JP2002513951A - Expanded depth of field optical system - Google Patents

Abstract

Abstract: A system (100, 110, 150, 160) for increasing the depth of field and reducing the wavelength dependence of a non-interfering optical system is a special purpose optical mask ( 20, 120, 124, 132). The optical mask is designed such that the optical transfer function remains essentially constant within some range from the point of focus. Signal processing of the resulting intermediate image counteracts the optical transmission modulation effects of the mask, resulting in a focused image over an increased depth of field. Generally, the mask is located at or near the aperture stop or image of the aperture stop of the optical system. Preferably, the mask modulates only the phase and not the amplitude of the light, but the amplitude can be changed by an associated filter or the like. Masks can be used to increase the coverage of passive ranging systems.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to the National Science Foundation and the Office of Naval Research.
Made with government assistance awarded by. The government has certain rights in the invention.

This application is a continuation-in-part of co-pending patent application 08 / 823,894 filed on March 17, 1997, relating to an enlarged depth of field optical system.

[0003] Issued on May 28, 1996, "Range Estimation Apparatus and Metho
U.S. Pat. No. 5,521,695 entitled "d" is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for increasing the depth of field and reducing the wavelength dependence of non-coherent optical systems. The invention is particularly useful for increasing the coverage of a passive ranging system. The same technology is applicable to passive acoustic ranging systems and passive electromagnetic ranging systems.

Description of the Prior Art Increasing the depth of field of optical systems has long been a goal of those studying imaging systems. There is still a need in the art for a simple imaging system that has one or only a few lenses and still provides focusing with greatly increased depth of field. The depth of field belongs to the depth of the scene to be imaged, and the depth of focus belongs to the depth in the image recording system.

A disadvantage of a simple optical system is that an image formed with a red light focus will focus on a different plane than an image formed with blue or green light. The wavelength band that is in focus in one plane is only narrow, and the other wavelengths are out of focus. This is called chromatic aberration. Presently, the expansion of the wavelength band that forms an in-focus image is achieved by using two or more lenses with different refractive indices to form what is called an achromatic lens. If it is possible to increase the depth of field of the system, the area will be expanded to where each wavelength forms a focused image. If these areas are made to overlap, the system can, after digital processing, provide high resolution images in (for example) three different color bands of the television camera. Of course, this expanded depth of field system can be combined with a chromatic aberration lens to still achieve high performance.

There are several other aberrations that lead to defocus. For example, astigmatism occurs when the vertical and horizontal lines focus on different planes. Spherical aberration occurs when a lens focuses on a plane with different radial bands. Field curvature occurs when an off-axis point focuses on a curved surface. Temperature dependence of the focus occurs when changes in the ambient temperature reach the lens and shift the optimal focus position. Each of these aberrations has traditionally been compensated for by using additional lens elements.

[0008] The effects of these aberrations leading to defocus can be reduced by increasing the depth of field of the imaging system. Increasing the depth of field gives lens designers greater flexibility in balancing their aberrations.

[0009] Improving image quality using optical masks is also a popular development area.
For example, Applied Optics , October 1971, Volume 10, Issue 10, M. Mino and Y. Okano, "Improvement in the OTF of a Defocussed Optical Sys
"Tem Through the Use of Shaded Apertures" discusses a gradual decrease in amplitude transmission from the center of the pupil to its periphery, resulting in a slightly better image. Applied Optics , June 1988. Vol. 27, No. 12, J. Ojeda-C
"High Focal Depth By A podization and Digital Restorat" by astaneda et al.
ion ”was previously apodized using an iterative digital reconstruction algorithm (apo
dized) to improve the optical transfer function of the optical system. March 1990 of Applied Opt ics, Vol. 29, "according to the seventh edition of J. Ojeda-Castaneda et al Zone
"Plate for Arbitrarily High Focal Depth" discusses the use of a zone plate as an apodizer to increase the depth of focus.

[0010] All of these inventors, as well as others skilled in the art, cannot achieve the point spread function of a focused standard optical system with a large depth of field by purely optical means. Trying to do something. Employing digital processing, it will slightly remove and sharpen the post-image.

SUMMARY OF THE INVENTION The system described herein provides focused resolution over an area of extended depth of field. Therefore, it is particularly effective in compensating for defocus aberrations such as spherical aberration, astigmatism, field curvature, chromatic aberration, and temperature-dependent focal shift.

