WO2024000181A1

WO2024000181A1 - Solid-state imaging device having tunable conversion gain, driving method, and electronic device

Info

Publication number: WO2024000181A1
Application number: PCT/CN2022/101994
Authority: WO
Inventors: Teppei Isobe
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2022-06-28
Filing date: 2022-06-28
Publication date: 2024-01-04

Abstract

A method for driving a display, the method comprising: receiving an input image; determining a first shift amount of a first DC balance A or a second shift amount of a second DC balance B based on the input image; outputting a first wave pulse W1, wherein the first wave pulse W1 is based on the first shift amount of the first DC balance A; outputting a second wave pulse W2, wherein the second wave pulse W2 is based on the second shift amount the second DC balance B, and wherein the first wave pulse W1 is different from the second wave pulse W2 when the first DC balance A is different from the second DC balance B; displaying the input image corrected by the first wave pulse W1 or the second wave pulse W2 on the display.

Description

SOLID-STATE IMAGING DEVICE HAVING TUNABLE CONVERSION GAIN, DRIVING METHOD, AND ELECTRONIC DEVICE

TECHNICAL FIELD

This application relates to the field of Electric-Paper-Display (EPD) . More particularly, the invention relates to a ghost reduction and a DC balance compensation in an EPD, methods thereof and a related electronic device.

BACKGROUND

In EPD, an activation period is needed before image refreshing to show a clear image, for example, without a previous image called a “ghost” such as shown in FIG. 1D. In this activation period, the display needs to switch between a white image and a black image many times. In a case where the display is showing a moving image, flickers always occur in the display due to such switching during the activation period. Furthermore, a user has to wait for a long time during the activation period in addition to a refreshing period. Because of these problems, the activation is not used when the display is showing a moving image.

Furthermore, when one or more pixels on a display continued to show the same still image or the same color in a moving image, a brightness level of those pixels will be shifted. For example, when one pixel on a display continued to display a white color, a brightness level of the pixel could be shifted to a white level. When the pixel on the display shows a different color other than white after the brightness level is shifted, the different color appears whiter than it should be. To make matters worse, this could result in burn-in on the display. This is also true for a black color.

To resolve these problems and show a clear image on a display, the prior art proposed some solutions as shown in FIG. 1A to 1C. As shown in FIG. 1A, one solution is an automatic initialization (activation) which applies a sequence of pulses repeatedly to pixels on a display. A timing to perform the automatic initialization is set by a user or set by default for example to when a display screen is switched to a predetermined image such as a menu screen, or the like. This solution mitigates a shift in a brightness level to prevent a burn-in on a display, but the pulses repeatedly applied produce flickers, a refresh rate is decreased, and this solution does not remove a ghost. This solution cannot be applied to a moving image.

Another solution proposed in JP2015176133A is shown in FIG. 1B, in which flushing pulses alternating between two voltage levels are applied to pixels on a display before applying addressing pulses. Patterns of pulses depend on transition types, such as white to white (W -> W) , black to white (B -> W) , black to black (B -> B) , or white to black (W -> B) . This solution mitigates a shift in a brightness level and DC balance and a ghost, but the pulses alternating between two voltage levels produce flickers, and a refresh rate is decreased.

Still another solution proposed in US20140092070A is shown in FIG. 1C, in which a pulse Pdrift is applied once in 6 minutes (plot 1) or 1 minute (plot 2) to pixels on a display to compensate a drift, that is, a shift of a brightness level. This solution mitigates flickers, increases a refresh rate, and mitigates a ghost, but a DC balance is shifted because the pulse Pdrift with the same voltage level is repeatedly applied and therefore, burn-in on the display could result.

Accordingly, there is a need to provide a new solution that prevents both of flickers and ghosts in displaying a moving image while a refresh rate is being maintained or increased.

SUMMARY

According to a first aspect, an embodiment of the present invention provides a method for driving a display, the method comprising:

receiving an input image;

determining a first shift amount of a first DC balance A or a second shift amount of a second DC balance B based on the input image;

outputting a first wave pulse W1, wherein the first wave pulse W1 is based on the first shift amount of the first DC balance A,

outputting a second wave pulse W2, wherein the second wave pulse W2 is based on the second shift amount the second DC balance B, and wherein the first wave pulse W1 is different from the second wave pulse W2 when the first DC balance A is different from the second DC balance B;

displaying the input image corrected by the first wave pulse W1 or the second wave pulse W2 on the display.

In a possible implementation, the first shift amount of the first DC balance A and the second shift amount of the second DC balance B is based on the content of the input image.

In a possible implementation, the first wave pulse W1 and/or the second wave pulse W2 is based on the source data, wherein the source data is generated from a waveform control unit.

In a possible implementation, the source data is based on at least one of a parameter L, a parameter M, a parameter N, wherein the parameter L is contributed from a ghost compensation unit, the parameter M is contributed from a DC balance adjustment unit, the parameter N is contributed from a timing control unit.

In a possible implementation, the parameter M is based on inputs from at least one of a max detection unit, the DC balance estimation unit, previous image and next image.

In a possible implementation, the parameter L is based on inputs from at least one of max detection unit, a previous image and a next image.

In a possible implementation, the parameter N is based on inputs from at least one of the previous image and the next image.

In a possible implementation, the input from the max detection unit is a maximum value among inputs from the DC balance estimation unit.

In a possible implementation, the input from the DC balance estimation unit is a shift amount of brightness caused by the input image.

In a possible implementation, the input from the previous image is a previous one of two images that are continuous in time obtained from the input image and stored in a frame memory.

In a possible implementation, the input from the next image is a later one of two images that are continuous in time obtained from the input image and stored in a frame memory.

In a possible implementation,

the source data is based on the parameter L when an image to be displayed by the display changes between a moving image and a static image according to the input image;

the source data is based on the parameter M when the display is initialized, when requested by a user, or both of those;

the source data is based on the parameter N based on whether colors displayed are the same between two images that are continuous in time obtained from the input image while the moving image is being displayed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates technologies for improving image representation on Electronic Paper Displays in prior arts.

FIG. 2 illustrates examples of a waveform for driving a pixel to eliminate flickers according to an embodiment of the present invention.

FIG. 3A illustrates an example waveform for driving a pixel to compensate for a shift of a brightness level according to an embodiment of the present invention.

