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
  • G09G3/22—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 using controlled light sources
  • G09G3/30—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 using controlled light sources using electroluminescent panels
  • G09G3/32—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 using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
  • G09G3/3208—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 using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
• • 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
  • G09G3/006—Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
  • G09G5/02—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the way in which colour is displayed
  • G09G5/06—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the way in which colour is displayed using colour palettes, e.g. look-up tables
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/02—Improving the quality of display appearance
  • G09G2320/0242—Compensation of deficiencies in the appearance of colours
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/02—Improving the quality of display appearance
  • G09G2320/0247—Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/02—Improving the quality of display appearance
  • G09G2320/0285—Improving the quality of display appearance using tables for spatial correction of display data

Definitions

• the disclosure relates generally to video display technology, and more specifically to systems and methods for measuring pixel-by-pixel energy emission variations on a display, encoding and storing these measurements as a set of global and per-pixel correction factors, and/or digitally manipulating imagery with the inverse effect as the measured variations, such that the appearance of artifacts caused by such variations is reduced.
• Certain display technologies exhibit luminosity and/or colorimetric (gamma) energy emission responses which vary from pixel to pixel. Such variations are sometimes referred to as “mura defects,” “mura variations,” or simply “mura,” although the terminology and its precise meaning is not known to be standardized in the display industry.
• LCDs Liquid Crystal Displays
• OLED Organic Light Emitting Diode
• adjacent pixels may exhibit substantially different color responses. These effects are particularly noticeable in regions of constant color and smooth gradients, where the region may appear "noisy” to an observer. This artifact is particularly objectionable on head mounted displays (“HMDs”),
• Figure 1 is an exemplary diagram of a computing device that may be used to implement aspects of certain embodiments of the present invention.
• Figure 2A is a grayscale version of a photograph depicting an exemplary all-green raw image sent to a display.
• Figure 2B is a grayscale version of a photograph depicting the exemplary all- green raw image sent to a display of Figure 2A, as displayed to an observer, and uncorrected according to exemplary embodiments of the present invention.
• Figure 2C is a photograph depicting exemplary pixel-by-pixel correction factors according to aspects of the present invention.
• Figure 2D is a grayscale version of a photograph depicting pre-corrected imagery according to aspects of the present invention, corresponding to the image shown in Figure 2B, as sent to an exemplary display.
• Figure 2E is a grayscale version of a photograph depicting an exemplary final image shown to an observer, according to aspects of the present invention, corresponding to the image depicted in Figure 2D.
• Figure 3 is a grayscale version of a photograph depicting an exemplary image capture on a display panel of a constant green image with resolution sufficient to achieve an energy estimate for each sub-pixel according to aspects of the present invention.
• Figures 5A and 5B are photographs depicting aspects of an exemplary image capture system and configuration according to aspects of the present invention.
• Figure 6 depicts two exemplary display panels (610, ozu; oeing uriven oy customized electronics (630) according to aspects of the present invention to simulate a head- mounted-display configuration.
• Figure 7 depicts a grid pattern shown on a display panel under test for use during calibration and to facilitate solving for geometric lens eccentricities according to aspects of the present invention.
• Figure 8 is a grayscale version of a photograph depicting a captured image according to aspects of the present invention, after dark field subtraction and lens undistortion steps used in certain embodiments.
• Figure 9 is a grayscale version of a photograph depicting corner-detection steps in a captured image according to aspects of the present invention.
• Figure 10 is a grayscale version of a photograph depicting an exemplary 32-by-32 pixel inset area in a captured image of a display panel under test after rectilinear alignment according to aspects of the present invention.
• Figure 11 graphically depicts pixel-by-pixel energy emission in a portion of an exemplary display panel under test according to aspects of the present invention.
• a computer readable storage medium which may be any device or medium that can store code and/or data for use by a computer system.
• the transmission medium may include a communications network, such as the Internet.
• FIG. 1 is an exemplary diagram of a computing device 100 that may be used to implement aspects of certain embodiments of the present invention.
• Computing device 100 may include a bus 101, one or more processors 105, a main memory 110, a read-only memory (ROM) 115, a storage device 120, one or more input devices 125, one or more output devices 130, and a communication interface 135.
• Bus 101 may include one or more conductors that permit communication among the components of computing device 100.
