JP2001159567A - Spectroscopic image pickup method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clearly get an image of a measurement target in an image spectroscope using a wavelength filter, especially to stabilize tracking an to prevent losing sight of the target when measuring the moving target with tracking the target, by doing away with a narrow-bandwidth bandpass filter for improving wavelength resolution to increase a light amount contributing to image pickup. SOLUTION: This image pickup method extracts an image spectrum similar to the use of the bandpass filter to realize the spectroscopic image pickup by picking up the image through a band rejection filter cutting off a specific wavelength in a narrow bandwidth oppositely to the bandpass filter and getting a difference between the image and an image (a reference image) picked up in a full wavelength transmission state. Thereby, the bright image can be gotten at any time to easily track the image pickup target.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectral imaging method and apparatus for acquiring a spectral image of a measurement target to be imaged.

[0002]

2. Description of the Related Art FIG.
1 shows a conventional spectroscopic imaging apparatus disclosed in Japanese Patent Application Laid-Open Publication No. HEI 10-125, FIG. In the figure, 26 is an objective lens for condensing infrared rays from an imaging target, 20 is a filter plate in which band-pass filters transmitting each wavelength band are arranged on the circumference, 21 is a relay lens for re-imaging, 22 Is a two-dimensional infrared image sensor that converts infrared rays into electric signals, 23 is a cold shield that removes unnecessary radiated infrared rays from inside the device, 24 is a dewar that cools the two-dimensional image sensor 22, and 25 is a motor that rotates the filter plate 20 It is.

Since the conventional spectral imaging apparatus is configured as described above, there is an effect that an apparatus capable of acquiring the spectral characteristics of a two-dimensional image can be configured with a simple structure and small.

[0004]

However, in the conventional spectral imaging apparatus configured as shown in FIG. 10, if the band width of the band-pass filter attached to the filter plate 20 is reduced in order to increase the wavelength resolution, it contributes to imaging. Since the amount of light decreases, a clear image of the measurement target cannot be obtained. For this reason, when trying to measure while tracking a moving target, there is a problem that tracking is not stable or the target is easily lost.

[0005]

A spectral imaging method according to the present invention is an image (all-wavelength image) captured in an all-wave transmission state from light emitted from a measurement target which is an imaging target received by an optical system. A reference image is generated and stored, and an image (a band rejection image) captured through a band rejection filter from which a specific wavelength is removed with a narrow bandwidth is generated, and this is subtracted for each pixel from the stored reference image. Thus, a spectral image is obtained.

A spectral imaging apparatus according to the present invention includes an optical system for capturing an image of a measurement target to be imaged, a filter bank including a plurality of band rejection filters having different wavelengths inserted into the optical system. Photoelectric conversion means for converting a light wave image passing through the filter bank into an electric signal; an A / D conversion circuit for A / D converting an output of the photoelectric conversion means; A reference image storage circuit to store as, an arithmetic circuit for performing processing of subtracting the reference image and the band rejection image for each pixel, selection of a band rejection filter to be inserted into the optical system, and the photoelectric conversion unit,
It includes an A / D conversion circuit, a reference image storage circuit, and a synchronization circuit that manages synchronization with the operation of the arithmetic circuit.

Further, an image change monitoring means for detecting an image change amount from an output of the photoelectric conversion means, and a switching speed of a band rejection filter of a filter bank based on image change amount information obtained by the image change monitoring means. And a filter switching speed control means for changing the filter switching speed.

Further, an image change monitoring means for detecting an image change amount from an output of the photoelectric conversion means, and a reference image switching control means for changing a reference image acquisition interval based on image change amount information obtained by the image change monitoring means. It is provided with.

A pre-reference image storing means for storing a pre-reference image; and an image change unit which evaluates a magnitude of an image change from the pre-reference image when a new reference image is obtained, and judges the validity of the measurement during the evaluation. Judgment means.

Further, a target tracking circuit for tracking the position of the measurement target in the output image of the photoelectric conversion means, and a band rejection picked-up image from the reference image based on the information on the target position from the target tracking circuit. And a pixel shift correction circuit that corrects the calculation so that the target pixel positions are aligned when performing the subtraction process for each pixel.

