WO2011019292A1

WO2011019292A1 - A method of controlling change of the image on the electrophoretic screen

Info

Publication number: WO2011019292A1
Application number: PCT/PL2010/000063
Authority: WO
Inventors: Peter Slikkerveer; Pawel Jarzewicz; Rafal Kleger-Rudomin
Original assignee: Mpcicosys-Embedded Pico Sytems Sp. Z.O.O.
Priority date: 2009-08-13
Filing date: 2010-07-23
Publication date: 2011-02-17
Also published as: PL388797A1

Abstract

A method of controlling change of the image displayed on an electrophoretic screen, consisting in transition from the currently displayed image to the next image via a homogeneous state in which the level of all pixels is identical, provided that the transition to and from the homogenous state is effected in a number or transition steps, each involving the running of a control frame, during which the scanning signal is fed to subsequent gateway lines in the pixel matrix and the data signals are fed to the data lines, where the method is characteristic in that at least two transition steps are of different duration.

Description

A Method of Controlling Change of the Image on the EIectrophoretic

Screen

The invention concerns the method of controlling change of the image on the electrophoretic screen. The invention is applicable when electrophoretic screens are used as flexible image displays, especially in portable devices and intelligent cards which require the lowest possible power consumption.

The electrophoretic material called the electronic ink is made up of millions of microcapsules containing charged particles suspended in dielectric liquid. When designated for image display screens, the electrophoretic material is placed on an appropriate base and fitted with electrodes on both sides to enable provision of an appropriate electric field which causes the charged particles to move up or down. In one of the approaches, the microcapsules contain positively charged white particles and negatively charged black particles. Under the impact of the negative electric field the white particles in the microcapsules move up causing that the viewer will see a white surface. Simultaneously, the black particles move down where they remain hidden, invisible to the eye. In another approach, the display devices can be built based on microcapsules containing one type of charged particles moving in an opaque medium, where the medium and the particles may be of different colours. Depending on the material and the technology, it is possible to obtain different types of electrophoretic screens, referred to under different names, e.g. e-paper, or bi-stable display. Such screens usually have two panels with the electrodes placed opposite, and dielectric liquid encapsulated in between, with charged pigments suspended therein. One of the electrodes is typically transparent. If the electrodes are fed with voltages of the opposite potentials, the pigment particles will move towards the electrode of the potential opposite to their own charge. If the same polarity is the same for both electrodes, the particles will migrate towards the electrode of the lower or higher potential, depending on the particle charge. In order to create the image in the expected scale of grey shades, the pigment-carrying particles must be moved to a specific location, or in other words to a specific height in between the two panels. Image creation on a screen of the type is achieved by transmitting appropriate sequences of scanning signals and data signals to the electrode rows and columns corresponding to the pixels forming the matrix, so that the particles corresponding to the specific pixels move to the predetermined level. The number of the required individual moves in the entire image differs depending on the required number of the grey levels, e.g. for 16 shades of grey the necessary number will be 16² = 256 moves.

Apart from their spatial flexibility, electrophoretic screens consume less power compared to CRT or LCD screens. However, they have their inconveniences such as: longer time of updating the image (creating a new one), or reduced possibility to control the accuracy of the grey levels. The material for the electrophoretic screens is called bi-stable because of its characteristic feature consisting in retaining the created image "recorded" in the material under the impact of the applied feeding signals after the electric field has been removed. This peculiar image memory requires, however, that the image be erased before a new one is created. The operation must be performed so as to make the transition between the images possibly least inconvenient to the user. Other disadvantages include the autogenous movement of the particles caused by the Brownian motion once the electric field is removed, and the characteristic non-linear optical properties of the material. There are various ways of solving problems of the kind, e.g. by driving all pixels to the maximum (or minimum) level, introducing various types of additional pulses in the control waveforms, or programming the control waveforms with complex calculation algorithms.

