Facebook Patent | Systems and methods for hiding dead pixels

Patent: Systems and methods for hiding dead pixels

Drawings: Click to check drawins

Publication Number: 20210110787

Publication Date: 20210415

Applicant: Facebook

Abstract

In one embodiment, a computing system may access a dead pixel position corresponding to a dead pixel of a display. The system may access an image and modify the image by applying a mask to a pixel region of the image containing a particular pixel value with a position that corresponds to the dead pixel position. The mask may include an array of first scaling factors for scaling pixels values in the pixel region. The array of first scaling factors may be configured to brighten one or more of the pixel values surrounding the particular pixel value. The system may cause the modified image to be output by the display.

Claims

1. A method comprising, by a computing system: accessing a dead pixel position corresponding to a dead pixel of a display; accessing an image; modifying the image by applying a mask to a pixel region of the image containing a particular pixel value with a position that corresponds to the dead pixel position, wherein the mask comprises an array of first scaling factors for scaling pixels values in the pixel region, the array of first scaling factors being configured to alter one or more of the pixel values surrounding the particular pixel value, wherein a particular first scaling factor of the array of first scaling factors is applied to the particular pixel value, and for each first scaling factor in the array of first scaling factors other than the particular first scaling factor, that first scaling factor has the same value as one or more other first scaling factors that are symmetrically positioned from that first scaling factor across orthogonal axes centered at the particular first scaling factor applied to the particular pixel value; and causing the modified image to be output by the display.

2. The method of claim 1, wherein the mask is generated by minimizing a mean-squared error caused by the dead pixel as modulated by a point spread function matched to human vision.

3. The method of claim 1, wherein the image after being modified has a first average brightness in the pixel region, and wherein the first average brightness is within a threshold range with respect to a second average brightness of the pixel region of the image before being modified.

4. The method of claim 1, wherein the mask is circular symmetric as determined by the point spread function matched to human vision.

5. The method of claim 1, wherein the modified image causes the dead pixel of the display to have a lower visibility level than the image before being modified.

6. The method of claim 1, wherein the array of scaling factor is configured to brighten or dim one or more of the pixels values surrounding the particular pixel value.

7. The method of claim 1, further comprising scaling each pixel value of the image by an overall scaling factor.

8. The method of claim 7, wherein the overall scaling factor is smaller than one, and wherein the mask comprises a 5.times.5 array of first scaling factors.

9. The method of claim 1, wherein the mask is applied to the pixel region by: accessing each pixel value within the pixel region of the image; accessing a corresponding scaling factor from the array of first scaling factors; and determining a modified pixel value by multiplying that pixel value by the corresponding scaling factor accessed from the array of first scaling factors of the mask.

10. The method of claim 9, furthering comprising clipping the modified pixel value to a normalized range of [0, 1].

11. The method of claim 1, wherein the pixel region of the image is centered at the dead pixel position, and wherein the mask has a same size to the pixel region containing the dead pixel position.

12. The method of claim 11, wherein the mask comprises a center scaling factor being equal to zero in a center position of the mask, and wherein the center scaling factor is applied to the dead pixel position of the image.

13. The method of claim 1, wherein the image is modified before being processed by one or more spatial or temporal dithering processes for propagating quantization errors.

14. The method of claim 1, wherein the image is modified by one or more processes of a graphic pipeline implemented on a display engine, and wherein the graphic pipeline comprises one or more of: warping one or more surfaces associated with the image; determining one or more pixel values of the image by sampling a plurality of texels; correcting one or more distortions of the image; or propagating, by one or more spatial or temporal dithering processes, quantization errors of the image spatially or temporally.

15. The method of claim 1, wherein the dead pixel of the display is associated with a color channel of RGB color channels of the display, and wherein the mask is applied to each color channel of the RGB color channels.

16. The method of claim 1, further comprising: accessing three pixel correction matrixes each comprising an array of second scaling factors for scaling pixel values of an associated color channel of the image for correcting pixel non-uniformity of the display; and combining the mask into each pixel correction matrix by multiplying each mask value in the mask to an associated second scaling factor of that pixel correction matrix, wherein that mask value and the associated second scaling factor are associated with a same pixel.

17. The method of claim 16, further comprising: applying the three pixel correction matrixes to respective color channels of the image by multiplying each matrix value to a corresponding pixel value of the image to correct pixel non-uniformity and the dead pixel using a same process and at the same time.

18. The method of claim 1, wherein the display is a micro-LED display having a single dead pixel within a display region corresponding a size of the mask.

19. One or more computer-readable non-transitory storage media embodying software that is operable when executed to: access a dead pixel position corresponding to a dead pixel of a display; access an image; modify the image by applying a mask to a pixel region of the image containing a particular pixel value with a position that corresponds to the dead pixel position, wherein the mask comprises an array of scaling factors for scaling pixels values in the pixel region, the array of scaling factors being configured to alter one or more of the pixel values surrounding the particular pixel value, wherein a particular first scaling factor of the array of first scaling factors is applied to the particular pixel value, and for each first scaling factor in the array of first scaling factors other than the particular first scaling factor, that first scaling factor has the same value as one or more other first scaling factors that are symmetrically positioned from that first scaling factor across orthogonal axes centered at the particular first scaling factor applied to the particular pixel value; and cause the modified image to be output by the display.

20. A system comprising: one or more non-transitory computer-readable storage media embodying instructions; and one or more processors coupled to the storage media and operable to execute the instructions to: access a dead pixel position corresponding to a dead pixel of a display; access an image; modify the image by applying a mask to a pixel region of the image containing a particular pixel value with a position that corresponds to the dead pixel position, wherein the mask comprises an array of scaling factors for scaling pixels values in the pixel region, the array of scaling factors being configured to alter one or more of the pixel values surrounding the particular pixel value, wherein a particular first scaling factor of the array of first scaling factors is applied to the particular pixel value, and for each first scaling factor in the array of first scaling factors other than the particular first scaling factor, that first scaling factor has the same value as one or more other first scaling factors that are symmetrically positioned from that first scaling factor across orthogonal axes centered at the particular first scaling factor applied to the particular pixel value; and cause the modified image to be output by the display.

Description

TECHNICAL FIELD

[0001] This disclosure generally relates to artificial reality, such as virtual reality and augmented reality.

