Method and system for stress compensation in display device

Abstract

The present invention relates to a method and system for stress compensation in a display device. The method for stress compensation in a display device includes: accumulating brightness values ​​of an image displayed by the display device, encoding the accumulated brightness values ​​to maintain a protected portion of the accumulated brightness values, compressing the accumulated brightness values, storing the compressed accumulated brightness values ​​in a memory, retrieving the compressed accumulated brightness values ​​and decompressing the compressed accumulated brightness values ​​to generate a decompressed value, and decoding the decompressed value based on the protected portion to generate a decoded value corresponding to the accumulated brightness value, the decoded value having lower compression noise than the decompressed value.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 851,872, filed on May 23, 2019, and entitled “REDUNDANCY ASSISTED NOISE CONTROL FOR ACCUMULATED ITERATIVE COMPRESSION ERROR,” the entire contents of which are expressly incorporated herein by reference.

[0003] This application is also related to U.S. Patent Application No. 15 / 980,623, filed on May 15, 2018, and entitled “PERMUTATION BASED STRESS PROFILE COMPRESSION,” which claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 643,630, filed on March 15, 2018, and entitled “PERMUTATION BASED STRESS PROFILE COMPRESSION,” the entire contents of which are expressly incorporated herein by reference. Technical Field

[0004] Aspects of the present disclosure relate to a stress compensation method and system for a display device. Background Art

[0005] Compensation for output degradation in video displays such as organic light emitting diode (OLED) displays can be used to maintain image quality as the display ages. The data used to perform such compensation can be stored in a compressed form to reduce memory requirements; however, errors in such compressed data can accumulate unevenly, resulting in a loss of image quality.

[0006] In addition, when an OLED (organic light emitting diode) display device displays a static image for a long period of time, it may suffer from image retention. As a result, once the static image is removed or changed, a blurred outline or ghost image of the original image may still be visible to the user even when the image content has changed. This is commonly referred to as image retention, image sticking, or image ghosting. The same method as stress distribution applies to image retention.

[0007] Therefore, there is a need for improved systems and methods for stress compensation.

[0008] The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not constitute prior art. Summary of the invention

[0009] This summary is provided to introduce a selection of features and concepts of embodiments of the present disclosure that are further described in the detailed description below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. One or more of the features described can be combined with one or more other described features to provide a viable device.

[0010] Aspects of example embodiments of the present disclosure are directed to a system and method for reducing or eliminating display output degradation by mitigating the effects of pixel degradation / aging in a display device.

[0011] According to some embodiments of the present disclosure, a method for stress compensation in a display device is provided, the method comprising: accumulating brightness values ​​of an image displayed by the display device through an adding circuit; encoding the accumulated brightness values ​​through an encoder to maintain a protected portion of the accumulated brightness values; compressing the accumulated brightness values ​​through a compressor; storing the compressed accumulated brightness values ​​in a memory through the compressor; retrieving the compressed accumulated brightness values ​​through a decompressor and decompressing the compressed accumulated brightness values ​​to generate decompressed values; and decoding the decompressed values ​​based on the protected portion through a decoder to generate a decoded value corresponding to the accumulated brightness value, the decoded value having lower compression noise than the decompressed value.

[0012] In some embodiments, the protected portion includes k bits of the accumulated luma value starting from the pth bit of the accumulated luma value (both p and k are integers greater than 1), and p+k-1 is less than the bit length of the accumulated luma value.

[0013] In some embodiments, the compression noise in the decompressed value is entirely contained within the first (p+k-1) bits of the decompressed value.

[0014] In some embodiments, the method further comprises discarding, by the truncate, less significant bits of the decoded value preceding the protected portion.

[0015] In some embodiments, the method further comprises providing the decoded value to a compensator of the input image for compensating for stress of the display device.

[0016] In some embodiments, encoding the accumulated luma values ​​includes: identifying, by the encoder, a protected portion of the accumulated luma values; and storing, by the encoder, the protected portion in a memory.

[0017] In some embodiments, the protected portion is stored in memory in an uncompressed state.

[0018] In some embodiments, decoding the decompressed value includes: identifying, by a decoder, a decompressed protected portion of the decompressed value; calculating, by the decoder, a difference between a protected portion of the accumulated luminance value and a decompressed protected portion to produce an estimated compression noise; and calculating, by the decoder, a decoded value based on the decompressed value and the estimated compression noise to reduce the compression noise in the decompressed value.

[0019] In some embodiments, the decompressed protected portion of the decompressed value corresponds in bitwise position to the protected portion of the accumulated luma value.

[0020] In some embodiments, calculating the difference between the protected portion of the accumulated luminance values ​​and the decompressed protected portion comprises: calculating, by the decoder, and Calculate the first error (E 1 ) and the second error (E 2 ), where x k represents the protected portion of the accumulated brightness value, represents the protected portion after decompression, and mod represents the modulo operation.

[0021] In some embodiments, calculating the decoded value includes: determining, by the decoder, that the first error is less than the second error; and in response to the determination, calculating, by the decoder, the decoded value according to Calculate the decoded value in, represents the decompressed value, and p represents the leading position of the protected part in the accumulated brightness value.

[0022] In some embodiments, calculating the decoded value includes: determining, by the decoder, that the first error is greater than the second error; and in response to the determination, calculating, by the decoder, based on Calculate the decoded value in, represents the decompressed value, and p represents the leading position of the protected part in the accumulated brightness value.

[0023] In some embodiments, calculating the decoded value includes: determining, by the decoder, that the first error is equal to the second error; and determining, by the decoder, that the decoded value is the decompressed value.

[0024] In some embodiments, encoding the accumulated brightness values ​​includes: copying the protected portion multiple times by an encoder to form a binary copy string, and wherein the method further includes: compressing the binary copy string by a compressor; storing the compressed binary copy string in a memory by the compressor; and retrieving the compressed binary copy string by a decompressor and decompressing the compressed binary copy string to produce a decompressed binary copy string.