Regular time intervals in the process of setting of the rows and columns of the pixel matrix is a characteristic feature of the known solutions. During a single frame the scanning signal is transmitted successively to all rows, i.e. the gateway lines, while the data signal is transmitted to all columns, i.e. data lines in the matrix. Completion of one frame results in shifting specific pixels by one level. In the known methods of controlling change of the image, on the electrophoretic screen the control frame is repeated at constant frequency, e.g. 50 Hz. In some approaches the pixels are shifted in such a way that the transition from the currently displayed image to the next one is direct, which means that each pixel is shifted from its current level to the level required for the subsequent image. Other approaches propose going through a homogenous state in the image change sequence. This means that in stage one each pixel is shifted from its current level in the image to the same level (highest or lowest), and in stage two each pixel is moved to the level required for the subsequent image. Hence, with 16 levels of grey such methods require running at least 15 control frames for each stage.

The method disclosed in the international patent application publication WO 2005/093705 envisages the following steps: entering the data defining the display status which precedes the current status, entering the data defining at least one voltage waveform according to each of: the previous image, current image, and the next image, and then driving at least a part of the bi-stable display from the current image to the next image in accordance with at least one voltage waveform so that at least a part of the bi-stable display is driven from the current state to a certain interim optical state by at least one reset pulse of at least one voltage waveform. Subsequently, transition is achieved from the interim optical state to the subsequent image by applying the control pulse of at least one voltage waveform, where the energy of at least a part of at minimum one voltage waveform is determined based on the previous image state. The method envisages different variants and specific embodiments. In one variant it is possible to use the first reset pulse to go from the current image state to the transitional state, which then leads to the next image. At least one reset pulse may also cause that the charged particles of the screen will simultaneously move to one of the extreme positions. The input data relating to the voltage waveform consist of the data of at least one signal out of the many available waveforms connected with the transition from the current to the next image. The adjustment may also be effected so that an additional pulse of the polarity opposite to the first reset impulse and preceding it is applied to at least a part of the screen.

Known too from the international application published under number WO 2008/153212 is the method of updating the image of the bistable display where many different control signal sequences are defined to shift the screen pixels from their current state to the final state. Here, the sequence selected for a specific pixel brings the effect of moving it to the required final state during the driving process. A single sequence can be the source of generating many different sequences by introducing zero or more frames specifying that no voltage should be fed. The sequence applied to the specific pixel can be selected stochastically out of a number of possible sequences. The sequence selection can, at least in part, be based on the location of the specific pixel on the screen, or on the signals applied for the neighbouring pixels. The transition effect can start from the bottom and move upwards, or the other way round. Alternatively, it can move from left to right of the screen or the opposite way, or from one corner to the opposite corner.

The method disclosed in the patent application puiblication US 2008/0303780 proposes application of control pulses to individual pixels on the electrophoretic screen and cyclic application of correction waveforms so that the control pulses are periodically aligned for all pixels. It is proposed to differentiate the durations of the control and correction pulses. A variety of the method applies control pulses to a specific pixel, and the cumulated number of the new settings for the first colour state and the second colour state, or for all states over a certain time interval. These settings are basically aligned within the time interval. Also applied, is the correction signal for the specific pixel to correct the imbalance of the constant electric field with respect to other individual pixels.

The method of controlling the electrophoretic screen known from the patent application publication US 2009/0066636 is made up of the following elements: feeding the scanning signal to the subsequent gateway line while simultaneously turning off the scanning signal in the previous gateway line in the refresh period; feeding the refresh voltage to the data lines in response to the scanning signal fed in the refresh period; feeding the scanning signal to the next gateway line at a certain delay after the turning off of the scanning signal of the previous gateway line in the data entry period; and feeding the voltage data signals to the data lines in response to the scanning signal over the data entry period. In a special embodiment, the scanning signal is fed over a longer time in the refresh period, than in the data entry period. The description presents different signal waveforms, their values, synchronisation, data entry periods, refresh periods, and delays, as well as setting the refresh period depending on the maximum data values. In particular, it is proposed to maximize the duration of the refresh period when the maximum value of the data signal corresponds with the black colour, and minimise the duration of the refresh period when the maximum signal value corresponds with the white colour. If, on the other hand, the maximum value corresponds with the grey colour, the duration of the period is proposed to be set in between the maximum and minimum duration values.

