CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and hereby claims priority to International Application No. PCT/EP2013/000788 filed on Mar. 14, 2013 and German Application No. 10 2012 009 881.2 filed on May 18, 2012, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a method for operating a display device of a motor vehicle, by which image content on a screen. The invention also includes a display device of a motor vehicle. 
         [0003]    In a motor vehicle, provision may be made for a list of function names to be displayed to a user on a screen of a display device, from which the user can choose in order to activate the named function. The display device may be part of a combination instrument or an infotainment system, for example. The user must then be able to move a cursor, for example, over the list elements in order to mark the desired function. Provision may similarly be made for the user to shift the list elements in the displayed list in such a manner that the desired list entry is at the very top, for example, and is activated hereby when a confirmation key is actuated. In order to move the cursor or shift the list contents, a rotary actuator or a rocker switch, for example, may be provided to the user in the motor vehicle as an operating element. Such operating elements generally cannot be used to produce continuous signals. The dial of a rotary actuator may therefore have latching positions. If the latching position changes, this is detected by an encoder of the rotary actuator in intervals of 30 ms to 60 ms, for example, and an electrical signal pulse is then generated, which pulse indicates the direction of rotation and signals the number of latching positions by which the dial has been shifted since the last detection. Such a signal pulse is also referred to as a tick. 
         [0004]    When the operating element is actuated, a cursor, for example, is nevertheless not shifted on the screen suddenly with each received signal pulse but rather in a sliding movement. For this purpose, memory content of a target position memory is changed in the display device on the basis of the signal pulses and the sliding scrolling is then shifted to the target position in a plurality of steps of shifting the image content on the screen. This technique is also referred to as “scrolling”. The screen display is updated during scrolling at an image refresh rate which may be 60 Hz or 120 Hz, for example, and therefore allows flowing movements to be represented. 
         [0005]    If the user generates a plurality of signal pulses by actuating the operating element, the memory content is successively updated as a result. The sliding scrolling is carried out in the meantime. After the user has then stopped rotating the dial, the target position has by no means been reached. Undesirably long running-on of the shifting operation on the screen may therefore result. If the user also changes the direction of rotation of the dial in this case during actuation, the situation may occur in which the cursor is first of all shifted in the one direction for a while and only then changes its movement direction, whereas the user has already stopped rotating the dial. In this case, the movement of the image content on the screen loses the relationship to the actual operating action. 
         [0006]    An animation acceleration method may therefore be provided for such animations. This is explained below using  FIG. 1 . 
         [0007]      FIG. 1  indicates by way of example, on a time axis along the time t (here indicated in seconds), when signal pulses P 1  to P 9  are generated by an operating element, for example a rotary actuator, and arrive at a control device of a display device of a motor vehicle. At the normal actuation speed, a pulse amplitude of these ticks is one. In this case, a tick with the pulse amplitude of one shifts image content, for example a cursor, by a particular shifting distance, for example 5 pixels or 10 pixels, on the screen of the display device. In the graph in  FIG. 1 , this applies to the signal pulses P 1  to P 5  and P 9 . The signal pulses P 6  to P 8  have larger pulse amplitudes since the user has adjusted the operating element with a faster movement in this case. The shifting of the image content must accordingly be greater. The graph in  FIG. 1  also indicates the memory content Z of the target position memory mentioned. It is changed with the arrival of each pulse P 1  to P 9 . The time grid in which the memory content Z is plotted against the time in  FIG. 1  corresponds to that stipulated by the image refresh rate of the display device. 
