Method for determining the start of relaxation after a burn-in process at optical display devices controllable pixel by pixel

Abstract

The invention relates to a method for determining a start of relaxation (t.sub.R) when switching over an optical display device (1) controllable pixel by pixel from a burn-in image (EB′) to a relaxation image (RB), wherein. A trigger image area (TB) having at least one image pixel is set to pixel values such that a parameter determined based on the at least one pixel value across the trigger image area (TB) differs between the burn-in image (EB′) and the relaxation image (RB). The local distribution of a greyscale value is continuously recorded by means of a camera (3, 13). A trigger subfield (20) comprising at least one sensor pixel (15) is defined matching the trigger image area (TB). A trigger parameter (T) is continuously determined from the pixel values of the at least one sensor pixel (15) in the trigger subfield (20) with a trigger clock rate and the start of relaxation (t.sub.R) is determined as the point in time at which the continuously determined trigger parameter (T) crosses the trigger threshold value (T.sub.S). The invention furthermore relates to a device and a method for determining the burn-in behavior of a display device (1) as well as the use of such a method for a display (1) determined for application in a vehicle.

Claims

1. A method for determining a start of relaxation when switching over an optical display device controllable pixel by pixel from a burn-in image to a relaxation image, wherein a trigger image area within the burn-in image and comprising at least one image pixel is set to pixel values such that a first parameter formed from the at least one pixel value in the trigger image area of the burn-in image differs from a second parameter formed from the at least one pixel value in the trigger image area of the relaxation image, the local distribution of a greyscale value corresponding to the local distribution of a photometric characteristic across the display device is continuously recorded by means of a camera comprising a sensor field of sensor pixels, wherein a trigger subfield comprising at least one sensor pixel is defined overlapping to the trigger image area of a display image presented on the display device, and a trigger parameter is continuously determined from the pixel values of the at least one sensor pixel in the trigger subfield with a trigger clock rate, and a trigger threshold value, which lies between the trigger parameter resulting for the recording of the burn-in image and the trigger parameter resulting for the recording of the relaxation image, is determined, and the start of relaxation is determined as the point in time at which the continuously determined trigger parameter crosses the trigger threshold value, wherein the trigger clock rate is chosen to be at least as high as the camera clock rate envisaged for reading out the sensor pixels of the sensor field.

2. The method according to claim 1, wherein the trigger parameter is only recorded in a period having a predetermined duration, comprising the point in time at which the display device is controlled to switch over from the burn-in image to the relaxation image.

3. The method according to claim 2, wherein a floating average is determined from a plurality of consecutive determined trigger parameters and compared with the trigger threshold value.

4. The method according to claim 1, wherein the pixel values in the trigger image area are selected such that a first average of pixel values in the trigger image area of the burn-in image is greater than a second average of pixel values in the trigger image area of the relaxation image.

5. The method according to claim 4, wherein the pixel values in the trigger image area are selected such that the maximum luminance density achievable with the display device is achieved in at least one subarea of the trigger image area of the burn-in image.

6. A method for determining the burn-in behavior of an optical display device controllable pixel by pixel, wherein the display device is controlled to present a reference image if it has not been subjected to a burn-in process, wherein a first camera image covering the local distribution of a greyscale value corresponding to the local distribution of a photometric characteristic across the display device is recorded by a camera while the same is controlled to present the reference image, the display device is controlled to present the burn-in image for a predetermined burn-in period, the display device is controlled to present the relaxation image, wherein at least one further camera image covering the local distribution of a greyscale value corresponding to the local distribution of a photometric characteristic across the display device is recorded by the camera while the same is controlled to present the relaxation image, and a start of relaxation is determined by means of the camera according to the method of claim 1, and the burn-in behavior for the display device is determined from the first camera image, the at least one further camera image and the start of relaxation.