[0025] In some embodiments, decoding the decompressed value includes: calculating, by the decoder, a decoded protected portion by applying a maximum likelihood decoding (MLD) process to the decompressed binary replica string to estimate the protected portion of the accumulated luminance value; calculating, by the decoder, a difference between the decoded protected portion and the decompressed protected portion of the decompressed value to produce an estimated compression noise; and calculating, by the decoder, a decoded value based on the decompressed value and the estimated compression noise to reduce the compression noise in the decompressed value.

[0026] In some embodiments, encoding the accumulated brightness values ​​includes: encoding the protected portion by an encoder to generate a plurality of parity bits, wherein compressing the accumulated brightness values ​​includes: compressing the parity bits together with the accumulated brightness values ​​by a compressor, and wherein decompressing the compressed accumulated brightness values ​​includes: decompressing the compressed parity bits together with the compressed accumulated brightness values ​​by a decompressor to generate a decompressed protected portion and a decompressed parity bit.

[0027] In some embodiments, encoding the protected portion is according to a Reed-Solomon code applied across a slice of accumulated luma values, and wherein the parity bits are compressed via a different compression than the accumulated luma values.

[0028] In some embodiments, decoding the decompressed value includes: calculating, by the decoder, the decoded protected portion based on the decompressed protected portion and the decompressed parity bit to estimate the protected portion of the accumulated luminance value; calculating, by the decoder, the difference between the decoded protected portion and the decompressed protected portion to generate an estimated compression noise; and calculating, by the decoder, the decoded value based on the decompressed value and the estimated compression noise to reduce the compression noise in the decompressed value.

[0029] According to some embodiments of the present disclosure, a method for stress compensation in a display device is provided, the method comprising: accumulating brightness values ​​of an output image displayed by the display device through an adding circuit; encoding the accumulated brightness values ​​through an encoder to keep a protected portion of the accumulated brightness values; compressing the accumulated brightness values ​​through a compressor; storing the compressed accumulated brightness values ​​in a memory through the compressor; retrieving the compressed accumulated brightness values ​​through a decompressor and decompressing the compressed accumulated brightness values ​​to generate decompressed values; decoding the decompressed values ​​based on the protected portion through a decoder to generate a decoded value corresponding to the accumulated brightness value, the decoded value having lower compression noise than the decompressed value; receiving an output image to be displayed on the display device through the adding circuit; adding the decoded value to the brightness value of the output image through the adding circuit to generate an updated accumulated brightness value.

[0030] According to some embodiments of the present disclosure, a system for performing stress compensation in a display device is provided, the system comprising: a memory; and a processing circuit, the processing circuit being configured to perform: accumulating brightness values ​​of an image displayed by the display device; encoding the accumulated brightness values ​​to maintain a protected portion of the accumulated brightness values; compressing the accumulated brightness values; storing the compressed accumulated brightness values ​​in the memory; retrieving the compressed accumulated brightness values ​​and decompressing the compressed accumulated brightness values ​​to generate decompressed values; and decoding the decompressed values ​​based on the protected portion to generate a decoded value corresponding to the accumulated brightness value, the decoded value having lower compression noise than the decompressed value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] These and other features of some example embodiments of the present disclosure will be appreciated and understood with reference to the specification, claims, and drawings, in which:

[0032] Figure 1 illustrates example embodiments of a display device according to some example embodiments of the present disclosure;

[0033] Figure 2A illustrates a block diagram of a system for stress compensation according to some example embodiments of the present disclosure;

[0034] Figure 2B illustrates a block diagram of a system for stress compensation using memory compression according to some example embodiments of the present disclosure;

[0035] Figure 2C illustrates a block diagram of a system for stress compensation using redundancy-assisted noise control for accumulating iterative compression errors according to some example embodiments of the present disclosure;

[0036] Figure 3 illustrates a process for mitigating noise through a partial protection pass system 202 for bits according to some example embodiments of the present disclosure;

[0037] Figure 4 is a flow chart illustrating a process for mitigating noise by a noise mitigation system according to some example embodiments of the present disclosure;

[0038] Figure 5 illustrates a process for mitigating noise through a noise mitigation system by partial protection with multiple replicated bits according to some example embodiments of the present disclosure;

[0039] Figure 6 illustrates a process for mitigating noise through a noise mitigation system by partial protection of bits with a Reed-Solomon code according to some example embodiments of the present disclosure;

[0040] 7A to 7D illustrating various arrangement options for inserting parity bits into corresponding accumulated luminance values ​​according to some example embodiments of the present disclosure; and

[0041] FIG. 8A to FIG. 8B is a diagram illustrating maximum absolute error compared to the number of iterations of a recursive system according to some example embodiments of the present disclosure. DETAILED DESCRIPTION

[0042] The detailed description set forth below in conjunction with the accompanying drawings is intended as a description of some example embodiments of the systems and methods for mitigating the effects of compression errors provided in accordance with the present disclosure, and is not intended to represent the only form in which the present disclosure may be constructed or utilized. The description sets forth features of the present disclosure in conjunction with the illustrated embodiments. However, it is to be understood that the same or equivalent functions and structures may be implemented by different embodiments that are also intended to be included within the scope of the present disclosure. As indicated elsewhere herein, the same reference numerals are intended to indicate the same elements or features.

[0043] Certain types of display devices may have characteristics that change with use. For example, an organic light emitting diode (OLED) display device may include a display panel having a plurality of pixels, each pixel including a number of sub-pixels (e.g., a red sub-pixel, a green sub-pixel, and a blue sub-pixel), and each of the sub-pixels may include an organic light emitting diode configured to emit a different corresponding color. Each organic light emitting diode may have a light efficiency that decreases with use, so that, for example, after the organic light emitting diode has been operated for some time, the light output at a certain current may be lower than its light output at the same current when the organic light emitting diode was new.

