JPH05168610A - Fingerprint detecting method - Google Patents

Abstract

PURPOSE:To execute a detection by non-contact and a stable detection, and to improve workability by converting thermal image information before irradiation of a projected light and after the irradiation stored in advance to an electric signal, displaying an image obtained by operating a difference of two-dimensional temperature distributions and specifying a location of a fingerprint raised line. CONSTITUTION:The examined specimen surface 1 containing a latent fingerprint 2 is irradiated with a lamp light source 5, and by an infrared-ray camera 4, a temperature distribution is detected through an infrared-ray transmission filter 3, and its image information is stored in a memory device 8 through an image arithmetic unit 6. Subsequently, by irradiating light of wavelength absorbed by an organic substance such as water, fat, etc., contained in a fingerprint component, thermal image information of the temperature distribution of the examined body 1 is stored in the memory device 8. Next, with respect to both thermal image information converted to numerical values as gradation information and stored, a difference of both numerical data is operated in the image arithmetic unit 6, and displayed on a display 9 for connecting isothermal parts, by which a location of a fingerprint raised line is specified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for optically detecting a latent fingerprint from a specimen including a fingerprint in the field of forensic technology.

[0002]

2. Description of the Related Art Current latent fingerprint detection methods include a solid-state method that uses a color difference between a specimen and powder by adhering fine powder such as aluminum or Ishimatsuko to water or fat in the fingerprint component, and a fingerprint component. A liquid method in which a chemical is reacted with an amino acid or salt contained therein to give a color, a method in which a fat content in a fingerprint component is reacted with iodine gas to give a color, and International Publication W085-
There is a gas method typified by a method of fixing the fingerprint ridges with a cyanoacrylate gas as shown in Japanese Patent Publication No.

Although many specimens can be detected by using these methods, bills with a complicated pattern on the surface and polymer coating on the surface like new building materials have fingerprints attached. Recently, there have been many cases in which it is difficult to detect only by applying conventional methods, such as difficult materials or special paper such as heat-sensitive paper or water-soluble paper which is weak against heat and water.

As a method of compensating for the above-mentioned drawbacks, a method of utilizing fluorescence generated by high-power, monochromatic light irradiation, usually a laser method, has been proposed, for example, in the following document (1). (1) E. R. Menzel: Identitya
Tion News, International A
association for Identitya
section, Vol. 33, No. 9 (Septembe
r 1983) In this laser method, in order to emphasize the light emission from the fingerprint ridges, a treatment is carried out such as contact with a dye solution having fluorescence or chemical treatment to increase fluorescence. These are generally called pretreatments or pretreatments.
Methods such as those disclosed in Japanese Patent Publication No. 1-154537 and methods utilizing chemical reactions as shown in the following documents (2) and (3) have been proposed. (2) D. W. Herod, E .; R. Menze
l: "Laser Detection of Lat
ent Fingerprints: Ninhydr
n Followed by Zinc Chlori
de ″, Journal of Forensic S
science, JFSCA, Vol. 27, No. Three
p513-518 (July 1982) (3) V.P. R. Sarares, C.I. R. Eves,
P. R. Carey: "On the Detecti
on of Fingerprint by Laser
r Exited Luminescence ", Fo
rensic Science Internet
nal, Vol. 14, p229 (1979) However, in the detection method as described above, the powder is directly applied to the sample, so that the powder adheres more than necessary and the latent fingerprint is destroyed. Therefore, it is desired to realize a method capable of detecting a fingerprint without contacting a sample. In addition, it is also true that there is a difference in the quality of fingerprints detected due to individual differences among workers in the work of applying powder or detection liquid.

In fields other than forensic technology, for example, JP-A-60-213854 and JP-A-61-952.
Although a method of measuring a defect in a structure, a tile, or the like using infrared rays as disclosed in Japanese Patent Publication No. 21 is also taught, these techniques, however, detect defects and peeling points inside the object to be measured. This is a technique for specifying and does not seek to obtain information about the two-dimensionally attached substance on the surface of the object to be measured.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention irradiates light having a wavelength in a region where organic substances such as water or fat in a fingerprint component are absorbed, such as infrared rays, and the temperature of the surface generated at that time is irradiated. It is possible to identify the location of the latent fingerprint by measuring the change. The present invention is
In view of the above-mentioned drawbacks, it realizes a non-contact detection method instead of directly touching a sample like a conventional fingerprint detection method, and has a constant quality regardless of individual differences of workers. It provides an effective method to detect fingerprints of humans.

[0007]

The present invention provides an optical fingerprint detection method for detecting a fingerprint by irradiating a specimen containing a fingerprint with light from a light source and processing the resulting fingerprint image to detect the fingerprint in advance. Measures the temperature and stores it as thermal image information,
Next, after projecting for a certain period of time a light of a wavelength in the region where the absorption characteristics change depending on the amount of organic substances such as water or fat contained in the fingerprint component, this projected light is cut, and the sample at that time The surface temperature is measured and captured as thermal image information, and the thermal image information before the irradiation of the projection light and the thermal image information after the irradiation of the projection light, which are measured and stored in advance, are converted into an electric signal, and 2 A fingerprint detecting method characterized in that the location of a fingerprint ridge is specified by calculating the difference between the dimensional temperature distributions and displaying the image obtained as a result of the calculation.

[0008]

As described above, in the technique of detecting a fingerprint by the laser method, which is a typical example of an optical fingerprint detecting method, a dye such as a rhodamine-based dye having fluorescence in order to enhance light emission from fingerprint ridges. It is necessary to perform treatment such as increasing the fluorescence by contacting with a solution or by reacting an amino acid contained in the fingerprint component with a chemical.