BACKGROUND

[0002] Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured content (e.g., real-world photographs). The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Artificial reality may be associated with applications, products, accessories, services, or some combination thereof, that are, e.g., used to create content in an artificial reality and/or used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

SUMMARY OF PARTICULAR EMBODIMENTS

[0003] Particular embodiments described herein relate to systems and methods for hiding dead pixels of display panels by dithering the pixel values or applying luminance masks to the neighboring pixels of the deal pixels. In the first method, a dithering model (e.g., a Floyd-Steinberg model) may be used to dither the target pixel value of the dead pixel to the neighboring pixels. The system may receive a dead pixel location and set the quantized value of the pixel at that location to zero. The dithering model may automatically spread the quantization error (which equals to the target pixel value of the dead pixel) to neighboring pixels. As a result, the surrounding pixels may be brightened to maintain the correct average brightness and to compensate for the dead pixel defect. This method may effectively correct the luminance forward and down to the dead pixels. In the second method, the system may generate a luminance mask for each dead pixel. The mask may be centered around the corresponding dead pixel. The size of the mask may depend on the likely minimum pixel distance between dead pixels in the display. For example, a luminance mask with a size of 5.times.5 pixels may be used for a display panel with a minimum dead pixel distance of 5 pixels (in other words, a 5.times.5 mask may be used if it is unlikely for two dead pixels to collocate within a 5.times.5 pixel region). The luminance mask may alter the luminance of the surrounding pixels to maintain the correct average brightness and compensate for the dead pixel defect. The luminance mask may be circularly symmetric (e.g., in a ring-like manner) based on a point spread function matched to human vision and may be generated to minimize the mean-squared error over the mask. To hide dead pixels, the system may first scale all image pixels by a constant factor less than 1 (e.g., 0.8) to ensure the pixel values have enough headroom (e.g., 20% of normalized pixel value) for compensation. Then, the system may (prior to other dithering processes) apply the luminance mask around each dead pixel to adjust (e.g., raising up or scaling down) the luminance of the surrounding pixels to maintain the correct average brightness and compensate for the dead pixel defect. As a result, the dead pixels may become invisible or have reduced visibility. The luminance mask method may be applicable to larger pixels (e.g., larger red/blue pixels).

[0004] In an embodiment, a method may comprise, by a computing system: [0005] accessing a dead pixel position corresponding to a dead pixel of a display; [0006] accessing an image; [0007] modifying the image by applying a mask to a pixel region of the image containing a particular pixel value with a position that corresponds to the dead pixel position, wherein the mask comprises an array of first scaling factors for scaling pixels values in the pixel region, the array of first scaling factors being configured to alter one or more of the pixel values surrounding the particular pixel value; and [0008] causing the modified image to be output by the display.

[0009] The mask may be generated by minimizing a mean-squared error caused by the dead pixel as modulated by a point spread function matched to human vision.

[0010] The image after being modified may have a first average brightness in the pixel region, and the first average brightness may be within a threshold range with respect to a second average brightness of the pixel region of the image before being modified.

[0011] The mask may be circular symmetric as determined by the point spread function matched to human vision.

[0012] The modified image may cause the dead pixel of the display to have a lower visibility level than the image before being modified.

[0013] The array of scaling factor may be configured to brighten or dim one or more of the pixels values surrounding the particular pixel value.

[0014] In an embodiment, a method may comprise scaling each pixel value of the image by an overall scaling factor.

[0015] The overall scaling factor may be equal to 0.8, and the mask may comprise a 5.times.5 array of scaling factors.

[0016] In an embodiment, the mask may be applied to the pixel region by: [0017] accessing each pixel value within the pixel region of the image; [0018] accessing a corresponding scaling factor from the array of scaling factors; and [0019] determining a modified pixel value by multiplying that pixel value by the corresponding scaling factor accessed from the array of first scaling factors of the mask.

[0020] In an embodiment, a method may comprise clipping the modified pixel value to a normalized range of [0, 1].

[0021] The the pixel region of the image may be centered at the dead pixel position, and the mask may have a same size to the pixel region containing the dead pixel position.

[0022] The mask may comprise a center scaling factor being equal to zero in a center position of the mask, and center scaling factor may be applied to the dead pixel position of the image.

[0023] The image may be modified before being processed by one or more spatial or temporal dithering processes for propagating quantization errors.

[0024] In an embodiment, the image may be modified by one or more processes of a graphic pipeline implemented on a display engine, and the graphic pipeline may comprise one or more of: [0025] warping one or more surfaces associated with the image; [0026] determining one or more first pixel values of the image by interpolating multiple second pixel values; [0027] correcting one or more distortion of the image; or dithering one or more quantization errors of the image spatially or temporally.

[0028] The dead pixel of the display may be associated with a color channel of RGB color channels of the display, and the mask may be applied to each color channel of the RGB color channels.

[0029] In an embodiment, a method may comprise, by a computing system: [0030] accessing three pixel correction matrixes each comprising an array of second scaling factors for scaling pixel values of an associated color channel of the image for correcting pixel non-uniformity of the display; and [0031] combining the mask into each pixel correction matrix by multiplying each mask value in the mask to an associated second scaling factor of that pixel correction matrix, wherein that mask value and the associated second scaling factor may be associated with a same pixel.

[0032] In an embodiment, a method may comprise, by a computing system: [0033] applying the three pixel correction matrixes to respective color channels of the image by multiplying each matrix value to a corresponding pixel value of the image to correct pixel non-uniformity and the dead pixel using a same process and at the same time.

[0034] In an embodiment, the display may be a micro-LED display having a single dead pixel within a display region corresponding a size of the mask.

[0035] In an embodiment, one or more computer-readable non-transitory storage media may embody software that is operable when executed to: [0036] access a dead pixel position corresponding to a dead pixel of a display; [0037] access an image; [0038] modify the image by applying a mask to a pixel region of the image containing a particular pixel value with a position that corresponds to the dead pixel position, wherein the mask comprises an array of first scaling factors for scaling pixels values in the pixel region, the array of first scaling factors being configured to alter one or more of the pixel values surrounding the particular pixel value; and [0039] cause the modified image to be output by the display.

[0040] In an embodiment, a system may comprise: one or more non-transitory computer-readable storage media embodying instructions; and one or more processors coupled to the storage media and operable to execute the instructions to: [0041] access a dead pixel position corresponding to a dead pixel of a display; [0042] access an image; [0043] modify the image by applying a mask to a pixel region of the image containing a particular pixel value with a position that corresponds to the dead pixel position, wherein the mask comprises an array of first scaling factors for scaling pixels values in the pixel region, the array of first scaling factors being configured to alter one or more of the pixel values surrounding the particular pixel value; and [0044] cause the modified image to be output by the display.