FIG. 3B illustrates an effect achieved by the example waveform shown in FIG. 3A.

FIG. 4 illustrates an example waveform for driving a pixel to compensate for a shortage of a refresh period according to an embodiment of the present invention.

FIG. 5 illustrates how to resolve a shortage of a refresh period according to an embodiment of the present invention such as shown in FIG. 4.

FIG. 6 illustrates effects in brightness of images on a display according to an embodiment of the present invention such as shown in FIG. 4.

FIG. 7 illustrates an example waveform for driving a pixel to compensate both for a shift of a brightness level and for a shortage of a refresh period according to an embodiment of the present invention.

FIG. 8A illustrates adjustment of shifts of brightness levels among pixels according to an embodiment of the present invention.

FIG. 8B illustrates example waveforms for driving a pixel to adjust the shifts of brightness levels according to an embodiment of the present invention.

FIG. 9A illustrates an example original waveform.

FIG. 9B illustrates an example adjusted waveform for driving a pixel to initialize a DC balance according to an embodiment of the present invention.

FIG. 10A is a flowchart of a method for compensating a shift amount of brightness according to an embodiment of the present invention.

FIG. 10B is a flowchart of a method for compensating a shift amount of a DC balance according to an embodiment of the present invention.

FIG. 10C is another flowchart of a method for compensating a shift amount of brightness according to an embodiment of the present invention.

FIG. 10D is a flowchart of a method for compensating a ghost and adjusting a DC balance according to an embodiment of the present invention.

FIG. 11 is a schematic structural diagram of a device for compensating a ghost according to an embodiment of the present invention.

FIG. 12 illustrates a method used to evaluate an effect achieved by the present invention.

FIG. 13A illustrates comparison of ghost reduction achieved by the present invention and the prior arts when displaying a static image after a moving image.

FIG. 13B illustrates comparison of ghost reduction achieved by the present invention and the prior arts in a shot during a moving image.

DESCRIPTION OF EMBODIMENTS

The terms used in this application are merely intended to describe a particular possible implementation rather than to limit this application. The terms "a" , "said" and "the" for a singular form used in this application including the attached claims are also intended to include a case of a plural form, unless otherwise clearly stated. It should be further understood that the term "and/or" used in this specification means any or all possible combinations of one or more listed related items. It should be further understood that, the term "include" used in this specification specifies presence of the features, data, information, entities, steps, operations, devices, units, elements and/or components, without excluding presence or attachment of one or more other features, data, information, entities, steps, operations, devices, units, elements, components, and/or a combination thereof.

It should be understood that, although terms such as "first" and "second" may be used in the embodiments of this application to describe various devices or units, these devices or units should not be limited by the terms. These terms are merely used to differentiate the devices or units from each other. For example, a first device and a first unit may be referred to as a second device and a second unit respectively without departing from the scope of the embodiments of this application. Similarly, a second device and a second unit may be referred to as a first device and a first unit respectively.

It should be noted that an order of steps in this application may be freely arranged. That is, the order of steps is not limited in this application.

The following describes technical solutions in the embodiments of this application with reference to the accompanying drawings.

FIG. 2 illustrates examples of a waveform for driving a pixel to eliminate flickers according to an embodiment of the present invention. According to the embodiment, simple pulses are used in refreshing pixels as shown in FIG. 2. After the display has been used for any time period, such as several seconds, minutes, or hours, the brightness levels of some or all of the pixels on the display could shift. For example, a shift amount of the brightness level may be determined as a difference between a luminance value derived from an input image and a luminance value derived from a display image which is actually displayed on a display screen based on the input image. To mitigate such shifts of the brightness levels without flickers, the pulses shown in FIG. 2 may be applied to the pixels on the display. When a transition in a color displayed on a pixel occurs from white to black, a pulse shown on a left side in FIG. 2 is applied to the pixel. By applying the pulse which has a positive voltage VPOS to a pixel which displays a black color in the next image, the pixel can display black clearly, and thereby provide a clear image. As described later with reference to FIG. 5, a width of the pulse defining a waveform shown in FIG. 2 may be determined based on a previous input image and a next input image, especially their colors (black or white in this embodiment) .

Similarly, when a transition in a color displayed on a pixel occurs from black to white, a pulse shown on a right side in FIG. 2, is applied to the pixel. By applying the pulse which has a negative voltage VNEG to a pixel which displays a white color in the next image, the pixel can display white clearly, and thereby provide a clear image. As described later with reference to FIG. 5, a width of the pulse defining a waveform shown in FIG. 2 may be determined based on a previous input image and a next input image, especially their colors (black or white in this embodiment) .

The pulse with VPOS or the pulse with VNEG is applied to each pixel depending on what color transition to be occurred in the pixel, that is, "white to black" or "black to white" .

These pulses may be applied to each pixel when refreshing all pixels on the display, when the display finishes showing a moving image and starts showing a still image, and/or when the display switches between significantly different images, for example, a bright image and a dark image, significantly different contents such as a city, nature, a person, indoor/outdoor, sports, scenes in TV shows/animations/movies, and any other images. Alternatively, and/or additionally, these pulses may be applied to each pixel at a predetermined timing set by a user of the display or set by default.

Since activation pulses and initializing pulses are not used, the embodiment able to mitigate flickers.

FIG. 3A illustrates an example waveform for driving a pixel to compensate for a brightness (or luminance) shift. The example waveform is similar to the pulse shown in the left side of FIG. 2. FIG. 3B illustrates an effect achieved on a pixel by applying the example waveform shown in FIG. 3A. In the graph shown in FIG. 3B, the horizontal axis shows time in minutes, and the vertical axis shows luminance in nits. As seen from the graph, in the plot without compensation, that is, when pulses are not applied to compensate a brightness shift, a luminance value of a pixel increases towards a black level over time. In contrast, when pulses are applied to compensate a brightness shift according to the embodiment of the present invention, a luminance value of a pixel does not increase and remains almost zero. This means that the present invention mitigates a brightness shift without flickers.

FIG. 4 illustrates an example waveform for driving a pixel to compensate for a shortage in voltage level or a shortage in programming period in refreshing in according to an embodiment of the present invention. This embodiment resolves a problem in which an image refresh rate is faster than a response time of material used in a display. In such a case, a previous image could remain as a ghost because a voltage level of a pixel could not be completely arrived at a target luminance level within a refresh period. To help the pixel arrive at the target luminance level, the pulses shown in FIG. 4 may be applied to the pixel on a display.

