JP2022179259A - Light flux separation optical system and image processing apparatus - Google Patents

Abstract

To provide a light flux separation prism configuration suitable to acquire a high dynamic range of an image and an image processing apparatus using the same.SOLUTION: An optical system comprises: a first prism which reflects a portion of incident visible light as a reflection light component by internal reflection of a prism glass material and transmits residual portions; a second prism which is arranged via the first prism and an air gap, and which reflects a portion of incident visible light from the first prism as a reflection component by external reflection of the prism glass material, transmits and emits a visible light residual portion; a first visible light image pick-up device which performs photoelectric conversion of the reflection light component of the incident visible light reflected by the internal reflection of the first prism and/or the external reflection of the second prism; and a second visible light image pick-up device which performs photoelectric conversion of the residual component of the visible light emitted from the second prism.SELECTED DRAWING: Figure 1

Description

The present invention relates to a beam separating optical system and an image signal processing apparatus having a beam separating prism, an imaging device, etc., and a beam separating prism configuration particularly suitable for acquiring a high dynamic range of an image, and an image using the same. It relates to processing equipment.

Advances in solid-state imaging devices used in video cameras, still image cameras, etc. have made it possible to produce a wide variety of compact imaging devices with high resolution. Various broadband multispectral cameras have been developed that also capture images in short wavelength infrared (SWIR), ultraviolet (UV), and the like. In addition to visible light images, these multispectral cameras can acquire images such as night vision images, images in fog, images under the skin, and images taken under water based on the wavelength characteristics of infrared light. It is used for a wide variety of purposes, such as a scope camera and a skin disease observation camera.

As the use of multispectral cameras is diversifying in this manner, there is a growing demand for performance characteristics that can be used under various usage environments and conditions. Surveillance cameras and in-vehicle cameras require clear images regardless of day or night, and medical observation and diagnostic cameras such as endoscopes and dermoscopes require images that can distinguish between bright and dark areas with high-resolution and miniaturized equipment. It is In particular, if there is a high-brightness light-emitting part such as a lighting in the captured image at night or at low illumination, the illumination light part may be blown out in white when capturing images of the entrance and exit of tunnels, capturing images of lighting reflection parts with endoscopes, etc. It is necessary to further expand the dynamic range because of blackouts in dark areas.

However, since a high-resolution and high-definition imaging device has a large number of pixels, the number of pixels has increased and the image has been miniaturized. As the imaging device becomes smaller and the number of pixels increases, the light receiving area of the incident image also decreases, the amount of charge in the pixels decreases, and as a result the dynamic range decreases and the S/N ratio decreases. Techniques for expanding the dynamic range by various methods have been disclosed in order to solve such problems. In order to extend the dynamic range, a technique of obtaining and synthesizing a low-illuminance (low-brightness) image and a high-illuminance (high-brightness) image is generally adopted.

In order to acquire a low-illuminance image and a high-illuminance image, a method of acquiring two low-illuminance and high-illuminance images by changing the illuminance or exposure amount for each frame or pixel of a plurality of images is considered. In Patent Document 1, a low-exposure image and a high-exposure image are alternately captured for each frame, and a temporal shift position when synthesizing the images is corrected. Further, Japanese Patent Application Laid-Open No. 2002-200003 discloses a technique of changing the amount of reflection using a DMD (Digital Mirror Device) for each pixel of an acquired image, and acquiring low-luminance and high-luminance images with the changed light amount. In such a technology that acquires and synthesizes a low-illuminance image and a high-illuminance image for each image frame or pixel, a time lag occurs and the amount of blurring is corrected, and the brightness change and detection for each pixel results in a complicated image. It contains issues to be dealt with.

In Patent Document 3, microlenses are alternately arranged on the pixels of an image pickup device, incident light is collected by the microlenses, and high-sensitivity pixels and light-receiving units without microlenses are used as low-sensitivity pixels for image synthesis. Illuminance image and high illuminance image are secured. However, this configuration not only complicates the configuration of the imaging element and the microlens, but also makes it difficult to manufacture high-resolution multi-pixels.

