Abstract:
A method for displaying a compacted data signal, comprising the steps of acquiring a data signal comprising a plurality of data values; computing a compaction table based upon said acquired data signal; generating a min/max pair for all data values of said data signal associated with each of a plurality of vertical pixel columns of a display device; drawing a single vertical line for each min/max pair; and repeating said acquiring, computing, generating and drawing steps for each data signal acquisition.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The recent evolution of in the speed of various electronics technologies now allows instruments to measure input data signals that are extremely large, and comprise a great number of samples. These larger data signals, and the great number of samples associated therewith require more and more memory to record the great amount of data associated therewith. In addition to merely storing this extensive amount of data in memory, this data must be somehow displayed to let the user analyze the input and sampled data signal.  
           [0002]    A conventional procedure for drawing a signal on a screen is to draw a line joining each pair of sample points representing the captured signal. After connection of all of the data points a continuous line is presented to the user as an approximation of the received and sampled signal. While this method works fine with a small number of data sample points, as soon as the number of data points increases, this method becomes very slow. This is because drawing of each line by the display device requires hardware access from the main processor to the display device that is a very slow operation as compared to the processor capability. The most advanced instruments can now record multiple millions of data values. However, drawing multiple millions of lines in the display device between these data values is a very slow process, and can take up to several seconds.  
         SUMMARY OF THE INVENTION  
         [0003]    In accordance with the invention, in order to avoid the problem of such a slow display, it is desirable to reduce to a minimum the number of times the display device is accessed. Therefore, in accordance with the invention, stored data is compacted before being forwarded to the display. Such a compaction may be performed when the number of data sample values is greater than the horizontal number of pixels of the display device. In such a situation, because the number of data sample values is greater than the number of pixels that can be displayed, multiple data values would “hit” and be displayed at the same vertical pixel column, resulting in a difficult to view display. This is because means multiple lines will be drawn overlapping each other vertically along the same pixel column.  
           [0004]    Therefore, in accordance with the invention a compaction algorithm comprises examining every data value that would normally “hit” or be displayed at a common vertical pixel column to determine the minimum and the maximum values of such data. Then using this min/max pair a single vertical line is draw at the appropriate vertical pixel column to represent all of the data values corresponding to the pixel column, instead of drawing a multitude of overlapped vertical lines. This method is then applied to every vertical pixel column to be displayed on the display device. The invention also comprises the steps necessary to insure that data values are associated with the appropriate vertical pixel column.  
           [0005]    In accordance with the invention, a clearer and easier display of an acquired signal is provided. Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and the drawings.  
           [0006]    The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts that are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    For a more complete understanding of the invention, reference is made to the following description and accompanying drawings, in which:  
         [0008]    [0008]FIG. 1 is a graph depicting time offsets resulting from an acquisition procedure;  
         [0009]    [0009]FIG. 2 is a graph depicting an artifact generated by the application of a compaction algorithm in accordance with the invention;  
         [0010]    [0010]FIG. 3 is a graph depicting a simple method of curing the artifact of FIG. 2;  
         [0011]    [0011]FIG. 4 is a graph depicting a curing of the artifact of FIG. 2 in accordance with the invention;  
         [0012]    [0012]FIG. 5 is a flow chart depicting a simple compaction method utilizing a single compaction table; and  
         [0013]    [0013]FIG. 6 is a flow chart depicting a compaction method in accordance with the invention in which a compaction table is recomputed for each acquisition. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    Therefore, in accordance with the invention, an improved method and apparatus for displaying a data signal is provided. Data representing a signal to be displayed is compacted before being forwarded to the display. Without compaction, because the number of data sample values is greater than the number of pixels that can be displayed, multiple data values would be displayed at the same vertical pixel column, resulting in a difficult to view display. This is because lines to connect the multiple data sample points in the same vertical pixel column will be drawn overlapping each other. These multiple lines would therefore overlap each other vertically along the same pixel column.  