Also referring to FIG. 5, FIG. 5 illustrates how to resolve a shortage in voltage level in a refresh period according to an embodiment of the present invention such as shown in FIG. 4. The graph shown in FIG. 5 shows a response profile specific to material of the display, and in which the horizontal axis shows time, and the vertical axis shows luminance level between 0.0 (black) and 1.0 (white) . The whole width of the horizontal axis corresponds to a response time (Tresponse) of a material used in a display. Tresponse is a necessary time period for the material to switch its voltage levels, one corresponding to a white level and another corresponding to a black level. Only a part of the response time corresponds to a refresh time (Trefresh) . If the Trefresh is too short for the material to change a luminance level from black to white, the transition is terminated halfway when the pixel on the display transitions between black and white. In a plot showing a transition from white to black, since the transition is terminated at the end of Trefresh, a shortage (502) of transition results in a difference between a target color and a color actually displayed on the pixel. This results in a gray level as shown in an upper part in FIG. 5. When a transition for an input image to be shown on a pixel is white -> black -> black, a display image actually displayed on the pixel becomes white -> gray -> gray. The same is applied to a transition from black to white and resultant shortage (501) .

In order to compensate for the shortage 501, the pulse with the voltage level VNEG may be applied to the pixel. In order to compensate for the shortage 502, the pulse with the voltage level VPOS may be applied to the pixel. Which pulse is applied is determined for each pixel depending on which transition occurs, and/or whether any pulse is applied or not is determined for each pixel depending on whether any transition occurs or not.

FIG. 6 illustrates effects in brightness (also referred to as "luminance" ) of images on a display according to an embodiment of the present invention such as shown in FIG. 4. White and black blocks in the top row show an input image. White and gray blocks in the second row show an image actually displayed on the display without compensation according to the embodiment of the present invention. White, gray, and black blocks in the third row show an image actually displayed on the display with compensation according to the embodiment of the present invention. Note that gray shades are indicated by hatching.

FIG. 6 further shows changes in brightness level, a plot 603, which is represented by a dashed-dotted line, corresponds to the second row of blocks which is without the compensation, and a plot 604, which is represented by a dashed double-dotted line, corresponds to the third row of blocks which is with the compensation. The plot 603 shows a change in brightness from white to gray corresponding to a gray block within a dashed box 601, and remains to be the same gray level. The plot 604 shows a change in brightness from white to gray corresponding to a gray block within a dashed box 601, and then gradually changes towards black corresponding to gray blocks within a dashed box 602 that gradually darkens. As seen from FIG. 6, the embodiment according to the present invention achieves compensation for a shift in brightness (or luminance) and thereby prevents a ghost.

FIG. 7 illustrates an example waveform for driving a pixel to compensate both for a brightness shift and for a shortage in a refresh period according to an embodiment of the present invention. The waveform shown in FIG. 7 may be generated by combining a waveform shown in FIG. 3 and a waveform shown in FIG. 4.

FIG. 8A illustrates adjustment of shifts of brightness levels among pixels, and FIG. 8B illustrates example waveforms for driving a pixel to adjust the shifts of brightness levels according to an embodiment of the present invention. As shown in FIG. 8A, an input image comprising four pixels such as pixA, pixB, pixC, and pixD is a moving image with each pixel changing its color over time. The changes of colors are shown by black and white blocks. Plots labeled as pixA to pixD under the blocks show a change in a brightness level for each pixel. For example, a pixel pixA located at an upper left corner of the input image is always black throughout the moving image and its brightness level changes from 0 to the black side max, and therefore, a plot labeled pixA shows a straight line linearly decreasing from 0 to the black side max. Conversely, a pixel pixC located at a lower left corner of the input image is always white throughout the moving image and its brightness level changes from 0 to the white side max, and therefore, a plot labeled pixB shows a straight line linearly increasing from 0 to the white side max. A pixel pixB located at an upper right corner of the input image changes from white to black, white, black, and then white during the moving image, and therefore, its brightness level changes up and down repeatedly within a white side as shown by a plot labeled pixB. A pixel pixD located at a lower right corner of the input image changes from black to white, black, white, and then black during the moving image, and therefore, its brightness level changes down and up repeatedly within a black side as shown by a plot labeled pixD. As a result, the four pixels have different brightness levels from each other.

In an embodiment, as shown in a static image immediately after the moving image, it is supposed that a color to be displayed on each pixel pixA, pixB, pixC, and pixD is to be black, white, white, and black.

With respect to the pixel pixC, its brightness level is shifted to the white side max. With respect to the pixel pixB, its brightness level is shifted towards the white side max halfway, and an amount of a shift in the pixel pixB is smaller than that in the pixel pixC.

In the embodiment, it is desirable that both pixels pixC and pixB display the same white according to the input image. However, there is a difference in color between pixels pixC and pixB due to a different shift in a brightness level caused in each pixel. To compensate for this different shift, a pulse B1 801 is applied to the pixel pixB and thereby a shift in a brightness level of the pixel pixB is aligned with the white side max which is a shift in a brightness level of the pixel pixC. This pulse is shown in FIG. 8B. A width of the pulse B1 may be determined based on the white side max, an amount of the shift in the brightness level, and the next color to be displayed for each pixel.

With respect to the pixel pixA, its brightness level is shifted to the black side max. With respect to the pixel pixD, its brightness level is shifted towards the black side max halfway, and an amount of a shift in the pixel pixD is smaller than that in the pixel pixA. It is desirable that both pixels pixA and pixD display the same black according to the input image. However, there is a difference in color between pixels pixA and pixD due to a different shift in a brightness level caused in each pixel. To compensate for this different shift, a pulse 804 is applied to the pixel pixD, and thereby a shift in a brightness level of the pixel pixD is aligned with the black side max which is a shift in a brightness level of the pixel pixA.

In another embodiment, although not shown in FIG. 8, it is supposed that a color to be displayed on each pixel pixA, pixB, pixC, and pixD is to be black, black, white, and white.