         [0008]    At a time t=0, an actual position I of the image content on the screen corresponds to the target position predefined by the memory content Z. A difference D between the memory content Z and the actual position I results with the arrival of a signal pulse. The image content is then moved at a constant speed to the target position Z in a sliding scrolling movement. The step size of each shifting step when updating the screen content is initially a basic step size on which the shifting is based until the arrival of the signal pulse P 6 . For this reason, a linear curve profile of the actual position I results until the time t=0.3 seconds at which the actual position corresponds to the target position again. The step size was determined by a scrolling speed for each image refresh (the graph with the solid line in  FIG. 1 ). With the arrival of the signal pulses P 5  and P 6 , the difference D exceeds a threshold value which may be 2 in this case, for example. For this reason, the scrolling speed is increased after the arrival of the signal pulse P 5 . The image content is therefore shifted in greater shifting steps for each new image structure. As a result, the difference D undershoots the threshold value again between the arrival of the signal pulses P 6  and P 7 . The scrolling speed is then reduced to 1 again (t=0.55 s). The signal pulse P 7  then arrives, with the result that the difference D is above the threshold value again and the scrolling speed is set to the value 3 again. The user perceives this change in the scrolling speed as an unsettled, jumpy movement of the image content on the screen. 
       SUMMARY 
       [0009]    One possible object is to enable uniform scrolling at a variable scrolling speed in a display device of a motor vehicle. 
         [0010]    The inventor proposes a method for shifting image content, perhaps in a scrolling movement. In this case, the image content is shifted to a target position in a shifting step or a plurality of shifting steps carried out in succession. The scrolling can be initiated by a user of the display device by actuating an operating element. When actuated, the operating element generates at least one signal pulse. The inventor proposes for a sequence of a plurality of partial pulses to be generated for at least one of the signal pulses, and for the memory content of the target position memory to be gradually changed at the image refresh rate on the basis of the partial pulses. In other words, the time grid in which the signal pulses are generated by the operating element is therefore adapted to the time grid of the screen animation using rate adaptation. The proposal has the advantage that the target position is never suddenly adapted according to the pulse amplitude of a signal pulse but rather only in small substeps. The jumpy movements described can therefore be avoided. The method achieves the object, in particular, for a display device in which image content, for example a cursor or a list, is shifted on a screen, the display of which is updated at an image refresh rate which is greater than the maximum pulse rate of the signal pulses generated by an operating element of the display device when actuated. The adaptation of the time grids has proved to be particularly favorable here, in particular. 
         [0011]    In connection with the proposal, moving image content may be, for example, a cursor which slides over a background image. In this case, the cursor need not completely cover the image background. It may also be, for example, a changed representation of the background, for example in inverted colors. Further examples of movable image contents are list contents, for instance selection menus, and other graphical representations or else shadow effects which are moved, as transparent colored fields, over stationary image contents. 
         [0012]    The method can be carried out using the display device. The latter has a screen, at least one operating element which, when actuated, generates at least one signal pulse, and a control device. The control device has a target position memory and is coupled to the operating element. It is also selected to display image content on the screen and to shift said image content on the screen according to one embodiment of the method. The display device is preferably a combination instrument, as can be installed behind the steering wheel of a motor vehicle, or an infotainment system. 
         [0013]    The operating element may comprise, for example, a rotary actuator, a toggle switch or a roller. However, the operating element may also comprise a touchpad. Such a touchpad has an operating surface across which a user can swipe, for example using a finger, which is then detected by a sensor device of the touchpad (for example using contact sensors, infrared sensors, capacitive sensors). The sensor device then generates, in a predetermined time pattern, a signal which describes the coordinates of the current contact point. The difference between the coordinates of the current contact point and the coordinates of the preceding contact point can then likewise be processed as a signal pulse. These difference pulses can also be divided into partial pulses. 
         [0014]    One development of the method provides for each signal pulse to be filtered using a filter in order to generate the partial pulses. The sequence of partial pulses which is then generated for a signal pulse corresponds to the pulse response of the filter. It is therefore possible to stipulate suitable sequences of partial pulses in a particularly simple and clear manner. It has proved to be particularly expedient in this case to use a filter having a pulse response consisting of the sequence of values 0.4; 0.4; 0.2, for example. In this case, the smaller last value 0.2 results in a fadeout effect. However, the division may also be selected differently. In addition, it is possible to provide switching logic which prevents partial pulses of successive signal pulses being directly superimposed. This makes it possible to additionally avoid jitter in the event of an approximately identical rotary actuator movement. 