A method of controlling the image on the electrophoretic screen according to this invention, consisting in transition from the current image to the subsequent image via a homogenous state, where all pixels are at the same level and where the transition to and from the homogenous state is effected in a number of transition steps, each including a control frame, during which the scanning signal is transmitted to the subsequent gateway lines of the pixel matrix and data signals are fed to the data lines, is characteristic in that at least two transition steps are of different duration.

In one mode of carrying out the invention the duration of the transition step is equal to the duration of the control frame.

In another embodiment the duration of the transition step is the sum of the durations of: the control frame and the wait time.

In yet another mode of carrying out the duration of the control frames in the subsequent transition steps is constant.

Possible too, is the mode where at least one additional control frame is run over the wait time of at least one transition step. The number of the transition steps in the process of moving to or from the homogenous state can be equal to the number of grey levels minus one in the current or next image, as appropriate.

Preferably, the durations of the transition steps are aligned to the optical characteristics of the screen material.

The number of the transition steps can be lower than the number of grey levels minus one of the current or next image, as appropriate.

The number of the transition steps depends on the number of bits describing the maximum number of grey levels in the current or next image.

Preferably, the number of the transition steps is equal to the number of bits needed to record the maximum required number of grey levels in the current or next image.

Preferably, at least one correction step is run in between the transitions steps.

The durations of individual transition steps are_; the multiple of the duration of the shortest transition step, which corresponds with the duration of the control frame.

The duration of each subsequent or previous transition step is longer or shorter than the previous or next transition step, as appropriate.

In the subsequent transition steps the pixels representing the same bit value, which defines the grey level value for the specific pixel at the position of the number compared to the number of the subsequent transition step, are driven.

In one of the embodiments the numbering of the bit positions starts from the most prominent bit.

In another embodiment, the bit position numbering starts with the least prominent bit.

At the stage of transition to the homogenous state the pixels to be shifted in the next transition step are selected based on their grey level in the previous transition step, whereas at the stage of transition from the homogenous state the pixels to be shifted in the next step are selected based on their grey level in the desired image. The main advantage of the solution proposed in the invention consists in reduction of power consumption thanks to the reduced number of transition steps needed to display an image composed of numerous levels of grey and the inherent wait periods, i.e. no-control periods in between the frames. The no-control periods in between the frames enable turning the controller to stand-by, which reduces the power consumed even further. The breaks in the control process can also be used to run data processing operations on the control, which accelerates the overall display process. Another major advantage consists in the fact that the image data processing operations are bit-based in nature, typical for digital machines.

An exemplary embodiment of the invention is illustrated on the drawings, where: fig. 1 visualises the general diagram of the control circuit, fig. 2 presents exemplary signals in the subsequent transition steps and the corresponding change in the pixel grey level, provided that fig. 2a illustrates the scanning signals in the control frames, and fig. 2b - the data signals in the control frames, fig. 3c - the charge accumulated on the electrodes of the respective pixels, fig. 2d - the change in the pixel grey levels corresponding to the signals, and fig. 3 pictures the subsequent transition steps in the process of moving from image A to image B, and from image B to image C, where the squares denote individual pixels, and the figures therein denote the levels of grey the pixels are positioned on.