In the present invention, instead of the above operation, the surface temperature of the sample is measured in advance and stored as thermal image information, and then the organic substance such as water or fat contained in the fingerprint component with respect to the sample. After projecting light with a wavelength in the region where the absorption characteristics change depending on the amount of light for a certain period of time, the projection light is cut, the temperature of the specimen surface at that time is measured and captured as thermal image information, and the projection is measured and stored in advance. The latent fingerprint is detected by converting the thermal image information before irradiating the light and the thermal image information after irradiating the projection light into an electric signal and calculating the difference in the two-dimensional temperature distribution.

Therefore, unlike the conventional fingerprint detecting method, the sample can be detected in a non-contact manner without directly touching the sample, so that the sample may be contaminated by powder or solution or the fingerprint itself may be washed away. In addition, there is no variation in detection results due to individual differences among workers. Further, since a wide range can be searched at once, the time required for detection is shortened and the workability is improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fingerprint detecting method according to an embodiment of the present invention will be described below with reference to the accompanying drawings. Consider a case where an infrared camera is used as a means for detecting thermal image information.
First, the temperature distribution on the surface of the sample is measured and the resulting thermal image information is stored. FIG. 2 is a block diagram showing an example of an apparatus for implementing the present invention. The sample surface 1 including the latent fingerprint 2 is illuminated by the lamp light source 5, the temperature distribution of the sample surface 1 is detected by the infrared camera 4 through the infrared transmission filter 3, and the thermal image information is stored in the memory device 8 via the image calculation device 6. Remember. This stored thermal image information is now A
And

Next, light having a wavelength absorbed by an organic substance such as water or fat contained in the fingerprint component is irradiated, the temperature distribution on the surface of the specimen 1 after irradiation is measured, and the thermal image information is stored. To do. It is a known fact that the absorption band of water in the near infrared region is 1.43 μm, 1.94 μm, 3 μm, etc. as shown in FIG. When the sample surface 1 is irradiated with light including these wavelengths from the lamp light source 5, fingerprint components such as moisture and fat absorb light energy, and the temperature of the fingerprint ridge portion becomes higher than the surface temperature of the sample itself. After irradiating the sample 1 with the light including the wavelength for a certain period of time by the lamp light source 5, the infrared camera 4 detects the temperature distribution of the sample surface 1 through the infrared transmission filter 3 and stores the thermal image information in the memory device 8. .. This stored thermal image information is now B. The irradiation time of the light from the lamp light source 5 is controlled by the controller 7 so that the irradiation time of the light can be changed according to the type, surface state, storage state, etc. of the sample 1.

The thermal image information A and B are digitized as grayscale information and stored in the memory device 8. In the image calculation device 6, the difference between the numerical data of the thermal image information A before irradiation with light and the numerical data of the thermal image information B after irradiation of light is calculated, and when the isothermal parts are connected, an image as shown in FIG. 3 is obtained. can get. Since the temperature corresponding to the fingerprint ridge portion is higher than the temperature of the surface of the sample, the curves 11, 12, 13 are shown in FIG.
The area surrounded by, for example, corresponds to the fingerprint ridge portion 10.

The method of extracting only the fingerprint ridge portion 10 from FIG. 3 is to set a certain threshold value by the image calculation device 6 and binarize the numerical data. By binarizing, it is possible to divide a portion having a relatively low temperature level, that is, a sample surface portion, and a portion having a relatively high temperature level, that is, a fingerprint ridge portion. The resulting image is shown in FIG. 4, and this image can be displayed on the display 9 for confirmation. The fingerprint ridge line portion 10 in FIG. 4 is represented by diagonal lines, and the positions of feature points such as branch points and end points used as fingerprint discrimination means can be recognized.

As described above, by measuring the temperature distribution on the surface of the sample, the location of the latent fingerprint can be clarified without contact.

[0016]

The fingerprint detection by the method of the present invention has the following advantages. (1) Since the sample can be detected in a non-contact manner without directly touching the sample unlike the conventional fingerprint detection method,
There is no concern about contamination of the sample by powder or solution and destruction of the fingerprint itself.

(2) There is no variation in the quality of the detected fingerprints due to individual differences among workers, and stable detection can always be performed. (3) Since a wide range can be searched at once, the time required for detection is shortened and workability is improved. It should be noted that the present invention is not limited to the above-mentioned specific embodiments, and it goes without saying that various modifications can be made within the technical scope of the present invention.

[Brief description of drawings]

FIG. 1 is a graph showing a spectral absorption characteristic of water.

FIG. 2 is a block diagram showing an embodiment apparatus for carrying out the method of the present invention.

FIG. 3 is an explanatory diagram showing an example of isothermal curves obtained by the method of the present invention.

FIG. 4 is a fingerprint ridge image obtained as a result of an example of the method of the present invention.

[Explanation of symbols]

 1 Sample Surface 2 Latent Fingerprint 3 Infrared Transmission Filter 4 Infrared Camera 5 Lamp Light Source 6 Image Processing Device 7 Controller 8 Memory Device 9 Display

Claims (1)

[Claims] 1. An optical fingerprint detection method for detecting a fingerprint by irradiating a specimen containing a latent fingerprint with light from a light source and processing the obtained fingerprint image to detect a fingerprint. It is stored as information, and then the light having a wavelength in the region where the absorption characteristic changes depending on the amount of water or an organic substance contained in the fingerprint component is projected onto the specimen for a certain period of time, and then the projected light is cut off. The temperature of the sample surface is measured and captured as thermal image information, and the thermal image information before the irradiation of the projection light, which is measured and stored in advance, and the thermal image information after the irradiation of the projection light is converted into an electric signal, A fingerprint detecting method, characterized in that a location of a fingerprint ridge is specified by calculating a difference between two-dimensional temperature distributions and displaying an image obtained as a result of the calculation.