         [0015]    Another development of the method provides for the sum of the pulse amplitude values of the partial pulses generated for a signal pulse to be the same as the pulse amplitude value of the signal pulse itself. This is achieved, for example, by the above-described filter with the pulse response 0.4; 0.4; 0.2. Restricting the sum of the pulse amplitude values avoids an amplification effect which might result in an excessively large value for the target position. 
         [0016]    Another embodiment of the method provides for the sequence of partial pulses formed for a signal pulse to be selected to be so short that it comprises no more than 4 partial pulses at an image refresh rate of 60 Hz and no more than 8 partial pulses at an image refresh rate of 120 Hz. This preserves a temporal relationship to the actual actuation of the operating element. Depending on the hardware used, this condition can also be met by virtue of all partial pulses generated for a signal pulse being entered in the target position memory within a period which is shorter than 80 ms, in particular shorter than 40 ms. These time values have proved to be particularly important benchmark figures in experiments. 
         [0017]    The described division of each signal pulse into a plurality of partial pulses makes it particularly easy to configure the scrolling speed to be variable when shifting image content. In this case, it is noted that the scrolling speed for a given image refresh rate directly results from the step size of a shifting step, that is to say the distance by which the image content on the screen is shifted for each new image structure. In order to provide a variable speed, one embodiment of the method now provides for a step size of at least one of the shifting steps to be stipulated on the basis of a difference value between an actual position of the image content on the screen and the target position. The jumpy effect is omitted here by generating and superimposing the partial pulses. 
         [0018]    According to one development of this approach, the difference value is assigned to a multiplication factor for a basic step size, and the step size is then calculated by multiplying the basic step size by the multiplication factor. This results in the advantage that fundamental dynamics, with which image contents move on the screen, can be stipulated very easily in a display device by stipulating the basic step size. A user then far more easily gets a feel for how he should actuate an operating element in order to shift a cursor, for example, by a desired distance. He can estimate its dynamics more easily. 
         [0019]    Dividing a signal pulse into a sequence of partial pulses even makes it possible to completely dispense with tracking of the image content at a limited scrolling speed. In this respect, one embodiment of the method provides for at least occasionally the image content to be immediately shifted to the target position currently predefined by the memory content of the target position memory in each shifting step. The fact that this still results in comprehensible scrolling for the user can be ensured here in a simple manner by accordingly stipulating the sequence of partial pulses. Only simple tests are required for this purpose. In this context, one preferred embodiment of the method provides for the image content to be shifted to a derived target position formed from the memory content of the target position memory using a smoothing filter, rather than being directly shifted to the target position. In particular, provision is made here for a PT 1  element to be used as the smoothing filter. In this respect, it has emerged that this variant provides very up-to-date animation during actuation of the operating element and a user can nevertheless very effectively view the changes on the screen. The haptic relationship can be set in a very favorable manner here. 
         [0020]    The scrolling speed need not necessarily be adapted on the basis of the difference value. This assumes that running-on must first of all be established. The scrolling speed is adapted in a very much quicker manner if the scrolling speed, that is to say the step size, is increased when signal pulses are generated at a predetermined maximum pulse rate and/or a pulse amplitude of at least one signal pulse is greater than a predetermined threshold value. It is then already clear that the user operates the operating element with particularly intense movements. This is a clear indication that he wants quick scrolling. 
         [0021]    If no new signal pulses then arrive for a period of between 30 ms and 60 ms, for example, the current animation speed should first of all be retained and the animation speed should be reduced to a normal degree again only after this period if a defined operating gap has been detected. Accordingly, one embodiment of the method provides for the scrolling speed to only be reduced again if no further signal pulses are generated for a predetermined period, wherein the period is preferably in a range of 30 ms to 60 ms, for example. 
