JPH1188896A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To select an optical filter corresponding to a light source. SOLUTION: An optical filter device 34 capable of optionally selecting one of four optical filters 40a to 40d having respectively different spectral transmission characteristics is arranged between a photographing lens 30 and an image pickup element 32. When a user lightly touches a photographing button, a part of an output image from the element 32 is entered into a white balance adjusting circuit 44 and white points in the image are detected. The circuit 44 allows a filter switching circuit 50 to select an optical filter 40 optimum to a specified light source based on the detected white point information. The circuit 50 supplies a processing parameter corresponding to the selected optical filter 40 to the circuit 44, a picture processing circuit 46 and a gamma processing circuit 48. The picture signal outputted from the element 32 is digitized by an A/D converter 42 and picture processing for the digital signal is executed through respective circuits 44, 46, 48.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device,
More specifically, the present invention relates to an imaging apparatus including two or more types of optical filters having different spectral transmittances and selecting one appropriate type of optical filter according to imaging.

[0002]

2. Description of the Related Art In a conventional imaging apparatus, as shown in FIG. 5, a quartz low-pass filter and / or a near-infrared ray is provided between a photographing lens 10 and an imaging element 12, for example, a subject light incident surface of the imaging element 12. An optical filter 14 such as a cut filter is provided. The image signal output from the image sensor 12 is converted into a digital signal by the A / D converter 16, the color balance is adjusted by the white balance adjustment circuit 18, and the image processing circuit 20 performs well-known operations such as contour enhancement and noise removal. And the gamma correction is performed by the gamma processing circuit 22.

[0003] The spectral transmission characteristics of the optical filter 14 are designed so as to utilize the performance of the image sensor 12 in accordance with the image sensor 12 to be used.

[0004]

As described above, in the conventional example, the optical filter installed on the front surface of the image sensor cannot be changed later in a commercialized state, so that there is no room for selection by the user.

[0005] However, the optical characteristics of the installed optical filter are not always optimal in all situations. For example, a near-infrared cut filter will be described as an example.

If the image is taken without a near-infrared cut filter, the image pickup element is affected by infrared light, especially on green leaves, and reproduced in a reddish cloudy color. This is due to the fact that the imaging device has a high sensitivity to near-infrared light, unlike a silver halide film that is usually used. Of course, there are films that have sensitivity in the infrared region, but are exceptional.
Think away.

In order to avoid such a phenomenon, in the case of an image pickup apparatus using an image pickup device, it is unnecessary when a silver halide film having no sensitivity in the near infrared region is used.
It is necessary to use a near-infrared cut filter that cuts the long wavelength.

FIG. 6 shows spectral transmittance distributions of near-infrared cut filters A and B having different thicknesses. FIG. 7 shows an example of the sensitivity of the yellow and magenta imaging elements 12 when the two types of near-infrared cut filters A and B shown in FIG. 6 are used as the complementary color sensors. In FIG. 7, A is the yellow sensitivity when the infrared cut filter B of FIG. 6 is used, B is the yellow sensitivity when the infrared cut filter A of FIG. 6 is used, and C is the infrared cut filter of FIG. M indicates the sensitivity of magenta when the filter B is used, and D indicates the sensitivity of magenta when the infrared cut filter A of FIG. 6 is used. The vertical axis is relative intensity, and the horizontal axis is wavelength.

As can be seen from FIG. 7, the sensitivity of the image pickup device 12 changes due to the difference in the spectral transmittance of the near infrared cut filter. Furthermore, as shown in FIG. 8, since the spectral distribution varies greatly depending on the light source, the image (particularly, its color reproducibility) greatly changes depending on the type of filter used and the type of spectral transmittance. . In FIG.
The vertical axis indicates the relative intensity and the horizontal axis indicates the wavelength, where A is a standard A light source, B is a standard D65 light source, and C is F6 (CCT: 41).
50K).

Therefore, for example, even in an image pickup apparatus provided with an optical filter having an optimum reproducibility for photographing under sunlight, if photographing is performed under an A light source different from sunlight, Since the amount of infrared light is different from that of the case (1), an optimum image cannot be obtained.

Further, as shown in FIG. 8, since the amount of light near 650 nm, which is largely affected by the infrared cut filter, is lower than that of other light sources, as shown in FIG. When shooting is performed, the amount of light near 650 nm becomes unnecessarily small, and a problem arises in that the sensitivity of the image sensor cannot be used effectively.

Further, when photographing is performed using a photographing lens different from the photographing lens used when determining the characteristics of the optical filter, the photographing lens is installed due to a difference in lens characteristics such as spectral characteristics of the photographing lens. Optical filters may not be optimal.

An object of the present invention is to provide an image pickup apparatus which solves such a problem.

[0014]

An image pickup apparatus according to the present invention comprises an image pickup means for converting an optical image into an image signal, and a plurality of optical filters having different spectral sensitivity characteristics. It is characterized by comprising optical filter means movable on the front face of the means and filter switching means for switching the optical filter arranged on the front face of the imaging means.

With such a configuration, an optimal optical filter can be selected according to the environment at the time of photographing and the lens characteristics.