[0044] This reduction in light efficiency can cause portions of the display panel that uniformly display brighter portions of the displayed image than other portions of the display to darken over the life of the display device. For example, a display device used to view a mostly unchanging image from a security camera (the field of view of the security camera contains a scene having a first portion, the first portion being illuminated by sunlight and relatively bright during most of the day, and a second portion being in shadow and relatively dim during most of the day) can eventually show a more significant reduction in light efficiency in the first portion than in the second portion. As a result, the fidelity of image reproduction by such a display device can degrade over time. As another example, a display device that is used part of the time to display white text at the bottom of an image (separated from the rest of the image by a black border) can experience less reduction in light efficiency in the black border than in other portions of the display panel, so that if the display device is later used in a mode where the scene fills the entire display panel, a brighter band can appear where the black border was previously displayed. This can be referred to as image persistence or image ghosting.

[0045] To reduce the impact of such non-uniformities on the light efficiency of a display device, the display device may include features for compensating for reduced light efficiency resulting from use of the display.

[0046] Figure 1 An example embodiment of a display device 100 is illustrated. The display device 100 may include a display panel 110, a processing circuit 115 (e.g., a processor or central processing unit (CPU)), and a memory 120. The memory 120 includes data that may be referred to as a “stress profile” or “stress table” for the display device 100. The “stress profile” or “stress table” stored in the memory 120 may be a table of numbers or “stress values” indicating the amount of stress that each sub-pixel in the display device 100 has been subjected to during the life of the display device 100. “Stress” may be the total (e.g., time-integrated) drive current that has flowed through each sub-pixel during the life of the display device 100, or the sum of the brightness values ​​displayed. For example, “stress” may be the total charge that has flowed through each sub-pixel during the life of the display device 100.

[0047] In some example embodiments, the method of determining the "stress distribution" may be a data-driven method for compensating for the drop in OLED output. In some example embodiments, in order to determine the "stress distribution" of the display device 100, the memory 120 may accumulate a number for one or some sub-pixels as a new entry in a "stress distribution" or "stress table" for the display device 100 each time a new image is displayed in the display device 100. For example, when a continuous stream of images together forms a display video in the display device 100, the drive current of each sub-pixel in each image may be measured, and a number indicating the current or brightness of the sub-pixel may be added to the corresponding number or "stress" of the sub-pixel in the "stress distribution" or "stress table" in the memory 120. In some examples, the stress value for each sub-pixel may be calculated as the sum of the brightness values ​​displayed by the sub-pixels.

[0048] In some example embodiments, the display device 100 includes a timing controller and a plurality of driver integrated circuits (e.g., a scan / gate driver and a data driver). The processing circuit 115 may be one or more driver integrated circuits, or may be a part of one or more driver integrated circuits. In some embodiments, each driver integrated circuit is responsible for driving a portion of the display panel 110, and it may therefore perform stress accumulation and stress compensation for that portion independently of other driver integrated circuits.

[0049] In some example embodiments, during operation of the display device 100, the drive current to each sub-pixel may be adjusted to compensate for the estimated loss of light efficiency. The estimated loss of light efficiency may be based on the life stress of the sub-pixel. For example, the drive current to each sub-pixel may be increased (e.g., as accumulated in the memory 120) according to the estimated loss of light efficiency of the sub-pixel (e.g., proportional to the estimated loss of light efficiency of the sub-pixel), so that the light output of the sub-pixel may be substantially the same as it would have been if the light efficiency of the sub-pixel had not been reduced and the drive current had not been increased. In some example embodiments, a nonlinear function based on empirical data or a physical model of the sub-pixel may be used to infer or predict the expected loss of light efficiency based on the life stress of the sub-pixel. The calculation of the predicted loss of light efficiency and the calculation of the drive current adjusted accordingly may be performed by the processing circuit 115. In some embodiments, the calculation result is stored in a lookup table in the memory 120, and the processing circuit 115 may use it for compensation. In some example embodiments, during operation of the display device 100 , a driving current to each sub-pixel may be adjusted according to a compensation factor that may be calculated based on a cumulative brightness captured from an output image of the sub-pixel.

[0050] Figure 2AA block diagram of a system 200 for stress compensation according to some example embodiments of the present disclosure is illustrated. The system 200 includes a memory 205 (which may be the same as the memory 120 or may be a part of the memory 120), a compensation module 210, a brightness / stress capture module 215, an adder circuit 220, and a memory controller 225. A stress table is stored in the memory 205. In operation, the stress values ​​in the stress table may be accessed (e.g., read out) via the memory controller 225 and may be used by the compensation module 210 to determine a compensation factor for a sub-pixel. The compensation module 210 may include a drive current adjustment circuit to calculate an adjusted drive current value for each sub-pixel based on the corresponding compensation factor for the sub-pixel. The compensation factor for each sub-pixel is based on the stress value of the sub-pixel. In some example embodiments, the adjusted drive current value for each sub-pixel may be an original drive current value adjusted according to the accumulated stress of the sub-pixel (e.g., based on the desired light output of the sub-pixel). The adjusted drive current value for each sub-pixel is read by the brightness / stress capture module 215, which may include a sub-pixel stress sampling circuit. The adjusted drive current value for each sub-pixel represents the current accumulation rate of stress for the sub-pixel being displayed. Each previously stored (e.g., in memory 205) stress value for each sub-pixel is increased (or "increased") in summing circuit 220 based on the current accumulation rate of stress (e.g., by a number proportional to the adjusted drive current value) and saved back to memory 205 via memory controller 225. Memory controller 225 controls read and write operations in memory 205 and feeds stress values ​​from memory 205 to the drive current adjustment circuit of compensation module 210 and to summing circuit 220 as needed. Memory controller 225 also stores the increased stress value (which has been increased by adding the current accumulation rate of stress at summing circuit 220) back to memory 205.

[0051] In some example embodiments, tracking the total stress for each sub-pixel may require a large amount of memory. For example, for a display with 1920×1080 pixels, each pixel having three sub-pixels, and the stress for each sub-pixel stored in a few bytes, the size of the memory required may be on the order of tens of megabytes. Furthermore, the computational burden of updating each stress number for each sub-pixel for each frame of video (e.g., for each displayed image) is considerable.

