Showing papers on "Dark-frame subtraction published in 1965"

Display system with spatial noise elimination using negative image of noise

Abstract: 1,051,802. Television; radar. MULLARD Ltd. Oct. 30, 1964 [Jan. 29, 1964], No. 3805/64. Headings H4D and H4F. An image display and/or conversion system includes a bundle of fibre optical elements and a filter arranged to filter the output of the bundle, the bundle and the filter being arranged in image planes of the system and the filter carrying a negative image of undesired " spatial noise ", i.e. any unwanted static visual pattern which would otherwise occur in the displayed or converted image. Television, Fig. 2. -Undesired " spatial noise ", modifying the image produced by a television system comprising an X-ray image converter tube 12, a television camera 14 and a cathode-ray display tube 1 associated with or including a fibre optical bundle and due for example to (1) a non-uniform X-ray field, (2) non-uniform sensitivity over the area of the photo-cathode and phosphor screen of the converter tube, and (3) non-uniform sensitivity of the phosphor screen of display tube 1, is eliminated by exposing a photographic film 4 to the system when operating without an object 11 so as to form a negative image of the undesired " noise " alone and then including the negative in an image plane when the system is operated normally. The resulting image may be viewed by a photo-cell 7 to produce a signal which is applied through processing circuits (introducing black level and gamma modification) to a final display tube 18. 6 denotes a diffusing layer. The invention may be applied to a system as in Fig. 2 in which elements 10, 11 and 12 are omitted. The invention may also be applied to a cathode-ray tube flying-spot scanner system, Fig. 1 (not shown), and a direct view X-ray or infra-red image-converter tube system, Fig. 3 (not shown). Radar.-In the system described above with reference to Fig. 2, elements 12 and 14 may be omitted and a radar video signal applied to display tube 1 over lead 15. Negative 4 may then be exposed to and thereafter used to remove unwanted signals, for example those due to uninteresting fixed objects in the area scanned by the radar system.