In addition, by changing the number of pixels of the image pickup device to obtain a low-luminance image and a high-luminance image, or by changing the light transmission amount of an ND (Neutral Density) filter, etc., to obtain images with different illuminance, A method for extending the dynamic range is also embodied. However, in any of these methods, complicated circuits and component configurations are required to extend the dynamic range, the performance and characteristics of the image sensor are degraded, and the resolution and S/N ratio are affected in the process of image processing. Therefore, it is not satisfactory for high-resolution, low-noise, high-level color reproducibility, and a simpler method for securing a wider dynamic range is desired.

JP 2013-118513 A JP-A-2003-8987 JP-A-2005-259750

The present invention is provided in view of the above situation, and is primarily capable of obtaining a color image with a high dynamic range and excellent color reproducibility as follows: a beam separating optical system, an image processing apparatus, and an imaging apparatus. for the purpose of providing
(1) To provide a beam separation optical system suitable for acquiring an extended dynamic range with a simple configuration of the beam separation optical system.
(2) To provide a high dynamic range image processing device using the above-described beam separation optical system and an imaging device to which it is applied.

In order to solve such problems and achieve the above objects, the light beam separating optical system of the present invention includes a first prism that reflects part of incident visible light as a reflected light component by internal reflection of a prism glass material and transmits the remaining part. and a second prism arranged with an air gap between the first prism and the first prism, wherein part of the incident visible light from the first prism is reflected as a reflected component by external reflection of the prism glass material, and visible light residual a second prism that transmits and emits a portion; and a first imaging for visible light that photoelectrically converts a reflected light component of incident visible light reflected by the internal reflection of the first prism and/or the external reflection of the second prism. and a second imaging device for visible light that photoelectrically converts the residual component of the visible light emitted from the second prism.

Further, the beam separation optical system of the present invention may be configured such that the air gap is formed in the range of 5 to 30 μm and the air gap is filled with nitrogen gas.

Furthermore, in the beam separating optical system of the present invention, the first prism and the second prism may be made of a high refractive index glass material.

Further, in the beam separation optical system of the present invention, the reflected light component incident on the first visible light imaging device is 4 to 20% of the incident light component, and is incident on the second visible light imaging device. It is possible to configure such that the transmitted light component to be reflected is a residual component of the reflected light component.

Furthermore, the beam separation optical system in the present invention is arranged such that the image output of the first image pickup device for visible light is synthesized so as to complement the saturated portion of the image output of the second image pickup device for visible light. Can be configured.

Furthermore, the beam separation optical system in the present invention is arranged on the incident side of the first prism and is in close contact with or via an air gap with the first prism, and reflects the infrared light component of the incident light from the imaging lens. Alternatively, a separation prism for transmitting visible light components and an infrared light imaging device for photoelectrically converting the infrared light components may be additionally provided.

Furthermore, the beam separation optical system in the present invention can be configured such that the image output of the infrared light imaging device is complementary synthesized with the image output of the second visible light imaging device.

Furthermore, either of the beam separating optical system in the present invention can be applied as an image processing device or an imaging device.

In order to expand the dynamic range, the main color image component and the sub color image component are acquired with different illuminance, but by acquiring the main color image component without the reflective film of the beam splitting prism, the amount of light in the main color image is reduced. High-sensitivity image acquisition is possible without In addition, by acquiring a low-sensitivity sub-color image obtained by reflection from the beam splitting prism glass material and synthesizing it with the high-sensitivity main color image, it is possible to ensure an image with excellent color reproducibility with an extended dynamic range. and Furthermore, compared to alternately acquiring images with different illuminance for each field or pixel, the beam splitting prism can separate and acquire the main color image and sub-color image in real time, resulting in color reproducibility without time lag. A color image with excellent noise and low noise can be obtained.