[0052] Various methods may be used to reduce the burden of tracking and correcting for reductions in light efficiency caused by sub-pixel stress. For example, the sub-pixel stress sampling circuit in the brightness / stress capture module 215 may sample only a subset of the adjusted drive current values ​​in each image (e.g., in each frame of a video). For example, in a display having 1080 lines (or rows) of pixels, if the scene changes relatively slowly in the displayed video, only one row of the stress table is updated for each frame of the video. The discarding of the middle 1079 adjusted drive current values ​​for any sub-pixel may result in only a small, acceptable loss of accuracy in the resulting stress value (e.g., as a measure of lifetime stress value) of the sub-pixel. In another embodiment, the sub-pixel stress sampling circuit in the brightness / stress capture module 215 may additionally sample only at a subset of the frames. For example, in a display having 1080 lines (or rows) with a refresh rate of 60 Hz (e.g., 60 frames are shown per minute), the stress sampling circuit in the brightness / stress capture module 215 samples all or part of the drive current values ​​in the image once every 10 frames and updates the stress table accordingly.

[0053] Various methods can also be used to reduce the size of the memory required to store the sub-pixel stress in the stress table. For example, the memory on the stress distribution chipset can be reduced by compressing the data stored in the memory.

[0054] Figure 2B A block diagram of a system 201 for stress compensation using memory compression is shown. The system 201 includes Figure 2AThe system 201 further includes a first decompressor 230, a compressor 235, and a second decompressor 240. In some example embodiments, a compressed representation of the stress table is stored in the memory 205. In operation, the compressed stress data may be accessed (e.g., read out) via the memory controller 225 and may be decompressed by the first decompressor 230 before being fed to the drive current adjustment circuit of the compensation module 210. The drive current adjustment circuit of the compensation module 210 calculates an adjusted drive current value for each sub-pixel based on the corresponding compensation factor for the sub-pixel. The compensation factor for each sub-pixel is based on the stress value of the sub-pixel. The adjusted drive current value for each sub-pixel is read by the brightness / stress capture module 215. The adjusted drive current value for each sub-pixel represents the current accumulation rate of stress for the sub-pixel being displayed. The compressed stress data in the memory 205 is also decompressed by the second decompressor 240 to obtain each previously stored (e.g., in the memory 205) stress value for each sub-pixel. The decompressed stress values ​​for the sub-pixels from the second decompressor 240 are sent to the adding circuit 220. Each previously stored stress value for each sub-pixel is increased (or "increased") in the adding circuit 220 based on the current accumulation rate of stress (e.g., by a number proportional to the adjusted drive current value). The increased stress values ​​from the adding circuit 220 are compressed by the compressor 235 before being stored in the memory 205. The compressor 235 compresses the data it receives in a manner that reduces the size of the stored data. In some examples, the compression applied by the compressor 235 may be lossy in order to reduce (e.g., minimize) the memory capacity consumed by the compressed data. Each of the first decompressor 230 and the second decompressor 240 decompresses the received data. For example, each of the first decompressor 230 and the second decompressor 240 performs an operation that is the inverse or approximately the inverse of the operation performed by the compressor 235. Various compression methods may be utilized, including entropy coding such as Huffman coding or arithmetic coding.

[0055] Figure 2B The system 201 can reduce the memory size required for storing sub-pixel stresses in the stress table. However, due to the iterative nature of the system, errors can accumulate in the memory or stress table compared to a system (e.g., 200) that does not use compression. The iterative additive nature of the stress distribution causes compression and decompression errors to accumulate from one iteration to the next. The error pattern may be similar for each iteration. In some examples, such errors may be too high to be effectively corrected using traditional error correction codes.

[0056] Figure 2CA block diagram of a system 202 for stress compensation using redundancy-assisted noise control for accumulating iterative compression errors is illustrated in accordance with some embodiments of the present disclosure.

[0057] Reference Figure 2C According to some embodiments, the system 202 includes Figure 2A All components of. System 202 also includes an encoder (e.g., a channel encoder) 222, a first channel decoder 232, a second channel decoder 242, and a truncation device 234. In some embodiments, encoder 222 encodes the accumulated brightness value (also referred to as "accumulated stress value") received from addition circuit 220 to protect (e.g., keep) a portion of the brightness value that is later used to mitigate noise. The protected portion of the brightness value may be k bits (k is an integer greater than 1) near the middle portion of the brightness value, as will be discussed below. Encoder 222 may store a duplicate copy of the protected portion in memory 205 for later use by first channel decoder 232 and second channel decoder 242. In some examples, the duplicate portion may be stored in uncompressed form, may be compressed using lossless / lossy compression before being stored in memory 205 (e.g., by compressor 235), or an encoded version of the protected portion may be stored in memory 205. Each of the first channel decoder 232 and the second channel decoder 242 can utilize the protected portion stored in the memory 205 to reduce compression noise caused by the compression and decompression operations performed by the compressor 235 and the corresponding one of the first decompressor 230 and the second decompressor 240, respectively. Without using the channel encoder 222 and the first channel decoder 232 and the second channel decoder 242, due to the iterative nature of the stress distribution, the compression / decompression error may increase over time and propagate from the position of the lower significant bit to the position of the higher significant bit. According to some embodiments of the present disclosure, when the brightness value of k bits is maintained, there may be no error in the remaining portion of the position of the higher significant bit.

[0058] The truncation unit 234 may discard a portion of the output of the first channel decoder 232. In some embodiments, the truncation unit 234 discards less significant bits before the protected portion of the luma value to reduce or minimize accumulated errors.

[0059] Figure 3 A process for mitigating noise through the partial protection of bits through the system 202 is illustrated in accordance with some embodiments of the present disclosure.

