JP2003230157A - Multiband image acquisition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiband image acquisition method capable of producing a picture having a wide angle to a certain extent, and obtaining a sharp spectral characteristic substantially equivalent to the characteristic obtainable by an interference filter. <P>SOLUTION: The multiband image acquisition method for a multiband camera employs multiband image forming filters disposed in front of an optical imaging system. Images for an identical object are acquired successively by use of sharp- cut color filters of more than, and inclusive of, six color variations, for use as the multiband image forming filters. The differences between paired narrowband images each obtained by use of the sharp-cut color filters of two color variations, among the images having more than and inclusive of six color variations, are calculated. The images produced from the differences are regarded as the images each corresponding to the narrowband. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiband image acquisition method, and more particularly to a multiband image having a sharp wavelength region without wavelength shift even when the screen is wide-angle. The present invention relates to an acquirable multiband image acquisition method. 2. Description of the Related Art In general, a multiband camera has an imaging optical system such as a lens, an imaging element such as a CCD, a control system for controlling these, and a front side of the above-described imaging optical system ( It consists of a spectral filter or the like placed on the object side), and performs imaging (photographing) by switching the wavelength of incident light with this spectral filter. In addition, as the above-described spectral filter, a type called a liquid crystal tunable filter, in which a wavelength is electrically switched, is often used. In a multiband camera using the above-described liquid crystal tunable filter, for example, 16 types of filter characteristics can be obtained by sending 16 signals.
In this respect, the liquid crystal tunable filter was easy to use as a filter for a multiband camera. As described above, the liquid crystal tunable filter has advantages when used in a multiband camera, but also has drawbacks. The disadvantage is that a filter using the principle of light interference, such as this liquid crystal tunable filter, can achieve a predetermined performance when the incident angle of light on the filter is vertical, but if the incident angle is shifted, This means that the wavelength may shift or the transmission wavelength band may become broad. Specifically, when the screen has a wide angle to some extent, the incident angle of light is vertical at the center of the screen.
Since the angle of incidence is shifted at the edge part,
Although the center part is imaged with the target spectral characteristic, the edge part is imaged with the spectral characteristic deviating from the target part. For such problems,
Actually, only measures to avoid using a wide-angle lens were taken. In addition to the liquid crystal tunable filter, for example, a so-called turret type interference filter in which 16 interference filters are prepared and arranged on a disk rotated by a motor is also used. However, this has the above-mentioned problem with respect to the incident angle, and at the same time, there is another problem that all 16 filters must be aligned at exactly the same angle.
This is a problem that when there is an inclination within the axis of the 16 filters, the pixel position of the channel related to the inclined filter is shifted and the entire image becomes blurred. . On the other hand, as a filter that does not use the principle of interference, there is a filter that uses a coloring material such as a dye or a pigment. In this example, a pigment or the like is coated on a transparent support, and there is an example in which this is configured in the turret type as described above and used in a multiband camera. In the case of a filter using this color material,
Unlike the interference filter, there is no problem with the incident angle, but the spectral characteristics are much broader than the interference filter, and another problem is that sharp bands (wavelength bands) cannot be set. There is.