7. The method according to claim 6, wherein a subfield of the sensor field is being read out from the at least one further camera image covering the local distribution of a greyscale value corresponding to the local distribution of a photometric characteristic across the display device while the same is controlled to present the relaxation image, the reading out being performed using a read out clock rate which is higher than the camera clock rate envisaged for the complete reading out of the sensor field.

8. The method according to claim 7, wherein the subfield read out using the read out clock rate at least partially overlaps the trigger subfield.

9. The method according to claim 6, wherein the camera is configured as a luminance density measurement camera.

10. The method according to claim 6, wherein the at least one further camera image is recorded within a predetermined temporal offset to the determined start of relaxation.

11. A device, comprising a control unit and a camera, wherein the control unit is configured for controlling an optical display device controllable pixel by pixel, wherein the control unit and the camera are configured to perform the method according to claim 6, and wherein the camera is configured as a complementary metal-oxide semiconductor (CMOS) camera or as a charged coupled device (CCD) camera.

12. The device according to claim 11, wherein the camera is configured for continuously determining the trigger characteristic from the at least one pixel value of the sensor pixels in the trigger subfield and for comparing the trigger characteristic with the trigger threshold value.

13. A device, comprising a control unit and a camera, wherein the control unit is configured for controlling an optical display device controllable pixel by pixel, wherein the control unit and the camera are configured to perform the method according to claim 6, and wherein the camera is configured as a complementary metal-oxide semiconductor (CMOS) camera or as a charged coupled device (CCD) camera.

14. The device of claim 13, wherein the camera is configured for continuously determining the trigger characteristic from the at least one pixel value of the sensor pixels in the trigger subfield and for comparing the trigger characteristic with the trigger threshold value.

15. The method according to claim 6, wherein the burn-in behavior of a display is determined for application in a vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, embodiments of the invention are described in more detail with reference to drawings.

(2) FIG. 1 is a schematic view of an arrangement for charting the burn-in behavior of a display,

(3) FIG. 2 is a schematic view of a sequence of images projected when charting the burn-in behavior,

(4) FIG. 3 is a schematic view of an arrangement for charting the burn-in behavior of a display,

(5) FIG. 4 is a schematic view of a sensor field of a CMOS camera, and

(6) FIG. 5 is a schematic view of a course of trigger integral value corresponding to a trigger image area.

(7) Corresponding parts are given the same reference signs in all figures.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(8) FIG. 1 is a schematic view of a measurement setup known in the art for charting the burn-in behavior of a display 1. The measurement setup comprises a computer 2 connected to the display 1 and to a camera 3.

(9) The display 1 to be charted may for example be a liquid crystal display (LCD) or an organic luminous display (OLED organic light emitting diode).

(10) The computer 2 is configured to output images or graphics on the display 1. Instead of the computer 2, a test image generator not shown in detail may be used to output images on the display 1.

(11) A burn-in image EB being output on the display 1 is presently illustrated. The burn-in image EG is configured as a chessboard pattern with square fields distributed across the entire image area. The square fields have an approximately homogenous luminance density, wherein adjacent fields differ from one another in luminance density. In an embodiment, the chessboard pattern consists of fields with a maximized difference in contrast.

(12) The connection between the computer 2 or the test image generator not shown in detail and the display 1 may for example be a VGA (Video Graphics Array) connection, a HDMI (High Definition Multimedia Interface) connection, a display port connection or a DVI (Digital Visual Interface) connection. Likewise, generic bus types not limited in application to the transmission of images or graphics may be used for connecting the computer 2 or the test image generator to the display 1. For example, a Controller Area Network (CAN) bus may be used for the connection.

(13) The camera 3 is configured for recording a camera image KB not shown in detail in FIG. 1, the camera image KB capturing the burn-in image EB presented by the display 1. The camera 3 is configured such that the luminance density emitted by the display 1 is captured pixel by pixel as a grey scale value or as a color value. In particular, the optical axis of the camera 3 is aligned perpendicular to the display 1. Moreover, the camera 3 is configured to provide photometric or colorimetric pixel values for a plurality of image pixels.