• Processor 105 may include any type of conventional processor, microprocessor, or processing logic that interprets and executes instructions.
• Main memory 110 may include a random-access memory (RAM) or another type of dynamic storage device that stores information and instructions for execution by processor 105.
• ROM 115 may include a conventional ROM device or another type of static storage device that stores static information and instructions for use by processor 105.
• Storage device 120 may include a magnetic and/or optical
• Input device(s) 125 may include one or more conventional mechanisms that permit a user to input information to computing device 100, such as a keyboard, a mouse, a pen, a stylus, handwriting recognition, voice recognition, biometric mechanisms, and the like.
• Output device(s) 130 may include one or more conventional mechanisms that output information to the user, including a display, a projector, an A/V receiver, a printer, a speaker, and the like.
• Communication interface 135 may include any transceiver-like mechanism that enables computing device/server 100 to communicate with other devices and/or systems.
• Computing device 100 may perform operations based on software instructions that may be read into memory 110 from another computer-readable medium, such as data storage device 120, or from another device via communication interface 135.
• the software instructions contained in memory 110 cause processor 105 to perform processes that will be described later.
• processor 105 may perform processes that will be described later.
• hard-wired circuitry may be used in place of or in combination with software instructions to implement processes consistent with the present invention.
• various implementations are not limited to any specific combination of hardware circuitry and software.
• memory 110 may include without limitation high-speed random access memory, such as DRAM, SRAM, DDR RAM or other random access solid state memory devices; and may include without limitation non- volatile memory, such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other non- volatile solid state storage devices.
• Memory 110 may optionally include one or more storage devices remotely located from the processor(s) 105.
• Memory 110, or one or more of the storage devices (e.g., one or more non-volatile storage devices) in memory 110 may include a computer readable storage medium.
• memory 110 or the computer readable storage medium of memory 110 may store one or more of the following programs, modules and data structures: an operating system that includes procedures for handling various basic system services and for performing hardware dependent tasks; a network communication module that is used for connecting computing device 110 to other computers via the one or more communication network interfaces and one or more communication networks, such as the Internet, other wide area networks, local area networks, metropolitan area networks, and so on; a client application that ma
• the computer program instructions may also be loaded onto a computer or other programmable apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flow chart block or blocks.
• blocks of the flow charts support combinations of structures for performing the specified functions and combinations of steps for performing the specified functions. It will also be understood that each block of the flow charts, and combinations of blocks in the flow charts, can be implemented by special purpose hardware-based computer systems that perform the specified functions or steps, or combinations of special purpose hardware and computer instructions.
• any number of computer programming languages such as C, C++, C# (CSharp), Perl, Ada, Python, Pascal, SmallTalk, FORTRAN, assembly language, and the like, may be used to implement aspects of the present invention.
• various programming approaches such as procedural, object-oriented or artificial intelligence techniques may be employed, depending on the requirements of each particular implementation.
• Compiler programs and/or virtual machine programs executed by computer systems generally translate higher level programming languages to aula ui
• machine-readable medium should be understood to include any structure that participates in providing data that may be read by an element of a computer system. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media.
• Non- volatile media include, for example, optical or magnetic disks and other persistent memory such as devices based on flash memory (such as solid-state drives, or SSDs).
• Volatile media include dynamic random access memory (DRAM) and/or static random access memory (SRAM).
• Transmission media include cables, wires, and fibers, including the wires that comprise a system bus coupled to a processor.
• Machine-readable media include, for example and without limitation, a floppy disk, a flexible disk, a hard disk, a solid-state drive, a magnetic tape, any other magnetic medium, a CD-ROM, a DVD, or any other optical medium.
• methods according to aspects of the present invention comprise three steps (each step is described in more detail after the following introductory list):
• a technique for display measuring This approach requires accurate estimation of the energy emitted for each sub-pixel of the display.
• the specific images captured are targeted to the known deficiencies of the display technology in conjunction with the correction model being utilized.
• step one is to image each color channel individually ⁇ e.g., red, green, blue) to reduce the number of emissive elements being imaged.
• Figure 2A is a grayscale version of a photograph (200A) depicting an exemplary all-green raw image sent to a display.
• Figure 2B is a grayscale version of a photograph (200B) depicting the exemplary all-green raw image sent to a display of Figure 2A, as displayed to an observer, and uncorrected according to exemplary embodiments of the present invention.