[0045] In an embodiment, one or more computer-readable non-transitory storage media may embody software that is operable when executed to perform a method according to or within any of the above mentioned embodiments.

[0046] In an embodiment, a system may comprise: one or more processors; and at least one memory coupled to the processors and comprising instructions executable by the processors, the processors operable when executing the instructions to perform a method according to or within any of the above mentioned embodiments.

[0047] In an embodiment, a computer program product, preferably comprising a computer-readable non-transitory storage media, may be operable when executed on a data processing system to perform a method according to or within any of the above mentioned embodiments.

[0048] The embodiments disclosed herein are only examples, and the scope of this disclosure is not limited to them. Particular embodiments may include all, some, or none of the components, elements, features, functions, operations, or steps of the embodiments disclosed above. Embodiments according to the invention are in particular disclosed in the attached claims directed to a method, a storage medium, a system and a computer program product, wherein any feature mentioned in one claim category, e.g. method, can be claimed in another claim category, e.g. system, as well. The dependencies or references back in the attached claims are chosen for formal reasons only. However, any subject matter resulting from a deliberate reference back to any previous claims (in particular multiple dependencies) can be claimed as well, so that any combination of claims and the features thereof are disclosed and can be claimed regardless of the dependencies chosen in the attached claims. The subject-matter which can be claimed comprises not only the combinations of features as set out in the attached claims but also any other combination of features in the claims, wherein each feature mentioned in the claims can be combined with any other feature or combination of other features in the claims. Furthermore, any of the embodiments and features described or depicted herein can be claimed in a separate claim and/or in any combination with any embodiment or feature described or depicted herein or with any of the features of the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1A illustrates an example artificial reality system.

[0050] FIG. 1B illustrates an example augmented reality system.

[0051] FIG. 1C illustrates an example architecture of a display engine.

[0052] FIG. 1D illustrates an example graphic pipeline of the display engine for generating display image data.

[0053] FIG. 2A illustrates an example scanning waveguide display.

[0054] FIG. 2B illustrates an example scanning operation of the scanning waveguide display.

[0055] FIG. 3A illustrates an example 2D micro-LED waveguide display.

[0056] FIG. 3B illustrates an example waveguide configuration for the 2D micro-LED waveguide display.

[0057] FIG. 4A illustrates an example process for hiding dead pixels using Floyd-Steinberg dithering.

[0058] FIG. 4B illustrates an example image with corrected dead pixels using Floyd-Steinberg dithering.

[0059] FIG. 5A illustrates an example luminance mask for correcting dead pixels.

[0060] FIG. 5B illustrates an example array of scaling factors corresponding to the mask in FIG. 5A.

[0061] FIG. 6A illustrates an example image with uncorrected dead pixels.

[0062] FIG. 6B illustrates an example image with dead pixels being corrected using a luminance mask.

[0063] FIG. 6C illustrates an example image portion with corrected dead pixels.

[0064] FIG. 7 illustrates an example method for correcting dead pixels using a luminance mask.

[0065] FIG. 8A illustrates an example set of three masks for correcting a green dead pixel.

[0066] FIG. 8B illustrates example mask values for the set of three masks for correcting a green dead pixel.

[0067] FIG. 8C illustrates example mask values for a set of three masks for correcting a red dead pixel.

[0068] FIG. 8D illustrates example mask values for a set of three masks for correcting a blue dead pixel.

[0069] FIG. 9 illustrates an example process for applying a set of three masks for correcting a green dead pixel.

[0070] FIG. 10 illustrates an example modulation transfer function (MTF) of the display.

[0071] FIGS. 11A-11B illustrate example images with corrected dead pixels before and after applying the modulation transfer function (MTF) of the display.

[0072] FIG. 12 illustrates an example method for correcting dead pixels using a set of three masks for RGB color channels of the image.

[0073] FIG. 13 illustrates an example computer system.

DESCRIPTION OF EXAMPLE EMBODIMENTS

[0074] FIG. 1A illustrates an example artificial reality system 100A. In particular embodiments, the artificial reality system 100 may comprise a headset 104, a controller 106, and a computing system 108. A user 102 may wear the headset 104 that may display visual artificial reality content to the user 102. The headset 104 may include an audio device that may provide audio artificial reality content to the user 102. The headset 104 may include one or more cameras which can capture images and videos of environments. The headset 104 may include an eye tracking system to determine the vergence distance of the user 102. The headset 104 may be referred as a head-mounted display (HDM). The controller 106 may comprise a trackpad and one or more buttons. The controller 106 may receive inputs from the user 102 and relay the inputs to the computing system 108. The controller 206 may also provide haptic feedback to the user 102. The computing system 108 may be connected to the headset 104 and the controller 106 through cables or wireless connections. The computing system 108 may control the headset 104 and the controller 106 to provide the artificial reality content to and receive inputs from the user 102. The computing system 108 may be a standalone host computer system, an on-board computer system integrated with the headset 104, a mobile device, or any other hardware platform capable of providing artificial reality content to and receiving inputs from the user 102.

[0075] FIG. 1B illustrates an example augmented reality system 100B. The augmented reality system 100B may include a head-mounted display (HMD) 110 (e.g., glasses) comprising a frame 112, one or more displays 114, and a computing system 120. The displays 114 may be transparent or translucent allowing a user wearing the HMD 110 to look through the displays 114 to see the real world and displaying visual artificial reality content to the user at the same time. The HMD 110 may include an audio device that may provide audio artificial reality content to users. The HMD 110 may include one or more cameras which can capture images and videos of environments. The HMD 110 may include an eye tracking system to track the vergence movement of the user wearing the HMD 110. The augmented reality system 100B may further include a controller comprising a trackpad and one or more buttons. The controller may receive inputs from users and relay the inputs to the computing system 120. The controller may also provide haptic feedback to users. The computing system 120 may be connected to the HMD 110 and the controller through cables or wireless connections. The computing system 120 may control the HMD 110 and the controller to provide the augmented reality content to and receive inputs from users. The computing system 120 may be a standalone host computer system, an on-board computer system integrated with the HMD 110, a mobile device, or any other hardware platform capable of providing artificial reality content to and receiving inputs from users.