The method of controlling the image change on the electrophoretic screen is carried out in a typical circuit consisting of the feeder PS, control C, screen D in the form of a pixel matrix with electrodes and pixel switches, plus row controller DG and column controller DD. In the circuit, the rows of the pixel matrix receive signals scanning the rows Ss, which open the gateways, whereas the columns or the respective electrodes defined in accordance with the recorded data receive the data signals S_D. A single waveform of the scanning signals S_s and data signals S₀ across all rows and columns forms one control frame F. The exemplary embodiment presents the image change process on the electrophoretic screen for 16 levels of grey in each of the subsequent images. In the described embodiment the transition from image A to image B goes through the homogenous state of the highest grey level, i.e. black, and the transition to the next image C goes through the homogenous state of the lowest grey level, i.e. white. Four bits are needed to record the values of the sixteen levels of grey, provided that the lowest level, white, carries the 0000 value in the binary system, and the highest level, black, is represented by the value 1111 in the system; the intermediate states carry subsequent intermediate values, as appropriate. The transition from image A to the black state of all pixels is achieved in four transition steps, where the duration of the first transition step Kl equals 8T, the time of the second transition step K2 is equal to 4T, the third transition step K3 equals 2T, and the fourth transition step K4 is equal to T, provided that T represents the duration of a single control frame F. At the outset of the first control step Kl the rows and columns of the pixel matrix receive the signals of one control frame F, provided that the data signals S_D are sent to the electrodes of the pixels P positioned on the grey levels from 0 to 7, i.e. on those levels of grey whose values recorded in four bits share the bit equal to 0 in the most prominent position. Over the duration of the control frame in the first transition step Kl the selected pixels move one grey level up. Upon the lapse of that control frame the pixels will have moved to subsequent, higher levels of grey in the same first transition step ^;Kl under the impact of the charge accumulated on the pixels' electrodes. Since the overall duration of the first transition step is 8T, the selected pixels will have moved 8 levels of grey in the step. In the second transition step K2 the signals of again one control frame F are transmitted, provided that the data signals S₀ of the frame are fed to the electrodes of the pixels positioned on levels 8 to 11, that is on those levels of grey whose values recorded in four bits show the 0 value on the second most prominent position. Upon the lapse of the control frame F of this transition step, the selected pixels will move under the impact of the charge accumulated on the electrodes, just like in step one. Over the duration of the second transition step K2, equal to 4T, the selected pixels will move 4 levels of grey. Similarly, in the third transition step K3, a move by 2 levels will be made by the pixels which were previously positioned on levels 12 and 13, i.e. those with the 0 value on the third position counting from the most prominent bit. In the last, fourth transition step K4, lasting the time of one control frame F, a one-level shift will be made by the pixels having the zero value on the fourth bit position counting from the most prominent one, i.e. those which were on the grey level 14. In this way, after four transition steps Kl , K2, K3, and K4 all pixels will find themselves on the highest grey level. On completion of the four transition step cycle the matrix receives signals zeroing the charges on the electrodes, i.e. the signals of the image freezing frame F₀. In the subsequent cycle the pixels are driven from the homogenous black state to image B in a similar, four transition step procedure. In that cycle the first transition step Kl lasting 8T will involve feeding the data signal over the control frame to those pixels which are to be positioned on grey levels 0 to 7 in image B, i.e. those with the zero value on the most prominent bit position in the binary notation. In this step, the pixels will move eight levels down. In the K2 step two, the pixels which are to be positioned on levels 0 to 3 and 8 to 11, i.e. those with zero on the second bit position counting from the most prominent, will be shifted four levels. The third step K3 will consist in moving the pixels having zero on the third position in the final image B, i.e. those on levels 0,1, 4, 5, 8, 9, 12, and 13 two levels down, and in the last, fourth transition step Kl a single-level move down will be made by the pixels having zero on the fourth, least prominent position, i.e. to levels 0, 2, 4, 6, 8, 10, 12, and 14 in the final image B. The transition from image B to the subsequent image C is, in this mode of carrying out the invention, achieved via the homogenous white state. In the subsequent four transition steps from image B to the white state, lasting 8T, 4T, 2T, and T subsequently, the data signal S₀ will be fed to the pixels positioned on the levels having value 1^' on the first, second, third, and fourth most prominent bit positions counting from the most prominent one, respectively. These will be the pixels of the grey levels 8 to 14 in step one, the pixels of levels 4 to 7 in step two, those from levels 2 and 3 in the third step, and the pixels from the grey level 1 in the fourth step. In the cycle of transition from the white level to image C, in another series of four transition steps lasting 8T, 4T, 2T, and T, respectively, the shifts will involve the pixels which are to have number one on the subsequent positions in the bit record system counting from the most prominent in the final image C, as appropriate. After each four-step transition cycle, the electrodes are fed the signals of the freezing frame F₀. In other embodiments,- the selection of the pixels to be moved in the subsequent steps can be made based on the zeros or ones on the subsequent bit positions, counting from the least prominent, and the duration of the subsequent steps can be growing, i.e. T, 2T, 4T, and 8T, as appropriate, for the sixteen levels of grey. It is possible to opt for various combinations of the order of the transition step durations in individual cycles, the bit position order, and its value depending on the intended homogenous state via which the transition of the images is to be achieved, and on the manner of building the subsequent image. In each mode of carrying out the data needed to drive the following transition step are calculated in the time following the completion of the control frame F.