(14) The computer 2 is configured to receive and process a camera image KB recorded by the camera 3.

(15) FIG. 2 is a schematic view of a sequence of images presented on the display 1 when charting the burn-in behavior according to the prior art. The process is divided into three phases P1, P2, P3.

(16) In a first phase P1 the display 1 is controlled by the computer 2 with a rolling sequence of warming-up images WB1 to WB3. The warming-up images WB1 to WB3 have an approximately homogenous grey scale value distribution with grey scales different from one another. The warming-up images WB1 to WB3 are configured such that the display 1 arrives at a stationary operating state and that no burn-in effects are caused on the display 1. The sequence of warming-up images WB1 to WB3 is only shown once in FIG. 2, however, it may be repeated in a cycle if required to arrive at a stationary operating state.

(17) At the end of the first phase P1 the display 1 is fed a reference image B0 having a homogenous grey scale reference value.

(18) In a second phase P2 following the first phase P1 the display 1 is fed the burn-in image EB described above with reference to FIG. 1.

(19) In a third phase P3 following the second phase P2, the display 1 is fed a relaxation image RB. In an embodiment, the relaxation image RB is identical to the reference image B0.

(20) At least one camera image KB(DB) is recorded by the camera for each display image DB presented on the display 1. A burn-in effect, in particular a relaxation time constant r may be determined by comparing the camera image KB(B0) pertaining to the reference image B0 with the camera image KB(RB) pertaining to the relaxation image RB.

(21) For an accurate determination of the burn-in effect it is advantageous to know the time difference between the presentation of the relaxation image RB on the display 1 and the recording of the related camera image KB(RB) as precisely as possible.

(22) The control of the display 1 by the computer, i.e.: Output of a respectively different image via the connection between the computer 2 and the display 1, occurs at control points in time t.sub.1, t.sub.3, . . . t.sub.9.

(23) Due to the signal transfer from the computer 2 to the display 1, due to the latency of the display 1, and due to the exposure time of the camera 3 which is typically a few hundredths to tenths of a second, and the clock for reading out the camera images KB being offset relative to the pulsing of the display images DB, the display images DB provided by the computer 2 appear in the camera 3 as camera images KB with a delay at switchover times t.sub.2, t.sub.4, . . . t.sub.10.

(24) The latency Δt.sub.i,i+1=t.sub.i+1−t.sub.i, i=1, 3, 5, 7, 9 between the switch over of the display image DB by the computer 2 and the point in time of recording the camera image KB pertaining to new display image DB can thus not be exactly determined with methods known in the art. This also affects the accuracy in determining the burn-in effect.

(25) The present invention has recognized and overcome this detriment as will be explained in the following with reference to the measurement setup shown in FIG. 3 which is modified relative to FIG. 1.

(26) The measurement setup comprises a modified camera 13 and a modified computer 12. The computer 12 is configured to present a modified burn-in image EB′ on the display 1. The modified burn-in image EB′ comprises a trigger image area TB with a homogenous grey scale distribution. In an embodiment, the trigger image area TB covers a plurality of fields of the chessboard pattern and has a grey scale value differing from the average grey scale value of the burn-in image EB′ as well as from the average grey scale image of the relaxation image RB as much as possible. For example, the trigger image area TB may have the maximum (brightest) grey scale value presentable by the display 1.

(27) The modified camera 13 is configured to read in and/or process a predetermined partial area of a camera image KB. In particular, the modified camera 13 is configured to read in this partial area with a higher speed and a higher frequency than the complete camera image KB. Thus, changes in the predetermined partial area captured by the camera image KB may be detected particularly fast.

(28) In an embodiment shown in FIG. 4 the camera 13 is configured as a CMOS (complementary metal-oxide-semiconductor) camera and comprises a sensor field 14 having a plurality of light sensitive sensor pixels 15 arranged in a matrix-like fashion. The digitalized measures of the sensor field 14 form the camera image KB.