With respect to the pixel pixA, its brightness level is shifted to the black side max. With respect to the pixel pixB, its brightness level is shifted towards the white side max halfway, and an amount of a shift in the pixel pixB is larger than that in the pixel pixA. To compensate for this different shift, a pulse B2 802 is applied to the pixel pixB, and thereby a shift in a brightness level of the pixel pixB is aligned with the black side max which is a shift in a brightness level of the pixel pixA. With respect to the pixel pixD, its brightness level is shifted towards the black side max halfway, and an amount of a shift in the pixel pixD is larger than that in the pixel pixC. To compensate for this different shift, a pulse 803 is applied to the pixel pixD, and thereby a shift in a brightness level of the pixel pixD is aligned with the white side max which is a shift in a brightness level of the pixel pixC.

In the embodiment, the white max and the black max are determined by measuring a shift of a brightness level of each pixel for a time period. This time period may be a duration of the moving image, a part of the duration of the moving image, a duration during which the display continues to display similar images, for example, a bright image or a dark image, similar contents such as a city, nature, a person, indoor/outdoor, sports, scenes in TV shows/animations/movies, or any other images. Alternatively, and/or additionally, these pulses may be applied to each pixel at a predetermined timing set by a user of the display or set by default.

Also, in the embodiment, which pulse is applied is determined for each pixel depending on which transition occurs, and/or whether any pulse is applied or not is determined for each pixel depending on whether any transition occurs or not.

The brightness levels are aligned among pixels according to the embodiment shown in FIG. 8, and as a result, a DC balance is aligned (to a position of DC balance=0 if FIG. 8A) , but the aligned DC balance potentially is not an ideal DC balance. The aligned DC balance needs to be restored to zero, that is the initial state. To achieve this, an embodiment shown in FIG. 9 is proposed.

FIG. 9A illustrates an example original waveform and FIG. 9B illustrates an example adjusted waveform for driving a pixel to initialize a brightness shift according to an embodiment of the present invention. As shown in FIG. 9A, the example original waveform generally includes multiple pulses of the same shape repeated many times. In order to recover the aligned DC balance to zero, a voltage level which is opposite to the aligned DC balance needs to be applied to the pixel. For example, when the aligned DC balance is between zero to the white side max, a positive voltage level should be applied to the pixel. Similarly, when the aligned DC balance is between zero to the black side max, a negative voltage level should be applied to the pixel.

In the embodiment, some adjustments are made to the original waveform. When the aligned DC balance is between zero to the white side max, a pulse width of one or more pulses whose voltage level is VPOS is adjusted to be wider than those in the original waveform. An adjusted amount of the pulse width is shown by 902 in a waveform on the upper right in FIG. 9B, and an adjusted waveform with an adjusted pulse width may be applied to pixels during a next initialization period 901. As a result, as shown in a graph on the left side in FIG. 9B, the aligned DC balance at the white side max ( "+max" on a vertical axis) could be recovered to zero at the end of the next initialization period 901.

Similarly, when the aligned DC balance is between zero to the black side max, a pulse width of one or more pulses whose voltage level is VNEG is adjusted to be wider than those in the original waveform. An adjusted amount of the pulse width is shown by 903 in a waveform on the lower right in FIG. 9B, and an adjusted waveform with adjusted pulse width may be applied to pixels during a next initialization period 901. As a result, as shown in a graph on the left side in FIG. 9B, the aligned DC balance at the black side max ( "-max" on the vertical axis) could be recovered to zero at the end of the next initialization period 901.

The pulse width and how many pulses should be adjusted may vary depending on how much the aligned DC balance deviates from zero. Alternatively, such adjustment may be made by changing a value of the voltage VPOS. These adjustments may be performed for each pixel, and the pulse width and/or the voltage level such as VPOS or VNEG may be determined as needed for each pixel, some pixels, or all the pixels of the display.

Additionally, as shown by circles 904, one or more durations of Vbase in the adjusted waveform may be changed such that a Vbase level appears at the end 905 of the initializing period.

FIG. 10A to FIG. 10D illustrates flowcharts of methods according to embodiments of the present invention. These methods can be performed by a display such as an EPD, or a device connected to or embedded in the display.

FIG. 10A is a flowchart of a method 1000A for compensating for an amount of brightness shift according to an embodiment of the present invention. The method 1000A can be performed in near real-time or prior to rendering the input image. The method 1000A includes the following steps.

Step 1010: The DC balance estimation unit receives the input image. The DC balance estimation unit may receive the input image by downloading or streaming the input image from any external source or by reading it out of the frame memory.

Step 1012: A ghost compensation timing control unit determines a ghost compensation timing. Specifically, the ghost compensation timing control unit determines as the ghost compensation timing when the image to be displayed by the display varies between the moving image and the still image in accordance with the input image. Alternatively, the ghost compensation timing control unit determines the timing of the ghost compensation, for example, when refreshing all pixels on the display, when the display displays a still image first after the moving image is displayed, when the display displays an image that is significantly different, at a predetermined timing set by the user of the display, or at a time set by default, and/or at other times.

Step 1014: The ghost compensation unit generates the first data representing the correction amount of the shift amount of brightness of the input image. Step 1014 may further include the following steps:

(i) The DC balance estimation unit determines the shift amount of brightness based on the input image for each pixel of the display or for more than one pixel;

(ii) The maximum value detection unit detects the maximum value in a black side of the shift amounts of brightness among the shift amounts of brightness determined by the DC balance estimation unit for all of the pixels on the display;

(iii) The maximum value detection unit detects the detecting a maximum value in a white side of the shift amounts of brightness among the shift amounts of brightness determined by the DC balance estimation unit for all of the pixels on the display;

(iv) The ghost compensation unit generates, for each pixel on the display or for more than one pixel, generating first data indicating correction amount of the shift amount of brightness based on the shift amounts of brightness, the maximum value in the black side of the shift amounts of brightness or the maximum value in the white side of the shift amounts of brightness, and the input image.

The shift amount of brightness may be determined for each pixel on the display, or for more than one pixel, based on a number of times a black color is displayed for a predetermined period and a number of times a white color is displayed for the predetermined period. Alternatively, the shift amount of brightness may be determined for each pixel on the display, or for more than one pixel, by adding a value obtained by multiplying a number of times a black color is displayed for a predetermined period by -1 and a value obtained by multiplying a number of times a white color is displayed for the predetermined period by +1.