It is an object of the present invention to increase the depth of field of a non-coherent optical imaging system by adding a special purpose optical mask to the system. The mask is designed such that the digital processing allows the resulting intermediate image to be digitally processed to yield an image with in-focus resolution for a wide range of defocus. The mask causes the optical transfer function to remain substantially constant to some extent away from the in-focus position. Digital processing counteracts the optical transfer function modulation effects of the mask, resulting in a focused high resolution over an increased depth of field.

A typical optical system includes a lens that focuses light from an object on an intermediate image,
Means for storing images such as film, video camera, charge coupled device (CCD), etc. The depth of field of such an optical system is increased by inserting an optical mask between the object and the CCD. The mask modulates the optical transfer function of the system such that for a certain range of distances the optical transfer function does not depend substantially on the distance between the object and the lens. Depth-of-field post-processing is performed on the stored image, and the image is restored by inversely modulating the optical transmission made by the mask. For example, the post-processing means causes a filter having an inverse function of the optical transfer function modulation performed by the mask to be implemented.

In general, the mask is located either at or near the aperture stop or the image of the aperture stop of the optical system. The mask is placed at a location in the optical system such that the resulting system can be approximated by a linear system. This result is obtained by placing the mask at the aperture stop or at the image of the aperture stop. Preferably, the mask is a phase mask, modulating only the phase of the light and not the amplitude of the light.
For example, the mask can be a three-dimensional phase modulation mask.

The mask is not a standard lens in a wide field of view single lens optical system,
Can be used in combination with self-focusing fibers or lenses.

A mask that extends the depth of field of the optical system considers an ambiguity function related to several candidate mask functions, and which particular mask function is nearly constant over the range of the object. It can be manufactured by determining whether it has an optical transfer function and by making a mask with a mask function of a particular candidate.
The function of the mask can be shared by two masks located at different locations in the system.

A second object of the present invention is to increase the effective range of a passive ranging system.
To this end, the mask modulates the optical transfer function to be independent of object distance, as described above, and further modulates the optical system such that the optical transfer function includes zero as a function of object distance. And encode the distance information into the image.
The post-ranging post-processing means connected to the depth-of-field post-processing means decodes the distance information encoded in the image and calculates distances to various points of the object from the distance information.
For example, the mask can be combined with a three-dimensional phase modulation mask or a linear phase modulation mask.

A third object of the present invention is to expand the wavelength (color) band for forming a focused image. By increasing the depth of field of the system, the area of interest is enlarged to where each wavelength forms a focused image. These regions of interest can overlap and the system can generate high resolution images in three different color bands after digital processing.

A fourth object of the present invention is to increase the depth of field of an imaging system comprising an element whose optical properties change with temperature, or especially an element prone to chromatic aberration.

A fifth object of the present invention is to increase the depth of field of an imaging system and minimize the effects of defocus aberrations such as spherical aberration, astigmatism, and field curvature. By increasing the depth of field, the defocus aberration can have a best focus overlap region. After digital processing, an image can be provided that minimizes the effects of defocus aberration.

A sixth object of the present invention is to increase the depth of field of an imaging system without adding another optical element, so that a mask that increases the depth of field is physically separated from other optical elements. It is joining.

Those skilled in the art will appreciate the above and other objects, features, advantages, and advantages of the present invention.
A more detailed description of the preferred embodiments, as illustrated in the accompanying drawings, and application will be understood from the following description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (Prior Art) shows a standard optical imaging system. Object 15 passes through lens 25 and forms an image on charge coupled device (CCD) 30. Of course, more lenses or different recording media can be used, but FIG. 1 shows a simple standard optical system. Such a system produces a sharp and focused image only when the object 15 is located on or very close to the focused object plane.
Distance from the principal plane of the lens 25 to the CCD 30 is in d _i, if the focal length of the lens 25 is f, so that the image is focused on the CCD 30, the distance from the main plane front of the lens 25 to the object 15 d ₀ is

[0024]

(Equation 1)

Must be selected as follows: The depth of field of the optical system is such that the object is away from the in-focus distance and the image is still in focus. In a simple system as in FIG. 1, the depth of focus is very small.

FIG. 2 illustrates the interaction and operation of a multi-part magnified depth of field system according to the present invention. The object 15 passes through the optical mask 20 and the lens 25 and passes through the charge-coupled device (C
An image is created in the CD) system 30 and post-processing of the image is performed in the digital processing system 35. Those skilled in the art will appreciate that any image recording and correction device can be used in place of the CCD system 30.