By performing image processing with image processing parameters corresponding to the selected optical filter, an image of better quality can be obtained.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic block diagram of a first embodiment of the present invention. An optical filter device 34 that can select one from a plurality of optical filters having different spectral transmission characteristics is disposed between the photographing lens 30 and the image sensor 32. FIG. 1 shows a cross-sectional view of the optical filter device 34,
FIG. 2 shows a front view of the optical filter device 34. The optical filter device 34 has a structure in which optical filters 40 a, 40 b, 40 c, and 40 d having different spectral transmittance characteristics are fixed at four circumferential positions of a disk 38 fixed to the rotating shaft 36. Is rotatably attached to a housing (not shown) in parallel with and away from the optical axis of the taking lens 30.

The image signal output from the image sensor 32 is A
After being converted into a digital signal by the / D converter 42,
The color balance is adjusted by a white balance adjustment circuit 44, and known image processing such as contour coordination and noise removal is performed by an image processing circuit 46, and gamma correction is performed by a gamma processing circuit 48.

The filter switching circuit 50 rotates the optical filter device 34 in response to an instruction from the user (manual mode) or a control signal (auto mode) from the white balance adjusting circuit 44 to rotate the optical filters 40a to 40a-4.
0d is positioned on the photographing optical path,
The processing parameters are supplied to the white balance adjustment circuit 44, the image processing circuit 46, and the gamma processing circuit 48 according to the selected optical filters 40a to 40d.

The optical filters 40a to 40d are respectively
It is assumed that the infrared cut filter is selected so as to obtain an optimal image corresponding to four different light sources, that is, daylight, a fluorescent lamp, a flash, and an A light source. Fluorescent lights and flashes do not have much infrared light, while daylight and A light sources
The amount of infrared light is relatively large.

The operation of this embodiment will be described. The user first determines the composition to be photographed. Then, when the user touches the shooting button (not shown) lightly, a part of the output image of the image sensor 32 is taken into the white balance adjustment circuit 44, where a white point in the image is detected. The light source is specified based on the detected white point information, and the white balance adjustment circuit 44 sends a filter selection control signal to the filter switching circuit 50 so as to select the optimal optical filters 40a to 40d for the specified light source. Supply. The filter switching circuit 50 rotates the optical filter device 34 about the rotation axis 36 according to the filter selection control signal from the white balance adjustment circuit 44, and the optical filters 40a to 40d optimal for the light source are located on the photographing optical path. To do.

The filter switching circuit 50 stores image processing parameters related to color processing, luminance processing, and edge enhancement processing optimized for each of the optical filters 40a to 40d, that is, for each of the four types of light sources. The filter switching circuit 50 selects an image processing parameter corresponding to the selected optical filter, and supplies the selected image processing parameter to the white balance adjustment circuit 44, the image processing circuit 46, and the gamma processing circuit 48.

At the stage where the optimum optical filters 40a to 40d are positioned on the photographing optical path, actual photographing is performed. The image sensor 32 converts an optical image formed by the imaging lens 30 and transmitted through desired optical filters 40a to 40d into an electric signal. The output of the image sensor 32 is the A / D converter 4
The signal is converted into a digital signal by 2 and applied to the white balance adjustment circuit 44. The white balance adjustment circuit 44 adjusts the white balance of the image data from the A / D converter 42 according to the processing parameters from the filter switching circuit 50. The image processing circuit 46 performs color processing on the image data from the white balance adjustment circuit 44 according to the image processing parameters from the filter switching circuit 50,
The gamma processing circuit 48 performs gamma processing on the image data from the image processing circuit 46 in accordance with the image processing parameters from the filter switching circuit 50.

As described above, in the present embodiment, the optimum one of the four types of optical filters 40a to 40d is selected according to the photographing light source, and the selected optical filters 40a to 40d are further selected.
Since the captured image is processed using the image processing parameters corresponding to 0d, an appropriate image can be obtained regardless of the light source, and good color reproducibility can be obtained. Since optimal processing is performed for each light source, the amount of light is not wasted by the optical filter.

In the present embodiment, the white balance processing is performed for each of the light source determination and the actual photographing. However, the image data used for the light source determination is stored in a memory, and the image data of the actual photographed image is stored and used. The white balance may be adjusted. In the present embodiment, the light source is determined by the white balance adjustment circuit 44, and one of the optical filters 40a to 40d is selected based on the result. Of course, one of the optical filters 40a to 40d is manually selected. You may do so.

Although the infrared cut filter has been described as an example, it is apparent that the present invention is not limited to the infrared cut filter.

In the present embodiment, color processing,
Although it is assumed that the brightness processing and the edge enhancement processing are performed and each image processing parameter can be selected for each of the optical filters 40a to 40d, it is also clear that the image processing in the image processing circuit 46 is not limited to these examples. . Also, not all image processing requires an image processing parameter for each type of optical filter, so only necessary image processing parameters need to be set according to the optical filter.