When the input image is a moving image, the predetermined period is a period while the moving image is being displayed. The DC balance estimation unit may receive a predetermined period of time from the ghost compensation timing control unit or from another unit, or may determine from a mode signal indicative of a moving image/still image mode.

The shift amount of brightness is determined at a predetermined interval and based on whether two images that are continuous in time obtained from the input image are the same. Whether two images that are continuous in time obtained from the input image are the same is determined depending on whether colors displayed are the same between the two images that are continuous in time.

The first data may be determined for each pixel on the display, or for more than one pixel, as follows.

(i) when it is determined, from the input image, that a color the pixel to display next is the black color, and the shift amount of brightness is an amount shifted to the black side, the first data is determined so as to compensate for a difference between the shift amount of brightness of the pixel and the maximum value in the black side;

(ii) when it is determined, from the input image, that a color the pixel to display next is a black color, and the shift amount of brightness is an amount shifted to the white side, the first data is determined so as to compensate for a sum of the shift amount of brightness of the pixel and the maximum value in the black side;

(iii) when it is determined, from the input image, that a color the pixel to display next is a white color, and the shift amount of brightness is an amount shifted to the black side, the first data is determined so as to compensate for a sum of the shift amount of brightness of the pixel and the maximum value in the white side;

(iv) when it is determined, from the input image, that a color the pixel to display next is a white color, and the shift amount of brightness is an amount shifted to the white side, the first data is determined so as to compensate for a difference between the shift amount of brightness of the pixel and the maximum value in the white side.

In order to specify the waveform shown in FIG. 3A, the first data may specify, for example, one or more of: defines one or more of: the first voltage corresponding to the black color; the second voltage corresponding to the white color; a reference voltage; a pulse width of the first voltage, or an amount of change in the pulse width of the first voltage; a pulse width of the second voltage, or an amount of change in the pulse width of the second voltage; a pulse width of the reference voltage, or an amount of change in the pulse width of the reference voltage; a number of times that pulses of the first voltage arise, or a period during which pulses of the first voltage arise; a number of times that pulses of the second voltage arise, or a period during which pulses of the second voltage arise; a number of times that pulses of the reference voltage arise, or a period during which pulses of the reference voltage arise.

Step 1016: The waveform control unit selects the first data as the source data. The waveform control unit selects the first data as the source data according to the ghost compensation timing determined by the ghost compensation timing control unit and outputs the source data to the display timing control unit (TCON) . The TCON may convert the source data into a format that can be interpreted by the source/gate driver.

Step 1018: The source/gate driver outputs the input image corrected by the first waveform generated based on the source data to the display. The first waveform may be generated and applied for each pixel on the display or for more than one pixel.

FIG. 10B is a flowchart of a method 1000B for compensating a shift amount of a DC balance according to an embodiment of the present invention. The DC balance of the pixels on the display or the display may be displaced after performing the method 1000A, or after the display displays any image. Accordingly, the method 1000B may be incorporated into or performed independently of the method 1000A, after the method 1000A, in parallel with the method 1000A. In particular, the method 1000B may be performed when the display is initialized, required by the user, or both. The method 1000B includes the following steps.

Step 1020: The DC balance adjustment unit generates second data indicating a correction amount of an offset between a DC balance displaced according to the first data and an initial DC balance. The second data is determined to align the DC balance differences between the pixels as described with reference to FIG. 8. Specifically, the DC balance displaced according to the first data is a DC balance aligned based on the first data determined by the ghost compensation unit, and the initial DC balance may be an ideal DC balance such as a zero brightness level.

Step 1022: The waveform control unit selects the second data as source data.

Step 1024: The source/gate driver outputs a second waveform generated based on the source data to the display. The second waveform may be generated and applied for each pixel on the display or for more than one pixel.

Alternatively, in step 1022, the waveform control unit may select a combination of the first data and the second data as the source data, and in step 1024, the source/gate driver may generate the second waveform based on the source data that is the combination of the first data and the second data.

In order to specify the waveform shown in FIG. 8B, FIG. 9B, or FIG. 1A (in a case where no correction is applied) , the second data may define one or more of: the first voltage corresponding to the black color; the second voltage corresponding to the white color; a reference voltage; a pulse width of the first voltage, or an amount of change in the pulse width of the first voltage; a pulse width of the second voltage, or an amount of change in the pulse width of the second voltage; a pulse width of the reference voltage, or an amount of change in the pulse width of the reference voltage; a number of times that pulses of the first voltage arise, or a period during which pulses of the first voltage arise; a number of times that pulses of the second voltage arise, or a period during which pulses of the second voltage arise; a number of times that pulses of the reference voltage arise, or a period during which pulses of the reference voltage arise.

FIG. 10C is another flowchart of a method 1000C for compensating a shift amount of brightness according to an embodiment of the present invention. The method 1000C may be implemented in parallel, in parallel, or independently after the method 1000A and/or 1000B. The method 1000C includes the following steps.

Step 1030: The waveform control unit or a unit positioned between the frame memory and the waveform control unit generates third data when the color displayed changes between two images that are continuous in time obtained from the input image. The third data is determined to indicate a first voltage corresponding to the black color when a color displayed changes from white to black; and the third data is determined to indicate a second voltage corresponding to the white color when a color displayed changes from black to white. In order to specify the waveform shown in FIG. 2, the third data may define one or more of: the first voltage corresponding to the black color; the second voltage corresponding to the white color; a reference voltage; a pulse width of the first voltage, or an amount of change in the pulse width of the first voltage; a pulse width of the second voltage, or an amount of change in the pulse width of the second voltage; a pulse width of the reference voltage, or an amount of change in the pulse width of the reference voltage; a number of times that pulses of the first voltage arise, or a period during which pulses of the first voltage arise; a number of times that pulses of the second voltage arise, or a period during which pulses of the second voltage arise; a number of times that pulses of the reference voltage arise, or a period during which pulses of the reference voltage arise.

Step 1032: The waveform control unit selects the third data as source data.

Step 1034: The source/gate driver outputs an input image corrected by the third waveform generated based on the source data to the display. The third waveform may be generated and applied for each pixel on the display or for more than one pixel.

Alternatively, in step 1032, the waveform control unit or the unit disposed between the frame memory and the waveform control unit may select the combination of the first data and/or the second data and the third data as the source data, and in step 1034, the source/gate driver may generate the third waveform based on source data that is a combination of the first data and/or the second data and the third data.