[0060] Reference Figure 3 In some embodiments, the encoder 222 may select k bits of the accumulated brightness value X starting from the start bit p as the protected portion x k, where both p and k are integers greater than one. The less significant portion x of the accumulated luminance value x represented by the bits from the least significant bit to bit p-1 l It can be discarded later by the truncation unit 234. The values ​​p and k are selected so that the compression / decompression noise is within the protected portion x. k and the less significant part x l That is, it is limited to the first to the (p+k-1)th bits of the accumulated brightness value X. The value of p+k-1 may be less than the bit length of the accumulated brightness value. k The length k of may be 4 to 6, and the value p may be between 6 and 8; however, the embodiments of the present disclosure are not limited thereto. According to some embodiments, the values ​​appearing in the less significant part x are ignored. l Error in, protection in the protected part x k The partial information contained in and the use of the partial information to perform error correction is sufficient to significantly reduce or minimize the higher significant portion x represented by the bits from the (p+k)th bit to the most significant bit of the accumulated luminance value X. h of error propagation.

[0061] like Figure 3 As shown in FIG. 1 , the output of the first decompressor 230 is composed of the decompressed accumulated brightness value (also referred to as "decompressed value"), and the output of the first channel decoder 232 consists of the decoded accumulated brightness value (also called "decoded value") indicates that the expected decoded value is As close as possible to the original accumulated brightness value X.

[0062] Here, the decompressed value Include compressed protected parts The less significant part after compression and the compressed higher significant part And the decoded value Include the decoded protected part The decoded less significant part and the decoded higher-significant portion The accumulated brightness value X and the decompressed value It can be related by formula 1:

[0063]

[0064] Where N represents the compression noise added to the original value X by the compression and decompression operations performed by the compressor 235 and the second decompressor 240, respectively. The first channel decoder 232 is based on the protected portion x that can be maintained intact by the channel encoder 222. k The compression noise is estimated and the estimated compression noise is generated The first channel decoder 232 uses the estimated compression noise To produce the decoded value For this operation to be performed, the values ​​k and p are selected so that they satisfy the conditions of Formula 2 (assuming that the maximum value of the compressed noise N is known, but the sign of N is unknown) or the conditions of Formula 3 (assuming that both the maximum value of the compressed noise N and its sign are known).

[0065] k+p–1>log 2 (|N|)(Formula 2)

[0066] k+p–2>log 2 (|N|)(Formula 3)

[0067] Where |N| represents the absolute value of the compression noise N. Conditional Formula 3 is more conservative than Conditional Formula 2 because satisfying Formula 3 automatically ensures that Formula 2 is satisfied. Under the conditions of Formula 1, there are two candidate Ns (ignoring the first p-1 bits), which can be expressed as:

[0068] or

[0069] For simplicity, it is assumed that In order to uniquely determine between two candidates N, one is required to satisfy:

[0070] X+div(N,2 (p-1) )≠X-div(N,2 (p-1) )mod 2 k (Formula 5)

[0071] Once the estimated compression noise The decision of (which is ambiguous in the first p-1 bits) can compensate for compression. Therefore, for each iteration, the decoded value Formula 6 can be satisfied:

[0072]

[0073] That is, the compression noise of each iteration is limited to the less significant part x which is ignored. l .

[0074] Figure 4is a flow chart illustrating a process 400 for mitigating noise by the system 202 according to some embodiments of the present disclosure.

[0075] Reference Figure 4 In block 402, the first channel decoder 232 / the second channel decoder 242 obtains the protected portion x from the memory 205. k And obtain the compressed protected part from the second decompressor 240 In block 404, the first channel decoder 232 / the second channel decoder 242 calculates the first error E according to equations 7 and 8. 1 and the second error E 2 .

[0076]

[0077]

[0078] Here, the expression "a mod b" is the remainder of Euclidean division of integer a by integer b. The first error E 1 and the second error E 2 Indicates adding to the protected section x k The first error E 1 represents a scenario where the compression noise N has a positive value, and the second error E 2 represents a scenario where the compression noise N has a negative value. Figure 4 In this scenario, it is assumed that only the weaker condition in Equation 2 is satisfied (and Equation 3 is not satisfied). In this scenario, there are two possible noise values ​​E 1 and E 2 (corresponding to the noise value in Formula 4 and Formula 5), ​​and the first channel decoder 232 / the second channel decoder 242 determines E 1 or E 2 Which one of them is the correct noise and which one should be compensated.

[0079] In block 406, the first channel decoder 232 / the second channel decoder 242 determines a first error E 1 Is it less than the second error E? 2 If so, then in block 408, the first channel decoder 232 / second channel decoder 242 calculates the decoded value according to Formula 9

[0080]

[0081] If not, then in block 410, the first channel decoder 232 / second channel decoder 242 determines a first error E 1 Is it equal to the second error E 2If not (i.e., E 1 >E 2 ), then in block 412, the first channel decoder 232 / the second channel decoder 242 calculates the decoded value according to formula 10

[0082]

[0083] Otherwise, if the first error E 1 Equal to the second error E 2 , then in block 414, the first channel decoder 232 / the second channel decoder 242 causes the decoded value With the decompressed value = are equal (ie, no noise mitigation is performed). However, the embodiments of the present disclosure are not limited thereto, and the first channel decoder 232 / the second channel decoder 242 may alternatively calculate the decoded value according to Formula 9 or Formula 10 In the embodiment where the values ​​k and p are selected to satisfy the conditions of Formula 3, the first error E 1 and the second error E 2 cannot be equal to each other. However, this situation may occur for some pixels only when the condition of Formula 2 is satisfied (and Formula 3 is not satisfied). Violating the condition of Formula 3 may cause some errors, but the mechanism provides a lower value p for the same value k, which may be desirable because fewer bits are discarded.

[0084] According to some embodiments, although the protected portion x for noise mitigation purposes k The protected portion x is kept intact (ie, not compressed / decompressed), but the embodiments of the present disclosure are not limited thereto. k Partial protection can be achieved by using multiple copies of

[0085] Figure 5 A process for mitigating noise through a partial protection pass system 202 with multiple replicated bits is illustrated in accordance with some embodiments of the present disclosure.