[0076] FIG. 1C illustrates an example architecture 100C of a display engine 130. In particular embodiments, the processes and methods as described in this disclosure may be embodied or implemented within a display engine 130 (e.g., in the display block 135). The display engine 130 may include, for example, but is not limited to, a texture memory 132, a transform block 133, a pixel block 134, a display block 135, input data bus 131, output data bus 142, etc. In particular embodiments, the display engine 130 may include one or more graphic pipelines for generating images to be rendered on the display. For example, the display engine may use the graphic pipeline(s) to generate a series of subframe images based on a mainframe image and a viewpoint or view angle of the user as measured by one or more eye tracking sensors. The mainframe image may be generated or/and loaded in to the system at a mainframe rate of 30-90 Hz and the subframe rate may be generated at a subframe rate of 1-2 kHz. In particular embodiments, the display engine 130 may include two graphic pipelines for the user’s left and right eyes. One of the graphic pipelines may include or may be implemented on the texture memory 132, the transform block 133, the pixel block 134, the display block 135, etc. The display engine 130 may include another set of transform block, pixel block, and display block for the other graphic pipeline. The graphic pipeline(s) may be controlled by a controller or control block (not shown) of the display engine 130. In particular embodiments, the texture memory 132 may be included within the control block or may be a memory unit external to the control block but local to the display engine 130. One or more of the components of the display engine 130 may be configured to communicate via a high-speed bus, shared memory, or any other suitable methods. This communication may include transmission of data as well as control signals, interrupts or/and other instructions. For example, the texture memory 132 may be configured to receive image data through the input data bus 211. As another example, the display block 135 may send the pixel values to the display system 140 through the output data bus 142. In particular embodiments, the display system 140 may include three color channels (e.g., 114A, 114B, 114C) with respective display driver ICs (DDIs) of 142A, 142B, and 143B. In particular embodiments, the display system 140 may include, for example, but is not limited to, light-emitting diode (LED) displays, organic light-emitting diode (OLED) displays, active matrix organic light-emitting diode (AMLED) displays, liquid crystal display (LCD), micro light-emitting diode (.mu.LED) display, electroluminescent displays (ELDs), or any suitable displays.

[0077] In particular embodiments, the display engine 130 may include a controller block (not shown). The control block may receive data and control packages such as position data and surface information from controllers external to the display engine 130 though one or more data buses. For example, the control block may receive input stream data from a body wearable computing system. The input data stream may include a series of mainframe images generated at a mainframe rate of 30-90 Hz. The input stream data including the mainframe images may be converted to the required format and stored into the texture memory 132. In particular embodiments, the control block may receive input from the body wearable computing system and initialize the graphic pipelines in the display engine to prepare and finalize the image data for rendering on the display. The data and control packets may include information related to, for example, one or more surfaces including texel data, position data, and additional rendering instructions. The control block may distribute data as needed to one or more other blocks of the display engine 130. The control block may initiate the graphic pipelines for processing one or more frames to be displayed. In particular embodiments, the graphic pipelines for the two eye display systems may each include a control block or share the same control block.

[0078] In particular embodiments, the transform block 133 may determine initial visibility information for surfaces to be displayed in the artificial reality scene. In general, the transform block 133 may cast rays from pixel locations on the screen and produce filter commands (e.g., filtering based on bilinear or other types of interpolation techniques) to send to the pixel block 134. The transform block 133 may perform ray casting from the current viewpoint of the user (e.g., determined using the headset’s inertial measurement units, eye tracking sensors, and/or any suitable tracking/localization algorithms, such as simultaneous localization and mapping (SLAM)) into the artificial scene where surfaces are positioned and may produce tile/surface pairs 144 to send to the pixel block 134. In particular embodiments, the transform block 133 may include a four-stage pipeline as follows. A ray caster may issue ray bundles corresponding to arrays of one or more aligned pixels, referred to as tiles (e.g., each tile may include 16.times.16 aligned pixels). The ray bundles may be warped, before entering the artificial reality scene, according to one or more distortion meshes. The distortion meshes may be configured to correct geometric distortion effects stemming from, at least, the eye display systems the headset system. The transform block 133 may determine whether each ray bundle intersects with surfaces in the scene by comparing a bounding box of each tile to bounding boxes for the surfaces. If a ray bundle does not intersect with an object, it may be discarded. After the tile-surface intersections are detected, the corresponding tile/surface pairs may be passed to the pixel block 134.

[0079] In particular embodiments, the pixel block 134 may determine color values or grayscale values for the pixels based on the tile-surface pairs. The color values for each pixel may be sampled from the texel data of surfaces received and stored in texture memory 132. The pixel block 134 may receive tile-surface pairs from the transform block 133 and may schedule bilinear filtering using one or more filer blocks. For each tile-surface pair, the pixel block 134 may sample color information for the pixels within the tile using color values corresponding to where the projected tile intersects the surface. The pixel block 134 may determine pixel values based on the retrieved texels (e.g., using bilinear interpolation). In particular embodiments, the pixel block 134 may process the red, green, and blue color components separately for each pixel. In particular embodiments, the display may include two pixel blocks for the two eye display systems. The two pixel blocks of the two eye display systems may work independently and in parallel with each other. The pixel block 134 may then output its color determinations (e.g., pixels 138) to the display block 135. In particular embodiments, the pixel block 134 may composite two or more surfaces into one surface to when the two or more surfaces have overlapping areas. A composed surface may need less computational resources (e.g., computational units, memory, power, etc.) for the resampling process.

[0080] In particular embodiments, the display block 135 may receive pixel color values from the pixel block 134, covert the format of the data to be more suitable for the scanline output of the display, apply one or more brightness corrections to the pixel color values, and prepare the pixel color values for output to the display. In particular embodiments, the display block 135 may each include a row buffer and may process and store the pixel data received from the pixel block 134. The pixel data may be organized in quads (e.g., 2.times.2 pixels per quad) and tiles (e.g., 16.times.16 pixels per tile). The display block 135 may convert tile-order pixel color values generated by the pixel block 134 into scanline or row-order data, which may be required by the physical displays. The brightness corrections may include any required brightness correction, gamma mapping, and dithering. The display block 135 may output the corrected pixel color values directly to the driver of the physical display (e.g., pupil display) or may output the pixel values to a block external to the display engine 130 in a variety of formats. For example, the eye display systems of the headset system may include additional hardware or software to further customize backend color processing, to support a wider interface to the display, or to optimize display speed or fidelity.

