Method of making an output filter for an image intensifier tube with color reproduction and an output made according to this method

[57] ABSTRACT

The invention provides a method of making an output filter for an image intensifier tube for colour display, which output filter is a reproduction of the image intensifier tube in order to avoid the influence of the distortion introduced by the tube.

Claims, 4 Drawing Figures

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PATENTED APR 21974

3,801,739

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3,801,739

METHOD OF MAKING AN OUTPUT FILTER FOR AN IMAGE INTENSIFIER TUBE WITH COLOR REPRODUCTION AND AN OUTPUT MADE ACCORDING TO THIS METHOD

The invention relates to a method of making an out- 5 put filter by means of which the image on the anode screen of an image intensifier tube containing white phosphorus and having an input and output fibre whose photo cathode receives an image via an input filter, can be transformed into a color image, wherein the input 10 filter contains groups of regions each of which groups can transmit different parts of the spectrum, and an output filter made according to this method.

It is known, for example, to mount a raster film with red, green and blue strips against the input fibre of an 15 image intensifier tube and afterwards to transfer the image on the anode screen on to a black-and-white film and then to view the image on the black-and-white film via a raster filter that is identical to the first filter. This shows the drawback that the distortion of the image in- 20 troduced by the image intensifier tube, and hence also the distortion of the image of the input filter, has the result that the lines of the image on the anode screen do not cover the lines in this latter raster filter.

The object of the invention is to provide a method of 25 making an output filter not showing this drawback.

The method according to the invention is to this end characterized in that the output filter is made in the form of a reproduction of the image of the input filter on the anode screen of the image intensifier tube. 30 The invention is further elucidated by reference to the drawing for the special case in which the filter contains red, green and blue strips.

FIG. 1 shows in outline an image intensifier tube with input and output filters. 35

FIG. 2 shows a black-and-white raster with the aid of which an input color raster has been made.

FIG. 3 shows in outline a set-up in which the blackand-white raster is placed against the input of the image intensifier tube in order to make a black-and-white ras- ⁴⁰ter that corresponds to the image formed on the anode screen of the image intensifier tube.

FIG. 4 shows in outline the method of making a color raster from the black-and-white raster made last.

In FIG. 1 an image intensifier tube 1 is shown with an ⁴⁵input raster filter 2 and an output raster filter 3, each containing groups of red (R), green (G) and blue (B) strips. An image falling via the input raster filter 2 upon the photo cathode of the image intensifier tube 1 is formed on the anode screen containing white phospho- ⁵⁰rus and will be observed as a colored image via the output raster filter 3.

FIG. 2 shows an input raster filter 2 and a black-andwhite raster 4 with dark strips 5, which hs been used for making the input raster filter 2. ⁵⁵

FIG. 3 shows the condition in which the black-andwhite raster 4 is mounted at the position of the input raster filter 2 in such a way that strips 5 occupy the position of the strips R in filter 2. The photo cathode of the image intensifier tube 1 is now exposed via the raster filter 4, and the anode screen is imaged 1 : 1 on the black-and-white film 6.

After this, as shown in FIG. 4, the black-and-white raster is imaged on a film 7 which, after development ₆₅in the exposed parts, only transmits, for instance, red, green or blue, and furthermore the entire spectrum, A suitable film for this is, for instance, 3M Colorkey.

These operations are repeated for the green and blue strips. The three prints are then combined on film portions 7 and are mounted precisely behind the anode screen of the image intensifier tube. It is to be noted that in many cases it will be sufficient to use one blackand-white raster 6 for making the three prints on film portions 7.

It will be obvious that the invention is not restricted to the use of raster filters and that other colors than red, green and blue or overlapping parts of the spectrum may also be used.