Further, an image storage circuit for storing each image obtained from the photoelectric conversion means when the band rejection filter is switched, and a plurality of picked-up images stored in the image storage circuit having a substantially flat wavelength characteristic of the filter. And a reference image generation circuit that generates a reference image that is a pseudo full-wavelength image by calculating such that

Further, an S / N determination circuit for detecting the S / N of the captured image from the output of the photoelectric conversion means, and a filter bank for obtaining a predetermined S / N based on the output of the S / N determination circuit. And a filter switching speed control means for changing the switching speed of the band rejection filter.

An S / N determination circuit for detecting the S / N of the picked-up image from the output of the photoelectric conversion means, and a reference image for obtaining a predetermined S / N based on the output of the S / N determination circuit. A reference image switching control means for changing an acquisition interval is provided.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram showing a spectral imaging apparatus according to Embodiment 1 of the present invention.
Reference numerals 1 and 2 denote optical systems that collect light emitted from a measurement target to be imaged and form an image. Reference numeral 3 denotes a filter bank in which an all-wavelength transmission filter and a band rejection filter for removing a specific wavelength with a narrow bandwidth are arranged, and one of the filters is selected and inserted into an optical system. For example, each filter is mounted on a rotating disk. Reference numeral 4 denotes a photoelectric conversion unit, which is a two-dimensional photoelectric conversion sensor such as a CCD, for example, and converts the formed two-dimensional light wave image into an electric signal. Reference numeral 5 denotes an A / D conversion circuit, which converts an electric signal output of the two-dimensional photoelectric conversion sensor 4 into digital data.

Reference numeral 6 denotes a reference image storage circuit which stores, for example, image data when the filter selection of the filter bank 3 is an all-wavelength transmission filter as a reference image. Reference numeral 7 denotes an arithmetic circuit which converts a band rejection image of a wavelength to be measured output from the two-dimensional photoelectric conversion sensor 4 through the A / D conversion circuit 5 from the reference image stored in the reference image storage circuit 6 for each pixel. By subtraction, a spectral image is obtained. Reference numeral 8 denotes a synchronization circuit, which is a filter switching timing of the filter bank 3 and the two-dimensional photoelectric conversion
The operations of the / D conversion circuit 5, the reference image storage circuit 6, and the operation circuit 7 are synchronized.

The spectral imaging apparatus configured as described above is
It operates as shown in FIG. Hereinafter, a case of measuring an imaging target having a radiation characteristic as shown in FIG. 2A will be described. The all-wavelength transmission filter in the filter bank 3 is shown in FIG.
It has the characteristics as in 1). In the imaging using the all-wavelength transmission filter, as shown in FIG. 2B2, all the wavelengths of the imaging target are received by the two-dimensional photoelectric conversion sensor 4, and the image of FIG. Obtain as an image.

On the other hand, the wavelength λn in the filter bank 3
2 (c1) has a characteristic as shown in FIG. 2 (c1). In imaging using this band rejection filter, as shown in FIG. 2 (c2), the wavelength excluding λn to λn + 1 is 2 The light is received by the three-dimensional photoelectric conversion sensor 4, and the band rejection image of FIG.

From the reference image of FIG. 2 (b3), FIG. 2 (c3)
2 (c4) is obtained as a spectral image of only the wavelengths λn to λn + 1 by subtracting the band rejection image for each pixel in the arithmetic circuit 7.

Normally, when the imaging wavelength band is narrowed, the amount of light (indicated by hatching in FIG. 2) contributing to imaging decreases.
The contrast of the obtained image is reduced, resulting in an unclear image. Therefore, in the conventional system shown by a solid line frame in FIG. 2, the filter bank is configured by a bandpass filter having a narrow transmission wavelength as shown in FIG. 2 (d1).
As shown in FIG. 2 (d2), the imaging is always performed with a low light quantity, and the obtained image is an unclear image with low contrast as shown in FIG. 2 (d3). For this reason, it has been difficult to grasp the target position.

