JP4661606B2 - Bending optical system and electronic imaging device - Google Patents

Description

  The present invention relates to a bending optical system and an electronic imaging device.

  In an electronic imaging apparatus such as a digital camera, a small-sized, particularly thin-shaped product is favored as a general-purpose product. As an example of such a thin digital camera, incident light is bent at 90 ° by a bending optical unit, and the optical axis of the imaging optical system is arranged in the lateral direction of the camera as light traveling in the lateral direction of the camera, whereby the camera For example, JP 2004-219516 A (Patent Document 1) describes a method for reducing the thickness of the above.

A schematic diagram of this is shown in FIG. The light incident on the housing 10 of the digital camera is bent by 90 ° by the bending optical unit 11, and an image of the subject is formed on the imaging surface of the image sensor 13 by the imaging optical system 12.
JP 2004-219516 A

  However, as can be seen from FIG. 3, the thickness (depth) D of the bent optical unit 11 is the same as the diameter of the opening 14 of the housing 10, and the thickness of the housing 10 cannot be made thinner than D. .

  The present invention has been made in view of such circumstances, and provides a bending optical system that is thinner (smaller in depth) than a conventional bending optical system and a thin electronic imaging device using the same. Let it be an issue.

The first means for solving the problem includes a bending optical unit, a plurality of imaging optical systems having the same entrance pupil position, and an image processing device. placed in the entrance pupil position by dividing the entrance pupil, said imaging optical system, the divided light passed through the divided the entrance pupil, onto a plurality of image plane of each of the plurality of imaging element The image processing apparatus performs image processing on the image formed on the plurality of image forming surfaces, and compares the corresponding pixels of the image formed on the plurality of image forming surfaces, thereby randomly A bending optical system characterized by having a function of removing noise .

Second it means for solving the above problems, a first means, pre-outs image processing apparatus receives an output from the non-effective pixels of the image sensor, based on the input value And having a function of removing thermal noise.

Third means for solving the above problems, in any one of the first or second means, pre-outs image processing apparatus, due to the anisotropy of the divided entrance pupil In this case, the anisotropy of the resolution that occurs is corrected.

A fourth means for solving the above problem is the first means, which occurs between the bending optical part and the imaging element due to anisotropy of the divided entrance pupil. It has an optical system for correcting the anisotropy of resolution.

A fifth means for solving the above-mentioned problem is an electronic imaging apparatus characterized by having a bending optical system of any one of the first to fourth means.

  According to the present invention, it is possible to provide a bending optical system that is thinner (smaller in depth) than a conventional bending optical system, and a thin electronic imaging apparatus using the bending optical system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of an electronic camera having a bending optical system according to the first embodiment of the present invention. The light beam that has passed through the opening 2 of the housing 1 is divided into two light beams that are perpendicular to the incident direction by a mirror 3 that is a bending optical unit. The mirror 3 is a mirror having two reflecting surfaces inclined by 45 ° with respect to the incident direction of the light beam.

  The two divided light beams form an object image on the imaging surfaces of the CCDs 5a and 5b, which are imaging elements, by the imaging optical systems 4a and 4b, respectively. Since the positions of the entrance pupils of the imaging optical systems 4a and 4b are the same, and the mirror 3 is placed at the position of the entrance pupil, the images formed on the CCDs 5a and 5b are the same. Therefore, by adding together the outputs from the corresponding pixels of the CCDs 5a and 5b, as described later, it is possible to obtain substantially the same output as when imaging with one imaging element as in the prior art. Further, as apparent from FIG. 1, the thickness of the mirror 3 can be D / 2 when the diameter of the opening 2 of the housing 1 is D, and the depth thereof is thinner than that of the conventional one. can do. Therefore, the thickness of the electronic camera can be reduced.

  In addition, although the example which divides a light ray into 2 is shown in FIG. 1, you may divide | segment into 2 or more. Therefore, the following description is made on the assumption that n (n is an integer of 2 or more) is divided.

  The individual optical systems that divide the pupil and image the divided luminous flux darken, so the S / N ratio decreases. However, the following method restores the value close to the S / N ratio before dividing the pupil. it can. Here, signals and noise are considered as follows.

(Signal): Signal = quantum efficiency x sensitivity x number of incident photons
(1) Quantum efficiency: Efficiency at which light is converted to electrons on the photocathode (%, mA / W)
(2) Sensitivity (Gain): Determined by adjustment of the current ratio with electrons → It can be adjusted many times, but increasing the sensitivity does not increase the S / N ratio because noise increases together.

(3) Number of incident photons: This is related to the CCD size, and the larger the pixel size, the more advantageous.

(Noise): Total noise = (N _r ² + N _d ² + N _s ² ) ^1/2
(1) N _r : Random noise ... proportional to sensitivity. Small influence of temperature. Irrelevant to exposure time.

(2) N _d : Thermal noise: somewhat proportional to sensitivity. Large temperature effect. Proportional to exposure time. When a highly sensitive CCD camera is used for detecting weak light, it becomes the largest noise source.

(3) N _s : Noise generated on the silicon photocathode, generally the square root of the amount of light incident on the photocathode.

  In the case of the embodiment shown in FIG. 1 in which the entrance pupil is divided into two, the signal is reduced to ½, so that the image is picked up with increased sensitivity. Therefore, random noise and thermal noise increase. Random noise can be removed by superimposing images obtained by imaging the divided light beams with the imaging optical systems 4a and 4b and processing the images. When the output is obtained from both pixels corresponding to the same position of two images obtained by dividing, it is difficult to distinguish a significant signal and noise, but it is output to one of the images obtained by dividing. Can be seen as random noise if it is not seen in the other image.