         [0022]    The method can also be combined with already known animation control methods. In this context, one embodiment of the method provides for a step size of at least one of the shifting steps to be set on the basis of an animation characteristic curve. If the target position is so far away from the actual position that a plurality of shifting steps are needed in any case, such an animation characteristic curve stipulates the practice of shifting the image content slowly at the start of the shifting process, more quickly in a central region of the shifting phase and slowly again as the target position is approached. This form of speed control is also called “ease in, ease out”. 
         [0023]    As already stated, provision may also be made for list entries in a list to be shifted or for a cursor to be shifted over such list entries using the described display device. If the scrolling speed is set to be so high during shifting that only one to two intermediate steps are represented on account of the permanently predefined image refresh rate, while the cursor, for example, moves from one list entry to the next, the representation of these intermediate steps should be dispensed with and instead a change should be made to fixed display positions on the individual list entries. In other words, the cursor is then moved exactly to the list entries and is moved from one list entry to the next virtually without animation. Otherwise, the user perceives the transitions only as unpleasant snapshots which are no longer perceived, however, as a clean animation with movement indication. On the basis of this knowledge, the proposal provides a development of the method in which a check is carried out in order to determine whether the pulse rate and/or a pulse amplitude of at least one signal pulse is/are greater than a predetermined threshold value. If necessary, a step size of at least one of the shifting steps is set to a grid spacing of list entries in a list or a multiple of the grid spacing. Different threshold values can naturally be used, depending on whether the pulse rate or the pulse amplitude is checked. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
           [0025]      FIG. 1  shows a graph for shifting image content, as is carried out according to the related art, 
           [0026]      FIG. 2  shows a schematic illustration of a preferred embodiment of the proposed display device, 
           [0027]      FIG. 3  shows a graph for shifting image content in accordance with one embodiment of the method, and 
           [0028]      FIG. 4  shows a graph for shifting image content in accordance with a further embodiment of the method. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0030]      FIG. 2  shows a display device  10  of a motor vehicle, for example an automobile. The display device may comprise a rotary actuator  12 . A rotary movement of a dial  13  is signaled by an encoder  14 , which is coupled to the dial  13 , by electrical signal pulses. A control device  16  of the display device  10 , for example a control unit, receives the signal pulses from the encoder  14 . The control device  16  controls a screen  18  of the display device on the basis of the received signal pulses. The display device  10  may be, for example, part of an infotainment system. The screen  18  may also be a combination instrument which is installed behind a steering wheel of a motor vehicle. Instead of the rotary actuator  12 , it is also possible to provide another operating element, for instance a roller or a toggle switch or a touchpad. 
         [0031]    In the present example, image content  22  is moved on the screen  18  on a display  20  in a flowing movement (animation) in a movement direction  24 , here downward. It is assumed here that the moving image content  22  constitutes a cursor. The display  20  may be, for example, a list which is formed from individual list entries  26 ,  28 ,  30 ,  32 . The list entries  26  to  32  may each represent, for example, a function which is provided by the motor vehicle and from which a driver (not illustrated) would like to choose one. For example, a list entry may represent activation of a radio. 
         [0032]    The moving image content  22  may also be an image detail which comprises part of the display  20  or the entire display  20 . The content of this image detail is then moved in a manner referred to as “scrolling”. The moving image content may therefore also be formed by the list entries  26  to  32 , for example. 
         [0033]    For the further explanation of the example, it is assumed that the cursor  22  was initially positioned at the list entry  28 . The driver would like to choose the list entry  32 . For this purpose, he rotates the dial  13  using his fingers  34 ,  36 . As a result, the dial  13  changes between individual latching positions. The changing of the latching positions is detected by the encoder  14 . The latter generates a signal pulse during each detection operation in a time grid of 30 ms or 50 ms, for example. A maximum pulse rate may therefore in this case be 1/30 ms=33.3 Hz or 1/50 ms=20 Hz, for example. The mathematical sign of a signal pulse indicates the direction of rotation and its pulse amplitude indicates the number of latching positions which have been passed through since the last detection operation. For the purpose of illustration,  FIG. 2  illustrates a time axis on which the exemplary signal pulses P 10  to P 14  are illustrated against the time t. 