However, according to the present embodiment, the spectral image FIG. 2 (c4) obtained as a final result is equivalent to the spectral image FIG. The image to be obtained is always an image (b3) captured in the entire wavelength band or an image (c3) obtained by rejecting only the wavelengths λn to λn + 1. Since the amount of light is relatively large, the contrast is good and the target on the screen is good. Tracking becomes easy, and spectroscopic imaging of a moving target becomes possible.

Embodiment 2 FIG. In the first embodiment, the switching of the filter bank is performed at a constant interval time. In the second embodiment, the change speed of the captured image is detected.
This is for adjusting the switching speed of the filter bank.

FIG. 3 shows a configuration diagram of the spectral imaging apparatus according to the present embodiment. In the figure, reference numeral 9 denotes an image change monitoring circuit which processes an output of the two-dimensional photoelectric conversion sensor 4 to monitor a magnitude of a change in a captured image. Reference numeral 10 denotes a filter rotation control circuit which is switching control means for the filter bank 3, and adjusts the rotation speed of the filter bank 3 based on the information obtained by the image change monitoring circuit 9 to change the filter switching speed. When the image change speed is high, the operation is performed to suppress the pixel shift by increasing the filter rotation accordingly.

Embodiment 3 FIG. In the second embodiment, the filter switching speed is changed by adjusting the rotation speed of the filter bank according to the magnitude of the change in the image. In the third embodiment, the rotation speed of the filter bank is changed according to the magnitude of the change in the captured image. , To adjust the acquisition interval of the reference image.

FIG. 4 shows a configuration diagram of the spectral imaging apparatus according to the present embodiment. Numeral 11 denotes an all-wavelength transmission filter switching control means, which is an all-wavelength transmission filter switching control circuit for adjusting the switching interval of all the wavelength transmission filters in the filter bank 3, for example, based on information obtained by the image change speed monitoring circuit 9. This controls the switching of the all-wavelength transmission filter and adjusts the acquisition interval of the reference image. When the image change is large, the acquisition interval of the reference image is shortened, and the operation is performed to suppress the deviation of the image shape.

Embodiment 4 In the present embodiment, when the image change between the acquisition of the reference image and the next image of the reference image is large, the measurement during that time is determined to be invalid, thereby suppressing the measurement error. .

FIG. 5 shows a configuration diagram of a spectral imaging apparatus according to the fourth embodiment. Reference numeral 12 denotes a pre-reference image storage circuit,
The previous reference image is stored. Reference numeral 13 denotes an image change determination circuit which compares the newly acquired new reference image with the previous reference image, determines the degree of posture change, and when there is a change equal to or more than a certain reference, the spectral imaging result during that period is determined. The result of invalid determination is output.

Embodiment 5 FIG. In the present embodiment, the accuracy of measurement is improved by correcting the pixel shift in accordance with the target movement and obtaining the difference between the band rejection image and the reference image.

FIG. 6 shows a configuration diagram of a spectral imaging apparatus according to the fifth embodiment. Reference numeral 14 denotes a target tracking circuit, and reference numeral 15 denotes a pixel shift correction circuit, which are inserted on the output side of the A / D conversion circuit 5 that outputs a band rejection image signal. The target tracking circuit tracks the position of the measurement target on the image. The pixel shift correction circuit 15 includes a reference image storage circuit 6
When the arithmetic circuit 7 calculates the difference between the reference image and the band rejection image stored in the target image, the pixel position shift is corrected based on the target tracking information obtained by the target tracking circuit 14 and the calculation is performed.

Embodiment 6 FIG. In the first embodiment, the image is captured in advance by the all-wavelength transmission filter and is used as the reference image. In the sixth embodiment, a plurality of images captured by the band rejection filter of the filter bank are calculated. By doing so, the same image as obtained by imaging with a filter having a flat wavelength characteristic is obtained, and this is used as a reference image, thereby omitting the all-wavelength transmission filter.