FIG. 10D is a flowchart of a method 1000D for compensating a ghost and adjusting a DC balance according to an embodiment of the present invention. The method 1000D may be implemented in parallel, in parallel, or independently after the

methods

1000A, 1000B, and/or 1000C. The method 1000D includes the following steps.

Step 1040: A ghost compensation timing control unit generates fourth data indicating a correction amount of a difference between an actual brightness level arrived in a refresh period and a target brightness level. In order to specify the waveform shown in FIG. 4 or the waveform shown by the combination of FIGS. 4 and 3A, the fourth data may define one or more of: the first voltage corresponding to the black color; the second voltage corresponding to the white color; a reference voltage; a pulse width of the first voltage, or an amount of change in the pulse width of the first voltage; a pulse width of the second voltage, or an amount of change in the pulse width of the second voltage; a pulse width of the reference voltage, or an amount of change in the pulse width of the reference voltage; a number of times that pulses of the first voltage arise, or a period during which pulses of the first voltage arise; a number of times that pulses of the second voltage arise, or a period during which pulses of the second voltage arise; a number of times that pulses of the reference voltage arise, or a period during which pulses of the reference voltage arise.

Step 1042: The waveform control unit selects the fourth data as source data.

Step 1044: The source/gate driver outputs the input image corrected by the fourth waveform generated based on the source data to the display. A fourth waveform may be generated and applied for each pixel on the display, or for more than one pixel.

Alternatively, in step 1042, the waveform control unit may select the combination of the first data, the second data, and/or the third data and the fourth data as the source data, and in step 1044, the source/gate driver may generate the fourth waveform based on source data that is the combination of the first data, the second data, and/or the third data and the fourth data.

FIG. 11 is a schematic structural diagram of a device for compensating a ghost according to an embodiment of the present invention. The device 1100 may be a display such as an EPD or a device connected to or embedded in the display. The device 1100 comprises a DC balance estimation unit 1102, a max detection unit 1104, a ghost compensation unit 1106, a DC balance adjustment unit 1108, a ghost compensation timing control unit 1110, a waveform control unit 1112, a frame memory 1114, and a display timing controller (TCON) 1116. The TCON 1116 is connected to the source/gate driver. The source/gate driver drives each pixel of the display to display an image on the display. Although not illustrated in FIG. 11, the device 1100 may further comprise any other unit commonly known to a person skilled in the art, such as an input/output unit, a display screen, a power supply unit, a communication interface, and the like.

The apparatus 1100 operates as follows according to a method 1000A for compensating for the amount of brightness shift in accordance with embodiments of the present invention.

The ghost compensation timing control unit 1110 determines a ghost compensation timing. Specifically, the ghost compensation timing control unit 1110 determines as the ghost compensation timing when the image to be displayed by the display varies between the moving image and the still image in accordance with the input image. Alternatively, the ghost compensation timing control unit 1110 determines the timing of the ghost compensation, for example, when refreshing all pixels on the display, when the display displays a still image first after the moving image is displayed, when the display displays an image that is significantly different, at a predetermined timing set by the user of the display, or at a time set by default, and/or at other times.

The ghost compensation unit 1106 generates the first data representing the correction amount of the shift amount of brightness of the input image. The first data may be determined as follows:

(i) The DC balance estimation unit 1102 determines the shift amount of brightness based on the input image for each pixel of the display or for more than one pixel;

(ii) The maximum value detection unit 1104 detects the maximum value in a black side of the shift amounts of brightness among the shift amounts of brightness determined by the DC balance estimation unit 1102 for all of the pixels on the display;

(iii) The maximum value detection unit 1104 detects the detecting a maximum value in a white side of the shift amounts of brightness among the shift amounts of brightness determined by the DC balance estimation unit 1102 for all of the pixels on the display;

(iv) The ghost compensation unit 1106 generates, for each pixel on the display or for more than one pixel, generating first data indicating correction amount of the shift amount of brightness based on the shift amounts of brightness, the maximum value in the black side of the shift amounts of brightness or the maximum value in the white side of the shift amounts of brightness, and the input image.

When the input image is a moving image, the predetermined period is a period while the moving image is being displayed. The DC balance estimation unit 1102 may receive a predetermined period of time from the ghost compensation timing control unit 1110 or from another unit, or may determine from a mode signal ( "Mode" in FIG. 11) indicative of a moving image/still image mode.

The waveform control unit 1112 selects the first data as the source data. The waveform control unit 1112 selects the first data as the source data according to the ghost compensation timing determined by the ghost compensation timing control unit 1110 and outputs the source data to the display timing control unit (TCON) 1116. The TCON 1116 may convert the source data into a format that can be interpreted by the source/gate driver.

The source/gate driver outputs the input image corrected by the first waveform generated based on the source data to the display. The first waveform may be generated and applied for each pixel on the display or for more than one pixel.

The device 1100 operates as flows according to the method 1000B for compensating a shift amount of a DC balance according to the embodiment of the present invention.

The DC balance adjustment unit 1108 generates a second data indicating a correction amount of an offset between a DC balance displaced according to the first data and an initial DC balance. The second data is determined to align the DC balance differences between the pixels as described with reference to FIG. 8. Specifically, the DC balance displaced according to the first data is a DC balance aligned based on the first data determined by the ghost compensation unit, and the initial DC balance may be an ideal DC balance such as a zero brightness level.

The waveform control unit 1112 selects the second data as source data.

The source/gate driver outputs a second waveform generated based on the source data to the display. The second waveform may be generated and applied for each pixel on the display or for more than one pixel.

Alternatively, the waveform control unit 1112 may select a combination of the first data and the second data as the source data, and in step 1024, the source/gate driver may generate the second waveform based on the source data that is the combination of the first data and the second data.

The device 1100 operates as follows according to the method 1000C for compensating a shift amount of brightness according to the embodiment of the present invention.

