GB1147390A - Improvements in or relating to electrical apparatus for simultaneously viewing two objects by the subtraction process - Google Patents

Abstract

1,147,390. Television. COMPAGNIE GENERALE DE RADIOLOGIE. 8 March, 1967 [8 March, 1966], No. 10836/67. Heading H4F. Apparatus for viewing two objects having identical portions and portions which differ in which the images thereof are combined to render visible only those portions which differ, i.e. utilizing the subtraction process, comprises a first television camera 3 providing to a first television monitor 10 a video signal the polarity of which may selectively be inverted, a second television camera 11 containing a storage pick-up tube 12 positioned to view the screen of monitor 10, and a second television monitor 13 fed with the video signal from camera 11. In operation, two radiographic negatives 2 and 6 having identical elements 7 and a different element 8 are mounted in frames 1 and 4 in an apparatus 9 including a light source. Optical superposition of the contours of the negatives is obtained by superposition of the two frames, frame 4 being slidably mounted and the position of negative 6 being adjustable. Frame 4 is then moved away and negative 2 is viewed by camera 3 and the resulting video signal is displayed on monitor 10 in its normal polarity. Camera 11 records this image and transmits it to monitor 13, camera 3 being shut off when the contrast of the image provided by the storage tube 12 on monitor 13 attains a predetermined value, e.g. half of the maximum possible contrast. Frame 2 is then removed and frame 4 slid into the field of view of camera 3. The output signal of camera 3 corresponding to negative 6 is inverted and the camera 3 is kept operative until the instant at which the storage tube 12 produces on monitor 13 a positive in which all contrast has disappeared in parts common to the two negatives. At this moment image 14 is obtained representing the result of the subtraction process.