FIG. 7 shows a configuration diagram of a spectral imaging apparatus according to the sixth embodiment. Reference numeral 16 denotes an image storage circuit that stores captured images that have passed through each band rejection filter of the filter bank 3. 17 is a reference image generation circuit,
A plurality of captured images are averaged to generate a reference image so that the wavelength characteristic of the filter is pseudo-flat. By doing so, there is no need to provide an all-wavelength transmission filter for taking a reference image, and a reference image can be sequentially generated based on the latest information, so that measurement errors can be suppressed.

Embodiment 7 In the first embodiment, the switching of the filter bank is performed at a constant interval time. However, in the present embodiment, the rotation speed of the filter bank is adjusted based on the result of determining the S / N of the captured image. is there.
When the S / N is good, the rotation is increased so as to switch at a fast interval, and when the S / N is bad, the rotation is slowed so as to lengthen the imaging time of each filter, thereby improving the S / N. .

FIG. 8 shows a configuration diagram of a spectral imaging apparatus according to the seventh embodiment. An S / N determination circuit 18 analyzes the contrast of the output image of the two-dimensional photoelectric conversion sensor 4 and determines the significance of the S / N. Filter rotation control circuit 10
Thus, the filter rotation speed of the filter bank 3 is adjusted based on the imaging S / N information from the S / N determination circuit 18.

Embodiment 8 FIG. In the seventh embodiment, the rotation speed of the filter bank is adjusted based on the S / N of the image. However, in the present embodiment, the S / N of the captured image is adjusted.
N is determined, the switching time of each band rejection filter is changed, and the measurement time by each filter is adjusted. When the S / N is good, the measurement can be performed in a short time, so that the filter is switched in a short time, and the measurement is performed with less blur to the moving target. When the S / N is bad, the measurement time is extended to increase the S / N. N can be improved. After the measurement, the measurement time is corrected to obtain a difference from the reference image.

FIG. 9 shows a configuration diagram of a spectral imaging apparatus according to the eighth embodiment. The filter switching control circuit 11 controls the S /
Based on the imaging S / N information from the N determination circuit 18, the switching time of each filter of the filter bank 3 is controlled by the filter switching time control circuit 19 to adjust the measurement time.

[0035]

According to the present invention, there is provided a spectral imaging method and apparatus.
Since spectral imaging is performed using a band rejection filter, the amount of incident light blocked by the filter is small, so it is possible to capture an image while always obtaining a bright image, and when measuring while tracking a moving target This has the effect of making it difficult to lose track of the target.

Further, by controlling the filter switching speed of the filter bank, the acquisition interval of the reference image, and the switching time of each filter according to the magnitude of the image change, the S / N, etc., more accurate measurement can be performed. it can.

Further, the accuracy of measurement can be improved by correcting the pixel shift in accordance with the target movement and obtaining the difference from the reference image.

Further, by calculating a plurality of captured images captured by the band rejection filter of the filter bank, the same image captured by a filter having a flat wavelength characteristic is obtained, and this is used as a reference image. By doing so, the all-wavelength transmission filter can be omitted, and a reference image can be sequentially generated based on the latest information, so that there is an effect that a measurement error can be suppressed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a spectral imaging device according to Embodiment 1 of the present invention.

FIG. 2 is an operation explanatory diagram of the first embodiment.

FIG. 3 is a configuration diagram illustrating a spectroscopic imaging device according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing a spectral imaging apparatus according to Embodiment 3 of the present invention.

FIG. 5 is a configuration diagram showing a spectral imaging apparatus according to Embodiment 4 of the present invention.

FIG. 6 is a configuration diagram showing a spectral imaging device according to Embodiment 5 of the present invention.

FIG. 7 is a configuration diagram illustrating a spectral imaging apparatus according to Embodiment 6 of the present invention.

FIG. 8 is a configuration diagram illustrating a spectral imaging apparatus according to Embodiment 7 of the present invention.

FIG. 9 is a configuration diagram showing a spectral imaging apparatus according to Embodiment 8 of the present invention.

FIG. 10 is a configuration diagram showing a conventional spectral imaging apparatus.

