Abstract:
A system for displaying three-dimensional data as a set of successive plots is described. Each individual plot is displayed on an oscilloscope and the successive plots are photographed. Amplitude information is quantized and represented in the plots, in combination, as the length and intensity of a segment, so that precise amplitude information is obtained as well as pattern enhancement.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention refers to the display of sets of two- or three-dimensional data and, more particularly, to a display system capable of providing precise magnitude information in all dimensions. 
     2. Description of the Prior Art 
     Display systems are used in various arts in the analysis of sets of two- or three-dimensional data both for visually detecting particular patterns and for obtaining magnitude information on the data. 
     In particular, display systems are used in the spectral analysis of complex waves as produced, for example, by a heartbeat or by a human voice, for the purpose of diagnosis or, respectively, recognition. When the complex wave is considered at a fixed instant of time, the analysis involves only two dimensions, namely, frequency and amplitude; while when the variations of wave with the time are also considered, the analysis involves three dimensions, namely, frequency, amplitude and time. 
     Various systems have been developed to display two- or three-dimensional data in order to give a synoptic image of the phenomenon to be analyzed. With particular reference to the spectral analysis, one prior art system consists of plotting a diagram in cartesian orthogonal coordinates with the time on the horizontal axis, the frequency on the vertical axis, and the relative amplitude of the spectrum components shown in terms of the darkness of the points of the diagram. Another prior art system consists of plotting a diagram in orthogonal coordinates with the time on the horizontal axis and the frequency on the vertical axis, the relative amplitude of each spectrum component being shown as a small deflection of the diagram in the direction of the horizontal axis. However, neither of such prior art systems provides precise magnitude information. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of this invention to provide a display system which, while giving a synoptic image of the phenomenon to be displayed, yields also precise magnitude information. 
     It is another object of this invention to provide a display system in which the display has a compact format. 
     It is another object of this invention to provide a display system in which magnitude information may be read without need for any particular instrument. 
     The foregoing objects are achieved in the present invention which provides means for displaying a signal as a two-dimensional surface and means for modulating stepwise the intensity of each cross section of the surface. In a preferred embodiment, a signal produced by a spectrum analyzer is displayed on a cathode ray tube as a two-dimensional surface in orthogonal coordinates with the frequency on the horizontal axis and the amplitude on the vertical axis, the amplitude of each spectrum component of a given frequency being represented in combination by the height and darkness of the surface corresponding to that frequency. The present invention will be more fully understood by considering the following detailed description of a preferred embodiment, with reference to the following drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 represents a diagram in conventional orthogonal coordinates useful for explaining the present invention; 
     FIG. 2 represents a two-dimensional diagram as produced by a display in accordance with the present invention; 
     FIGS. 3-6b represent diagrams useful for explaining the present invention; 
     FIGS. 7a-7b represent a block diagram of an apparatus in accordance with the present invention; 
     FIGS. 8-9 represent particulars of the block diagram of FIG. 7; 
     FIG. 10 represents an arrangement for recording three-dimensional diagrams in accordance with the present invention; and 
     FIG. 11 represents a three-dimensional diagram as produced by an arrangement in accordance with FIG. 10. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, there is illustrated a spectral diagram E(t) in conventional cartesian orthogonal coordinates of amplitude and frequency, shown in a particular instant of time t. The diagram E(t) is divided into zones 12a-12c by four amplitude levels 11a-11d, with level 11a coinciding with the zero of the amplitude scale and h being the increment of amplitude between one level and the next immediately greater level. In FIG. 1 the area 13 comprised between the diagram E(t) and an immediately underlying one of levels 11 is differentially hatched according to the zone in which such area is comprised, to symbolize different tones in a gray scale. 
     With reference to FIG. 2, the same spectral diagram of FIG. 1 is represented in a different, more compact, format. Each value of frequency is associated with a segment BD of length h divided by a discontinuity point C into two segments BC and CD. Segment BC has a tone of gray corresponding to the tone of gray of the highest zone 12b reached at that frequency by the diagram of FIG. 1. The height of segment BC corresponds to the difference between the amplitude of E(t) at that frequency and the amplitude of the bottom level 11b of the corresponding zone 12b. Segment CD has the next lower tone of gray with respect to segment BC. 
     The format described with reference to FIG. 2 dramatically shows the variations in amplitude of the diagram of FIG. 1. Moreover, the format of FIG. 2 has the advantage of being more compact (which advantage will be more fully understood with reference to the recording of diagrams varying with time, as discussed below), and it can be estimated without the need for any kind of mechanical aids such as a ruler. For example, let us assume that level 11a corresponds to zero db, level 11b to 16 db, level 11c to 32 db, and level 11d to 48 db. Accordingly, the tone of gray of zone 12a corresponds to zero db, the tone of gray of zone 12b corresponds to 16 db and the tone of gray of zone 12c corresponds to 32 db. With these assumptions, the amplitude corresponding to the segment BC of FIG. 2 is immediately estimated as about one-half of 16 db (because segment BC is about one-half as long as h) plus the amplitude corresponding to the tone of gray of segment CD, i.e., 16 db; thus the estimated amplitude is about 8+ 16= 24 db. 