1 is an explanatory diagram showing a configuration example of Example 1 according to the present invention; FIG. It is explanatory drawing which shows the modification structural example of Example 1 by this invention. FIG. 4 is an explanatory diagram showing sensor output with respect to illuminance of an image sensor according to the present invention; 1 is a block explanatory diagram of a dynamic range expansion circuit according to the present invention; FIG. FIG. 4 is a block explanatory diagram showing an example of infrared light image processing according to the present invention; FIG. 5 is an explanatory diagram of the effect of an image captured using the optical system of Example 1 according to the present invention; It is explanatory drawing which shows the structural example of Example 2 by this invention. It is explanatory drawing which shows the example of a modified structure of Example 2 by this invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a beam separating optical system and an image processing apparatus or imaging apparatus having the same according to the present invention will be described in detail with reference to the drawings. It should be noted that any explanatory diagrams and drawings described in the following examples are drawn as schematic or schematic diagrams for explaining the present invention, and actual dimensions and shapes are not particularly limited. Moreover, the system configuration, block diagrams, dimensions, materials, shapes, relative arrangements, and usage examples used in the examples are not intended to limit the technical scope of the invention unless otherwise specified.

FIG. 1 is an explanatory diagram showing Example 1 of a beam separating optical system according to the present invention. A beam separating optical system 1 is arranged in a video camera device, and various lenses are connected by a lens 2 and an interchangeable lens mount 3 so as to be exchangeable. An image light beam picked up by the lens 2 is incident on the infrared light separation prism 4, the infrared light component is reflected by the reflecting surface 5, is totally reflected by the total reflection surface 6 in the infrared light separation prism 4, and is reflected on the exit surface. The light is emitted from the prism 7 and enters the infrared light imaging device 8 . The infrared light imaging element 8 photoelectrically converts the infrared light image and outputs it as an infrared light image signal.

The infrared light reflecting film 5 has wavelength selectivity so as to reflect long wavelengths of infrared light having a wavelength of 700 nm or more and transmit visible light components having a wavelength of 700 nm or less. The wavelength band and reflectance of the reflective film 5 are selected depending on the purpose of use. When using near-infrared light, the reflective film is configured to reflect a wavelength band of 700 to 1000 nm. The reflective film is formed by depositing a multi-layered dielectric or metal thin film, and it is preferable to form a non-reflective coating or a high-efficiency anti-reflective film. A visible light cut filter 9 that transmits only infrared light is provided between the infrared light exit surface 7 and the infrared light imaging device 8 . Here, near-infrared light (NIR) is assumed as an example, but short-wave infrared light (SWIR) or ultraviolet light (UV) can be similarly applied depending on the purpose of use.

The visible light component transmitted through the infrared light separating prism 4 enters the first visible light prism 10 arranged in close contact with the infrared light separating prism 4 . The incident visible light component is guided to the reflecting surface 11 . Here, the reflection of the visible light by the reflecting surface 11 of the visible light first prism 10 is internal reflection by the glass material of the prism 10, and the configuration is such that no deposition film or coating such as a reflecting material having wavelength selectivity is applied. do. No anti-reflection film is applied in order to utilize the internal reflection of the prism glass material. Of course, the angle .theta. of the reflecting surface is set to an angle .theta. at which total reflection does not occur with respect to the incident visible light optical axis x. The angle at which total reflection does not occur is within 45° in borosilicate crown glass (commonly known as BK7), but the angle is narrower in the case of a high refractive index.

A second visible light prism 15 is arranged behind the first visible light prism 10 with an air gap (small gap) 16 interposed therebetween. When the visible light first prism 10 and the second prism 15 are in close contact with each other, the refractive index of the prism glass material is the same and the reflection is very small, so an air gap is set. Good results are obtained when the distance of the air gap 16 is about 5 to 30 μm. air gap is sufficient.

The air gap 16 between the first visible light prism 10 and the second visible light prism 15 has different reflectances due to the difference between the refractive index of air (1.0 in vacuum) and the refractive index of the prism glass material. A borosilicate crown glass (refractive index of 1.512) has a surface reflection of about 2%, and a high refractive index glass (refractive index of 1.67 or more) has a surface reflection of about 4% or more. Therefore, as the glass material of the first prism 10 and the second prism for visible light, it is desirable to use a high-index type glass material having a high refractive index. Also, the air gap may be configured to be filled with nitrogen. By enclosing nitrogen gas, oxidation of the prism glass surface can be prevented. In this case, the refractive index of nitrogen is 1.000297, and the refractive index of air is 1.000293. .

