JP2003288581A - Water area extraction processing method, water area extraction processing apparatus, water area extraction processing program, and recording medium for the program - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To automatically extract a water area based on multispectral features when automatically extracting a water area from a satellite photograph image, an aerial photograph image, or the like. In a determination value calculation process, an R image capturing an electromagnetic wave having a wavelength in a red region of visible light and an NIR image capturing an electromagnetic wave in a near-infrared region are input, and a corresponding image in the image is input. At each point, a determination value such as “luminance value of NIR image / luminance value of R image” is calculated. In the water area determination process 23, when the calculated determination value is equal to or less than a certain value, the point is determined as a water area. This process is repeated for each point in the image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water region extraction processing method, a water region extraction processing device, a water region extraction processing program, and a program recording the program for automatically extracting a water region from an image based on multispectral information. It concerns media.

[0002]

2. Description of the Related Art Extraction of water regions such as oceans, lakes and rivers from images of the surface of the earth is important in the field of remote sensing using satellite photographs and aerial photographs. They used a method of extracting water regions by collating with, or using human hands.

[0003]

However, the conventional method of this kind has a problem that the photographing time may be different from the map making time, and it may be costly to use manpower.

The present invention is intended to solve the problems of the above-mentioned conventional methods, and an image capturing an electromagnetic wave in the near infrared region (referred to as NIR image), which is generally used in satellite photography and aerial photography, and a red region of visible light. The object is to enable stable water region extraction by using an image (referred to as an R image) that captures an electromagnetic wave having a wavelength of.

[0005]

The present invention focuses on the spectral reflectance characteristic that the reflectance of water is greatly different between the visible red region and the near infrared region, and the water region is extracted from the image of the ground surface. It is characterized by extracting. As a means of realization,
The following method is used. 1. An image capturing an electromagnetic wave having a wavelength in the red region of visible light (R image) and an image capturing an electromagnetic wave in the near infrared region (N image)
At each corresponding point of the (IR image), "luminance value of NIR image / luminance value of R image" is calculated. 2. If the obtained value is less than a certain value, the point is determined to be a water region.

As described above, it is possible to stably extract the water region based on the multi-spectral feature.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a configuration example of a water region extraction processing device according to this embodiment. In the figure, 1 is a water region extraction processing device including a CPU and a memory, 10 is an R image storage unit that stores an image (R image) that captures an electromagnetic wave having a wavelength in the red region of visible light, and 11 is a near infrared ray. An NIR image storage unit that stores an image (NIR image) obtained by capturing electromagnetic waves in a region,
12 is a determination value calculation processing unit that calculates a value for determining whether each pixel is a water region from the R image and the NIR image, and 13 is a determination value calculated by the determination value calculation processing unit 12. The water area determination processing unit 14 for determining whether or not the water area is the water area is water area information output from the water area determination processing unit 13.

FIG. 2 shows a water area extraction processing apparatus 1 shown in FIG.
The flow of processing is shown. The input R image 20 is an image that captures an electromagnetic wave having a wavelength in the red region of visible light,
The NIR image 21 is an image that captures electromagnetic waves in the near infrared region. For example, in remote sensing using satellite photographic images or aerial photographic images, these two types of images are often used in order to determine the coverage of plants.

The judgment value calculation process 22 is a process performed by the judgment value calculation processing unit 12 shown in FIG.
And the NIR image 21 are used to calculate a determination value for determining whether or not the region is the water region. First, it may be necessary to align two images due to affine transformation. When the alignment is completed, X = (luminance value in NIR image) / (luminance value in R image) is calculated as the determination value X at each corresponding point.

The reflectance of water greatly differs between the red region of visible light and the near infrared region, and the reflectance in the near infrared region is much smaller than the reflectance of the visible light red region. Therefore, the judgment value X takes a small value in the water region.

The water area determination processing 23 is processing performed by the water area determination processing unit 13. In the water area determination processing 23, when the value of X is equal to or less than a certain value, the point is determined to be the water area. Although the value of this constant value varies greatly depending on the illumination conditions and the camera characteristics, for example, when NIR / R <0.7, the pixel is determined to be the water region.

In addition to the judgment value X, for example, NI
The difference between the brightness value of the R image 21 and the brightness value of the R image 20 is used as a criterion, and Y = (brightness value in NIR image−brightness value in R image) / (brightness value in NIR image + brightness value in R image) It is also possible to use a method such as a value of Y calculated by

The end determination process 24 is a process for determining whether or not to end the process, and here it is determined whether or not the water region determination process 23 has been performed for all pixels. If there are still unprocessed pixels, the judgment value calculation process 2
Returning to step 2 again, the same processing is performed on the unprocessed portion.

The processing performed by the water area extraction processing apparatus 1 described above can be realized by a computer and a software program, and the program is an appropriate computer-readable portable medium memory, semiconductor memory, hard disk, or the like. It can be executed by a computer by storing it in a recording medium and reading it from there. Further, the program can be downloaded from another computer via a communication line, and can be installed and executed.

[0016]

As described above, according to the present invention, the water region extraction is performed by focusing on the spectral reflectance characteristic of water, that is, the reflectance of water is largely different between the visible light red region and the near infrared region. To do. For this reason, stable water region extraction is possible by using general NIR images and R images in satellite photographic images and aerial photographic images.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a water region extraction processing device according to the present embodiment.

FIG. 2 is a diagram showing a processing flow of a water region extraction processing device.

[Explanation of symbols]

1 Water area extraction processing device 10 R image storage unit 11 NIR image storage unit 12 Judgment value calculation processing unit 13 Water area determination processing unit 14 Water area information

Continued front page    (72) Inventor Naoki Ito             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Akio Shio             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F-term (reference) 5B057 AA14 BA02 BA08 BA30 DA08                       DA12 DB02 DB09 DC22 DC32                       DC36                 5L096 AA06 BA18 CA04 FA14 GA08                       JA22

Claims (5)

[Claims] 1. A method of extracting a water region based on multi-spectral information from an image by a computer, acquiring and storing a first image of an electromagnetic wave having a wavelength in the red region of visible light, and A process of acquiring and storing a second image capturing electromagnetic waves in the infrared region, and a luminance value of the first image and a luminance value of the second image at corresponding points in the first and second images. And a step of determining whether or not the point is a water area based on a value calculated from the water area extraction processing method. 2. The water area extraction processing method according to claim 1, wherein in the process of determining whether or not the water area is included, the second image of the second image is obtained at each corresponding point in the first and second images. A water area extraction processing method, characterized in that the brightness value is divided by the brightness value of the first image, and whether or not the point is a water area is determined based on the value obtained by the division. 3. A device for extracting a water region based on multi-spectral information from an image by a computer, means for acquiring and storing a first image capturing an electromagnetic wave having a wavelength in the red region of visible light, and a means for storing the first image. Means for acquiring and storing a second image capturing electromagnetic waves in the infrared region, and luminance values of the first image and luminance values of the second image at corresponding points in the first and second images And a means for determining whether or not the point is a water area based on a value calculated from the water area extraction processing apparatus. 4. A water area extraction processing program for causing a computer to execute the water area extraction processing method according to claim 1 or 2. 5. A recording medium for a water area extraction processing program, wherein a program for causing a computer to execute the water area extraction processing method according to claim 1 or 2 is recorded.