The mask 20 is made of an optical material such as a glass film or a plastic film having different opacity, thickness, or refractive index. Preferably, the mask 20 is a phase mask and acts only on the phase of the transmitted light, not on the amplitude.
This results in a highly accurate optical system. However, the mask 20
Can be a single amplitude mask or a combination of two amplitude masks. The mask 20 modulates the incoherent optical system in such a way that the system response to a point image or point spread function (PSF) is relatively independent of the distance of the point image from the lens 25 over a predetermined range of object distance. Designed to be. Thus, the optical transfer function (OTF) is also relatively independent of object distance over this range. The resulting PSF itself is not a point. However, as long as the OTF does not include zero, the post-processing of the image will result in the resulting PSF being approximately equal to the focused response of a standard optical system over a given range of object distance. So, P
Used to modify SF and OTF.

The purpose of the mask 20 is to modulate the optical system in such a way that the OTF of the system of FIG. 2 is not affected by the defocus distance over a certain range of object distance. In addition, the OTF should not contain zeros so that the effects of the mask (other than increased depth of field) can be eliminated in post-processing.

An effective way to describe the optical mask function P (x) (P (x) is described below in connection with FIGS. 3-30) is that of the fuzzy function. The OTF equation of the optical system can be shaped similar to the well-known fuzzy function A (u, v). Ambiguous functions are used in radar applications and have been widely studied. Understanding the use of ambiguous functions in radar systems is quite different from OTF, but the similarity in the form of equations helps in dealing with OTF. The ambiguous function is

[0030]

(Equation 2)

Is given by Here, * means a conjugate complex number, and the mask function P (x) is a normalized coordinate.

[0032]

(Equation 3)

Where D is the length of the one-dimensional mask. In the above equation, a separable two-dimensional orthogonal mask is assumed for simplification. Such a system can in theory be described entirely with a one-dimensional mask. A simple extension of the above fuzzy function can be used to evaluate a general two-dimensional mask.

As is known to those skilled in the art, given a general optical mask function, the response of the decoupling OTF to any defocus value を is given by the equation

[0035]

(Equation 4)

Can be calculated by The independent spatial parameter x and spatial frequency parameter u have no units since the equations have been normalized. Ψ is a normalized defocus parameter, which depends on the size of the lens 25 and the focus state.

[0037]

(Equation 5)

Here, L is the depth of the lens, λ is the wavelength of light, f is the focal length of the lens 25, d ₀ Is the distance from the front principal plane to the object 15, d_iIs placed on the CCD 30 from the rear main plane
This is the distance to the image plane. Defocused given fixed optical system parameters
Re is monotonically the object distance d₀Is associated with

OTF and ambiguous function are

[0040]

(Equation 6)

It can be shown that they are related as follows. Thus, the OTF is given by the radial part passing through the ambiguity function A (u, v) with respect to the optical mask function P (x). This radial line has a slope of Ψ / π. OTF from ambiguous function
The procedure for detecting is shown in FIGS. The output and usefulness of the relationship between the OTF and the fuzzy function is that a single two-dimensional function A (u, v), which is uniquely dependent on the optical mask function P (x), for all values of defocus It lies in the fact that OTF can be represented. Without this measure, it would be necessary to calculate the OTF for each value of defocus, making it difficult to determine whether the OTF is essentially constant over a range of object distances.

A common form of one set of phase masks is three-dimensional phase modulation (three-dimensional PM). The general form is

[0043]

(Equation 7)

Is as follows.

By selecting the constants a, b, g, and d, the modulation transfer function is circularly symmetric (a = b = a ₀ , G = d = −3a₀), A separable orthogonal phase function is possible for the system
It works. For simplicity, we use symmetric and separable orthogonal shapes. this
Is

[0046]

(Equation 8)

Is given by

Since this shape is separably orthogonal, most analyzes need only consider one-dimensional elements,

[0049]

(Equation 9)

Here, a is a parameter used to adjust the increase in the depth of field.

FIG. 3 shows a mask that performs this separable orthogonal three-dimensional phase function. α
If = 0, it is a standard orthogonal function given by an unmasked or transparent mask. As the absolute value of α increases, the depth of field also increases. As α increases, the image contrast before post-processing decreases. This is because the ambiguous function spreads as α increases and becomes less dependent on defocus. However, since the overall size of the fuzzy function is constant, the fuzzy function becomes flatter as it spreads.

For a sufficiently large α, the OTF of a system using a three-dimensional PM mask is

[0053]

(Equation 10)

Is approximated by Appendix A of this parent patent gives the mathematical processing required to reach the OTF function described above.