• Figure 2C is a photograph (200C) depicting exemplary pixei-oy-pixei correction factors according to aspects of the present invention.
• Figure 2D is a grayscale version of a photograph (200D) depicting pre-corrected imagery according to aspects of the present invention, corresponding to the image shown in Figure 2B, as sent to an exemplary display.
• Figure 2E is a grayscale version of a photograph (200E) depicting an exemplary final image shown to an observer, according to aspects of the present invention, corresponding to the image depicted in Figure 2D.
• Figure 3 is a grayscale version of a photograph (300) depicting an exemplary image capture on a display panel (320) of a constant green image with resolution sufficient to achieve an energy estimate for each sub-pixel according to aspects of the present invention.
• sub-regions may be imaged in certain embodiments and then the resulting data sets may be smoothly blended.
• Figures 5A and 5B are photographs depicting aspects of an exemplary image capture system and configuration according to aspects of the present invention.
• the following equipment may be used: a Canon 5Ds digital SLR camera, a 180mm macro photograph lens (510), and a rigid macro stand.
• L ⁇ ⁇ v >- included (630, shown in Figure 6), which drive the displays (610, 620) in a manner that matches HMD usage (i.e., low persistence, 90 Hz or 120 Hz frame rate).
• HMD usage i.e., low persistence, 90 Hz or 120 Hz frame rate.
• measurements are typically taken in a dust-free and light-blocking enclosure in certain embodiments.
• the imaging system In order to accurately predict the placement for each of millions of sub-pixels, the imaging system (lens) must be spatially calibrated beyond the sub-pixel level in certain embodiments. This correction is typically dependent upon factors such as camera lens model and live focus, fstop settings.
• Figure 7 depicts a grid pattern (710) shown on a display panel under test for use during calibration and to facilitate solving for geometric lens eccentricities according to aspects of the present invention.
• a black image is captured to determine the dark field response of the camera.
• an image suitable for characterizing the per-pixel response is displayed.
• this is typically a monochrome image of constant color.
• Figure 8 is a grayscale version of a photograph depicting a captured image according to aspects of the present invention (800), after dark field subtraction and lens undistortion steps used in certain embodiments.
• a deconvolution kernel may be applied in certain embodiments, which removes local flares in the imaging chain. This flare compensation can be validated using an image which measures the "PFS" (point-spread function). Typically, a single point pixel is illuminated in an otherwise constant valued region to compute this value.
• PFS point-spread function
• the pixel corners for the captured rectangular area are detected, and a four-corner perspective warp creates an axis-aligned representation, where each sub-pixel has a consistent size and alignment.
• Figure 9 is a photograph depicting corner- detection steps in a captured image (900) according to aspects of the present invention.
• Figure 10 is a grayscale version of a photograph (1000) depicting an exemplary 32-by-32 pixel inset area in a captured image of a display panel under test after rectilinear alignment according to aspects of the present invention.
• Each sub-pixel is centered in each box in certain embodiments, allowing for accurate energy estimation, where each box is the area integrated for each sub-pixel.
• Each sub-pixel typically has a different intensity, as shown in Figure 11; this is the effect that is measured and/or corrected in whole or in part according to aspects of the present invention.
• the energy for each pixel is calculated by summing all values in each pixel area.
• Figure 11 graphically depicts pixel-by-pixel energy emission in a portion of an exemplary display panel under test (1100) according to aspects of the present invention.
• This process is typically highly sensitive to dust landing on the panel during image acquisition. If dust or fibers land on the display, they will absorb and/or scatter some light so the overlapping pixels will be incorrectly measured as dim. When compensation is applied, these pixels will have strong positive gain factors applied and will stand out as objectionable "overbright" pixels. To compensate for dust, multiple images of the panel may be taken in certain embodiments, with a blast of air (or other
• Each sub-pixel in the display should correspond to a known, axis aligned box of constant size in the aligned output image, o Sum energy in each box corresponding to a sub-pixel. For estimates robust to dust, repeat N times with a cleaning / air blast between captures. Merge captures using the maximum value estimate for each sub-pixel across all captures.