     The apparatus for providing a display of the type as shown in FIG. 2 in accordance with a preferred embodiment of this invention will be described with reference to FIGS. 7a and 7b. The apparatus uses a display means, such as an oscilloscope 15 (FIG. 7a) in which an electron beam describes a diagram on a phosphor screen 16. The oscilloscope 15 is provided with X-axis and Y-axis deflecting means 17 and 18, respectively, as well as Z-axis modulating means 19. Such oscilloscopes are well known in the art. 
     An electrical signal S to be analyzed (FIG. 7b), which may be obtained for example by transducing with a microphone a heartbeat or a human voice, is connected with a spectrum analyzer 20. Spectrum analyzers are well known in the art and generally comprise a mechanism for scanning a band of frequencies and producing an output signal corresponding to the amplitude detected at the various frequencies within the band. A signal 21 produced by analyzer 20 in synchronism with the frequency scanning, is connected with the X-axis deflecting means 17 to cause the electron beam of oscilloscope 15 to horizontally scan the screen 16. Spectrum analyzer 20 also produces a signal E(t) corresponding, on a logarithmic scale, to the amplitude of signal S detected at the various scanned frequencies. Such signal E(t) is connected with a quantizer 22, to which is also connected three electric signals La, Lb, Lc having constant magnitudes h, 2h and 3h, respectively. 
     The quantizer 22 comprises three comparator circuits 23a, 23b, 23c (FIG. 8), connected in parallel with signal E(t) and, respectively, with signals La, Lb, Lc. The output signal 24 i  where = a, b or c of each comparator 23 i  is equal to zero when the amplitude of E(t) is less than the amplitude of Li and is equal to Li when the amplitude of E(t) is equal to, or greater than, the amplitude of Li. The signals 24 i  are combined in a summing circuit 25 providing a quantized signal A(t). The shape of signal A(t), as a function of signal E(t), is shown in FIG. 3 with reference to FIG. 1. In this description, only three signals Li are considered for convenience, but, of course, the number of signals Li of quantizer 22, and correspondingly the number of steps of signal A(t) may be greater than three. 
     Signal A(t) (FIG. 7b) is connected with an inverter 26 providing an output signal -A(t). Signals -A(t) and E(t) are combined in a summing circuit 28 providing an output E(t)-A(t). 
     A sawtooth generator 27 provides a sawtooth signal Y(t) and a blanking pulse signal R(t). Signal Y(t) is connected with the Y-axis deflecting means 18 to cause the electron beam of oscilloscope 15 to scan the screen 16 by subsequent vertical scans. Signals Y(t) and E(t)-A(t) t) are connected with a comparator circuit 29 which provides an output signal S(t) being: 
     
         S(t)= 0 when Y(t)≧ E(t)-A(t) 
    
     
         S(t)= b when Y(t)&lt; E(t)-A(t) 
    
     Fig. 4 shows the waveform of E(t)-A(t) for a waveform of E(t) as shown in FIG. 1. A section k-j of the waveform of E(t)-A(t), with an enlarged frequency scale, is shown in FIG 5a superimposed on the waveform of Y(t). FIG. 5b shows the corresponding waveform of S(t). With reference to FIGS. 5A and 5B, it will be noted that the signal S(t) decreases in value from b to zero corresponding to a point of variation in the tone of gray, such as at point C (FIG. 2). 
     The signal A(t) is connected with an amplifier 33 (FIG. 7b) which provides an output signal Az(t). The amplification of amplifier 33 is b/h, so that the signal Az(t) has the same shape as that of A(t) but with steps b high rather than h. The signals Az(t) and S(t) are combined in a summing circuit 34 which produces a signal 30 equal to Az(t)+S(t). 
     The blanking signal R(t) from sawtooth generator 27 is connected with a baseline generator 35. Baseline generator 35 comprises a one-shot multivibrator which produces a pulse of a short duration with respect to the period of the sawtooth signal Y(t). The parameters of such one-shot multivibrator are so selected that the produced pulses are in synchronism with the passage of the electron beam of cathode ray tube 15 by the origin of the amplitude axis on screen 16. 
     The signal S(t) is connected with a plot generator 36. The signal A(t) is connected with a plot inhibit circuit 37 which is in turn connected with plot generator 36. With reference to FIG. 9, the circuit for the plot generation and inhibition is described in more detail. Signal S(t) is connected with a differentiator 38 which is in turn connected, through a gate 39, with a one-shot multivibrator 41 responding to negative pulses. Signal A(t) is connected with a differentiator 42 which is in turn connected with a rectifier 43. Rectifier 43 controls the one-shot multivibrator 41 through gate 39. 