[0086] Reference Figure 5 , different from maintaining the protected portion x k intact, the channel encoder 222 creates the protected portion x kn copies (n is an integer greater than 1) of the binary copy string S and combine them together to form a binary copy string S. In some embodiments, the binary copy string S is compressed by the compressor 235 and later decompressed by the first decompressor 230. The compression and decompression may be the same as the compression and decompression applied to the accumulated brightness values ​​X; however, the embodiments of the present disclosure are not limited thereto. For example, the compression and decompression applied to the binary copy string S may be different from the compression and decompression applied to the accumulated brightness values ​​X. For example, different compression techniques and / or different compression ratios may be used.

[0087] like Figure 5 As shown in , the decompressed copy string An uncompressed copy of (for example, ) each experiences a different amount of noise.

[0088] In some embodiments, the first channel decoder 232 / the second channel decoder 242 applies a maximum likelihood decoding (MLD, e.g., majority voting) process to the decompressed copy to calculate the decoded protected portion ex k , which is the protected portion x of the accumulated brightness value X k The MLD process can reduce the decoded protected part ex k noise in the decoded part, but it may not be possible to reduce it to the protected part after decoding k With protected part x k The number of copies n can be determined based on simulations, experiments, and / or available memory. In some examples, the number of copies n is selected to be an odd number. However, when the number of copies n is an even number, the compressed protected portion is It can be combined with the binary replica string S to make the total number an odd number. The embodiments of the present disclosure are not limited to the MLD process and can be replaced by any other suitable process.

[0089] Once the first channel decoder 232 / the second channel decoder 242 determines the decoded protected portion ex k , we can use ex in equations 7 and 8 k Replace x k And continue to calculate the decoded value As mentioned above Figure 4 described.

[0090] Figure 6 The process of mitigating noise through the system 202 by partial protection of bits with independent coding of multiple pixels through enhanced coding techniques such as Reed-Solomon codes is illustrated in accordance with some embodiments of the present disclosure. 7A to 7D Various arrangement options for inserting parity bits into corresponding accumulated luminance values ​​X according to some embodiments of the present disclosure are illustrated.

[0091] Reference Figure 6 , the channel encoder 222 may encode the accumulated luminance values ​​X of k' (k' is an integer greater than 1) pixels, whereby these pixels of the display are within a slice of the image being compressed. According to some examples, the less significant portion x of these pixels l , protected part x k and the higher effective part x h They are shown as x l,1 ...x l,k′ ,x k,1 ...x k,k′ , and x h,1 ...x h,k′ The channel encoder 222 then generates k,1 ...x k,k′ The bit string formed generates the parity bit p 1 to p r .

[0092] Each of the pixels 1 to k' and the parity bit p is compressed separately or partially using compressor 235 or using multiple different compressors. 1 to p r Each of the compressed pixels 1 to k' and the compressed parity bits to And later decompressed by the corresponding decompressor. Parity bit p 1 to p r can be used with the bit string x k,1 ...x k,k′ The same or different compression (e.g., the same or different compression technique, compression ratio, compression parameters, etc.) is used to compress. The parity bit after compression to It is then used by the first channel decoder 232 / second channel decoder 242 to Producing Value These values ​​are then used by the first channel decoder 232 / second channel decoder 242 to decode the value x k,1 ...x k,k′ An estimate is made, which can be used to mitigate noise, as described above with reference to Figure 3 to Figure 4 described.

[0093] According to some embodiments, the compressed parity bits to Can be appended / interleaved at any point in the accumulated brightness values. For example, parity bits after compression to can be appended to the end of the accumulated brightness value (e.g. Fig. 7A ), may be appended to the beginning of the accumulated brightness values ​​(e.g., Figure 7B ), may be appended somewhere between the LSB and MSB of the accumulated luminance value (e.g., Figure 7C ), or may be interleaved with the bits of the accumulated brightness values ​​(e.g. Fig.7D ).

[0094] In the above embodiment, the values ​​p and k are fixed and based on an estimate or knowledge of the noise. However, due to the recursive structure of the system 202, the noise is not fixed and accumulates over time. As a result, the selected values ​​p and k may be too aggressive at the beginning.

[0095] Thus, it may be desirable to adaptively select values ​​p and k to more closely match the noise level at each subsequent iteration / run. Each iteration / run may correspond to a frame of an image displayed at a display device. In some examples, each subsequent frame may correspond to a subsequent iteration. In other examples, an iteration may be performed every m (m is an integer greater than 1) frames. The latter scheme may reduce the demand for memory and computation time.

[0096] Adaptive parameters allow easy parameter initialization, since inappropriate parameters can be corrected in subsequent executions. Further, employing adaptive parameters can provide better performance at the beginning, and thus allow less error accumulation during early runs. Furthermore, no knowledge of noise is required.

[0097] Because the accumulated noise starts out small, but grows over time (i.e., starting from the least significant bit (LSB) and moving toward the most significant bit (MSB)), it is desirable to select a smaller value for p+k (also referred to as the sum parameter c) at the beginning. According to some embodiments of adaptive parameter selection, the value k remains constant. Thus the value of p increases over time (e.g., from the LSB toward the MSB).

[0098] FIG. 8A to FIG. 8B is a diagram illustrating maximum absolute error compared to the number of iterations of the recursive system 202 according to some example embodiments of the present disclosure. FIG. 8A to FIG. 8B The figure shows the step-like characteristics of the accumulated compressed quantization noise.

[0099] Fig. 8A The noise mitigation using a fixed sum parameter c (=p+k) is shown. Figure 8B The adaptive noise mitigation using a varying sum parameter c is illustrated. Further, appropriate values ​​of the sum parameter c at each step are shown in Figure 8B In. Figure 8B In the example above, the sum parameter c increases in increments of one.

[0100] According to some examples, data accumulation, and therefore noise accumulation, may continue for long periods of time (e.g., months or years), and the sum parameter c may be updated at intervals (e.g., regular intervals, such as once every few weeks or months). Thus, changes to the sum parameter c may be relatively infrequent. As a result, even if the noise calculation for one iteration may be unacceptable (e.g., incorrect) after the sum parameter c is incremented, the error is diluted by the number of iterations using the correct value of c, and therefore there is no noticeable impact on the image quality of the display.