• a set of global and per- pixel correction factors may be computed in certain embodiments. Iterative and non-iterative approaches to computing the correction factors may be implement, m, u ⁇ v -uiauuuo and/or combinations of these approaches, depending on the particular requirements of each implementation
• the following model may be used as the starting point, which accounts for more than 90% of the mura effect in OLED panels. (For other display technologies, alternative formulations may be employed to compactly represent the artifact, as known to those of ordinary skill in the art).
• CCV Corrected code value in the device native gamma encoding
• ICV Input code value in the device native gamma encoding
• PPD per-pixel delta
• (x,y) denotes that the quantity varies as a function of the output pixel location (x,y) in display space.
• CCV Corrected code value in the device native gamma encoding
• ICV Input code value in the device native gamma encoding
• PPV per-pixel value encoded with limited bits
• CO correction offset
• Gain/offset global values used to interpret per-pixel deltas
• a representative code value is selected and the energy estimate is measured, per pixel, for a flat-field image.
• code value 51 (out of 255) may be selected. This value is dim enough that a fixed additive offset has a high signal-to-noise ratio, but it is bright enough that exposure times are not prohibitive.
• PPD TCV -pow( LPE(x,y) /LPELA(x,y) * pow(TCV, DG), 1.0 / DG) where:
• TCV target code-value (that sent to display during measurement)
• LPE linear pixel energy
• LPE linear pixel energy, local area average (local energy average for surrounding neighborhood, often center/Gaussian weighted ).
• PPD TCV - inv_display_response(LPE(x,y) / LPELA(x,y) * display _response (TCV) )
• PPD TCV + pow( LPELA(x,y)/ LPE(x,y) * pow(TCV, DG), 1.0 / DG)
• CCV Corrected code value in the device native gamma encoding
• ICV Input code value in the device native gamma encoding
• PPD per-pixel delta
• PPR per-pixel residual, which is a function of the input code value
• the per-pixel residuals are much smaller than the per-pixel deltas, multiple residuals can be efficiently stored in a similar amount of space to the original per-pixel factor.
• the mura artifacts onen cnange in lniensny This may be accounted for in certain embodiments by manipulating the correction gain factor to apply more, or less, of the correction as needed.
• the per-pixel deltas with greater precision than the display, it is possible to globally recreate output luminance values with greater precision than the number of steps in the input (i.e., each individual pixel may only have 256 addressable steps, but local regions on average may have many more discrete output levels in certain embodiments).
• Synthetic pixel variation patterns can be created which have more compact representations and lower sampling discrepancy than the natural mura seen on OLED displays.
• One formulation is to use a tileable noise pattern, with a uniform sampling over the luma domain of +/- 0.5 code values.
• the noise tiling is a jittered stratified sampling or blue noise in certain embodiments, such that pixel values are unlikely to have an offset similar to their neighbors.
• the appropriate quantization per-pixel may be applied such that banding appearance is reduced.
• a tileable noise pattern may also be created that varies over time to further reduce banding artifacts, though in such a system the image synthesis in certain embodiments needs to encode and transmit which 'frame' of noise to apply to the pixel variation.
• code value 0 presumes uniform random biases in the range of [0.0,1.0], for an intermediate code value (128), [-0.5,0.5] is selected, and for cod ⁇
• mura correction processing in accordance with aspects of the present invention is performed host-side on the graphics processing unit ("GPU').
• GPU graphics processing unit
• processing may be effected in silicon, in the headset itself, on a tether, or in the display panel electronics, for example.
• Such alternative implementations may provide greater image compressibility, which is important in situations involving limited link bandwidths (e.g. , wireless systems).

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• Engineering & Computer Science (AREA)
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• General Physics & Mathematics (AREA)
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• Control Of Indicators Other Than Cathode Ray Tubes (AREA)
• Transforming Electric Information Into Light Information (AREA)
• Controls And Circuits For Display Device (AREA)

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• 2016
  • 2016-08-18 JP JP2018507716A patent/JP6688878B2/ja active Active
  • 2016-08-18 KR KR1020187007665A patent/KR102556275B1/ko active IP Right Grant
  • 2016-08-18 WO PCT/US2016/047470 patent/WO2017031268A1/en unknown
  • 2016-08-18 CN CN201680060751.XA patent/CN108140359B/zh active Active
  • 2016-08-18 EP EP16837801.6A patent/EP3338274A4/en active Pending
• 2018
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