(29) By means of a column address decoder 16 and a row address decoder 17, a sensor pixel 15 whose address matches an address predetermined by an address generator 18, is selected to be output. The selected sensor pixel 15 is made available in a read-out register 19 as a digital value. In the same way, a range of sensor pixels 15 in a row of the sensor field 14 may be made available as a plurality of digital values in the read-out register 19.

(30) Thus, it is possible to particularly rapidly read out all sensor pixels 15 lying within a square or rectangular trigger subfield 20 of the sensor field 14, in particular much faster and within much shorter intervals than the entirety of the sensor pixels 15 of the sensor field 14.

(31) Moreover, the camera 13 comprises a camera control 21 connected to the address generator 18 and the read-out register 19 and having an interface for exchanging data with the computer 2.

(32) The following is a description of the operation of the camera 13 shown in FIG. 3 according to the invention.

(33) A camera image KB is transferred to the computer 2 as the entirety of all digitalized pixel values of the sensor pixels 15 of the sensor field 14. In the computer 2, a partial area of pixels of the camera image KB covering the trigger image are TB of the burn-in image EB′ presented on the display 1 is identified. In an embodiment, a rectangular or square partial area of the camera image KB covering an area of the trigger image area TB which is a large as possible is determined.

(34) This partial area may be determined by automatic image processing. Determination of the partial area in the camera image KB may also be carried out by manual tagging, wherein the camera image KB is presented on a display device not shown in detail and a rectangle or square inscribed in the trigger image area TB is selected, e.g. by means a pointing device.

(35) By transferring the coordinates of pixels of the camera image KB to row addresses and column addresses of sensor pixels 15 of the sensor field 14, the address range of the trigger subfield 20 may be determined and transmitted to the camera control 21 based on the indication of the partial area in the camera image KB. For example, the indices of the first and the last column and of the first and the last row of the sensor field 14 delimiting the trigger subfield 20 may be transmitted.

(36) The camera control 21 is configured and programmed such that the digitalized pixel values of the trigger subfield 20 are continuously read out and that, based on them, a respective trigger parameter T is determined from the pixel values of the trigger subfield 20. For example, the sum or the average of the pixel values of the trigger subfield 20 may be determined as a trigger parameter T.

(37) Due to the very small trigger subfield 20 compared to the sensor field 14, the trigger parameter T may be determined at very short intervals.

(38) FIG. 5 shows the course of the trigger parameter T determined this way over the time axis t. As the trigger subfield 20 is adapted to the trigger image area TB of the display image DB presented on the display 1, the course of the trigger parameter T over time has particularly high values when the burn-in image EB′ with the superposed trigger image area TB is presented with a particularly high (bright) grey scale value on the display 1.

(39) This way it is possible to more precisely determine the switchover time t.sub.10, at which the display 1 switches over between the presentation of the burn-in image EB′ and the presentation of the relaxation image RB. For example, a trigger integral threshold value T.sub.S may be determined based on the particularly high (bright) grey scale value presented in the trigger image area TB and based on the extension of the trigger image area TB as well as based on the exposure time during which the trigger image area TB is respectively exposed. If the trigger parameter T determined by the camera control 21 exceeds the trigger integral threshold value T.sub.S, then this exceedance indicates that the camera 13 has recorded the burn-in image EB′.

(40) Accordingly, the subsequent first instance where the trigger parameter T falls below the trigger integral threshold value T.sub.S at the point in time t.sub.R indicates that the relaxation image RB is presented by the display 1 and that the same is recorded by the camera 13. This point in time may be recorded as the start of relaxation t.sub.R, at which the relaxation of the display 1 starts and to which the temporally decreasing deviation of the camera image KB(RB) recorded during the third phase P3 (relaxation phase) compared to the camera image KB(B0) recorded at the end of the first phase P1 (warming-up phase) is to be related.