         [0034]    The cursor  22  is shifted in the movement direction  24  by rotating the dial  13 . The display  20  which changes as a result is represented at an image refresh rate of 60 Hz, for example. In this case, the cursor  22  is illustrated as having been shifted by a step size  38  in two respective successive representations.  FIG. 2  illustrates this shift for the first shifting step when the cursor  22  moves away from the list entry  28  in the movement direction  24 . 
         [0035]    In this case, the scrolling speed of the cursor  22  and the movement direction depend on the speed and the direction of rotation with which the user rotates the rotary actuator  12 . The control unit  16  evaluates the signal pulses (or pulses for short) P 10  to P 14  in order to determine how the cursor  22  should be moved on the display  20 . For this purpose, the control device  16  has a keying-up device  40 , a target position memory  42  and a representation device  44 . The keying-up device  40 , the target position memory  42  and the representation device  44  may each comprise, for example, a program of a digital signal processor or part of an ASIC (application specific integrated circuit) or of an FPGA (field programmable gate array). 
         [0036]    Upon receiving each pulse P 10  to P 14 , the keying-up device  40  generates a plurality of partial pulses T 1  to T 10  from the received pulse. In this respect,  FIG. 2  illustrates the signal comprising the partial pulses T 1  to T 10 , which is shown for the pulses P 10  to P 14  by the keying-up device  40 , in a graph plotted against the time t. For the sake of better clarity, this graph additionally shows which of the pulses P 10  to P 14  the partial pulses T 1  to T 10  are formed from. For example, the sequence of partial pulses T 1  and T 2  is formed from the pulse P 10 . However, only the partial pulses T 1  to T 10  themselves are output by the keying-up device  40 . The respective partial pulses generated for a pulse are output to the target position memory  42  at a pulse rate which corresponds to the image refresh rate. In other words, an interval of time  46  between two partial pulses which belong to the same pulse is the same as the inverse value of the image refresh rate. The keying-up device  40  may be a filter, for example. In the example shown in  FIG. 2 , the pulse response of the filter may be formed from a sequence of the values 0.5 and 0.5. 
         [0037]    The target position memory  42  stores a value for the target position to which the cursor  22  is intended to be moved on the display  20  by the animated shifting. The animation therefore lasts until the true actual position of the cursor  22  on the screen  20  corresponds to the target position. With each arrival of a partial pulse T 1  to T 10  at the target position memory  42 , the value for the target position is changed according to the pulse amplitude of this partial pulse. 
         [0038]    With each reception of a partial pulse T 1  to T 10 , the value for the target position in the target position memory  42  is changed according to the pulse amplitude and the mathematical sign of the partial pulse. 
         [0039]    The representation device  44  compares the actual position of the cursor  22  with the value of the target position from the target position memory  42 . In this case, when calculating a new display for an image refresh, provision may be made for the step size  38  to be stipulated on the basis of how great the difference is between the actual position and the current target position. Provision may also be made for the step size  38  to be selected to be equal to a grid dimension  48  or a multiple of the grid dimension  48  if the difference exceeds a threshold value. 
         [0040]    After the step size  38  has been stipulated, the representation device  44  calculates a display (that is to say pixel values in a graphics memory or position values in a 3-D graphics chip) in which the cursor  22  has been shifted by the step size  38  in comparison with the current display  20 . The new display calculated in this manner is then represented on the screen  18 . This is cyclically repeated by the representation device  44  at the image refresh rate. 
         [0041]    The movement sequence of image content, for example the cursor  22 , is described again in more detail below using  FIG. 3  and  FIG. 4 . For these explanations, it is now assumed here that the keying-up device  40  divides each received signal pulse into three partial pulses, each signal pulse being divided into three successive partial pulses, the signal amplitude of which is divided by the following factors from the pulse amplitude of the signal pulse: 0.4; 0.4; 0.2. Furthermore, the signal pulse sequence from the signal pulses P 1  to P 9  is taken as a basis, as already described in connection with  FIG. 1 .  FIG. 3  and  FIG. 4  illustrate graphs of the same type as in  FIG. 1 . For simplifying the comparison with the example from  FIG. 1 ,  FIG. 3  and  FIG. 4  also illustrate the course of the target position Z, as would result if the target position memory  42  were directly changed on the basis of the signal pulses P 1  to P 9  without the keying-up device  40 . 