Specifically, the half-value width of the average transmittance is about 80 nm, and even those with particularly good performance are about 50 to 45 nm. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to solve various problems in the prior art and to support a wide-angle screen to some extent. An object of the present invention is to provide a multiband image acquisition method that is capable of obtaining sharp characteristics comparable to interference filters in terms of spectral characteristics. To achieve the above object, a multiband image acquisition method according to the present invention forms an image of a subject by an imaging optical system and the imaging optical system. A multiband image acquisition method using a multiband camera having an image sensor and a multiband forming filter disposed in front of the imaging optical system, wherein the multiband forming filter has six or more types of sharp The same subject is sequentially imaged using the cut dye filter, and the difference between the images obtained using the two-color sharp-cut dye filter that can obtain a narrow band is calculated for the obtained six or more images. The difference is an image corresponding to the narrow band. The present invention can be embodied as a multiband image acquisition apparatus (that is, a multiband camera) to which the multiband image acquisition method as described above is applied. That is, the present invention relates to an image pickup optical system, an image pickup element on which an image of a subject is formed by the image pickup optical system, and a multiband forming filter disposed in front of the image pickup optical system. A multi-band camera having six or more types of sharp-cut dye filters as a multi-band forming filter and an image pickup that controls the six-color or more sharp-cut dye filters to sequentially capture the same subject. For the control means and six or more images obtained by imaging, the difference between the images obtained using the two-color type sharp-cut dye filter that obtains a narrow band is calculated and obtained by this calculation processing. The present invention is embodied as a multi-band camera having an image processing means for using the difference as an image corresponding to the narrow band. In the multiband camera according to the present invention, it is preferable to use a CMOS light receiving element having a dynamic range of 5 or more as the image pickup element. The multiband image acquisition method according to the present invention can be executed by a computer under program control, and the present invention can also be commercialized as such a program. . The program can be recorded on a recording medium or directly distributed via a network. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of a multiband camera that embodies a multiband image acquisition method according to an embodiment of the present invention. As shown in FIG. 1, the multiband camera 10 according to the present embodiment basically includes a lens 12, a CCD 14 and an image memory 16, a CCD camera 18 including a control unit (not shown), and the lens 12 described above. It is composed of a sharp cut dye filter device 20 arranged in front (subject side). As the CCD camera 18 used here,
For example, various commercially available products such as CA-D4-1024A manufactured by DALSA can be used. The DALSA CCD camera CA-D4-1024A has a pixel count of 1024 × 1024 pixels and a pixel size of 12 × 1.
It is a 2 μm monochrome camera. Sharp-cut dye filter device 20
Is the above-mentioned 16 types of sharp cut dye filters,
Arranged on a disk that is rotated by a motor (not shown),
This is a so-called turret filter device. Here, the sharp-cut dye filter of 16 color types is divided into approximately 20 n that substantially divides the visible range between approximately 400 to 700 nm.
Selected at intervals of m. FIG. 2 schematically shows the turret of the above-described sharp-cut dye filter device 20. As shown in FIG. 2, the sharp cut dye filter device 20
On the turret, filters 20a, 20b,..., 20p are arranged in the order of the cut wavelengths of the filters, and the turret is rotated by the above-described motor to sequentially capture images. FIG. 3 illustrates the transmittance of the filters 20a, 20b,... Attached to the turret of the above-described sharp cut dye filter device 20. Also, FIG.
Is the principle of the multiband image acquisition method according to the present invention, and the difference between adjacent ones of the filters shown in FIG. 3 (however, the difference between the long wave on the right side and the short wave on the left side is subtracted). ). As shown in FIG. 4, the difference (31, 32,...) Between adjacent filters provides a sharp color channel signal. Here, the half-value width of each signal is 2
0-30 nm. When this is compared with the characteristics of the filter using the conventional color material described above, the wavelength half-value width is about 1 /.
2 Thus, according to the multiband image acquisition method of the present invention, it is possible to obtain a multiband image based on a sharp band setting without dependency on the incident angle of the incident light to the multiband camera. It is to become. Returning to FIG. 1, the description will be continued. The multiband camera 18 according to the present embodiment passes a subject 24 illuminated by a light source 22 through each filter and lens 12 on a sharp cut dye filter device (hereinafter also simply referred to as a filter device) 20 according to a predetermined order. The image is taken. Here, as the light source 22, either natural light or artificial light may be used.
It is preferable that light in the wavelength region of m is included. About light with a wavelength of 700 nm or more, it is preferable to cut it with an appropriate filter. The subject may be of any shape and color, but it does not change with the light source 22 (moving or moving) during continuous imaging (in this case, 16 times). It must have no color change). FIG. 5 is a flowchart showing the operation when a multiband image is acquired using the multiband camera 18 according to this embodiment. Hereinafter, an operation when acquiring a multiband image will be described. First, the light source 22 and the subject 24 are prepared, and one filter in the filter device 20 of the multiband camera 10 is set in the imaging system (step 41).
At this time, in general, it is preferable to set in consideration so that images are taken in order from the short wave side to the long wave side (or from the long wave side to the short wave side). Then, the subject is imaged under the control of the above-described control means under a predetermined condition using the set filter (step 42). The captured image data is also stored in the image memory 16 under the control of the control means (step 4).