The visible light component incident on the visible light first prism 10 includes not only the reflected component internally reflected by the reflecting surface 11 of the first prism 10, but also the external reflection from the incident side outer surface 17 of the second prism 15 as a reflected component. Added. This visible light reflection component may be either one of the internal reflection of the first prism 10 and/or the external reflection of the second prism 15, but it is more desirable to obtain both reflection components. In this way, without forming a reflective film by vapor deposition or coating, the reflected component of about 4% or more of the visible light component incident on the first prism is reduced by the internal reflection of the visible light first prism 10 and the external reflection of the second prism 15. can be obtained. These reflected components vary depending on the refractive index of the prism glass material, the angle of reflection θ, the wavelength of the reflected light, etc., but depending on the design conditions, it is expected that approximately 4 to 20% of the reflected component will be obtained. The visible light reflected component of the first visible light prism 10 is emitted from the emission surface 12 of the first prism and provided to the first imaging device 13 for visible light. About 4 to 20% of the incident visible light component is photoelectrically converted by the imaging device 13 and output as a visible light image and a sub-color C'. In addition, it is desirable to provide an infrared light cut filter 14 that transmits only visible light between the visible light exit surface 12 and the first visible light imaging device 13. However, the infrared light cut filter 14 is , is not required.

The remaining visible light component (residual component) transmitted through the first visible light prism 10 and incident on the second visible light prism 15 is emitted from the exit surface 18 of the second prism 15, and is transferred to the second visible light imaging device. 19. The visible light image sensor image 19 photoelectrically converts the incident visible light image and outputs it as a visible light image signal and a main color C. FIG. 4 to 20% of the visible light component is reflected by the internal reflection component of the first prism 10 and the external reflection component of the second prism 15, and the remaining portion is transmitted. About 80 to 96% of the incident visible light can be expected to be input to the visible light imaging device, and most of the visible light components are input to the second imaging device 19 and can be obtained as the main color C. Further, it is desirable to provide an infrared light cut filter 20 that transmits only visible light between the visible light exit surface 18 and the second imaging device 19 for visible light.

By constructing the beam separation optical system in this way, 4 to 20% of the incident visible light component is reflected by the internal surface of the first prism 10 and the external surface of the second prism, resulting in a visible light image and a sub-color C′. , and the visible light residual component is obtained as the main color C from the second image pickup device 19 . That is, since the sub-color C' image and the main color C image have different visible light input components, two color images with different illuminances can be obtained. The output of the second imaging device with a large visible light component (eg, 90%) is used as the main color C signal, and the output with a small visible light component (eg, 10%) obtained from the first imaging device 13 is used as the main color C signal. Synthesize as a sub-color C' signal to extend the dynamic range.

Next, the extension of the dynamic range using the beam separating optical system described above will be described. Here, it is assumed that 90% of the main color signal component C and 10% of the sub color signal component C' are obtained. FIG. 3 is an explanatory diagram showing the output levels of the main color signal and the sub color signal with respect to the illuminance of the visible light imaging device. It is assumed that each visible light imaging element has the same characteristics and its saturation level is 300% as an example. In order to perform knee processing to keep the signal amplitude within the standardized signal amplitude of the normal video signal without inputting only white light, the saturation level is increased several times (300%) to the specified level (100% level). is set to .

The straight line A represents the sensor level with respect to the illuminance of the main color C signal component, and the straight line B represents the sensor level with respect to the illuminance of the sub-color C' signal component. The horizontal axis indicates the illuminance (lx), and the vertical axis indicates the sensor level. In both cases, the upper part shows the numerical value of the main color C signal, and the numbers in parentheses in the lower part indicate the sub-color C' signal. The ratio of the main color C signal component to the sub color C' signal line segment is 90%:10% in this example, and the illuminance input to each imaging element is also 90:10. Therefore, the illuminance that reaches 300% (approximately 6,000 lux), which is the saturation level of the image sensor set by the main color C signal, corresponds to 3,000% (approximately 60,000 lux) in the sub-color image sensor. .