         [0042]    In the display device  10 , the keying-up device  40 , now with the new pulse response (0.4; 0.4; 0.2), divides each signal pulse P 1  to P 9  into a sequence of three partial pulses which are transmitted to the target position memory  42  in the time grid of the image refresh and at the image refresh rate. In this case, the sequence of partial pulses may have a duration of up to 40 ms, for example. Partial pulses may also be accordingly superimposed on one another. Therefore, not every individual partial pulse is provided with a reference symbol in  FIG. 3 , but rather the overall sequence F of partial pulses is illustrated. Each partial pulse changes the memory content in the memory of the target position memory  42 , resulting in the target position Zn at the different times. In the manner described, the control device  44  calculates the difference D between the actual position of the cursor  22  and the target position Zn. A multiplication factor M is determined on the basis of a magnitude of the difference D. The multiplication factor M is multiplied by a value for a basic step size, resulting in the step size  38  with which the cursor  22  is intended to be shifted to the respective current display  20  in comparison with the immediately preceding display. The resultant actual position  11  which is variable over time is likewise plotted in  FIG. 3 . As an alternative to using the multiplication factor M, a speed value G can also be directly calculated from the difference D, for example using a PT 1  element. In this respect, a resulting actual position  12  is likewise recorded in  FIG. 3 . 
         [0043]    The example in  FIG. 4  shows how the target position is accordingly adapted and is also accordingly approached when the operating element, that is to say the rotary switch  12  for instance, is actuated in the opposite direction. For this purpose, the previously underlying sequence of signal pulses P 1  to P 9  is extended by two further pulses P 15  and P 16  which have an inverse mathematical sign in comparison with the signal pulses P 1  to P 9 . When the signal pulses are divided into partial pulses, the sequence F of signal pulses results and causes the target position Zn, as is determined when using the keying-up device  40 , to not have a sudden transition  50 , as is the case with the target position Z. 
         [0044]    The example in  FIG. 4  shows that the division of the signal pulses P 1  to P 9 , P 15 , P 16  into the sequence F of partial pulses also makes it possible to shift the cursor  22  in such a manner that its actual position  13  corresponds to the target position Zn at any time. In other words, the actual position is always adjusted to a changed target position Zn within an individual shifting step. As a result, the user of the display device  10  gains the impression that he directly controls the position of the cursor  22  without delay using the rotary actuator  12  and no jumpy movements are nevertheless carried out by the cursor  22  on the display  20 . In order to illustrate the immediacy of the control,  FIG. 4  also illustrates the course of the actual position  14  which corresponds to the course  12 . This immediate adaptation of the actual position can also be carried out in the example illustrated in  FIG. 3 . The target position Zn ( FIG. 3 ) would then correspond to the actual position. As a further variant, a position characteristic curve Zn (not illustrated) filtered using a PT 1  element may also be provided in this context. 
         [0045]    The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide  v.  DIRECTV,  69 USPQ2d 1865 (Fed. Cir. 2004).
A method for operating a display device of a motor vehicle, by which image content in a shift step or in a plurality of shift steps which are carried out one after another with an image repetition frequency are shifted to a target position on a screen, and in the process the target position is predefined by a memory content of a target position memory, and the memory content is changed as a function of signal pulses which are generated by an operator control element, activated by a user, the pulse rate of which is lower than the image repetition frequency. The scrolling is intended to take place uniformly. For this purpose, a sequence composed of a plurality of component pulses is generated for at least one of the signal pulses, and the memory content is changed with the image repetition frequency on the basis of the component pulses.