Thus, a three-dimensional PM mask is one example of a mask that modulates an optical system to have a substantially constant OTF over a range of object distances. The specific range over which the OTF does not change significantly depends on α. This range (and depth of field) increases with α. However, the amount by which the depth of field can be increased is actually limited by the fact that the contrast decreases with increasing α and eventually falls below the system noise.

4 to 30, the performance of the standard imaging system of FIG. 1 and the C-PM of FIG.
FIG. 4 compares and contrasts the preferred embodiment of the enlarged depth of field of FIG. 2 using a mask.

In the following description, the systems of FIGS. 1 and 2 are discussed using three methods. First, the magnitude of the OTF in the two systems is considered for various defocus values. The size of the OTF of the system does not completely indicate the quality of the final image. In other circumstances, comparing an ideal OTF (the standard system of FIG. 1 in focus) to this OTF gives a qualitative feel about the goodness of the system.

Second, the PSFs of the two systems are compared. The full width at half maximum of the PSF gives a qualitative value comparing the two systems. Third, compare the spoked drawing images produced by the two systems. The spoke drawings are easily recognizable and include a wide range of spatial frequencies. This comparison is qualitative, but very accurate.

FIG. 4 shows the fuzzy function in the standard optical system of FIG. Most of the output is concentrated along the v = 0 axis and is very dependent on the system defocus. FIG. 5 is a plan view of FIG. In this figure, a large value of the fuzzy function is represented by a dark shade. The horizontal axis extends from -2π to 2π. As discussed above, the projection of the radial line drawn through the fuzzy function with slope Ψ / π determines the OTF for defocus Ψ. This radial line is the spatial frequency u
Projected on axis. For example, the dotted line in the figure is drawn with a slope of 1 / (2π). This line is the OT of the standard system of FIG. 1 for defocus values of Ψ = １ ／.
It corresponds to F. FIG. 7 shows the size of the OTF.

FIG. 6 shows the OTF in the standard system of FIG. 1 without defocus. This drawing corresponds to the radial line drawn horizontally along the horizontal u-axis in FIG.

FIG. 7 shows the magnitude of the OTF for a relatively light defocus １ ／. This OT
F corresponds to the dotted line in FIG. Even for 1/2 defocus, this OTF
Is dramatically different from the OTF in the focused system shown in FIG.

FIG. 8 shows the fuzzy function of the expanded depth of field of FIG. 2 using the C-PM mask of FIG. 3 (C-PM system). This fuzzy function is relatively flat, so that a change in defocus results in little change in the system OTF. 12
The α defined on the page is set to be equal to 3 for a particular system, referred to herein as the “C-PM system”.

FIG. 10 shows the size of the OTF in the C-PM system of FIG. 2 before performing the digital filter operation. This OTF does not look like the ideal OTF of FIG. 6 at all. However, the C-PM EDF system shown in FIG.
The TF (including the filter operation) is very similar to FIG. High frequency ripple does not significantly affect the quality of the output image, and can be reduced in magnitude by increasing α.

FIG. 12 shows C in FIG. 2 with a slight defocus (Ψ = １ ／) before the filter operation.
-Indicates the size of the OTF in the PM system. Moreover, the OTF does not look like FIG. However, as in FIG.
It is similar to F. Thus, a similar filtering operation results in the final OTF shown in FIG. 13, which is similar to FIG.

FIG. 14 shows the CP of FIG. 2 having a large defocus (Ψ = 3) before the filter operation.
5 shows the size of the OTF in the M system. FIG. 15 shows the size of the OTF in the entire C-PM system. In all three cases (no defocus, slight defocus, and large defocus), the OTF before processing is almost the same, and since the OTF is restored to almost ideal, the same post-processing or filter operation is possible. Note that

Note that while the OTF in the C-PM system of FIG. 2 is nearly constant for the three defocus values, it is not similar to the ideal OTF of FIG. Therefore, before obtaining a clear image, it is desirable to remove the influence (other than the depth of field) of the mask of FIG. 3 by post-processing. The effects of the mask can be removed in various ways. In a preferred embodiment, the function implemented in post-processing 35 (preferably digital signal processing in a special purpose electronic chip, but could be a digital computer or an electronic or optical analog processor) is the inverse function of the OTF (さ れ る is approximated as a function H (u) that is constant with respect to Ψ). Therefore, post-processing 35 is generally represented by the formula

[0067]

[Equation 11]

Must be executed.

FIGS. 16 to 23 show the point spread function (PSF) of the standard system of FIG. 1 and the C-PM system of FIG. 2 for varying amounts of defocus. FIG.
4 shows a full width drawing normalized to the full width at half maximum (FWHM) of the point spread function for defocus for two systems. The FWHM changes slightly for the C-PM system of FIG. 2, but rises rapidly for the standard system of FIG.