[0081] In particular embodiments, the dithering methods and processes (e.g., spatial dithering method, temporal dithering methods, and spatio-temporal methods) as described in this disclosure may be embodied or implemented in the display block 135 of the display engine 130. In particular embodiments, the display block 135 may include a model-based dithering algorithm or a dithering model for each color channel and send the dithered results of the respective color channels to the respective display driver ICs (DDIs) (e.g., 142A, 142B, 142C) of display system 140. In particular embodiments, before sending the pixel values to the respective display driver ICs (e.g., 142A, 142B, 142C), the display block 135 may further include one or more algorithms for correcting, for example, pixel non-uniformity, LED non-ideality, waveguide non-uniformity, display defects (e.g., dead pixels), etc.

[0082] In particular embodiments, graphics applications (e.g., games, maps, content-providing apps, etc.) may build a scene graph, which is used together with a given view position and point in time to generate primitives to render on a GPU or display engine. The scene graph may define the logical and/or spatial relationship between objects in the scene. In particular embodiments, the display engine 130 may also generate and store a scene graph that is a simplified form of the full application scene graph. The simplified scene graph may be used to specify the logical and/or spatial relationships between surfaces (e.g., the primitives rendered by the display engine 130, such as quadrilaterals or contours, defined in 3D space, that have corresponding textures generated based on the mainframe rendered by the application). Storing a scene graph allows the display engine 130 to render the scene to multiple display frames and to adjust each element in the scene graph for the current viewpoint (e.g., head position), the current object positions (e.g., they could be moving relative to each other) and other factors that change per display frame. In addition, based on the scene graph, the display engine 130 may also adjust for the geometric and color distortion introduced by the display subsystem and then composite the objects together to generate a frame. Storing a scene graph allows the display engine 130 to approximate the result of doing a full render at the desired high frame rate, while actually running the GPU or display engine 130 at a significantly lower rate.

[0083] FIG. 1D illustrates an example graphic pipeline 100D of the display engine 130 for generating display image data. In particular embodiments, the graphic pipeline 100D may include a visibility step 152, where the display engine 130 may determine the visibility of one or more surfaces received from the body wearable computing system. The visibility step 152 may be performed by the transform block (e.g., 2133 in FIG. 1C) of the display engine 130. The display engine 130 may receive (e.g., by a control block or a controller) input data 151 from the body-wearable computing system. The input data 151 may include one or more surfaces, texel data, position data, RGB data, and rendering instructions from the body wearable computing system. The input data 151 may include mainframe images with 30-90 frames per second (FPS). The main frame image may have color depth of, for example, 24 bits per pixel. The display engine 130 may process and save the received input data 151 in the texel memory 132. The received data may be passed to the transform block 133 which may determine the visibility information for surfaces to be displayed. The transform block 133 may cast rays for pixel locations on the screen and produce filter commands (e.g., filtering based on bilinear or other types of interpolation techniques) to send to the pixel block 134. The transform block 133 may perform ray casting from the current viewpoint of the user (e.g., determined using the headset’s inertial measurement units, eye trackers, and/or any suitable tracking/localization algorithms, such as simultaneous localization and mapping (SLAM)) into the artificial scene where surfaces are positioned and produce surface-tile pairs to send to the pixel block 134.

[0084] In particular embodiments, the graphic pipeline 100D may include a resampling step 153, where the display engine 130 may determine the color values from the tile-surfaces pairs to produce pixel color values. The resampling step 153 may be performed by the pixel block 134 in FIG. 1C) of the display engine 130. The pixel block 134 may receive tile-surface pairs from the transform block 133 and may schedule bilinear filtering. For each tile-surface pair, the pixel block 134 may sample color information for the pixels within the tile using color values corresponding to where the projected tile intersects the surface. The pixel block 134 may determine pixel values based on the retrieved texels (e.g., using bilinear interpolation) and output the determined pixel values to the respective display block 135.

[0085] In particular embodiments, the graphic pipeline 100D may include a bend step 154, a correction and dithering step 155, a serialization step 156, etc. In particular embodiments, the bend step, correction and dithering step, and serialization steps of 154, 155, and 156 may be performed by the display block (e.g., 135 in FIG. 1C) of the display engine 130. The display engine 130 may blend the display content for display content rendering, apply one or more brightness corrections to the pixel color values, perform one or more dithering algorithms for dithering the quantization errors both spatially and temporally, serialize the pixel values for scanline output for the physical display, and generate the display data 159 suitable for the display system 140. The display engine 130 may send the display data 159 to the display system 140. In particular embodiments, the display system 140 may include three display driver ICs (e.g., 142A, 142B, 142C) for the pixels of the three color channels of RGB (e.g., 144A, 144B, 144C).

[0086] FIG. 2A illustrates an example scanning waveguide display 200A. In particular embodiments, the head-mounted display (HMD) of the AR/VR system may include a near eye display (NED) which may be a scanning waveguide display 200A. The scanning waveguide display 200A may include a light source assembly 210, an output waveguide 204, a controller 216, etc. The scanning waveguide display 200A may provide images for both eyes or for a single eye. For purposes of illustration, FIG. 3A shows the scanning waveguide display 200A associated with a single eye 202. Another scanning waveguide display (not shown) may provide image light to the other eye of the user and the two scanning waveguide displays may share one or more components or may be separated. The light source assembly 210 may include a light source 212 and an optics system 214. The light source 212 may include an optical component that could generate image light using an array of light emitters. The light source 212 may generate image light including, for example, but not limited to, red image light, blue image light, green image light, infra-red image light, etc. The optics system 214 may perform a number of optical processes or operations on the image light generated by the light source 212. The optical processes or operations performed by the optics systems 214 may include, for example, but are not limited to, light focusing, light combining, light conditioning, scanning, etc.

[0087] In particular embodiments, the optics system 214 may include a light combining assembly, a light conditioning assembly, a scanning mirror assembly, etc. The light source assembly 210 may generate and output an image light 219 to a coupling element 218 of the output waveguide 204. The output waveguide 204 may be an optical waveguide that could output image light to the user eye 202. The output waveguide 204 may receive the image light 219 at one or more coupling elements 218 and guide the received image light to one or more decoupling elements 206. The coupling element 218 may be, for example, but is not limited to, a diffraction grating, a holographic grating, any other suitable elements that can couple the image light 219 into the output waveguide 204, or a combination thereof. As an example and not by way of limitation, if the coupling element 350 is a diffraction grating, the pitch of the diffraction grating may be chosen to allow the total internal reflection to occur and the image light 219 to propagate internally toward the decoupling element 206. The pitch of the diffraction grating may be in the range of 300 nm to 600 nm. The decoupling element 206 may decouple the total internally reflected image light from the output waveguide 204. The decoupling element 206 may be, for example, but is not limited to, a diffraction grating, a holographic grating, any other suitable element that can decouple image light out of the output waveguide 204, or a combination thereof. As an example and not by way of limitation, if the decoupling element 206 is a diffraction grating, the pitch of the diffraction grating may be chosen to cause incident image light to exit the output waveguide 204. The orientation and position of the image light exiting from the output waveguide 204 may be controlled by changing the orientation and position of the image light 219 entering the coupling element 218. The pitch of the diffraction grating may be in the range of 300 nm to 600 nm.