  That is, as an example of one processing method, when attention is paid to a certain pixel, the output of that pixel is compared with the neighboring pixels. Also check to see if similar output appears. If no protruding output appears in the corresponding pixel of the output of the other CCD, the protruding output is regarded as noise, and the output of that pixel is converted to the output of the corresponding pixel of the other CCD. Replace (if there are two or more other CCDs, the average value is used).

The probability P _random that a random noise is generated with a certain exposure time in one pixel of the CCD detector is a Poisson probability P _λ (x) (x is the number of events occurring in the Poisson process, λ is the average number of events in the Poisson process) ), The probability of random noise occurring simultaneously in the pixels corresponding to the same target position in the image obtained by imaging the light beams obtained by dividing the entrance pupil into two by the imaging optical systems 4a and 4b is as follows: It is proportional to the square of P _λ (x). As the number of divisions increases, the probability of random noise occurring simultaneously in pixels corresponding to the same position in each image decreases, so that random noise can be removed with high accuracy.

  As for thermal noise, optical black (a portion where light does not enter) is provided in an ineffective pixel portion on the CCD surface, and the amount of thermal noise is estimated by detecting an output from the pixel. The thermal noise is removed by subtracting the estimated noise amount from the output value of each pixel of the CCD. Then, a signal value obtained from each CCD of the divided system is obtained, and the signal value is added to each corresponding pixel, so that the S / N ratio lowered by dividing the pupil can be recovered.

When a light beam having a circular aperture before the division is divided into two, the pupil shape after the division becomes a semicircle, and thus anisotropy of resolution occurs. This resolution anisotropy is corrected by the following method. If an object having an intensity distribution g (x ′, y ′) (where x ′, y ′ are local coordinates on the object boundary side) exists on the object boundary side, the intensity distribution on the image plane of the image i (x, y) (where x and y are local coordinates on the image plane) is

Given in. Here, r (x, y, x ′, y ′) is a point spread function of the imaging optical systems 4a and 4b with respect to the divided pupil, and can be obtained in advance by calculation by simulation. . Taking the two-dimensional Fourier transform F for both sides of equation (1),

It becomes. However, the variables s and t are spatial frequencies. When formula (2) is transformed,

It becomes.

  Accordingly, the Fourier spectrum of the image obtained by the imaging optical systems 4a and 4b is obtained, and the point image intensity distribution r (x, y, x ′, y ′) of the imaging optical systems 4a and 4b with respect to the divided pupil is obtained. By dividing by the Fourier spectrum and obtaining a two-dimensional inverse Fourier transform of the obtained result, the intensity distribution g (x ′, y ′) of the object to be obtained can be obtained.

  FIG. 2 is a diagram showing an outline of an electronic camera having a bending optical system according to the second embodiment of the present invention. The embodiment shown in FIG. 2 differs from the embodiment shown in FIG. 1 only in that the variable magnification optical systems 6a and 6b are provided, and is therefore the same as the components shown in FIG. Constituent elements are denoted by the same reference numerals and description thereof is omitted.

  In the embodiment shown in FIG. 2, the variable magnification optical systems 6a and 6b having aspherical surfaces having different refractive powers depending on the direction component are arranged in front of the imaging optical systems 4a and 4b, so that the direction with the highest resolving power can be obtained. The resolution in each direction component is matched with the resolution. In the case of this method, since the magnification of the zooming system varies depending on the direction component, the scale of the image varies depending on the direction component. Therefore, the image is obtained on the detector surface in a deformed state, but a correct image can be obtained by correcting the deformation by image processing including distortion of the imaging optical systems 4a and 4b.

  In any of the embodiments described above, the description has been made on the assumption that there is no optical system on the incident side of the mirror 3 which is a bending optical unit. However, when an optical system is provided on the incident side, the exit pupil It is preferable to adjust the position to the position of the mirror 3. As a result, the exit pupil of this optical system and the imaging optical systems 4a and 4b (in this case, when the optical system on the incident side of the mirror 3 forms part of the imaging optical system, 4a and 4b are also imaged). The position of the entrance pupil (which becomes a part of the optical system) can be made the same position, and the kicking of the light beam by the pupil can be minimized.

It is a figure which shows the outline | summary of the electronic camera which has a bending optical system which is the 1st Embodiment of this invention. It is a figure which shows the outline | summary of the electronic camera which has a bending optical system which is the 2nd Embodiment of this invention. It is a figure which shows the outline | summary of the digital camera using the conventional bending optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Housing, 2 ... Aperture, 3 ... Mirror, 4a, 4b ... Imaging optical system, 5a, 5b ... CCD, 6a, 6b ... Variable magnification optical system

Claims (5)

A bending optical unit, a plurality of imaging optical systems having the same entrance pupil position, and an image processing device , wherein the bending optical unit is placed at the entrance pupil position to divide the entrance pupil. the imaging optical system, the divided light passed through the divided the entrance pupil, an image is formed on the plurality of image plane on each of the plurality of imaging element, the image processing apparatus, the plurality of Bending characterized by having a function of removing random noise by performing image processing on an image formed on an image forming surface and comparing corresponding pixels of the image formed on the plurality of image forming surfaces Optical system. Before Kiga image processing apparatus receives an output from the non-effective pixels of the imaging element, bending optical according to claim 1, based on the input value, and having a function of removing thermal noise system. Before Kiga image processing apparatus, bending optical according to claim 1 or 2, characterized in that to correct the anisotropy of resolution caused by the anisotropy of the divided entrance pupil system.   The optical system for correcting anisotropy in resolution caused by anisotropy of the divided entrance pupil is provided between the bending optical unit and the imaging element. Bending optical system. An electronic imaging apparatus comprising the bending optical system according to any one of claims 1 to 4 .

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