FIGS. 17, 18 and 19 show the standard system of FIG. 1 with defocus values of 0.5, 0.5 and 3, respectively (no defocus, light defocus, large defocus). Shows the PSF associated with. The PSF changes dramatically even for light defocus, and is completely unacceptable for large defocus.

FIG. 20 shows the PSF in the C-PM system of FIG. 2 without defocus before filtering (post-processing). Although it does not look like the ideal PSF of FIG. 17 at all, it also looks like the one shown in FIG. 21 after the filtering operation. The PSF in the C-PM system of FIG. 2 for a slight defocus is shown in FIG. 22, and the PSF in the C-PM system of FIG. 2 having a large defocus is shown in FIG.
All three PSFs of the entire system are almost distinguishable from each other and from FIG.

FIG. 24 shows an image of a spoke drawing made with the standard system of FIG. 1 without defocus. FIG. 25 shows a similar image made with the standard system of FIG. 1 with slight defocus. The spokes are still distinguishable, but the high frequency center part of the drawing is missing. FIG. 26 shows the standard system of FIG. 1 formed with a large defocus. This image carries little information.

FIG. 27 shows an image of a spoke-like drawing produced by the C-PM system of FIG. 2 before digital processing. An image created after post-processing is shown in FIG. Images produced with the complete system of FIG. 2 with light and large defocus are shown in FIGS. 29 and 30, respectively. Furthermore, they are substantially distinguishable from each other and from the ideal image of FIG.

FIG. 31 shows an optical system according to the present invention for extended depth of field passive ranging. Passive ranging using an optical mask has been described by the inventors in the Range Estimation App.
No. 08 / 083,829, entitled "aratus and Method," and incorporated herein by reference.
No. 3,829 describes a system including a distance-dependent null space, which is equal to the distance-dependent zero described below.

In FIG. 31, a typical lens system 40 has an entrance pupil 42 and an exit pupil 43. Generally, the optical mask 60 is placed at or near the aperture stop, but the mask 60 can also be placed at the image of the aperture stop as shown in FIG. This is a beam splitter 45 that produces a sharp image 50 of an object (not shown).
give. The lens 55 projects the image of the exit pupil 43 on the mask 60. The mask 60 combines enlarged depth of field and passive ranging. CCD 65
Samples the image from the mask 60. Digital filter 70 is a fixed digital filter that is aligned with the expanded depth of field element of mask 60. The filter 70 returns the image of the PSF to the point described above. The distance estimation device 75
Estimate the distance to various points of the object (not shown) by estimating the null, ie, the period of the distance dependent zero.

Briefly, passive ranging is achieved by modulating the incoherent optical system of FIG. 2 in such a way that a distance dependent zero exists in the point spread function (OTF). Note that the OTFs of the EDF system described above cannot include zeros, since zeros cannot be removed by post-filtering to restore the image. However, in FIG. 31, zero is added to encode a wavefront having distance information. It is not important to restore the image, but it is important to detect the object distance. To detect the distance associated with a particular small block of an image, the period of zeros within the block is associated with the distance to the object making the image within the block. Application No. 08 / 083,829 describes primarily amplitude masks, but phase masks also have zero as a function of object distance, and can produce OTFs without losing optical energy. Current passive ranging systems can only operate over very limited object depths, beyond which the main lobe of the OTF narrows and the zero in the OTF lobe loses the ranging zero. So it will be impossible to put a zero. The expanded depth of field of passive ranging is
Making such a system even more useful.

[0077]

(Equation 12)

Consider a general mask 60 of passive ranging that is mathematically described as μ _s (x) = 0 for | x |> π / s. This mask is composed of an S phase modulation element μ _s (x) having a length T, and S · T = 2π. The phase modulation of each part is given by an exponential term. When the above-described mask is a phase mask, a portion μ _s (x) where s = 0, 1,..., S−1 satisfies | μ _s (x) | = 1. A simple example of this type of mask is shown in FIG. This is, w ₀ = -2 /
It is a phase mask of two parts (S = 2) where π and w ₁ = 2π.