         [0015]    The compaction algorithm of the invention comprises examining the data sample values that would normally be displayed at a common vertical pixel column to determine a minimum and the maximum value of such data. Using this min/max pair, a single vertical line is then drawn at the appropriate vertical pixel column between the two points, rather than drawing a multitude of overlapped vertical lines between all of the originally presented pixels. This method is then repetitively applied to every vertical pixel column to be displayed on the display device.  
         [0016]    In order to implement the compaction algorithm in accordance with the invention, it is first necessary to determine all the data sample values that would be displayed as belonging to the same pixel column. A compaction table is therefore computed that first determines the number of data sample values belong to each vertical pixel column. This procedure may be implemented by dividing the total number of data sample values by the total number of horizontal pixels on the display device. Alternatively, an acquisition time for a data signal may be divided by the number of horizontal pixels in the display device. This result will represent the time portion of the sampled signal that corresponds to each vertical pixel column. The number of data sample values during this determined time period is the number of data sample values that will be associated with each vertical pixel column in the display device.  
         [0017]    Then, using this determined compaction table to isolate the data sample values to be associated with a particular vertical pixel column, each data value defined by the compaction table to be associated with the particular vertical pixel column is examined to find the minimum and maximum value among the data sample values. This determined min/max pair is then used to define the ends of a vertical line to be drawn for the particular vertical pixel column. As noted above, this procedure is performed for each vertical pixel column of the display device.  
         [0018]    However, the use of this method, called min/max compaction may create, under certain condition, minor artifacts which consist of having some hole between certain drawn min/max lines when the maximum value of a vertical pixel column x is smaller than minimum value of a vertical pixel column x+1 (and for reverse situation where the minimum value of a vertical pixel column x is greater than maximum value of a vertical pixel column x+1). This artifact is depicted in FIG. 2, where a space  210  is shown between vertical lines ( 220 ,  230 ) drawn in adjacent vertical pixel columns. In a simplified solution to the problem, the two min/max lines are extended symmetrically vertically by extending portions  320 ,  330  to be joined to fill up the hole, as shown in FIG. 3.  
         [0019]    This artifact has typically been generated as a result of the procedure used for generating the compaction table, and is in fact inherent therein. In a simpler embodiment, such as the procedure shown in FIG. 5, after data is acquired at step  510 , a generated compaction table is used at step  520 , and the rendering is drawn at step  530 , a single vertical line for each min/max pair. The compaction table is computed only when the number of acquisition data or the display width is changed. Because of the way acquisition hardware works, each acquisition (consecutive or otherwise) does not occur at the exact same time for each sweep. A small arbitrary time offset  130  between the timing of acquisition in a first sweep  110  and the timing of acquisition in a second sweep  120  is shown in FIG. 1. This means the same indexed (numbered) data value may occur at a slightly different time between different acquisition. However, as noted above, each vertical display pixel column represents a fixed range of time that is not designed to vary between acquisitions because the display is provided independently of the timing of the acquisition system. Employing such a variable data acquisition time but fixed display pixel range results in same indexed (numbered) data value possibly corresponding to one vertical pixel column in a first acquisition ( 112 ,  113 ) and corresponding to the adjacent vertical pixel column during the next acquisition ( 114 ,  115 ). The connected circles shown in FIG. 1 indicate this difficulty. With this simplified embodiment, this small time shift between acquisitions is not accounted for, and as a result some data sample values are associated with the wrong vertical pixel column.  
         [0020]    A second problem arising with the use of such a simplified compaction method is that to fill up a hole occurring between two adjacent min/max, the two min/max lines are joined, each being extended an equal amount, as described above and shown in FIG. 3. This only results in an approximation of reality, because the line joining the last data value of the previous min/max to the first data value of the next min/max may ideally start from the bottom of the previous min/max  410  to the bottom of the next min/max  420 , as shown in FIG. 4. In this case, because of the precise location of the min/max pixel values, the middle of a line  430  that would have been drawn without the use of a compaction algorithm to connect these points does not necessarily correspond to the middle of a line drawn using the compaction algorithm employing the nearest value for both the min/max and simply extending each line an equal amount to connect them.  