[0088] In particular embodiments, the output waveguide 204 may be composed of one or more materials that can facilitate total internal reflection of the image light 219. The output waveguide 204 may be composed of one or more materials including, for example, but not limited to, silicon, plastic, glass, polymers, or some combination thereof. The output waveguide 204 may have a relatively small form factor. As an example and not by way of limitation, the output waveguide 204 may be approximately 50 mm wide along X-dimension, 30 mm long along Y-dimension and 0.5-1 mm thick along Z-dimension. The controller 216 may control the scanning operations of the light source assembly 210. The controller 216 may determine scanning instructions for the light source assembly 210 based at least on the one or more display instructions for rendering one or more images. The display instructions may include an image file (e.g., bitmap) and may be received from, for example, a console or computer of the AR/VR system. Scanning instructions may be used by the light source assembly 210 to generate image light 219. The scanning instructions may include, for example, but are not limited to, an image light source type (e.g., monochromatic source, polychromatic source), a scanning rate, a scanning apparatus orientation, one or more illumination parameters, or some combination thereof. The controller 216 may include a combination of hardware, software, firmware, or any suitable components supporting the functionality of the controller 216.

[0089] FIG. 2B illustrates an example scanning operation of a scanning waveguide display 200B. The light source 220 may include an array of light emitters 222 (as represented by the dots in inset) with multiple rows and columns. The light 223 emitted by the light source 220 may include a set of collimated beams of light emitted by each column of light emitters 222. Before reaching the mirror 224, the light 223 may be conditioned by different optical devices such as the conditioning assembly (not shown). The mirror 224 may reflect and project the light 223 from the light source 220 to the image field 227 by rotating about an axis 225 during scanning operations. The mirror 224 may be a microelectromechanical system (MEMS) mirror or any other suitable mirror. As the mirror 224 rotates about the axis 225, the light 223 may be projected to a different part of the image field 227, as illustrated by the reflected part of the light 226A in solid lines and the reflected part of the light 226B in dash lines.

[0090] In particular embodiments, the image field 227 may receive the light 226A-B as the mirror 224 rotates about the axis 225 to project the light 226A-B in different directions. For example, the image field 227 may correspond to a portion of the coupling element 218 or a portion of the decoupling element 206 in FIG. 2A. In particular embodiments, the image field 227 may include a surface of the coupling element 206. The image formed on the image field 227 may be magnified as light travels through the output waveguide 220. In particular embodiments, the image field 227 may not include an actual physical structure but include an area to which the image light is projected to form the images. The image field 227 may also be referred to as a scan field. When the light 223 is projected to an area of the image field 227, the area of the image field 227 may be illuminated by the light 223. The image field 227 may include a matrix of pixel locations 229 (represented by the blocks in inset 228) with multiple rows and columns. The pixel location 229 may be spatially defined in the area of the image field 227 with a pixel location corresponding to a single pixel. In particular embodiments, the pixel locations 229 (or the pixels) in the image field 227 may not include individual physical pixel elements. Instead, the pixel locations 229 may be spatial areas that are defined within the image field 227 and divide the image field 227 into pixels. The sizes and locations of the pixel locations 229 may depend on the projection of the light 223 from the light source 220. For example, at a given rotation angle of the mirror 224, light beams emitted from the light source 220 may fall on an area of the image field 227. As such, the sizes and locations of pixel locations 229 of the image field 227 may be defined based on the location of each projected light beam. In particular embodiments, a pixel location 229 may be subdivided spatially into subpixels (not shown). For example, a pixel location 229 may include a red subpixel, a green subpixel, and a blue subpixel. The red, green and blue subpixels may correspond to respective locations at which one or more red, green and blue light beams are projected. In this case, the color of a pixel may be based on the temporal and/or spatial average of the pixel’s subpixels.

[0091] In particular embodiments, the light emitters 222 may illuminate a portion of the image field 227 (e.g., a particular subset of multiple pixel locations 229 on the image field 227) with a particular rotation angle of the mirror 224. In particular embodiment, the light emitters 222 may be arranged and spaced such that a light beam from each of the light emitters 222 is projected on a corresponding pixel location 229. In particular embodiments, the light emitters 222 may include a number of light-emitting elements (e.g., micro-LEDs) to allow the light beams from a subset of the light emitters 222 to be projected to a same pixel location 229. In other words, a subset of multiple light emitters 222 may collectively illuminate a single pixel location 229 at a time. As an example and not by way of limitation, a group of light emitter including eight light-emitting elements may be arranged in a line to illuminate a single pixel location 229 with the mirror 224 at a given orientation angle.

[0092] In particular embodiments, the number of rows and columns of light emitters 222 of the light source 220 may or may not be the same as the number of rows and columns of the pixel locations 229 in the image field 227. In particular embodiments, the number of light emitters 222 in a row may be equal to the number of pixel locations 229 in a row of the image field 227 while the light emitters 222 may have fewer columns than the number of pixel locations 229 of the image field 227. In particular embodiments, the light source 220 may have the same number of columns of light emitters 222 as the number of columns of pixel locations 229 in the image field 227 but fewer rows. As an example and not by way of limitation, the light source 220 may have about 1280 columns of light emitters 222 which may be the same as the number of columns of pixel locations 229 of the image field 227, but only a handful rows of light emitters 222. The light source 220 may have a first length L1 measured from the first row to the last row of light emitters 222. The image field 530 may have a second length L2, measured from the first row (e.g., Row 1) to the last row (e.g., Row P) of the image field 227. The L2 may be greater than L1 (e.g., L2 is 50 to 10,000 times greater than L1).