[0101] There are two methods of adaptively changing the sum parameter c: (1) setting / adjusting the sum parameter c by the compressor 235 and passing the value of c to the channel encoder 222 and the first channel decoder 232 and the second channel decoder 242, and (2) setting / adjusting the sum parameter c by one or more of the channel encoder 222 and the first channel decoder 232 and the second channel decoder 242 using information available to the encoder / decoder and passing the value of c to the other one(s) of the encoder and the decoder. The second scheme may be referred to as adaptive.

[0102] Under the first approach, compressor 235 may utilize a quantization table (which may be different from the stress profile and stress table maintained in memory 205), and in some examples, when the compression quantization changes (such as by Figure 8B The increment of c occurs when the quantization level changes (indicated by the step change in ). In this case, the compressor 235 sends a signal to the channel encoder and decoder to increment the sum parameter c each time the quantization level changes. The quantization levels and their corresponding relationship with c can be based on empirical numbers or theoretical calculations.

[0103] Under the second (ie, adaptive) scheme, according to some embodiments, the first channel decoder 232 / second channel decoder 242 observes The value of (which represents the value added to the protected portion x k noise), and when determining When the value of is invalid (ie exceeds the noise threshold), the sum parameter c is incremented by one. The noise threshold can be defined based on the values ​​of p and k and the number of iterations (or time).

[0104] According to some embodiments, when one of the first channel decoder 232 and the second channel decoder 242 changes the sum parameter c, it transmits the change to the other channel decoder so that there is no noise caused by mismatch c. However, in an example where the first channel decoder 232 and the second channel decoder 242 do not transmit the change of the sum parameter c, when one decoder changes c, it causes mismatch noise in the other decoder; however, the other decoder can detect the mismatched c by utilizing the same adaptive logic (the same adaptive logic utilizes the additional noise caused by the mismatched c), and increments the sum parameter c by one.

[0105] In some embodiments, to avoid large correction errors, noise mitigation is not performed by the channel encoder 222 and the first channel decoder 232 and the second channel decoder 242 when c changes.

[0106] In some embodiments, assuming that an increment of the sum parameter c typically occurs when there is a step change in the quantization noise, rather than the channel encoder / decoder self-adjusting the sum parameter c, when there is a change in the quantization noise, the compression block (i.e., compressor 235) adjusts the value of c and communicates the change to the channel encoder 222 and the first channel decoder 232 and the second channel decoder 242. Here, the decision to change c can be made in the same manner as for the adaptive scheme.

[0107] It will be understood that although the terms "first", "second", "third", etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited to these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Therefore, the first element, component, region, layer or section discussed herein may be referred to as a second element, component, region, layer or section without departing from the spirit and scope of the present inventive concept.

[0108] In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

[0109] The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the inventive concept. As used herein, the terms "substantially," "approximately," and similar terms are used as terms of approximation rather than as terms of degree, and are intended to take into account the inherent deviations of measurements or calculations that would be recognized by one of ordinary skill in the art.

[0110] As used in this article, the singular form "one" is intended to also include the plural form, unless the context clearly indicates otherwise. It will be further understood that when used in this specification, the term "include" and / or "comprising" specifies the existence of the features, integers, steps, operations, elements and / or parts, but does not exclude the existence or addition of one or more other features, integers, steps, operations, elements, parts and / or their groups. As used in this article, the term "and / or" includes any and all combinations of one or more associated listed items. When after the element list, statements such as "at least one of" modify the entire element list without modifying the single element of the list. Further, when describing the embodiment of the present invention, the use of "can" relates to "one or more embodiments of the present disclosure". In addition, the term "exemplary" is intended to indicate an example or diagram. As used in this article, the terms "use", "being used" and "being used" can be regarded as synonymous with the terms "utilize", "being utilized" and "being utilized" respectively.

[0111] It will be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “adjacent to” another element or layer, it can be directly on, directly connected to, directly coupled to, or “immediately adjacent to” the other element or layer, or one or more intervening elements or layers may be present. In contrast, when an element or layer is referred to as being “directly on,” “directly connected to,” “directly coupled to,” or “immediately adjacent to” another element or layer, there are no intervening elements or layers.

[0112] The electronic or electrical devices and / or any other related devices or components according to the embodiments of the present disclosure described herein can be implemented using any suitable hardware, firmware (e.g., application specific integrated circuits), software, or a combination of software, firmware, and hardware. For example, the various components of these devices can be formed on an integrated circuit (IC) chip or can be formed on a discrete IC chip. Further, the various components of these devices can be implemented on a flexible printed circuit film, a tape carrier package (TCP), a printed circuit board (PCB), or formed on a substrate. Further, the various components of these devices can be processes or threads that run on one or more processors in one or more computing devices, execute computer program instructions, and interact with other system components for performing various functions described herein. Computer program instructions are stored in a memory, which can be implemented in a computing device using a standard storage device, such as a random access memory (RAM). Computer program instructions can also be stored in other non-transient computer-readable media (such as, for example, CD-ROMs, flash drives, etc.). In addition, those skilled in the art should recognize that, without departing from the spirit and scope of the exemplary embodiments of the present disclosure, the functions of various computing devices can be combined or integrated into a single computing device, or the functions of a specific computing device can be distributed across one or more other computing devices.

[0113] Although exemplary embodiments of systems and methods for mitigating the effects of compression errors have been specifically described and illustrated herein, many modifications and variations will be apparent to those skilled in the art. Therefore, it is to be understood that systems and methods for mitigating the effects of compression errors using stress distribution compression constructed according to the principles of the present disclosure may be embodied other than as specifically described herein. The scope of the present disclosure is defined by the appended claims and their equivalents.

Claims

1. A method for compensating stress in a display device, the method comprising: accumulating brightness values ​​of an image displayed by the display device by an adding circuit; encoding, by an encoder, the accumulated luma values ​​to preserve protected portions of the accumulated luma values; compressing the accumulated brightness value by a compressor; storing the compressed accumulated brightness values ​​in a memory by the compressor; retrieving, by a decompressor, the compressed accumulated luminance values ​​and decompressing the compressed accumulated luminance values ​​to produce decompressed values; as well as The decompressed value is decoded by a decoder based on the protected part to generate an estimated compression noise, and a decoded value corresponding to the accumulated brightness value is calculated based on the decompressed value and the estimated compression noise, wherein the decoded value has lower compression noise than the decompressed value.