FIG. 32 shows an example of a phase passive ranging mask 80 that can be used as the mask 60 of FIG. This mask is called a linear phase modulation (LPM) mask because each part modulates the phase linearly. Mask 80 comprises two wedges or prisms pointing in opposite directions. Without the additional filter 85, the image created would be the sum of the left and right parts. The additional filter 85 comprises two halves 86 and 87, one under each wedge. The half 86 is orthogonal to the half 87 so that light passing through one half does not pass through the other half. For example, the filters can be different colors (red and green, green and blue, or blue and red, etc.) or polarized in orthogonal directions. The purpose of the filter 85 is to create a single lens stereoscopic image. The stereoscopic image has a distance between the same points of each image determined by the object distance, and is composed of two overlapping images.

FIG. 33 shows an optical mask function combining LPM passive ranging and the three-dimensional PM mask 60 of FIG. 31 suitable for passive ranging over a large depth of field. This mask is

[0081]

(Equation 13)

Where μ (x) = 1 or 0 for 0 ≦ x ≦ π. Mask 60
By using the two parts of the LPM element, two lobes of the OSF are created.

Using a mask 60 having the characteristics shown in FIG. 33, defocus y = 0 (no defocus)
FIG. 34 shows a PSF in the imaging system of FIG. This system is referred to as EDF / PR system for extended depth of field / passive ranging. Due to the two parts of the mask 60, the PSF has two maxima.

FIG. 35 shows the PSF of the EDF / PR system with y = 10. Positive y means that the object is on the focused side far from the lens. PS
The two maximum values of F are close together. Therefore, the defocus (or distance from the focal plane) is related to the distance between the maximum values of the PSF. Of course, the actual processing performed by the digital distance estimator 75 is fairly complex since the entire scene is received by the estimator 75 and is not just a point source image. This process is described in detail in application Ser. No. 08 / 083,829.

FIG. 36 shows the PSF of an EDF / PR system with y = −10. Negative y means that the object is closer to the lens than the focal plane. The two maximum values of the PSF have been moved away. Therefore, the estimating device 75 can determine not only the distance from the focal plane to the object but also the direction.

It is important to note that even though the maximum value of the PSF varies with distance, the maximum value itself remains narrow and sharp because the EDF portion of the mask 60 is combined with the operation of the digital filter 70. It is.

FIG. 37 shows a PSF for a system having the LPM mask 80 of FIG. 31 and no EDF portions and no defocus. FIG. 37 is very similar to FIG. 34 since there is no defocus. FIG. 38 shows the PSF of the mask 80 without EDF and with a large positive defocus (y = 0). As shown in FIG. 35, the maximum value has been moved. However, the amount of any digital processing is very difficult to determine from the PSF because the maximum is quite wide. FIG. 39 shows the PSF of the mask 80 without EDF and with a large negative defocus (y = −10). Although the maximum value is moving away, it is difficult to determine how much it has moved because of the large amount of defocus.

That is, FIG. 39 shows that there is no enlarged depth of field and a large negative defocus (y = 0)
2 shows the PSF of an LPM system having Although the maximum moves further away, it is very difficult to determine the position of the maximum.

FIG. 40 shows the optical transfer function of the combined EDF and LPM system shown in FIG. 31 with a small amount of defocus (y = 0). The OTF envelope is essentially the triangle of the complete system (see FIG. 6). The function added to the OTF by the ranging portion of the mask of FIG. 33 includes a distance dependent zero or minimum. Digital processing looks for these zeros to determine the distance to different points of the object.

FIG. 41 shows the optical transfer function of the embodiment of FIG. 31 without the extended depth of field function and with a small defocus (y = 1). The envelope moves from the ideal triangle (see FIG. 6) to have a narrow central lobe with side lobes. It is still possible to distinguish distance dependent zeros, but it is becoming difficult due to the low value of the envelope between the main and side lobes. As the defocus increases, the main lobe becomes narrower and the envelope has a lower value over a larger area. Distance dependent local minima and zeros tend to match the envelope zeros to the extent that digital processing 70, 75 cannot be reliably distinguished.

FIG. 42 shows an optical system 100 similar to the imaging system of FIG. 2, but using plastic optical elements 106 and 108 instead of lens 25. The elements 106,108 are intended to hold the elements 106,108 in a fixed position in the optical system and have a fixed spacing 1 between the elements 106,108.
02 and 104. All optical elements, and especially plastic elements, undergo a change in temperature as well as a change in refractive index as well as a change in geometry. For example, PMMA, a plastic often used as an optical element, has a refractive index that changes 60 times faster than glass depending on temperature. Furthermore, spacer 1
02 and 104 vary in size with temperature and become slightly longer with increasing temperature. Thus, as the temperature increases, the elements 106, 108 move away.