[0093] In particular embodiments, the number of rows of pixel locations 229 may be larger than the number of rows of light emitters 222. The display device 200B may use the mirror 224 to project the light 223 to different rows of pixels at different time. As the mirror 520 rotates and the light 223 scans through the image field 227, an image may be formed on the image field 227. In some embodiments, the light source 220 may also has a smaller number of columns than the image field 227. The mirror 224 may rotate in two dimensions to fill the image field 227 with light, for example, using a raster-type scanning process to scan down the rows then moving to new columns in the image field 227. A complete cycle of rotation of the mirror 224 may be referred to as a scanning period which may be a predetermined cycle time during which the entire image field 227 is completely scanned. The scanning of the image field 227 may be determined and controlled by the mirror 224 with the light generation of the display device 200B being synchronized with the rotation of the mirror 224. As an example and not by way of limitation, the mirror 224 may start at an initial position projecting light to Row 1 of the image field 227, and rotate to the last position that projects light to Row P of the image field 227, and then rotate back to the initial position during one scanning period. An image (e.g., a frame) may be formed on the image field 227 per scanning period. The frame rate of the display device 200B may correspond to the number of scanning periods in a second. As the mirror 224 rotates, the light may scan through the image field to form images. The actual color value and light intensity or brightness of a given pixel location 229 may be a temporal sum of the color various light beams illuminating the pixel location during the scanning period. After completing a scanning period, the mirror 224 may revert back to the initial position to project light to the first few rows of the image field 227 with a new set of driving signals being fed to the light emitters 222. The same process may be repeated as the mirror 224 rotates in cycles to allow different frames of images to be formed in the scanning field 227.

[0094] FIG. 3A illustrates an example 2D micro-LED waveguide display 300A. In particular embodiments, the display 300A may include an elongate waveguide configuration 302 that may be wide or long enough to project images to both eyes of a user. The waveguide configuration 302 may include a decoupling area 304 covering both eyes of the user. In order to provide images to both eyes of the user through the waveguide configuration 302, multiple coupling areas 306A-B may be provided in a top surface of the waveguide configuration 302. The coupling areas 306A and 306B may include multiple coupling elements to receive image light from light emitter array sets 308A and 308B, respectively. Each of the emitter array sets 308A-B may include a number of monochromatic emitter arrays including, for example, but not limited to, a red emitter array, a green emitter array, and a blue emitter array. In particular embodiments, the emitter array sets 308A-B may further include a white emitter array or an emitter array emitting other colors or any combination of any multiple colors. In particular embodiments, the waveguide configuration 302 may have the emitter array sets 308A and 308B covering approximately identical portions of the decoupling area 304 as divided by the divider line 309A. In particular embodiments, the emitter array sets 308A and 308B may provide images to the waveguide of the waveguide configuration 302 asymmetrically as divided by the divider line 309B. For example, the emitter array set 308A may provide image to more than half of the decoupling area 304. In particular embodiments, the emitter array sets 308A and 308B may be arranged at opposite sides (e.g., 180.degree. apart) of the waveguide configuration 302 as shown in FIG. 3B. In other embodiments, the emitter array sets 308A and 308B may be arranged at any suitable angles. The waveguide configuration 302 may be planar or may have a curved cross-sectional shape to better fit to the face/head of a user.

[0095] FIG. 3B illustrates an example waveguide configuration 300B for the 2D micro-LED waveguide display. In particular embodiments, the waveguide configuration 300B may include a projector device 350 coupled to a waveguide 342. The projector device 320 may include a number of light emitters 352 (e.g., monochromatic emitters) secured to a support structure 354 (e.g., a printed circuit board or other suitable support structure). The waveguide 342 may be separated from the projector device 350 by an air gap having a distance of D1 (e.g., approximately 50 .mu.m to approximately 500 .mu.m). The monochromatic images projected by the projector device 350 may pass through the air gap toward the waveguide 342. The waveguide 342 may be formed from a glass or plastic material. The waveguide 342 may include a coupling area 330 including a number of coupling elements 334A-C for receiving the emitted light from the projector device 350. The waveguide 342 may include a decoupling area with a number of decoupling elements 336A on the top surface 318A and a number of decoupling elements 336B on the bottom surface 318B. The area within the waveguide 342 in between the decoupling elements 336A and 336B may be referred as a propagation area 310, in which image light received from the projector device 350 and coupled into the waveguide 342 by the coupling element 334 may propagate laterally within the waveguide 342.

[0096] The coupling area 330 may include coupling elements (e.g., 334A, 334B, 334C) configured and dimensioned to couple light of predetermined wavelengths (e.g., red, green, blue). When a white light emitter array is included in the projector device 350, the portion of the white light that falls in the predetermined wavelengths may be coupled by each of the coupling elements 334A-C. In particular embodiments, the coupling elements 334A-B may be gratings (e.g., Bragg gratings) dimensioned to couple a predetermined wavelength of light. In particular embodiments, the gratings of each coupling element may exhibit a separation distance between gratings associated with the predetermined wavelength of light and each coupling element may have different grating separation distances. Accordingly, each coupling element (e.g., 334A-C) may couple a limited portion of the white light from the white light emitter array of the projector device 350 if white light emitter array is included in the projector device 350. In particular embodiments, each coupling element (e.g., 334A-C) may have the same grating separation distance. In particular embodiments, the coupling elements 334A-C may be or include a multiplexed coupler.

[0097] As illustrated in FIG. 3B, a red image 320A, a blue image 320B, and a green image 320C may be coupled by the coupling elements 334A, 334B, 334C, respectively, into the propagation area 310 and may begin to traverse laterally within the waveguide 342. A portion of the light may be projected out of the waveguide 342 after the light contacts the decoupling element 336A for one-dimensional pupil replication, and after the light contacts both the decoupling elements 336A and 336B for two-dimensional pupil replication. In two-dimensional pupil replication, the light may be projected out of the waveguide 342 at locations where the pattern of the decoupling element 336A intersects the pattern of the decoupling element 336B. The portion of the light that is not projected out of the waveguide 342 by the decoupling element 336A may be reflected off the decoupling element 336B. The decoupling element 336B may reflect all incident light back toward the decoupling element 336A. Accordingly, the waveguide 342 may combine the red image 320A, the blue image 320B, and the green image 320C into a polychromatic image instance which may be referred as a pupil replication 322. The polychromatic pupil replication 322 may be projected to the user’s eyes which may interpret the pupil replication 322 as a full color image (e.g., an image including colors addition to red, green, and blue). The waveguide 342 may produce tens or hundreds of pupil replication 322 or may produce a single replication 322.

