PROCEDURE AND MEANS FOR PRODUCING A FALSE COLOUR PICTURE

Abstract: The invention concerns a procedure and means for forming a wrong colour picture, in said procedure being utilized a video camera comprising advantageously a plurality of semiconductor detectors, having a sensitivity range in respect of wavelength extending into the near infra-red range. The invention is characterized in that before the semiconducto detector array (2) of the camera is placed a high-pass filter (4) cutting off blue light so that only near infra-red radiation has access to the blue light detectors (N'), both near infra-red radiation and green light have access to the green light detectors (G') and both near infra-red radiation and red light have access to the red light detectors (R'), whereby from the outputs (B, G, R) of the camera (1) or equivalent are obtained signals (ir, ir + g, ir + r) representing the respective combinations of radiation.

Description: PROCEDURE AND MEANS FOR PRODUCING AFALSE COLOUR PICTURE The present invention concerns a procedure as specified in the preamble of the independent claim, for producing a wrong colour picture. The invention also concerns a means implementing said procedure for pro¬ ducing a wrong colour picture. Semiconductor video cameras comprise a plural- ity of semiconductor detectors, usually silicon-based detectors, which have been arranged in linear array or in matrix array. These detectors are moreover mostly connected to operate as CCD detectors. Such CCD detec¬ tors are sensitive both to visible light and to near infra-red rays, as shown in Fig. 1. In common colour video cameras, however, access of near infra-red radia¬ tion to the detectors is prevented by placing before the semiconductor detectors a filter cutting off near infra-red radiation. The colours of the picture, blue, green and red, are separated with second filters pro¬ vided in front of individual detectors in the array of detectors. However, as a rule these colour-separating filters do not filter out near infra-red radiation, and for this reason double filters are required in the camera in order that it might operate as a conventional video camera. The object of the invention is to disclose a novel procedure for producing wrong colour pictures, wherein video cameras known in themselves in the art are utilized, which most advantageously contain a plu¬ rality of semiconductor detectors, such as CCD detec¬ tors, having a sensitivity range in respect of wave¬ length extending into the near infra-red range. This is achieved with the aid of those features characteristic of the invention which are stated, regarding the proce¬ dure, in the independent claims and regarding the means, in Claim 4. Previous wrong colour (or colour-infra) video cameras are based on tube cameras. The drawback of tube cameras, compared with the present invention, is that they may suffer damage under strong light, that they are otherwise likely to break, and that they are ex¬ pensive. As far as the inventor is aware, available wrong colour video cameras are not fitted with shutters because attaching a shutter to a tube camera is rather more awkward than it is in the case of a CCD camera. The invention has been associated with a camera with shutter, which is a prerequisite for most of the embod¬ iments of the present invention. With the aid of the procedure and means of the invention the drawbacks of the above-mentioned wrong colour picture producing methods can be avoided and the production of such pictures can be carried out in a way which is considerably more simple. The invention is described in the following in detail with the aid of the attached drawings, wherein:- Fig. 1 displays the sensitivity range of the CCD detec¬ tor commonly employed in semiconductor video cameras; Fig. 2 presents schematically a means according to the invention for producing a moving wrong colour picture. The video camera 1 comprises in Fig. 2 a de- tector array 2 and optics 3 placed therebefore, with the aid of the latter an image being formed on the sur¬ face of the detector array 2. Before the detector array 2 is placed only a filter 4 cutting off blue light. At the high end thereof the cut-off wavelength of the fil- ter is advantageously 500 n . To the blue light detec¬ tors B' of the video cameras will then be admitted only near infra-red radiation, to the green light detectors G 1 , both near infra-red radiation and green light, and to the red light detectors R* is admitted both near infra-red radiation and red light.From the outputs B, G, R of the camera 1, or equivalent detector unit, are then obtained the signals representing the respective radiation combinations, i.e., from the output repre¬ senting blue radiation, or the blue output B, a signal ir representing the intensity of near infra-red radia¬ tion, from the green output a a summed signal ir+g 5 representing the intensity of near infra-red radiation and green light, and similarly from the red output R a summed signal ir+r representing the intensity of near infra-red radiation and red light. The camera 1 is connected to a subtractor 5. 10. The colour signals ir, ir+g, ir+r obtained through the camera outputs B, G, R are carried to the inputs Bla, Gla, Rla of the subtractor. In the subtractor 5, the signal ir containing near infra-red radiation is sub¬ tracted from the signal ir+g containing beam divider 15 and green light and from the signal ir+r containing near infra-red radiation and red light. These processed signals ir, g, r are put out from the outputs Bib, Gib, Rib in corresponding order. The signals ir, g, r obtained after the sub- 20 tracting operation just described are processed to ob¬ tain the desired wrong colour signal. This is most ad¬ vantageously implemented with the aid of a swapper 6. To the inputs B2a, G2a, R2a of this swapper are con¬ nected, respectively, the outputs Bib, Gib, Rib of the 25 subtractor 5. With the aid of the swapper 5 the input signals ir, g, r are swapped in such a way that the desired signals will appear at the outputs B2b, G2b, R2b. The above-mentioned signal processing in the 30 swapper 6 may take place in one of two ways, which pro¬ duce wrong colour pictures of different appearance. First, the succession of the signals ir, g, r obtained from the outputs Bib, Gib, Rib of the subtrac¬ tor 5 is changed in the swapper so that from the out- 35 puts B2b, G2b, R2b of the swapper the signals g, r, ir are obtained, in this order. In other words, the green g, red r and near infra-red ir signals are changed. respectively, to the blue b, green g and red r signal when the colour is related to the signal sequence in a normal video camera. This is equivalent to the tradi¬ tional wrong colour picture. Secondly, the wrong colour picture may be realized in the following way. The signals ir, g ob¬ tained from the outputs Bib, Gib of the subtractor 5 after the subtracting operation are changed to become, respectively, the output signals g, ir on the outputs B2b and R2b of the swapper 6. In other words, the green and near infra-red signals g, ir are changed to become, respectively, the blue and green signal b, g, while the red signal r is left unchanged, as related to the colour signal sequence in a normal video camera. In a wrong colour picture of this type the plant cover ap¬ pears green, whereas it is seen as reddish in a tradi¬ tional wrong colour picture. The swapper 6 is connected to an assembler 6. The outputs B2b, G2b, R2b of the swapper 6 are connect- ed to the inputs B3a, G3a, R3a, respectively, of the assembler. From the output S of the assembler 7 is ob¬ tained the combined, standard format video signal s , which may be carried e.g. to a monitor or to a suitable recording means. In the foregoing the invention has been de¬ scribed in the first place with reference to one advan¬ tageous embodiment thereof, but it is obvious that the invention may be modified in numerous ways within the scope of the inventive idea defined by the claims fol- lowing below.