Therefore, the main color signal is used until the specified level (100%) of the main color image sensor is reached, and the sub color signal is used for the illuminance portion above that. The threshold value for synthesizing the main color signal with the sub-color signal and using the color image with low illuminance above which illuminance can be adjusted and set according to the purpose of use of the camera. , is set to the specified 100% level of the sensor so as not to cause overexposed saturation in the acquired sensor image.

FIG. 4 is a block diagram showing an example of a specific circuit configuration for synthesizing a main color image and a sub-color image to expand the dynamic range. The main color sensor 31 and the sub-color sensor 32 correspond to the second visible light imaging element 19 and the first visible light imaging element 13 in FIG. 1, respectively. The main color sensor 31 and the sub color sensor 32 are composed of single-plate color sensors. The output signal of each image pickup device is obtained by acquiring two identical real-time images instead of acquiring and synthesizing images with different illuminance for each pixel or consecutive fields. It is also possible to overlay (mix) the output as it is to complement the saturated portion of the image sensor.

However, in the circuit configuration of FIG. 4, a method is proposed in which a portion of the luminance signal exceeding a predetermined threshold value is detected and interpolated for each pixel. A luminance signal component is extracted from the output signal of the main color sensor 31 and the output signal of the sub color sensor 32 by the signal converter 33 . The signal converter 33 converts the RGB signal into a LAB signal. The output main color signal is subjected to knee correction processing in the knee correction section 35, and since the sub color signal is at a lower level than the main color signal, it is amplified by the amplification section 34 so that the main color signal and the sub color signal are the same. level is adjusted.

The level-matched main color signal and sub color signal are supplied to the differential signal detector 36 . The difference detection circuit 36 is composed of a subtraction circuit for extracting the difference between both color signals. When the lightness component of the main color signal is saturated by this subtraction circuit, the level of the sub-color signal increases, and saturation occurs in the main color image. The output of the difference detector 36 is supplied to the synthesizer 38 via the noise remover 37 . In other words, the portion where the output is generated by the difference detection section 36 is detected, and this detection signal is used as a control signal for synthesizing the sub-color signal with the main color signal. This control signal is a threshold for synthesizing the sub-color signal with the main color signal, and by adjusting and setting the control signal value, the adaptive illuminance range is changed.

The synthesizing unit 38 synthesizes the sub-color signal with the saturated portion of the main color signal according to the control signal supplied from the noise removing unit 37 to complement the saturated portion. Comparing the control signal with a set threshold, correcting and selecting for each pixel whether or not the main color signal is saturated, and complementing the sub-color signal acquired at low illuminance in the portion where the main color signal is saturated. . The interpolated image signal is provided to a gamma correction circuit and processed as a color image signal. Here, the interpolation of the luminance signal, which has the greatest effect on the extension of the dynamic range, was explained as an example, but the saturation level of each of the color difference signals and R, G, and B is complemented using the same means to expand the dynamic range. It is also possible to

The color image signal obtained in this way is saturated at approximately 6000 lux in the main color image pickup device 31, whereas the sub-color image pickup device 32 does not reach saturation in the vicinity of 60000 lux. Complementing the saturated portion of the color image acquired by the element 31 with the sub-color signal can greatly expand the dynamic range. In the light beam splitting prism according to the present invention, the sub-color component is acquired only by the reflection of the prism glass material without the vapor deposition film or the coating film of the metal thin film. That is, since the main color components do not pass through the separation film and enter the main color imaging device, it is possible to obtain a color image with excellent color reproducibility and little noise without being affected by the separation film.