(41) The recordation of the camera image KB(RB) which records a relaxation image RB presented on the display 1 after the start of relaxation t.sub.R is released by a trigger signal. The trigger signal may be generated immediately at the determined start of relaxation t.sub.R. In an embodiment, the trigger signal is generated after a predetermined delay or waiting time Δt.sub.R, i.e. at the point in time t.sub.R+Δt.sub.R, wherein this delay is chosen depending on the switchover time interval [t.sub.9, t.sub.10] which is known or being determined for the display device, as will be described in even more detail in the following.

(42) An advantage of the method according to the invention is therefore, that the accuracy in determining the start of the relaxation of the display 1 is basically only limited by the accuracy in determining the trigger integral threshold value T.sub.S and by the time period during which the camera 13 can respectively read out and sum up all sensor pixels 15 within the trigger subfield 20.

(43) As opposed to the prior art, latencies and jitter do not play any role when transferring a display image DB from the computer 2 to the display 1. Furthermore, the latency of the display 1 does not or only marginally affect the accuracy in determining the start of relaxation.

(44) The more precise determination of the start of relaxation t.sub.R also allows for a more precise determination of the burn-in effect compared to methods known in the art. For example, a relaxation time constant r may be determined more reliably and with higher precision.

(45) In an embodiment, the determination of the trigger parameter T may be carried out only in a time interval around the control time t.sub.9 while the computer 2 transmits the relaxation image RB to the display 1 after the burn-in image EB′. This time interval may be coarsely narrowed down, e.g. to a few tenths of a second. For example, the computer 2 may be programmed such that, immediately prior to the switchover of the display image DB from the burn-in image EB′ to the relaxation image RB, a signal is transmitted to the camera control 21 which triggers the determination of the trigger parameter T for a predetermined time period, e.g. 500 milliseconds.

(46) The camera control 21 may also be configured such that the exposure of the camera image KB(RB) related to the relaxation image RB starts after a predetermined waiting time Δt.sub.R beginning at the start of relaxation t.sub.R has elapsed. The predetermined waiting time Δt.sub.R may for example be entered at the computer 2 by the user and submitted by the computer 2 to the camera control 21.

(47) It is possible to set the predetermined waiting time Δt.sub.R such that the switchover process of the display 1 from the presentation of the burn-in image EB′ to the presentation of the relaxation image RB is safely completed when the camera image KB(RB) related to the relaxation image RB is being exposed. In an embodiment, the waiting time Δt.sub.R is set to be equal to or slightly greater than the switchover time interval [t.sub.9, t.sub.10]. [t.sub.9, t.sub.10] indicates the period in which the image pixels of the presented image are safely switched over from the burn-in image EB to the relaxation image RB.

(48) This way it is avoided to record a camera image KB at a time at which the display device 1 still partially presents the burn-in image EB, in particular in image areas outside the trigger image area TB, so that the burn-in effect would be overestimated. This way, the reliability in the assessment of the relaxation behavior of the display 1 is improved.

(49) It is also possible to set the predetermined waiting time Δt.sub.R depending on criteria characterizing specific requirements when using the display 1 and/or which may be required by test standards.

(50) In an embodiment, the burn-in behavior of the display 1, e.g. the relaxation time constant τ, may be determined based on a partial area of the camera image KB(RB) recorded corresponding to the relaxation image RB. For example, the burn-in behavior may be determined by analyzing only those image pixels of the camera image KB(RB) which are provided by the sensor pixels 15 within the trigger subfield 20, wherein the burn-in image EB′ and the relaxation image RB are selected such that the sum or the average of the image pixels respectively assigned to the trigger image area TB differ between the burn-in image EB′ and the relaxation image RB.

(51) Likewise, in order to determine the burn-in behavior, it is possible to read out a sensor pixel 15 or several sensor pixels 15 of the camera image KB(RB) recorded of the relaxation image not or only partially lying within the trigger subfield 20 and to compare it/them with the camera image KB(EB) of the burn-in image EB.

