PROCEDURE AND MEANS FOR PRODUCING A FALSE COLOUR PICTURE

METHODE ET DISPOSITIF DE PRODUCTION D'IMAGES EN FAUSSES COULEURS

English Abstract

PROCEDURE AND MEANS FOR
PRODUCING A FALSE COLOUR PICTURE
ABSTRACT OF DISCLOSURE
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, such as CCD
detectors, having a sensitivity range in respect of
wavelength extending into the near infra-red range. The
invention is characterized in that before the semicon-
ductor detector array (2) of the camera is placed a
high-pass filter (4) cutting off blue light so that
only near infra-red radiation gas 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 equival-
ent are obtained signals (ir,ir+g,ir+r) representing
the respective combinations of radiation. From the sig-
nal (ir+g) representing the intensity of near infra-red
radiation and green light obtained from the camera (1)
and from the signal (ir+r) representing the intensity
of near infra-red radiation and red light is in a sub-
tractor (5) subtracted the signal (ir) representing the
intensity of near infra-red radiation, whereupon the
output signals indicate, in equivalent order, the in-
tensity of green and red light (g,r) and the intensity
of near infra-red radiation (ir), whereupon in a swap-
per (5) the order of the signals (g,r,ir) is changed in
order to obtain the desired combined wrong colour sig-
nal.
(Fig. 2)

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 of 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'),
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 (B1b,G1b,R1b)
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 (B1a,G1a,R1a) of the subtractor (5) are
connected and with the aid of which the incoming sig-
nals are swapped so that on the outputs (G2b,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.

Description

~3:~7'~2
PROCEDURE AND MEANS FOR PRODUC:[NG A FALSE 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 tha invention which are stated, regarding the proce-
dure, in the independent claims and regarding the
means, in C:Laim 4.
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Previous wrong colour (or colour-infra) video
cameras are based on tube cameras. The drawback of tube
cameras, co~pared with the present invention, is that
they may suf~er 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 attachiny a shutter to a tube camera is rather
more awkward than it is in the ca~e of a CCD camera.
The invention has been associated with a camera with
shutter, which is a prerequisike ~or 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 picturas can be carried out in a way
which is considerably more simple.
The invention is d~scribed 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 w.rong colour pictura.
The video camera 1 comprises in Fig. 2 a de-
tector array 2 and optics 3 placed therebefore, withthe aid of the latter an image being formed on the sur-
~ace of the detector array 2. Before the detector array
2 is placed only a filter 4 cutting off blue light. At
the high snd thereof the cut-off wavelength of the fil-
ter is advantageously 500 nm. To the blue light detec-
tors B' o~ the video cameras will then be admltted only
near infra-red radiation, to the green light detectors
Gl, both near infra~red radiation and green light, and
to the red light detectors R* i~ admitked 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
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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
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.
The colour signals ir, ir+g, :ir+r obtalned 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
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 Blb, Glb,
Rlb in corresponding order.
The signals ir, g, r obtained after the sub-
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 Blb, Glb, Rlb of the
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 slgnal processing in the
swapper 5 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 fro~ the outputs Blb, Glb, Rlb of the subtrac-
tor 5 is changed in the swapper so that from the out-
puts B2b, G2b, R2b of the swapper the signals g, r, irare obtained, in this order. In other words, the green
g, red r and near infra-red ir signals are changed,
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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 e~uivalent 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 Blb, Glb 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 in~ra-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 outputæ 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 th~ 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.
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Representative Drawing