Patent GB-1328121-A (GB)
Title: Method of and apparatus for determining the quantity and physical parameters of objects
IPC: G06V10/28
Filed: 1970-06-23
Abstract: 1328121 Counting and sizing particles BAUSCH & LOMB Inc 23 June 1970 [23 June 1969] 30506/70 Headings G4D and G4H The Specification relates to a line-scanning image analysis system. In order to measure a selected dimension of one object lying in a field of objects a video signal is generated which represents the boundaries of all the objects in the field, the portion representing the selected particle is separated from the video signal and an indication of the selected dimension is generated as a function of the separated signal. A television camera 10 views the image of the objects through a microscope 12 (Fig. 1, not shown) or alternatively it might view a phctograph of the objects (Fig. 38, not shown). The output of the camera is applied to a threshold circuit 53 which produces a binary signal representing the image; the threshold level is either set manually or automatically at an average level as in Specification 1,328,123 and the arrangement is set up to give a binary 1 when the scan crosses the objects and a zero for the background independently of the relative colours. The binary video signal is displayed by a monitor 14 which also shows a frame surrounding those objects which constitute the field, a dark band upon which are displayed figures representing the measurements made by the system and various marker signals. The system as will as measuring various dimensions of an individual particle can measure total or average values for the whole field of objects and can count the total number of objects in the field (see Specification 1,328,124) or just those objects greater than a specified size. A selected particle to be measured is indicated by a light pen as described in Specification 1,328,122. The pen is directed at the top of an image; when the pulses from it coincide with a pulse of the binary video signal, representing an intercept of the scanning beam with the selected particle, the video signal is gated into a measurement circuit 54; by a delay circuit the gate is closed for almost one line scan following each intercept so that only the portions of the video signal representing the selected particle pass the gate. To measure the area of the particle clock pulses are counted for the total length of all the binary 1 pulses of the video signal representing the particle. To measure its maximum dimension perpendicular to scan lines the total number of intercepts of the image are counted the circuit ignoring holes or depressions in the image. To measure its maximum dimension parallel to the scan lines the counter counts the clock pulses during each line of the image; on each succeeding line it starts counting either at the start of the image or where it started in the last line whichever is the earlier; similarly it stops counting either at the end of the image or where it stopped in the last line whichever is the later; thus the count during the last line of the image represents the maximum dimension. The clock pulses occur at intervals of half the separation between two scan lines. If, instead of starting and stopping at the points where it did so in the preceding line as above, the counter stops and starts two pulses earlier or later in each line, then it measures the distance between two tangents at 45 degrees to the scan lines. If the result is divided by #2 the maximum dimensions of the particle at 45 degrees are determined. The maximum of these four dimensions at 45 degrees to one another can be selected for display. Measurements can also be made by a module 56 of the total area of the particles in the field or of the sum of the dimensions perpendicular to the scan lines. Which of these measurements is to be displayed is selected by a module 62 and is then corrected for the magnification of the microscope objective by module 64 and stored in a counter 68. The number of particles falling within a number of preset size ranges can be determined by logic 66 and displayed in a series of mechanical counters 70. A counting module 58 responds once to each particle at the first intercept; it is cut off during succeeding intercepts by feeding back the preceding intercept through a delay of approximately one line scan period to block a gate. A module 67 may be inserted to cut off the binary video signal from counting module 58 until an intercept greater than a preset value is detected (the value set is displayed during this measurement by way of the selector 62) so that only particles above a certain size are counted. The particles are counted one at a time and as they are counted a marker pip is inserted against their images on the t.v. screen. An averaging module 69 is arranged to divide a total area or height measurement by the total number of particles thus displaying the average particle area, &c. in counter 68. The values of size and count stored in counters 68, 72 are read out and converted to seven segment displays on the t.v. screen (Fig. 34, not shown). The Specification describes each part of Fig. 3 in considerable detail.