(52) For example, the burn-in image EB′ may comprise a chessboard pattern with dark (black) and bright (white) fields, wherein one or more bright (white) fields of the chessboard pattern are assigned to the trigger image area TB. Herein, the reference image B0 is chosen to be homogenous with an average (grey) greyscale image value.

(53) The burn-in behavior is then determined by analyzing the sensor pixels 15 which are located within the trigger subfield 14 or within another subfield of the sensor field 14 and on which the selected white field/fields are mapped during the burn-in (second phase P2) and then, during the relaxation (third phase P3), the average greyscale values interfered by the burn-in. It is likewise possible to assign selected dark (black) fields of the chessboard pattern to the trigger image area TB instead of the selected bright (white) fields of the chessboard pattern.

(54) An advantage of this embodiment is that the possibility of faster determination whether the trigger parameter T determined over the trigger image area TB crosses (i.e. exceeds or falls below) the trigger threshold value T.sub.S. This way, a higher temporal resolution is achieved when determining the point in time at which the trigger parameter T crosses the trigger threshold value T.sub.S. The start of relaxation t.sub.R may thus be determined more precisely and the burn-in behavior of the display 1 may be determined more precisely.

(55) Moreover, by reading out only a subfield of the sensor field 14 during relaxation (third phase P3), a read out clock rate, which is higher than the camera clock rate envisaged for completely reading out all sensor pixels 15 of the camera 13, is achieved. This way, the temporal course of the greyscale values presented by the display 1 and potentially interfered by the burn-in may be recorded during the relaxation with a higher temporal resolution and the burn-in behavior of the display 1 may be determined more precisely on this basis.

(56) It is possible but not necessary that the subfield of the sensor field 14 read out during the relaxation is chosen to be identical or overlapping with the trigger subfield 20 which is analyzed for continuous determination of the trigger parameter T and for determining the start of relaxation t.sub.R. Likewise, it is possible but not necessary that the subfield read out during the relaxation is chosen to be contiguous. The subfield is chosen such that it may be read out with a read out clock rate which is increased relative to the camera clock rate. This results in the advantage of a higher temporal resolution when determining the relaxation behavior and thus when assessing the burn-in behavior for the display 1.

(57) In an alternative embodiment, the analysis of the image pixels of the camera image KB may also be carried out on the computer 2, wherein the camera control 21 is configured such that the camera image KB or the part of the camera image KB corresponding to the trigger image area TB is transmitted to the computer 2. The advantage of this embodiment is that the analysis of the camera image KB may be implemented independent from the camera 13 actually applied and that therefore different types of cameras 13 may be flexibly applied.

(58) In contrast, the embodiment in which the [analysis of the] sensor values of the sensor field 14 and/or the trigger subfield 20 is carried out by the camera control 21 has the advantage that less data have to be transmitted between the camera 13 and the computer 2. This allows for lower latency and lower jitter between the control time t.sub.9 of the switchover to the relaxation image RB and the determined start of relaxation t.sub.R.

LIST OF REFERENCES

(59) 1 display, display device 2, 12 computer, control unit 3, 13 camera 14 sensor field 15 sensor pixel 16 column address decoder 17 row address decoder 18 address generator 19 read-out register 20 trigger subfield 21 camera control B0 reference image P1 first phase, warm-up phase P2 second phase, burn-in phase P3 third phase, DB display image EB, EB′ burn-in image KB camera image RB relaxation image TB trigger image area T trigger parameter t time axis t.sub.1, t.sub.3, t.sub.5, t.sub.7, t.sub.9 control time t.sub.2, t.sub.4, t.sub.6, t.sub.8, t.sub.10 switchover time t.sub.R start of relaxation, point in time Δt.sub.R waiting time WB1, WB2, WB3 first to third warming-up image