Thus, a change in temperature will result in a change in performance in an optical system such as 100. Specifically, the image plane of the optical system, such as 100, moves with temperature. EDA mask 20 in combination with digital processing 35 increases the depth of field of system 100 and reduces the effects of temperature effects. In FIG. 42, the mask 20 is located between the elements 102, 104, but the mask 20 can be located elsewhere in the optical system.

The EDF mask 20 (combined with the process 35)
Also reduces the effect of chromatic aberration. Plastic optical elements are particularly susceptible to chromatic aberrations due to the limited variety of different plastics that have good optical properties. Common methods of reducing chromatic aberration, such as combining two elements with different refractive indices, are almost unavailable. Therefore, the increased depth of field provided by the EDF elements 20, 35 is particularly important in systems with plastic elements.

FIG. 43 shows an infrared lens 112 used in place of the lens 25 in the imaging system of FIG. The dashed line 114 indicates the dimensions of the lens 112 at a high temperature. Infrared materials, such as germanium, tend to be subject to thermal effects, such as changes in refractive index, especially with dimensional changes and temperature changes. The change in refractive index with temperature is 230
It is twice. EDF filter 20 and process 35 increase the depth of field of optical system 110 and reduce the effects of these thermal effects.

[0095] Like plastic optical elements, infrared optical elements tend to be more susceptible to chromatic aberration than glass. It is particularly difficult to reduce the chromatic aberration of the infrared element due to the limited number of available infrared materials. Common methods of reducing chromatic aberration, such as combining two elements with different refractive indices, are almost unavailable.
Therefore, the increased depth of field provided by the EDF element is particularly important in infrared systems.

FIG. 44 shows a color filter 118 bonded to the EDF mask 20. In some optical systems, it is desirable to process or create an image of only one wavelength of light, for example, infrared. In other systems, it is possible to use a gray filter. In a system using a color filter, the EDF mask 120 is used.
Can be fixed to a color filter to make a single element, or can be integrated with a single material color filter.

FIG. 45 shows the combined lens / EDF (EDF mask is not to scale). For example, this element can replace lens 25 and mask 20 of the imaging system of FIG. In this particular example, the mask and lens are integrally configured. First surface 126 performs the function of focusing, and second surface 128 performs the EDF mask function. Those skilled in the art will appreciate that these two functions can be achieved with various mask shapes.

FIG. 46 shows the combined diffraction grating / EDF mask 130. For example, the diffraction grating 134 can be added to the EDF mask 132 by embossing. The diffraction grating 134 can include a modulation diffraction grating, for example, to compensate for chromatic aberration. Alternatively, it may include a refractive optical element that functions as a lens or an anti-aliasing filter.

FIG. 47 shows an EDF optical system similar to FIG. In this figure, the lens 14
2 indicates a defocus aberration. Defocus aberration is the astigmatism that occurs when the vertical and horizontal lines are focused on different planes, the spherical aberration that occurs when the lens is focused on a plane with different radial bands, and the off-axis point is a curved surface. Includes the field curvature that occurs when the image is in focus. In conjunction with post-processing 35, mask 20 increases the depth of field of the optical system to reduce the effects of defocus aberration.

FIG. 48 shows an optical system 150 using two masks 152, 156 at different locations in the system. This system combines the EDF of the mask 20
Execute the mask function. For example, it may be beneficial to perform a horizontal variant on the mask 152 and a vertical variant on the mask 156. In the particular example of FIG. 48, masks 152, 156 are provided on either side of lens 153. For example, this assembly can replace lens 25 and mask 20 in the imaging system of FIG.

FIG. 49 shows an optical imaging system similar to that of FIG. 2 with the lens 25 replaced by a self-focusing element 162. Element 162 focuses light not by a change in the thickness of the optical material across the cross section of the element, but rather by a change in the refractive index of the material across the cross section of the element.

While the preferred embodiment according to the present invention has been described by way of example and with reference to specific cases, those skilled in the art will now elaborate upon this description without departing from the spirit of the invention. Understand what other changes, modifications, additions, and applications have been made.

[Brief description of the drawings]

FIG. 1 shows a standard prior art imaging system.

FIG. 2 illustrates an extended depth of field (EDF) imaging system according to the present invention.

FIG. 3 shows an outline of a mask for a three-dimensional PM (C-PM) mask used in FIG. 2;

FIG. 4 shows the fuzzy function of the standard system of FIG.

5 shows a plan view of the fuzzy function of FIG.

FIG. 6 shows the OTF for the standard FIG. 1 system without defocus.

FIG. 7 shows the OTF for the standard FIG. 1 system with slight defocus.