         [0021]    Therefore, in accordance with the invention, and in an attempt to overcome the drawbacks inherent in the simpler embodiment, as shown in FIG. 6, a compaction table is computed between each acquisition at step  615  in order to account for the small time offset that may be generated between acquisitions. To account for this small time offset, the compaction table no longer relies on the number of data sample values as compared with and the number of display pixel columns. Rather, the compaction table is generated in accordance with the real absolute time of the acquisition of the data sample values including any generated time offset.  
         [0022]    The second problem noted above regarding the inability to insure a proper connection between adjacent vertical lines that must be joined to remove any generated artifacts is solved by storing, in addition to the min/max values for each of the vertical pixel columns, the first and last data value corresponding to the same vertical pixel column. Thus, when extending adjacent vertical lines to remove an artifact, the middle of those two values can be used to compute the exact position for joining the disconnected adjacent min/max lines. Thus, as is shown in FIG. 4, extended portions  430 ,  431  of different sizes may be provided to better follow an ideal line.  
         [0023]    As noted above, in the simplified compaction method embodiment, the compaction table is computed only once, using the number of vertical pixel columns and the number of data sample points only. Each pixel has a fixed number of data sample points associated therewith (FIG. 1. Example: 5, 4, 5, 5 data sample points for the shown vertical pixel columns). This generic compaction table is then used for all subsequent acquisitions. Because each vertical pixel column on the display represents a period of time that is always the same, using the same compaction table for 5 every acquisition causes some data sample values to be associated with a wrong vertical pixel column (see FIG. 1).  
         [0024]    Another problem with the simplified compaction method embodiment comes from the fact that the total number of data sample points is used to compute the compaction table. Thus, looking at FIG. 1, a point to the left of the first pixel and a point to the to the right of the last pixel are also displayed. This is improper because, these displayed pixels are not within the predetermined time slice the pixels are to represent and the absolute time of the data sample values.  
         [0025]    Because the compaction table in accordance with the invention is computed for each acquisition, any generated time offset between each acquisition is sure to be accounted for. This in turn insures that all data sample values are associated with the correct pixel for any acquisition. If any generated offset remains the same between two acquisitions, the compaction table need not be recomputed. The major difference simpler embodiment and the embodiment of the invention is that the translation from data value to pixel is performed without computing an absolute horizontal domain and unit (usually time [s]) for the data values.  
         [0026]    Therefore, for reasons of enhancing performance, not each data value need be translated to an absolute value for comparison because this translation is very time consuming. Therefore, to avoid this time-consuming step of translation, the compaction table noted above is computed in advance for each acquisition. The compaction table predetermines a range of data values to be associated with the time range of each pixel, as shown in FIG. 1, but accounts for time offsets by being generated for each acquisition. The generated compaction table therefore consists of a pair of data points representing the first and last data values to be associated with a particular pixel. A compaction table generated for the first waveform in FIG. 1 for the first waveform would be 2-6/7-10/11-15/16-20. The compaction algorithm for the second waveform would be 2-5/6-10/11-14/15-19.  
         [0027]    These two values for each entry of the compaction table consist of a first data when entering the pixel range and a last data when exiting the pixel in the time-domain range. These values are also used to connect disconnected adjacent min/max points, as shown in FIG. 4 by a properly positioned line. The connection between the two points is made by extending both adjacent min/max pair to the middle point between the last value of the left (first in time) min/max pair and the first value of the right (next in time) min/max pair. The step where the connection between the two lines occurs is typically not a simple middle point between the two adjacent vertical lines. Thus, a line is rendered between the pairs in the same location as if no compaction has occurred.  
         [0028]    Therefore, in accordance with the invention, more accurate and rapid rendering of a received signal can be achieved.  
         [0029]    It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, because certain changes may be made in carrying out the above method and in the construction(s) set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.  
         [0030]    It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.