FIG. 2 is an explanatory diagram showing a modified configuration example of the beam separating optical system in FIG. In the beam splitting optical system 50 of FIG. 2, the same numbers are assigned to the same component configurations as in FIG. In this prism configuration, an air gap 21 of about 5 to 15 μm is provided between the infrared light separating prism 4 and the visible light first prism 10 in a general-purpose dichroic separating prism or the like. 4 is reflected by the reflecting surface 11 of the first visible light prism 10 and/or the outer surface 17 of the second visible light prism 15, and is totally reflected by the reflecting surface 22 of the first visible light prism 10. is configured to The reflected visible light component totally reflected by the reflecting surface 22 is emitted from the first prism 10, and the sub-color C' component is output from the first visible light imaging device 13. FIG. Here, the important point is that, like the prism configuration in FIG. The light component can be acquired as the main color C component as transmitted light.

The main difference between the beam separation optical system 1 in FIG. 1 and the beam separation optical system 50 in FIG. 2 is that the visible light (color ) The reflected component is totally reflected by the reflecting surface 22 of the first prism to obtain the sub-color C' component. A surface image can be obtained by acquiring the sub-color C' component reflected in the prism by total reflection again in the visible light first prism. In the prism configuration of FIG. 1, the sub-color C′ is acquired as an inverted image (back image), so in order to match it with the main color image, it is necessary to invert it once in image processing and acquire a front image. However, in the prism configuration of FIG. 2, it can be combined with the main color C image without inverting image processing of the sub color C'. Also, in order to have such a prism configuration, it is necessary to set the reflection angle of the reflecting surfaces of the first visible light prism 10 and the second visible light prism 15 to an angle θ' smaller than θ in FIG. That is, since the angle of reflection θ' approaches the right angle with respect to the optical axis x, the P/S polarization characteristics are improved although the amount of reflection is reduced. Therefore, it is suitable for acquisition of images in which the influence of polarization characteristics should be avoided.

Next, infrared light image processing obtained by the infrared light separation prism 1 of FIGS. 1 and 2 will be described. Infrared light images are used for surveillance cameras, in-vehicle cameras, medical endoscope cameras, skin disease observation cameras, etc., and acquire images such as night vision images, images in fog, images under the skin, and images taken under water. . Therefore, as image processing, an image is acquired in accordance with the purpose of use by synthesizing, comparing, or processing with a visible light (color) image. Therefore, by acquiring an infrared light image in addition to the dynamic range-expanded color image acquired by the above-described configuration, it is possible to obtain a more diverse and highly visible image.

Infrared light has different wavelength bands depending on the purpose of use, but wavelengths in the 0.7 to 2.5 μm band called near infrared light (NIR) and short wavelength infrared light (SWIR) are mainly used. . The image in this wavelength band is a black and white image, but the image contrast is relatively strong, and since it is in a longer wavelength band than visible light, it is less susceptible to the diffuse reflection of fog and smoke. Since photography is possible, the present invention is expected to be applied to day and night surveillance, all-weather surveillance cameras, endoscopes, dermos cameras, and the like.

FIG. 5 is an explanatory diagram showing an example of a block circuit for image processing using an infrared light image in addition to the dynamic range expansion described above. The same numbers are assigned to the same component parts as those in FIG. The dynamic range expansion circuit 30 supplements the saturated portion of the main color C image with the sub-color C' image of the low illuminance component by synthesizing two images with different color components from the main color imaging device 31 and the sub-color imaging device 32. An infrared light image signal is combined with a color signal with an extended dynamic range.

Infrared light images (especially NIR images) are black and white images, although they have relatively high contrast. Night vision images necessary for images and conditions such as subcutaneous veins can be captured as images with higher visibility. The infrared light imaging device 41 is a sensor similar to the infrared light imaging device 8 in FIG. 1, and generates an infrared light image signal. The infrared light image signal is supplied to the noise suppression processing circuit 42 . Here, noise suppression is performed using a low-pass filter, median filter, or the like in order to prevent noise components from being enhanced by enhancing the edge portion of the image by contour correction. This noise suppression circuit uses a high-pass filter to extract edge signals, suppressing dark signals below a certain level through coring processing, and suppressing noise with a dynamic filter that suppresses noise. Removal is also possible.