3). This operation is continued for the number of times corresponding to a predetermined number of bands while sequentially switching the filters in the filter device 20, and a predetermined number of images are taken (steps 44, 45, 42 to 44). When the imaging of the number of times corresponding to the predetermined number of bands is completed (the determination result of step 44 is N), the difference image is also calculated under the control of the control means (step 46). ). This calculation is to take a difference between images corresponding to predetermined adjacent filters. Actually, an image obtained by a filter having a cut wavelength of a short wave side is obtained from an image obtained by a filter having a cut wavelength of a short wave side. Is deducted. The above calculation is performed here by the filter 20.
Subtracting the acquired image by the filter 20o from the acquired image by p, subtracting the acquired image by the filter 20n from the acquired image by the filter 20o, subtracting the acquired image by the filter 20m from the acquired image by the filter 20n, ..., by the filter 20b This is done by subtracting the acquired image from the acquired image by the filter 20a. It should be noted here that the CCD used
If the dynamic range of the camera 18 is not set sufficiently large, the difference signal of the image may be an extremely small signal. Therefore, in order to obtain a sufficient difference image signal, the dynamic range of the CCD camera 18 to be used should be 5 or more, more preferably 7 or more. The resolution of the CCD camera 18 is also 12 bits or 14
It is preferable that there are bits or more. This is also an effective condition for improving the signal quality of the image difference. By the above-described arithmetic processing, a sharp acquired image corresponding to the band defined by each filter pair is obtained. In step 47, the image thus obtained is output to an arbitrary output device. The image obtained here is a multiband image cut out for each sharp band having a wavelength half width of about 20 to 30 nm. According to the multiband camera shown in the above embodiment, a multiband image which can be applied to a wide-angle screen to some extent and can obtain sharp characteristics similar to an interference filter in terms of spectral characteristics. It becomes possible to get. The above embodiment shows an example of the present invention, and the present invention should not be limited to this. Appropriate changes or improvements are made without departing from the scope of the present invention. Needless to say, it may be. For example, in the above-described embodiment, an example in which a filter for setting a band obtained by dividing the visible range into 16 has been shown, but the number of divisions can be appropriately determined according to the purpose. Further, the filter switching method is not limited to the disk-shaped turret shown in the embodiment, and a linear slide method or the like can also be used. As described above, the above-described multiband image acquisition method can be commercialized as a program for causing a computer to execute this method. As described above, this program can be recorded on a recording medium or directly distributed via a network. As described above in detail, according to the present invention, it is possible to cope with a wide-angle screen to some extent, and in terms of spectral characteristics, sharp characteristics comparable to interference filters can be obtained. It is possible to realize a multiband image acquisition method that can be realized. More specifically, the half-wavelength width is substantially 2
It is possible to easily acquire a multiband image clipped for each sharp band of about 0 to 30 nm, and to provide a device that embodies this, that is, a multiband camera. It is.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing a schematic configuration of a multiband camera according to an embodiment of the present invention. 2 is a view schematically showing a turret of the sharp cut dye filter device 20 in FIG. 1. FIG. 3 shows a filter 20 mounted on the turret of the sharp-cut dye filter device 20 shown in FIG.
It is a figure which illustrates the transmittance | permeability of a, 20b, ..., 20p. 4 is a diagram showing a difference between adjacent ones of filters shown in FIG. 3, that is, a substantial bandwidth. FIG. FIG. 5 is a flowchart illustrating an operation when a multiband image is acquired using the multiband camera according to the embodiment. [Explanation of Symbols] 10 Multiband Camera 12 Lens 14 CCD 16 Image Memory 18 CCD Camera 20 (Sharp Cut Dye) Filter Device 22 Light Source 24 Subject 31, 32,... Difference Bands 41-47 between Adjacent Filters Processing Steps

Claims (1)

What is claimed is: 1. An imaging optical system; an imaging element on which an image of a subject is formed by the imaging optical system; and a multiband forming system disposed in front of the imaging optical system. A multiband image acquisition method using a multiband camera having a filter, wherein six or more sharp cut dye filters are used as the multiband forming filter to sequentially image the same subject, and the obtained six or more A multiband image characterized by calculating a difference between images obtained by using a two-color type sharp-cut dye filter capable of obtaining a narrow band, and setting the difference as an image corresponding to the narrow band. Acquisition method.