[Explanation of symbols]

1 optical system, 2 optical system, 3
Filter bank, 4 two-dimensional photoelectric conversion sensor, 5 A / D conversion circuit, 6 reference image storage circuit, 7 arithmetic circuit, 8
Synchronization circuit, 9 image change monitoring circuit, 10 filter rotation control circuit, 11 full wavelength transmission filter switching control circuit, 12 pre-reference image storage circuit, 13 image change determination circuit, 14 target tracking circuit,
15 pixel shift correction circuit, 16 image storage circuit,
17 reference image generation circuit, 18 S / N determination circuit, 19 filter switching time control device.

Claims (9)

[Claims] 1. A reference image, which is an image (all-wavelength image) imaged in an all-wavelength transmission state, is generated and stored from radiation emitted from a measurement target, which is an imaging target, received by an optical system, and has a narrow bandwidth. Generating an image (band rejection image) captured through a band rejection filter from which a specific wavelength has been removed, and subtracting the image for each pixel from the stored reference image to obtain a spectral image. Spectral imaging method. 2. An optical system for imaging a measurement target to be imaged, a filter bank including a plurality of band rejection filters having different wavelengths inserted into the optical system, and a light wave image passing through the filter bank is electrically converted. Photoelectric conversion means for converting the output of the photoelectric conversion means into an A / D signal
A / D conversion circuit for conversion, a reference image storage circuit for storing a full-wavelength image to be measured as a reference image from the output of the photoelectric conversion means, and an operation for subtracting the reference image and the band rejection image for each pixel A circuit, selection of a band rejection filter to be inserted into the optical system, the photoelectric conversion means, an A / D conversion circuit, a reference image storage circuit,
And a synchronous circuit for managing synchronization with the operation of the arithmetic circuit. 3. An image change monitoring means for detecting an image change amount from an output of a photoelectric conversion means, and a switching speed of a band rejection filter of a filter bank based on image change amount information obtained by the image change monitoring means. 3. A filter switching speed control means for changing a filter switching speed.
The spectroscopic imaging apparatus according to any one of the preceding claims. 4. An image change monitoring means for detecting an image change amount from an output of the photoelectric conversion means, and a reference image switching control means for changing a reference image acquisition interval based on image change amount information obtained by the image change monitoring means. The spectral imaging apparatus according to claim 2, further comprising: 5. A pre-reference image storing means for storing a pre-reference image, and an image change unit for evaluating a magnitude of an image change from the pre-reference image at the time of acquiring a new reference image and determining the validity of the measurement during the change. The spectral imaging apparatus according to claim 2, further comprising a determination unit. 6. A target tracking circuit for tracking a position of a measurement target in an output image of a photoelectric conversion means, and a band rejection image from a reference image is calculated from a reference image based on information on the target position from the target tracking circuit. 3. The spectral imaging apparatus according to claim 2, further comprising: a pixel shift correction circuit that corrects the calculation so that the target pixel positions are aligned when performing the subtraction processing for each pixel. 7. An image storage circuit for storing each image obtained from a photoelectric conversion unit when a band rejection filter is switched, and a plurality of captured images stored in the image storage circuit, wherein a wavelength characteristic of the filter is substantially flat. 3. The spectral imaging apparatus according to claim 2, further comprising: a reference image generation circuit that generates a reference image that is a pseudo full-wavelength image by performing an operation to obtain a reference image. 8. The S / S of a picked-up image is obtained from the output of the photoelectric conversion means.
An S / N determination circuit for detecting N, and a filter switching speed control means for changing a switching speed of a band rejection filter of a filter bank based on an output of the S / N determination circuit so as to obtain a predetermined S / N. The spectral imaging apparatus according to claim 2, further comprising: 9. The S / S of a captured image is determined from the output of the photoelectric conversion means.
An S / N determination circuit for detecting N; and a filter switching time control means for changing a switching time of each band rejection filter based on an output of the S / N determination circuit so as to obtain a predetermined S / N. 3. The method according to claim 2, wherein
The spectroscopic imaging apparatus according to any one of the preceding claims.