A signal subjected to noise processing by the noise suppression circuit 42 is supplied to the contour correction circuit 43 . The contour correction circuit 43 performs contour correction such as image edge raising by various proposed known differentiating circuits. The contour-corrected infrared light image is level-matched in the operational amplifier 44, and then combined with the color signal of the dynamic range expansion circuit 30 in the synthesizing unit 45 to generate an output signal. By synthesizing the contour-corrected infrared light image with the color image signal whose dynamic range has been expanded in this way, an image suitable for various photographing environments with an expanded dynamic range for infrared light imaging as described above can be obtained. can be obtained, and the range of applications is greatly expanded.

FIG. 6 is an explanatory diagram showing the comparative effect of images shot using the configuration according to Example 1 including the infrared light separating prism. This figure is intentionally drawn as a schematic diagram for explanation. In FIG. 6 (A), the objects in the fog and clouds and water droplets in the backlight environment are unclear such as birds, airplanes, and drones. As shown in B), object recognition with high visibility is possible even in a backlight environment. By using this kind of beam separation optical system, it is possible to reproduce images that are overexposed due to backlight in nighttime imaging, improve the visibility of night vision images using infrared light, and use near infrared light in bad weather and fog. It is also possible to acquire an image with improved visibility of an object detection image that has passed through clouds, and an image showing the blood vessel (vein) state in subcutaneous tissue imaging using near-infrared light.

7 and 8 are explanatory diagrams showing a configuration example of a second embodiment according to the present invention. In FIG. 7, the configuration of a beam separating optical system 60 for expanding only the dynamic range of a visible light (color) image and acquiring it is shown. is shown. 7 and 8, the same numbers are assigned to the same functions and members as in FIG. The difference from FIG. 1 is that the infrared light separating prism is omitted, visible light images with different visible light components are acquired only for the main color image C and the sub-color image C′, and a color image for dynamic range extension is acquired. The point is that

The configuration for expanding the dynamic range of color images is the same as in the first embodiment. The image light flux incident from the imaging lens 2 enters the first prism 61 , is internally reflected by the reflecting surface 11 of the first prism 61 , and enters the first visible light imaging element 13 . The reflecting surface 11 of the first prism 61 is not provided with any metal thin film or coating having wavelength selectivity, and a reflected image (sub-color image C') is acquired by internal reflection of the prism glass material. A second prism 15 is arranged behind the first prism 10 .

An air gap is provided between the first prism 61 and the second prism 15 . Incident visible light is also reflected on the outer surface (incidence surface) 17 of the second prism 15, and this reflected image also enters the imaging device 13 of the first prism 61 to form a reflected image (sub-color image C'). The imaging device 13 photoelectrically converts the reflected visible light image and outputs a sub-color image C'. The visible light component transmitted through the first prism 61 is emitted from the exit surface 18 and enters the second visible light imaging device 19 . The image sensor 19 photoelectrically converts the acquired visible light image and outputs a main color image C. FIG.

It is desirable to use a high-index type prism glass material and set the air gap to about 5 to 30 μm. Further, as in the first embodiment, the air gap can be filled with nitrogen gas to prevent oxidation of the prism glass surface. With such a configuration, the reflected visible light image (sub-color image C′) is about 4 to 20% of the total visible light component incident on the beam separation optical system 60, and the transmitted visible light component (main color component) can be obtained about 80-96%. The dynamic range of the acquired main color image and sub-color image is expanded by supplementing the saturated portion of the main color image with the sub-color image due to the difference in the incident light component, which is caused by the low-illumination image and the high-illuminance image with different illuminance. Enlarged color images can be obtained. In addition, the obtained main color image does not have a metal film or a coating film in the separation film, so a color image excellent in color reproducibility can be obtained without being affected by the separation film.