2. The method according to claim 1, wherein: The protected portion includes k bits of the accumulated luminance value starting from the pth bit of the accumulated luminance value, wherein both p and k are integers greater than 1, and Here, p+k-1 is less than the bit length of the accumulated brightness value.

3. The method according to claim 2, wherein: The compression noise in the decompressed value is completely contained within the first (p+k-1) bits of the decompressed value.

4. The method according to claim 1, further comprising: The less significant bits of the decoded value preceding the protected portion are discarded by the truncate.

5. The method according to claim 1, further comprising: The decoded values ​​are provided to a compensator for compensating an input image for stress of the display device.

6. The method according to claim 1, wherein: The encoding of the accumulated brightness value comprises: identifying, by the encoder, the protected portion of the accumulated luma values; and The protected portion is stored in the memory by the encoder.

7. The method according to claim 6, wherein: The protected portion is stored in the memory in an uncompressed state.

8. The method according to claim 1, wherein: Generating the estimated compression noise comprises: identifying, by the decoder, a decompressed protected portion of the decompressed value; and A difference between the protected portion and the decompressed protected portion of the accumulated luminance values ​​is calculated by the decoder to produce the estimated compression noise.

9. The method according to claim 8, wherein: The decompressed protected portion of the decompressed value corresponds in bitwise position to the protected portion of the accumulated luma value.

10. The method according to claim 8, wherein: The calculating a difference between the protected portion and the decompressed protected portion of the accumulated luminance values ​​comprises: By the decoder according to: and Calculate the first error E1 and the second error E2, Among them, x k represents the protected portion of the accumulated luminance value, represents the decompressed protected portion, and mod represents a modulo operation.

11. The method according to claim 10, wherein: The calculating the decoded value comprises: determining, by the decoder, that the first error is less than the second error; and In response to the determination, the decoder Calculate the decoded value in, represents the decompressed value, and p represents the leading position of the protected part in the accumulated brightness value.

12. The method according to claim 10, wherein: The calculating the decoded value comprises: determining, by the decoder, that the first error is greater than the second error; and In response to the determination, the decoder Calculate the decoded value in, represents the decompressed value, and p represents the leading position of the protected part in the accumulated brightness value.

13. The method according to claim 10, wherein: The calculating the decoded value comprises: determining, by the decoder, that the first error is equal to the second error; and The decoded value is determined by the decoder to be the decompressed value.

14. The method according to claim 1, wherein: The encoding of the accumulated brightness value comprises: Replicating the protected portion a plurality of times by the encoder to form a binary replica string; and Wherein, the method further comprises: compressing the binary copy string by the compressor; storing the compressed binary copy string in the memory by the compressor; and The compressed binary copy string is retrieved by the decompressor and the compressed binary copy string is decompressed to generate a decompressed binary copy string.

15. The method according to claim 14, wherein: Generating the estimated compression noise comprises: calculating, by the decoder, a decoded protected portion by applying a maximum likelihood decoding (MLD) process to the decompressed binary replica string to estimate the protected portion of the accumulated luminance values; and A difference between the decoded protected portion and a decompressed protected portion of the decompressed value is calculated by the decoder to produce the estimated compression noise.

16. The method according to claim 1, wherein: The encoding of the accumulated brightness value comprises: encoding the protected portion by the encoder to generate a plurality of parity bits; The compressing the accumulated brightness value comprises: The parity check bits are compressed together with the accumulated brightness values ​​by the compressor; and wherein the decompressing the compressed accumulated brightness values ​​comprises: The compressed parity bits are decompressed by the decompressor together with the compressed accumulated luminance values ​​to produce a decompressed protected portion and a decompressed parity bit.

17. The method according to claim 16, wherein: The encoding of the protected portion is based on a Reed-Solomon code applied across a slice of accumulated luma values, and The parity bits are compressed via a different compression than the accumulated brightness values.

18. The method according to claim 16, wherein: Generating the estimated compression noise comprises: calculating, by the decoder, a decoded protected portion based on the decompressed protected portion and the decompressed parity bits to estimate the protected portion of the accumulated luminance value; and The estimated compression noise is generated by calculating, by the decoder, a difference between the decoded protected portion and the decompressed protected portion.

19. A method for compensating stress in a display device, the method comprising: accumulating brightness values ​​of an output image displayed by the display device by an adding circuit; encoding, by an encoder, the accumulated luma values ​​to preserve protected portions of the accumulated luma values; compressing the accumulated brightness value by a compressor; storing the compressed accumulated brightness values ​​in a memory by the compressor; retrieving, by a decompressor, the compressed accumulated luminance values ​​and decompressing the compressed accumulated luminance values ​​to produce decompressed values; decoding, by a decoder, the decompressed value based on the protected portion to produce an estimated compression noise, and calculating a decoded value corresponding to the accumulated luminance value based on the decompressed value and the estimated compression noise, the decoded value having a lower compression noise than the decompressed value; receiving, by the adding circuit, the output image to be displayed on the display device; as well as The decoded value is added to the luminance value of the output image by the adding circuit to produce an updated accumulated luminance value.

20. A system for performing stress compensation in a display device, the system comprising: Memory; as well as A processing circuit configured to perform: Accumulating brightness values ​​of an image displayed by the display device; encoding the accumulated luma values ​​to preserve protected portions of the accumulated luma values; compressing the accumulated brightness values; storing the compressed accumulated brightness values ​​in the memory; retrieving compressed accumulated luminance values ​​and decompressing the compressed accumulated luminance values ​​to produce decompressed values; as well as The decompressed value is decoded based on the protected portion to produce estimated compression noise, and a decoded value corresponding to the accumulated brightness value is calculated based on the decompressed value and the estimated compression noise, the decoded value having lower compression noise than the decompressed value.

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