[0098] In particular embodiments, the AR/VR system may use scanning waveguide displays or 2D micro-LED displays for displaying AR/VR content to users. In order to miniaturize the AR/VR system, the display system may need to miniaturize the space for pixel circuits and may have limited number of available bits for the display. The number of available bits in a display may limit the display’s color depth or gray scale level, and consequently limit the quality of the displayed images. Furthermore, the waveguide displays used for AR/VR systems may have nonuniformity problem cross all display pixels. The compensation operations for pixel nonuniformity may result in loss on image grayscale and further reduce the quality of the displayed images. For example, a waveguide display with 8-bit pixels (i.e., 256 gray level) may equivalently have 6-bit pixels (i.e., 64 gray level) after compensation of the nonuniformity (e.g., 8:1 waveguide nonuniformity, 0.1% dead micro-LED pixel, and 20% micro-LED intensity nonuniformity).

[0099] To improve the displayed image quality, displays with limited color depth or gray scale level may use spatio-temporal dithering to spread quantization errors to neighboring pixels and generate the illusion of increased color depth or gray scale level. To further increase the color depth or gray scale level, displays may generate a series of temporal subframe images with fewer gray level bits to give the illusion of a target image which has more gray level bits. Each subframe image may be dithered using spatio-temporal dithering techniques within that subframe image. The average of the series of subframe image may correspond to the image as perceived by the viewer. For example, for display an image with 8-bit pixels (i.e., 256 gray level), the system may use four subframe images each having 6-bit pixels (i.e., 64 gray level) to represent the 8-bit target image. As another example, an image with 8-bit pixels (i.e., 256 gray level) may be represented by 16 subframe images each having 4-bit pixels (i.e., 16 gray level). This would allow the display system to render images of more gray level (e.g., 8-bit pixels) with pixel circuits and supporting hardware for fewer gray levels (e.g., 6-bit pixels or 4-bit pixels), and therefore reduce the space and size of the display system.

[0100] Display panels (e.g., .mu.LED panels) used by AR/VR systems may have dead pixels due to limitations of the state of art in manufacturing. The dead pixels may negatively impact display quality and user experience of the AR/VR systems. Particular embodiments of the system may hide dead pixels of display panels by modifying the image to be output by the display. For example, the system may use a mask including an array of scaling factors to alter the pixel values of the image in a pixel region containing the dead pixel position. The image after being modified and output by the display may cause the dead pixel of the display to be invisible or have reduced visibility than the image before the modification, and therefore provide better display quality and improved user experience.

[0101] In particular embodiments, the RGB display panels of an AR/VR system may operate independently and not share color data between the three display panels. In particular embodiments, for correcting or hiding the dead pixels, the system may use luminance correction methods to correct the luminance of the pixel values of each color channel without using the color information between different color channels. The dead pixels may be independently associated with any color channel of the display. In particular embodiments, the system may use a luminance mask to modify the images before outputting the images on the display. The modified images may have their pixels values being altered (e.g., brightened or dimmed) in the pixel region containing the dead pixel position. The images, after being modified and output by the display may cause the dead pixels of the display to have a lower visibility than the images without the modification. In particular embodiments, the system may modify the images by using a dithering algorithm (e.g., a spatial dithering algorithm such as Floyd-Steinberg dithering) or a luminance mask to alter the pixel values in a pixel region containing the dead pixel position, as will be described below.

[0102] FIG. 4A illustrates an example process 400A for hiding dead pixels using Floyd-Steinberg dithering. As an example and not by way of limitation, the system may use a scalar dithering algorithm (e.g., a Floyd-Steinberg dithering algorithm) to spread the pixel value at the dead pixel position to the neighboring pixels (e.g., the next pixel on the right, pixels below the dead pixel position) to reduce the visibility of the dead pixels. As shown in FIG. 4A, the Floyd-Steinberg dithering algorithm may propagate a dithering value (e.g., a pixel value, a quantization error) associated with a current pixel 401 to its neighboring pixels using a pre-determined set of dithering coefficients, as shown in FIG. 4A. The system may scan the image from left to right and top to bottom to process (e.g., quantize) each pixel value one by one. For a current pixel 401, the system may determine a dithering value, for example, a quantization error, to be spread onto neighboring pixels. The Floyd-Steinberg dithering algorithm may push 7/16 of the dithering value to the pixel 402 which is next to the current pixel 401 on the right and in the same row, push 3/16 of the dithering value to the pixel 403 which is in the next row and a former column to the current pixel 401, push 5/16 of the dithering value to the pixel 404 which is in the next row and the same column to the current pixel 401, and push 1/16 of the dithering value to the pixel 405 which is in the next row and next column to the current pixel 405.

[0103] FIG. 4B illustrates an example image 400B with corrected dead pixels (e.g., 411A, 411B, 411C, 411D) using Floyd-Steinberg dithering. In particular embodiments, for correcting a dead pixel, the system may access or receive a dead pixel position corresponding to the dead pixel and a corresponding target pixel value in the image to be displayed. Then, the system may set the dithered pixel value (e.g., the actual pixel value to be displayed) as zero for the pixel at the dead pixel position (since the dead pixel may emit no light). The Floyd-Steinberg dithering algorithm may determine a dithering value (e.g., based on the difference of the target pixel value and the dithered pixel value) equal to the target pixel value. The algorithm may dither a portion of the target pixel value to each of the four neighboring pixels as shown in FIG. 4A. As a result, the four neighboring pixels of the pixel at the dead pixel position may be brightened to maintain the correct average brightness to compensate for the dead pixel defect. The average brightness of the modified image in the region containing the dead pixel position may be substantially the same (e.g., within a threshold value) to the average brightness of the corresponding region of the image before the modification. As shown in FIG. 4B, the corrected dead pixels (e.g., 411A, 411B, 411C, 411D) may have a reduced visibility in the modified image as output by the display with dead pixels.

[0104] In particular embodiments, the system may include one or more dithering algorithms for propagating quantization errors spatially or/and temporally. For the systems that already include a Floyd-Steinberg dithering algorithm, the system may use the same dithering algorithm for correcting dead pixels without implementing separate dithering algorithms. The Floyd-Steinberg dithering algorithm may use a row buffer to store one or more dithering values and may effectively propagate the dithering values to the forward pixels along the scanning order. In particular embodiments, the system that uses the dithering algorithm for correcting dead pixels may correct any number of dead pixels at any locations of the display. For example, the system may use the dithering algorithm to correct a number of dead pixels at a number of arbitrary locations of the display. It is notable that the Floyd-Steinberg dithering algorithm is for example purpose only and the dithering algorithm is not limited thereto. For example, the dithering algorithm may be any suitable dithering algorithms with any suitable dithering coefficients that can propagate dithering values to surrounding or neighboring pixels.

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