is displayed by the LCD 100 prior to storage.
• the image data is simply transformed in a one-dimensional transformation using the orthonormal functions stored in the orthonormal function database 520 (FIG. 5).
• the column values thus generated are used to drive columns of the LCD 100, and the orthonormal functions are used to drive rows of the LCD 100, as described above.
• the compression process is completed by performing a further one-dimensional transform of the column values to arrive at the two- dimensionally transformed data. Subsequent to quantization and entropy encoding, the resulting compressed data is stored, thereby consuming a lesser amount of space in the RAM 535.
• the electronic device exploits the similarities between data compression and active-addressing techniques to reduce both the complexity of necessary circuitry and the number of calculations performed thereby, resulting in a smaller amount of power consumption by the electronic device. More specifically, the electronic device, upon receiving image data, compresses the image data in a two- dimensional transformation using orthonormal functions before storage of the image data. In this manner, the compressed data advantageously requires less storage space than would the image data itself. Thereafter, when the image data is to be displayed, the electronic device simply performs, after decoding the compressed data, a one-dimensional transformation of the compressed data utilizing the orthonormal functions, which results in column values which are already in a form suitable for active-addressing columns of an rms-responding display, such as an LCD.
• the battery life of the electronic device is longer than that of a conventional device for compressing and subsequently displaying image data on an active-addressed display. It may be appreciated by now that there has been provided a method and apparatus which minimizes the power consumption required to display image data on an active-addressed display.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Multimedia (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Computer Hardware Design (AREA)
• Control Of Indicators Other Than Cathode Ray Tubes (AREA)
• Liquid Crystal Display Device Control (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=22062573

Family Applications (2)

Family Applications After (1)

Country Status (7)

Cited By (3)

Citations (6)

Family Cites Families (4)

• 1994
  • 1994-04-19 WO PCT/US1994/004238 patent/WO1994028508A1/en not_active Application Discontinuation
  • 1994-04-19 CA CA002163024A patent/CA2163024C/en not_active Expired - Fee Related
  • 1994-04-19 AU AU70146/94A patent/AU7014694A/en not_active Abandoned
  • 1994-04-19 EP EP94919088A patent/EP0700547A1/en not_active Withdrawn
  • 1994-04-19 JP JP7500624A patent/JPH08510844A/ja active Pending
  • 1994-04-19 KR KR1019950705229A patent/KR100203319B1/ko not_active IP Right Cessation
  • 1994-05-02 AU AU70162/94A patent/AU7016294A/en not_active Abandoned
  • 1994-05-02 WO PCT/US1994/004898 patent/WO1994028537A1/en active Application Filing
  • 1994-05-21 CN CN94106180A patent/CN1037032C/zh not_active Expired - Fee Related

Patent Citations (6)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events