     The baseline generator 35 and the plot generator 36 are connected with a majority circuit 40 producing a signal 44. The majority circuit 40 and the summing circuit 34 are connected with the Z-axis modulating means 19 of oscilloscope 15 through a majority circuit 45. The signal Mz connected by circuit 45 with the Z-axis modulating means 19 is the signal with the highest magnitude between signals 30 and 44. Signal 44 is, in turn, the signal with the highest magnitude between the signals produced by circuits 35 and 36. The modulation of Z-axis is such that signal Mz applied to modulation means 19 increases the intensity of the electron beam of oscilloscope 15, so that if the amplitude of Mz increases, the image on screen 16 will be negative with respect to the image shown in FIG. 2. 
     The operation of the apparatus will be better understood with reference to FIGS. 2, 6a, and 6b. FIG. 6a shows a diagram of the signal Mz applied to the Z-axis modulating means 19, corresponding to the scan of section W--W of FIG. 2. For convenience, the operation of baseline generator 35 and plot generator 36 is omitted in FIG. 6a. The magnitude of signal Mz between points B and C is equal to the corresponding magnitude of the sum of Az(t) and S(t), i.e., b+ b= 2 b. Between points C and D, S(t) is zero; accordingly, the corresponding magnitude of Mz is b+ 0= b. Correspondingly, the electron beam of oscilloscope 15 describes on screen 16 a segment which has on its lower portion corresponding to BC a tone of gray proportional to 2b, and on its higher portion corresponding to CD a tone of gray proportional to b. Since the vertical scans on the oscilloscope are very close together, the observer will see on screen 16 uniform areas of different tones of gray, rather than the different hatchings as shown for convenience in FIG. 2. It will be noted that signal Az represents the gray tone of the area above the discontinuity point C, while the signal S(t) represents the variation of gray tone between below and above the discontinuity point C. 
     FIG. 6b shows the diagram of Mz corresponding to the scan of section W--W of FIG. 2, taking into account also the operation of baseline generator 35 and plot generator 36. Baseline generator 35 applies to the Z-axis modulation means 19 a short pulse corresponding to point B, describing in the subsequent scans a baseline 51. Another short pulse is produced by one-shot multivibrator 41 of plot generator 36 corresponding to point C, when the signal S(t) decreases from b to zero, describing in the subsequent scans a plot 52. The plot inhibit circuit 37 has the purpose of avoiding a plot signal generated by plot generator 36 when the signal A(t) increases a step, as shown at point F (FIG. 5a). Otherwise, a plot signal would be produced, because the signal S(t) correspondingly decreases from b to zero, and on screen 16 of cathode ray tube 15 there would be described a point which actually does not belong to the plot. Accordingly, the plot inhibit circuit 37 inhibits a plot pulse from being produced when A(t) increases. 
     FIG. 10 shows an arrangement for providing a record of the variation of the spectral diagram E(t) with time. The display on screen 16 of oscilloscope 15 is recorded on a continuous motion photographic film 56 by means of a camera 57. In this arrangement, screen 16 must have a very low persistence. Film 56 is driven by conventional film driving means 58 provided with a speed adjustment 59. FIG. 11 shows a sample of such a record on a negative film, obtained with the arrangement of FIG. 10. The spacing d between individual diagrams 60, 61 (FIG. 11) relative to successive times is provided by the film motion. Spacing d can be adjusted by means of film speed adjustment 59 to prevent skewing of the image on film 56 due to film motion; a reduced version of X-axis sawtooth 22 is applied to the Y-axis deflecting means 18 for adjusting each vertical scan by the electron beam by oscilloscope 15 of an amount proportional to the order number of each of the vertical scans made during a single horizontal scan, to compensate for the film movement during a single horizontal scan. To this end, signal 22 is connected through an attenuator 62 (FIG. 10) to a summing circuit 63 which is also connected with the Y-axis sawtooth signal Y(t); summing circuit 62 is connected to the Y-axis deflecting means 18. The attenuation of attenuator 62 is set according to the film speed adjustment 59. It is apparent from FIG. 11 the advantage of having compact individual time sequential diagrams 60, 61 for displaying patterns as regions of uniform darkness is that a region of repetitively large magnitude appears as a dark stripe running generally along the longitudinal axis of the film (which axis is horizontal in FIG. 11, where the film is obviously on its &#34;side&#34;). Patterns can be particularly enhanced by adjusting the speed of film 56 in order to have lower spacing d between successive diagrams. For low spacing values of d, due to the limited resolution power of the eye, each segment of a scan like BD in FIG. 2 will be perceived as having a uniform tone of gray, given by the average of the respective tones of BC and CD. For such low values of spacing, it will be convenient to disconnect the baseline and plot generators 35 and 36, respectively, (FIG. 7b), from the Z-axis modulation means 18 by means of a suitable switch (not shown), for avoiding baseline and plot pulses that alter the average tone of gray perceived by the eye. 
     It will be apparent to those of ordinary skill in the art that various modifications can be made to the preferred embodiment herein described without departing from the spirit and scope of the present invention.