In the second exemplary mode of carrying out the invention the number of the transition steps from or to the homogenous state is equal to the number of grey levels minus one, and in each step the selected pixels move by one level. The duration of individual transition steps is, however, different and suited to the non-linear optical characteristics of the screen material.

Claims

Patent Claims

1. A method of controlling change of the image on the electrophoretic screen consisting in transition from the current image to the next image through a homogenous state where all pixels are at the same level, provided that the transition to and from the homogenous state is effected in a number of transition steps, each including a control frame during which the subsequent gateway lines of the pixel matrix are fed a scanning signal, and the data lines are fed the data signals, wherein at least two transition steps are of different durations.

2. The method according to Claim 1, wherein the duration of the transition step is equal to the duration of the control frame.

3. The method according to Claim 1, wherein the duration of the transition step is the sum of the control frame duration and the wait period.

4. The method according to Claim 3, wherein the duration of the control frames in the subsequent transition steps is constant.

5. The method according to Claims 3-4, wherein at least one additional control frame is run in the wait period of at least one transition step.

6. The method according to Claims 1-5, wherein the number of the steps in the transition from or to the homogenous state is equal to the number of grey levels minus one in the current or next image, as appropriate.

7. The method according to Claim 6, wherein the durations of the transition steps are matched to the optical characteristics of the screen material.

8. The method according to Claims 1-5, wherein the number of the transition steps is lower than the number of the grey levels minus one in the current or next image, as appropriate.

9. The method according to Claims 1-5, wherein the number of the transition steps is dependent on the number of bits describing the maximum number of levels of grey in the current or next image.

lO.The method according to Claim 8, wherein the number of the transition steps is equal to the number of bits needed to record the maximum required number of the levels of grey in the current or next image.

11. The method according to Claims 1-10, wherein at least one correction step is run in between the transition steps.

12. The method according to Claims 10-11, wherein the durations of individual transition steps are multiples of the duration of the shortest transition step, corresponding with the duration of the control frame.

13. The method according to Claims 10-12, wherein the duration of each next or preceding transition step is higher or lower, as appropriate, from the preceding or next transition step.

14. The method according to Claims 10-13, wherein driven in subsequent transition steps are pixels of the same bit value defining the grey level of a specific pixel, all on the position whose number is compared to the number of the subsequent transition step.

15. The method according to Claim 14, wherein the bit position numbering starts from the most prominent bit.

16. The method according to Claim 14, wherein the numbering of the bit position starts from the least prominent bit.

17.The method according to Claims 14-16, wherein the pixels to be moved in the transition to the homogenous state are selected based on their grey level in the preceding transition state, whereas in the transition from the homogenous state the selection of the pixels to be moved in the subsequent step is based on their level of grey in the final image.