FIG. 3 is a schematic block diagram of a second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. In this embodiment, a special external light sensor 52 for detecting a light source is provided, and a filter switching circuit 5 is provided.
4 selects the optimum optical filters 40a to 40d according to the output of the external light sensor 52. The white balance adjustment circuit 56 is obtained by omitting the light source detection function from the white balance adjustment circuit 44.

In the embodiment shown in FIG.
However, the light source is always detected, and the detection result is supplied to the filter switching circuit 54. Therefore, there is no need to perform a process of detecting a white point by capturing a part of a captured image into a white balance adjustment circuit as in the embodiment illustrated in FIG.
You can shoot quickly.

Optical filters 40a to 40d corresponding to light sources
Since the processing after is disposed on the photographing optical path is the same as that of the embodiment of FIG. 1, detailed description will be omitted.

FIG. 4 is a schematic block diagram of a third embodiment of the present invention. 1 and 3 are denoted by the same reference numerals.

In the embodiment shown in FIG. 4, the present invention is applied to an image pickup apparatus in which a photographing lens can be exchanged, and the lens characteristic information of the interchangeable photographing lens 58 can be taken into a filter switching circuit 60. I have. In this case, the optical filters 40a to 40a
Reference numeral 40d denotes a lens 40d having a different thickness and a different material for correcting the lens aberration and correcting the spectral transmittance, which are selected according to the photographing lens 58 that can be mounted. The filter switching circuit 60 selects the optimal optical filters 40a to 40d according to the lens characteristics of the mounted photographing lens 58, arranges them on the photographing optical path, and performs image processing according to the selected optical filters 40a to 40d. The parameters are supplied to a white balance adjustment circuit 56, an image processing circuit 46, and a gamma processing circuit 48.

Since the flow of processing of a photographed image itself is the same as that of the embodiment shown in FIG. 1, detailed description will be omitted.

In the embodiment shown in FIG. 4, the lens information of the photographed lens that has been driven is automatically filtered by the filter switching circuit 60.
However, it is obvious that the user may manually input to the filter switching circuit 60.

It is obvious that a function of detecting the type of light source by the white balance adjustment circuit 44 or the external light sensor 52 and selecting an optical filter according to the light source may be added to the embodiment shown in FIG. is there. For example, an optical filter device capable of selecting an optical filter corresponding to a light source may be provided in addition to an optical filter device capable of selecting an optical filter corresponding to a mounted photographing lens.

[0037]

As can be easily understood from the above description, according to the present invention, an appropriate optical filter can be selected according to a light source and a photographing lens to be used, and image processing parameters can be selected according to the selected optical filter. Is set, an optimum image can be obtained regardless of the light source and the photographing lens.

In particular, in the case of an infrared cut filter, a filter whose type and thickness are optimized in accordance with the light source is selected based on the photographing environment and the lens characteristics, and particularly, the reproduction of red light is started. The color reproducibility is improved, and an optimal image utilizing the characteristics of each light source can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a first embodiment of the present invention.

FIG. 2 is a plan view of the optical filter device 34. FIG.

FIG. 3 is a schematic configuration block diagram of a second embodiment of the present invention.

FIG. 4 is a schematic block diagram of a third embodiment of the present invention.

FIG. 5 is a schematic block diagram of a conventional example.

FIG. 6 is an example of spectral transmittance of two infrared cut filters.

FIG. 7 is an example of a difference in sensitivity of an image sensor due to a difference in spectral transmittance of an infrared cut filter.

FIG. 8 is an example of a spectral distribution of a standard light source.

[Explanation of symbols]

 10: Photographing lens 12: Image sensor 14: Optical filter 16: A / D converter 18: White balance adjustment circuit 20: Image processing circuit 22: Gamma processing circuit 30: Photographing lens 32: Image sensor 34: Optical filter device 36: Rotation axis 38: Disk 40a, 40b, 40c, 40d: Optical filter 42: A / D converter 44: White balance adjustment circuit 46: Image processing circuit 48: Gamma processing circuit 50: Filter switching device 52: External light sensor 54: Filter switching circuit 56: White balance adjustment circuit 58: Interchangeable photographing lens 60: Filter switching circuit

Claims (6)

[Claims] 1. An image pickup means for converting an optical image into an image signal, an optical filter means comprising a plurality of optical filters having different spectral sensitivity characteristics, and any optical filter movable to the front of the image pickup means; An imaging apparatus comprising: a filter switching unit that switches the optical filter disposed on a front surface of the imaging unit. 2. The image processing apparatus according to claim 1, further comprising: light source detecting means for detecting a light source, wherein said filter switching means arranges said optical filter corresponding to a detection result of said light source detecting means on a front surface of said imaging means. 2. The imaging device according to 1. 3. The imaging apparatus according to claim 2, wherein the light source detection unit is included in a white balance processing unit. 4. The imaging apparatus according to claim 2, wherein said light source detecting means comprises an external light sensor for detecting external light. 5. The imaging apparatus according to claim 1, wherein the filter switching unit switches the optical filter according to lens information of a mounted photographing lens. 6. An image processing unit for processing an output image signal of the imaging unit, wherein the filter switching unit supplies an image processing parameter corresponding to the selected optical filter to the image processing unit. Item 2. The imaging device according to Item 1.