The waveform control unit 1112 or a unit positioned between the frame memory 1114 and the waveform control unit 1112 generates third data when the color displayed changes between two images that are continuous in time obtained from the input image. The third data is determined to indicate a first voltage corresponding to the black color when a color displayed changes from white to black; and the third data is determined to indicate a second voltage corresponding to the white color when a color displayed changes from black to white. In order to specify the waveform shown in FIG. 2, the third data may define one or more of: the first voltage corresponding to the black color; the second voltage corresponding to the white color; a reference voltage; a pulse width of the first voltage, or an amount of change in the pulse width of the first voltage; a pulse width of the second voltage, or an amount of change in the pulse width of the second voltage; a pulse width of the reference voltage, or an amount of change in the pulse width of the reference voltage; a number of times that pulses of the first voltage arise, or a period during which pulses of the first voltage arise; a number of times that pulses of the second voltage arise, or a period during which pulses of the second voltage arise; a number of times that pulses of the reference voltage arise, or a period during which pulses of the reference voltage arise.

The waveform control unit 1112 selects third data as source data.

The source/gate driver outputs an input image corrected by the third waveform generated based on the source data to the display. The third waveform may be generated and applied for each pixel on the display or for more than one pixel.

Alternatively, the waveform control unit 1112 or the unit disposed between the frame memory 1114 and the waveform control unit 1112 may select the combination of the first data and/or the second data and the third data as the source data, and the source/gate driver may generate the third waveform based on source data that is a combination of the first data and/or the second data and the third data.

The device 1100 operates as follows according to the method 1000D for compensating a ghost and adjusting a DC balance according to the embodiment of the present invention.

The ghost compensation timing control unit 1110 generates fourth data indicating a correction amount of a difference between an actual brightness level arrived in a refresh period and a target brightness level. In order to specify the waveform shown in FIG. 4 or the waveform shown by the combination of FIGS. 4 and 3A, the fourth data may define one or more of: the first voltage corresponding to the black color; the second voltage corresponding to the white color; a reference voltage; a pulse width of the first voltage, or an amount of change in the pulse width of the first voltage; a pulse width of the second voltage, or an amount of change in the pulse width of the second voltage; a pulse width of the reference voltage, or an amount of change in the pulse width of the reference voltage; a number of times that pulses of the first voltage arise, or a period during which pulses of the first voltage arise; a number of times that pulses of the second voltage arise, or a period during which pulses of the second voltage arise; a number of times that pulses of the reference voltage arise, or a period during which pulses of the reference voltage arise.

The waveform control unit 1112 selects the fourth data as source data.

The source/gate driver outputs the input image corrected by the fourth waveform generated based on the source data to the display. A fourth waveform may be generated and applied for each pixel on the display, or for more than one pixel.

Alternatively, the waveform control unit 1112 may select the combination of the first data, the second data, and/or the third data and the fourth data as the source data, and in step 1044, the source/gate driver may generate the fourth waveform based on source data that is the combination of the first data, the second data, and/or the third data and the fourth data.

FIG. 12 illustrates a method used to evaluate an effect achieved by the present invention. An evaluation flow is shown in the left side of FIG. 12.

The evaluation flow starts and at step 1201 a display is initialized, for example, all the pixels on the display are set to the initial state with no shift in a brightness level or DC balance.

At step 1202, a still image 1212 is used as an input image and is displayed on the display. The still image 1212 may be black throughout the display in <1> White burn-in test on the upper right in FIG. 12. In the left half of the display, the compensation for ghost according to the present invention is applied, and in the right half of the display, the compensation for ghost according to the present invention is not applied.

At step 1203, one or more pixels 1213 are sampled and measured with respect to brightness level.

At step 1204, a moving image is displayed for a period 1214 on both sides 1218 on the display. In this test, the moving image is all white in both sides 1218 except for the center line, for testing the worst case.

At step 1205, the still image 1215 same as the still image 1212 is used as an input image and is displayed on the display.

At step 1206, one or more pixels 1216 which are in the same location as the one or more pixels 1213 are sampled and measured with respect to brightness level.

At step 1207, the brightness level of the one or more pixels 1216 measured at step 1206 is compared with the brightness level of the one or more pixels 1216 measured at step 1203. Then, the evaluation flow ends.

As a result of <1> White burn-in test, when the compensation for ghost according to the present invention (that is, the compensation for the shift of brightness level and DC balance) is applied, the DC balance is shifted only 0.48 %. On the other hand, when the compensation for ghost according to the present invention is not applied, the DC balance is shifted 5.75 %. Accordingly, it is seen from the test that the compensation for ghost according to the present invention significantly prevents the ghost from appearing.

As shown on the lower right in FIG. 12, another test: <2> Black burn-in test was also performed according to the evaluation flow described above. At step 1202, a still image 1222 is used as an input image. At step 1203, one or more pixels 1223 are sampled and measured with respect to brightness level. At step 1204, a moving image is displayed for a period 1224 on both sides 1228 on the display. At step 1205, the still image 1225 same as the still image 1222 is used as an input image and is displayed on the display. At step 1206, one or more pixels 1226 which are in the same location as the one or more pixels 1223 are sampled and measured with respect to brightness level. At step 1207, the brightness level of the one or more pixels 1226 measured at step 1206 is compared with the brightness level of the one or more pixels 1226 measured at step 1203. As a result of <2> Black burn-in test, when the compensation for ghost according to the present invention is applied, the DC balance is shifted only 2.55 %. On the other hand, when the compensation for ghost according to the present invention is not applied, the DC balance is shifted 31.77 %. Accordingly, it is seen from the test that the compensation for ghost according to the present invention significantly prevents the ghost from appearing.

FIG. 13A illustrates comparison of ghost reduction achieved by the present invention and the prior arts when displaying a static image immediately after a moving image, and FIG. 13B illustrates comparison of ghost reduction achieved by the present invention and the prior arts in a shot during a moving image. In FIG. 13A, a left image shows a result of displaying a black raster immediately after a moving image such as used in <1> White burn-in test in FIG. 12, and it shows a result 1301 with the compensation for ghost according to the present invention and a result 1302 without the compensation for ghost. It is seen that the compensation for ghost according to the present invention significantly improves the DC balance and provides a clear black image without a ghost.

In FIG. 13A, a right image shows a result of displaying a white raster immediately after a moving image such as used in <2> Black burn-in test in FIG. 12, and it shows a result 1303 with the compensation for ghost according to the present invention and a result 1304 without the compensation for ghost. It is seen that the compensation for ghost according to the present invention significantly improves the DC balance and provides a clear white image without a ghost.

