Bright field and dark field directional reflection light source assembly based on combined light source

Abstract

The invention provides a bright field and dark field directional reflection light source assembly based on a combined light source, which can meet the requirements of realizing directional reflectionlight distribution of a bright field and a dark field at the same time and improve the fingerprint imaging quality. The light source structure comprises a light source and further comprises a light flux adjusting piece, the light source is of a combined light source structure and comprises a central light source and peripheral light sources, the brightness of the central light source and the peripheral light sources can be independently adjusted, the light flux adjusting piece is arranged at the light outlet end of the light source, and the light flux adjusting piece and the light source are coaxially arranged.

Description

technical field [0001] The invention relates to the technical field of forensic science, in particular to a bright field and dark field directional reflection light source assembly based on a combined light source. Background technique [0002] Photography is an important link in the inspection of fingerprints and other traces and physical evidence. If visible fingerprints or fingerprints that have been processed by physical or chemical methods are found on the scene or on inspection materials, they must be photographed and recorded as soon as possible to prevent fingerprints from fading or being accidentally destroyed. Light distribution photography is to adjust and control the brightness distribution of the reflected light of the test material by selecting a white light source or a light source of other wavelengths, and by changing the incident angle and direction of the illumination light, so as to enhance the contrast between the fingerprint lines and the background patte...

AI Technical Summary

Problems solved by technology

[0002] Photography is an important link in the inspection of fingerprints and other traces and physical evidence. If visible fingerprints or fingerprints that have been processed by physical or chemical methods are found on the scene or on inspection materials, they must be photographed and recorded as soon as possible to prevent fingerprints from fading or being accidentally destroyed. Light distribution photography is to adjust and control the brightness distribution of the reflected light of the test material by selecting a white light source or a light source of other wavelengths, and by changing the incident angle and direction of the illumination light, so as to enhance the contrast between the fingerprint lines and the background pattern of the object, and weaken the Or eliminate the interference of the background pattern of the object. Among them, there are various methods for photographing with light distribution. For fingerprints attached to the surface of smooth, non-permeable and semi-permeable plane objects, the most commonly used bright field photography is directional reflection photography, and the most commonly used dark field photography is It is dark field photography, and in different scenes, the types and conditions of fingerprints and their objects are different, and it is also necessary to choose different light distribution methods to effectively display fingerprint lines and details. However, different light distribution devices often The purpose is single. For example, the directional mirror device commonly used in fingerprint photography can only be used for directional reflection photography in bright field; the dark field light distribution device can only be used for dark field photography

[0003] For directional reflection photography in bright field, a spectroscope set at 45° is usually used, and a surface light source is used next to the spectroscope for illumination. The light emitted by the surface light source is reflected by the spectroscope and then vertically illuminates the fingerprint object, and the light reflected by the fingerprint object is transmitted through the spectroscope. Entering the camera imaging, the surface of the smooth plane object attached to the fingerprint is equivalent to a mirror, and the surface light source image reflected by it appears as a bright field light background; while the light emitted by the fingerprint on the object under the illumination of the light source belongs to diffuse reflection superimposed directional reflection The mixed reflected light of the reflective mirror is diffuse, and the light entering the camera lens is relatively small, which appears as dark lines with lower brightness than the light background. However, because the light output area of ​​the surface light source used by the traditional directional reflector cannot be adjusted, As a result, the surface light source image is much larger than the fingerprint image, and the light emitted by the surface light source corresponding to the surface light source image outside the fingerprint area does not contribute to increasing the brightness of the surface light source image within the fingerprint area, but it can irradiate the fingerprint and The background pattern on the lower surface of the object increases the brightness of the fingerprint lines and the background pattern, which reduces the contrast between the fingerprint lines and the light background, the fingerprint imaging quality is poor, and the background pattern is difficult to weaken or eliminate; Field of view photography, usually using a point light source located next to the camera lens for illumination, the illumination light illuminates the fingerprint object obliquely, the incident angle is 10°-30°, after being reflected by the surface of the smooth plane object, very little light enters the camera lens, The image is a dark background in a dark field, and the light emitted by the fingerprint on the object under the illumination of the light source belongs to the mixed reflection light of diffuse reflection and directional reflection, which has a scattering property, and relatively more light enters the camera lens, showing a darker color Light-colored lines with high background brightness. Specifically, when the incident angle is small, the fingerprint lines appear brighter, but the brightness of the lines on both sides of the fingerprint is uneven, and the edge lines are easily interfered by the reflected bright spots of the light source. When the incident angle is too large, the brightness of the fingerprint lines decreases, resulting in a decrease in the contrast between the fingerprint lines and the dark background, and the fingerprint imaging quality is poor.

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