Claims: CLAIMS 1. A procedure for forming a wrong colour picture, in said procedure a video camera being util¬ ized, which advantageously comprises a plurality of semiconductor detectors, such as CCD detectors, of which the sensitivity range regarding wavelength ex¬ tends into the near infra-red range, and in said proce¬ dure a high-pass filter being placed before the semi¬ conductor detectors, characterized in that - before the semiconductor detector array (2) is placed a high-pass filter (4) specifically cutting off blue light so that only near infra-red radiation has access to the blue light detectors (B'), both near infra-red radiation and green light has access to the green light detectors (G') and both near infra-red radiation and red light has access to the red light detectors (E 1 ), whereby at the outputs (B, G, R) of the camera (1) or equivalent are obtained signals (ir, ir+g, ir+r) repre¬ senting the respective combinations of radiation; - from the signal, obtained from the camera (1), repre¬ senting the intensity of near infra-red radiation and green light (ir+g) and from that representing the in¬ tensity of near infra-red radiation and red light (ir+r) is subtracted the signal representing the inten- sity of near infra-red radiation (ir) , whereupon the output signals indicate, in respective order, the in¬ tensities of green and red light (g,r) and the inten¬ sity of near infra-red radiation (ir) ; - The order of succession of the signals (g,r,ir) is changed to obtain a combined wrong colour signal. 2. Procedure according to claim 1, character¬ ized in that the signals obtained after the subtracting operation which represent the intensity of green light, red light (R) and near infra-red radiation (ir) are changed to become, respectively, the blue (b) , green (g) and red (r) signal, as related to the succession of signals' in a normal video camera, and are assembled to constitute the desired, standard format video signal. 3. Procedure according to claim 1, character¬ ized in that the signals obtained after the subtracting operation which represent the intensity of green light (g) and near infra-red radiation (ir) are changed to become, respectively, the blue and green (g) signal, while the red (r) signal is kept unchanged, as related to the succession of signals in a normal video camera. 4. A means for forming a wrong colour pic- ture, comprising a video camera and a high-pass fil¬ ter, said video camera most advantageously comprising a plurality of semiconductor detectors, such as CCD de¬ tectors, and said high-pass filter being placed before said semiconductor detector array, characterized in that the apparatus comprises - a high-pass filter specifically cutting off blue light; - a subtractor (5) to the inputs (B, G, R) of which the colour signals (ir, ir+g, ir+r) obtained from the de- tectors (2) from the outputs (B, G, R) are conducted and in which from the signal (ir+g) containing near infra-red radiation and green light and from the signal (ir+r) containing near infra-red radiation and red light is subtracted the signal (ir) containing near infra-red radiation, and from the outputs (Blb,Glb,Rlb) of said subtractor the processed signals proper (ir,g,r) are fed out; - a swapper (6) to the inputs (B2a,G2a,R2a) of which the outputs (Bla,Gla,Rla) of the subtractor (5) are connected and with the aid of which the incoming sig¬ nals are swapped so that on the outputs (B2b,G2b,R2b) of said swapper (4) there are the desired signals (g,r,ir; g,ir,r) ; - an assembler (7) of which the inputs (B3a,G3a,R3a) are connected to the outputs (B2b,G2b,R2b) of the swap¬ per (6) and from the output (S) of which the desired combined, standard video signal (s) is obtained.

Inventors: HAEME TUOMAS, HAEME, TUOMAS
Applicants: VALTION TEKNILLINEN, VALTION TEKNILLINEN TUTKIMUSKESKUS
Application year: 1989
Main classification: H04N9
IPC codes: H04N5, H04N9