In Embodiment 1, the infrared light separation prism 4 is arranged on the light flux incident side from the lens 2, and the infrared light image acquisition and the color image acquisition with the extended dynamic range are acquired, thereby expanding the application variation. However, in Example 2, since it is only a prism configuration for acquiring a sub-color image and a main color image, the dynamic range of visible light (color) images that does not require the infrared light separation prism of Example 1 can be applied to an image processing apparatus that extends the

FIG. 8 shows a beam separation optical system 70 of a modified type of FIG. 7 that acquires two different visible light components, a main color image C and a sub-color image C'. In the first prism 62 of FIG. 8, the incident light beam is reflected by the reflecting surface 11, the reflected light beam is further reflected by the inner surface of the reflecting surface 63, and is emitted out of the prism. C' is obtained. Since the sub-color image C' is obtained by obtaining an image totally reflected by the reflecting surface 63, it has the same surface relationship as the main color image C obtained by obtaining the transmitted light as it is. Therefore, in image synthesis, with the prism configuration of FIG. 7, it is necessary to match the directions of both acquired images, but with the prism configuration of FIG. ' and can be combined.

In the present invention, a low-illuminance color image and a high-illuminance color image for expanding the dynamic range are separated, and about 90% of the main color component is obtained without deposition films or coating films such as prisms and reflecting mirrors, and sub-color components are obtained. obtains about 10% by utilizing the internal or external reflection component of the prism. Therefore, a sufficient amount of light can be secured for the main color image, and a color image with high sensitivity, excellent color reproducibility, and an expanded dynamic range can be obtained.

The beam separation optical system according to the present invention is capable of obtaining a visible light image with high sensitivity, color reproducibility, excellent visibility, and an extended dynamic range by eliminating separation films such as vapor deposition films and coating films. Since the system can be provided, it can be used in a wide range of applications such as surveillance cameras, observation cameras, in-vehicle cameras, weather cameras, aircraft cameras, and endoscope cameras. expands the availability of

REFERENCE SIGNS LIST 1 beam separation optical system 2 imaging lens 3 lens mount 4 infrared light separation prism 5 infrared light reflection film 6 total reflection surface 7 exit surface 8 infrared light imaging element 9 visible light cut filter 10 visible light first prism 13 th One visible light image sensor 14 Infrared light cut filter 15 Second visible light prism 19 Second visible light image sensor 20 Infrared light cut filter 30 Dynamic range expansion circuit

Claims (8)

a first prism that reflects part of the incident visible light as a reflected light component by internal reflection of the prism glass material and transmits the remaining part;
A second prism disposed with an air gap between the first prism and the first prism, wherein a part of the incident visible light from the first prism is reflected as a reflected component by external reflection of the prism glass material, and the remaining part of the visible light is a second prism that transmits and emits;
a first imaging device for visible light that photoelectrically converts a reflected light component of the incident visible light reflected by the internal reflection of the first prism and/or the external reflection of the second prism;
and a second imaging device for visible light that photoelectrically converts the residual component of the visible light emitted from the second prism. 2. A beam separating optical system according to claim 1, wherein said air gap is formed in a range of 5 to 30 [mu]m, and is filled with nitrogen gas. 2. The beam separating optical system according to claim 1, wherein said first prism and said second prism are made of a high refractive index glass material. The reflected light component incident on the first visible light imaging device is 4 to 20% of the incident light component, and the transmitted light component incident on the second visible light imaging device is the reflected light component. 4. The beam separating optical system according to claim 3, wherein the remaining component is a residual component. 5. The image output of said first imaging device for visible light is synthesized so as to complement the saturation portion of the image output of said second imaging device for visible light. beam separation optical system. a separation prism arranged on the incident side of the first prism in close contact with the first prism or with an air gap interposed therebetween, for reflecting the infrared light component of the incident light from the imaging lens and transmitting the visible light component;
an infrared light imaging device that photoelectrically converts the infrared light component;
2. The beam separating optical system according to claim 1, further comprising: 7. The beam separating optical system according to claim 6, wherein the image output of said infrared light imaging device is complementary combined with the image output of said second visible light imaging device. 8. An image processing apparatus or imaging apparatus comprising any one of the beam separating optical systems according to claim 1.

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