In FIG. 13B shows a shot during a moving image. A left image in FIG. 13B shows a result 1305 without the compensation for ghost according to the present invention, and a right image shows a result 1306 with the compensation for ghost according to the present invention. It is seen that the compensation for ghost according to the present invention significantly improves the DC balance and provides a clear actual image without a ghost even while the moving image is being displayed.

Some embodiments are described above in the case that a static image is displayed immediately after a moving image. However, the present invention also may be applied to a case that a moving image is displayed and then another moving image is displayed, that a static image is displayed and then another static image is displayed, that a moving image or a static image is displayed only in a part on a display, and/or any other case.

Some embodiments are described above in the case of black and white images. However, the present invention also may be applied to a color image such as RGB (Red, Green, Blue) , CYGM (Cyan, Yellow, Green, and Magenta) , RGBE (Red, Green, Blue, and Emerald) , or any other color space existing or to be developed in the future.

Obviously, a person skilled in the art may understand that the present invention may be applied to various types of display, which are affected by ghosts, existing or to be developed in the future.

Obviously, a person skilled in the art may make various modifications and variations to this application without departing from the scope of this application. In this way, this application is also intended to cover these modifications and variations of this application provided that these modifications and variations fall within the protection scope defined by the following claims and their equivalent technologies.

Example 1. A method for driving a display, the method comprising:

receiving an input image;

when an image to be displayed by the display changes between a moving image and a static image according to the input image, generating first data indicating correction amount of a shift amount of brightness of the input image;

selecting the first data as source data; and

outputting, to the display, the input image corrected by a first waveform generated based on the source data.

Example 2. The method according to Example 1, wherein the shift amount of brightness is determined based on a number of times a black color is displayed for a predetermined period and a number of times a white color is displayed for the predetermined period.

Example 3. The method according to Example 1, wherein the shift amount of brightness is determined by adding a value obtained by multiplying a number of times a black color is displayed for a predetermined period by -1 and a value obtained by multiplying a number of times a white color is displayed for the predetermined period by +1.

Example 4. The method according to Example 2 or 3, wherein when the input image is a moving image, the predetermined period is a period while the moving image is being displayed.

Example 5. The method according to Example 4, wherein the shift amount of brightness is determined at a predetermined interval and based on whether two images that are continuous in time obtained from the input image are the same.

Example 6. The method according to Example 5, wherein whether two images that are continuous in time obtained from the input image are the same is determined depending on whether colors displayed are the same between the two images that are continuous in time.

Example 7. The method according to Example 6, further comprising:

when the display is initialized, when requested by a user, or both of those, generating second data indicating a correction amount of an offset between a DC balance displaced according to the first data and an initial DC balance;

selecting the second data as the source data; and

outputting, to the display, a second waveform generated based on the source data.

Example 8. The method according to Example 7, further comprising:

when a color displayed changes between two images that are continuous in time obtained from the input image, selecting third data as the source data; and

outputting, to the display, the input image corrected by a third waveform generated based on the source data;

wherein when a color displayed changes from white to black, the third data indicates a first voltage corresponding to the black color; and

wherein when a color displayed changes from black to white, the third data indicates a second voltage corresponding to the white color.

Example 9. The method according to Example 8, further comprising:

while the display is displaying a moving image, generating fourth data indicating a correction amount of a difference between an actual brightness level arrived in a refresh period and a target brightness level;

selecting the fourth data as the source data; and

outputting, to the display, the input image corrected by a fourth waveform generated based on the source data.

Example 10. The method according to Example 9, wherein each of the first data, the second data, the third data, and the fourth data defines one or more of:

the first voltage corresponding to the black color;

the second voltage corresponding to the white color;

a reference voltage;

a pulse width of the first voltage, or an amount of change in the pulse width of the first voltage;

a pulse width of the second voltage, or an amount of change in the pulse width of the second voltage;

a pulse width of the reference voltage, or an amount of change in the pulse width of the reference voltage;

a number of times that pulses of the first voltage arise, or a period during which pulses of the first voltage arise;

a number of times that pulses of the second voltage arise, or a period during which pulses of the second voltage arise;

a number of times that pulses of the reference voltage arise, or a period during which pulses of the reference voltage arise.

References

JP2015176133A

US20160133196A1

Claims

A method for driving a display, the method comprising:

receiving an input image;

determining a first shift amount of a first DC balance A or a second shift amount of a second DC balance B based on the input image;

outputting a first wave pulse W1, wherein the first wave pulse W1 is based on the first shift amount of the first DC balance A,

outputting a second wave pulse W2, wherein the second wave pulse W2 is based on the second shift amount the second DC balance B, and wherein the first wave pulse W1 is different from the second wave pulse W2 when the first DC balance A is different from the second DC balance B;

displaying the input image corrected by the first wave pulse W1 or the second wave pulse W2 on the display.
The method according to claim 1,

the first shift amount of the first DC balance A and the second shift amount of the second DC balance B is based on the content of the input image.
The method according to claim 2, the first wave pulse W1 and/or the second wave pulse W2 is based on the source data, wherein the source data is generated from a waveform control unit.
The method according to claim 3, the source data is based on at least one of a parameter L, a parameter M, a parameter N, wherein the parameter L is contributed from a ghost compensation unit, the parameter M is contributed from a DC balance adjustment unit, the parameter N is contributed from a timing control unit.
The method according to claim 4, the parameter M is based on inputs from at least one of a max detection unit, the DC balance estimation unit, previous image and next image.
The method according to claim 4, the parameter L is based on inputs from at least one of max detection unit, a previous image and a next image.
The method according to claim 4, the parameter N is based on inputs from at least one of the previous image and the next image.
The method according to claim 5, the input from the max detection unit is a maximum value among inputs from the DC balance estimation unit.
The method according to any of claims 5 or 8, the input from the DC balance estimation unit is a shift amount of brightness caused by the input image.
The method according to any of claims 5 to 7, the input from the previous image is a previous one of two images that are continuous in time obtained from the input image and stored in a frame memory.
The method according to any of claims 5 to 8, the input from the next image is a later one of two images that are continuous in time obtained from the input image and stored in a frame memory.
The method according to claim 11, wherein

the source data is based on the parameter L when an image to be displayed by the display changes between a moving image and a static image according to the input image;

the source data is based on the parameter M when the display is initialized, when requested by a user, or both of those;

the source data is based on the parameter N based on whether colors displayed are the same between two images that are continuous in time obtained from the input image while the moving image is being displayed.