FIG. 8 shows the optical transfer function (OT) for the standard FIG. 1 system with large defocus.
F) is shown.

FIG. 9 shows an ambiguous function of the C-PM mask of FIG. 3;

FIG. 10 shows the OTF for the expanded depth of field of FIG. 2 with the C-PM mask of FIG. 3, without defocus and before digital processing.

FIG. 11 shows the OTF for the C-PM system of FIG. 2 after processing without defocus.

FIG. 12 shows the OTF for the C-PM system of FIG. 2 with slight defocus (before processing).

FIG. 13 shows the OTF for the C-PM system of FIG. 2 with slight defocus (after processing).

FIG. 14 shows the OTF for the C-PM system of FIG. 2 with a large defocus (before processing).

FIG. 15 shows the OTF for the C-PM system of FIG. 2 with large defocus (after processing).

FIG. 16 shows a diagram of the full width at half maximum (FWHM) of the point spread function such that defocus increases for the standard system of FIG. 1 and the C-PM system of FIG. 2;

FIG. 17 shows the PSF for the standard imaging system of FIG. 1 without defocus.

FIG. 18 shows the PSF for the standard system of FIG. 1 with slight defocus.

FIG. 19 shows the PSF for the standard system of FIG. 1 with large defocus.

FIG. 20 shows the PSF for the C-PM system of FIG. 2 before defocus-free processing.

FIG. 21 shows the PSF for the C-PM system of FIG. 2 after processing without defocus.

FIG. 22 shows the PSF for the C-PM system of FIG. 2 after processing with a small defocus.

FIG. 23 shows the PSF for the C-PM system of FIG. 2 after processing with significant defocus.

FIG. 24 shows a spoke-like drawing from the standard system of FIG. 1 without defocus.

FIG. 25 shows a spoke-like drawing from the standard system of FIG. 1 with a slight defocus.

FIG. 26 shows a spoke-like drawing from the standard FIG. 1 system with large defocus.

FIG. 27 shows a spoke-like drawing from the C-PM system of FIG. 2 without defocus (before processing).

FIG. 28 shows a spoke-like drawing from the C-PM system of FIG. 2 without defocus (after processing).

FIG. 29 shows a spoke-like drawing from the C-PM system of FIG. 2 with a slight defocus (after processing).

FIG. 30 shows a spoke-like drawing from the C-PM system of FIG. 2 with large defocus (after processing).

FIG. 31 shows an imaging system according to the present invention that combines an extended depth of field function with passive ranging.

FIG. 32 shows a phase mask for passive ranging.

FIG. 33 shows a phase mask for expanded depth of field and passive ranging used in the apparatus of FIG. 31.

FIG. 34 shows a point spread function of the embodiment of FIG. 31 without defocus.

FIG. 35 shows the point spread function of the embodiment of FIG. 31 with a large positive defocus.

FIG. 36 shows the point spread function of the embodiment of FIG. 31 with a large negative defocus.

FIG. 37 illustrates the point spread function of the embodiment of FIG. 31 without the extended depth of field function and defocus.

FIG. 38 shows the optical transfer function of the embodiment of FIG. 31 without the extended depth of field function and with a large positive defocus.

FIG. 39 shows the optical transfer function of the embodiment of FIG. 31 without the extended depth of field function and with a large negative defocus.

FIG. 40 shows the optical transfer function of the expanded depth of field passive ranging of FIG. 31 with a small amount of defocus.

FIG. 41 shows the optical transfer function of a passive ranging system without an extended depth of field feature and with a small amount of defocus.

FIG. 42 has a plastic optical element used in place of the lens of FIG.
1 shows an EDF imaging system similar to the F imaging system.

FIG. 43 shows an EDF imaging system similar to the EDF imaging system of FIG. 2 with an infrared lens used in place of the lens of FIG.

FIG. 44 shows a color filter bonded to the EDF mask of FIG. 3;

FIG. 45 illustrates a combined lens / EDF mask according to the present invention.

FIG. 46 illustrates a combined diffraction grating / EDF mask according to the present invention.

FIG. 47 shows an EDF optical system similar to the EDF optical system of FIG. 2, wherein the lens has defocus aberration.

FIG. 48 illustrates an EDF optical system according to the present invention using two masks at different locations of the combined system to perform the EDF function.

FIG. 49 shows an EDF imaging system similar to the EDF imaging system of FIG. 2 with a self-focusing fiber used in place of the lens of FIG.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY , CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE, GH, GM, HR, HU, ID, IL, IS, JP, KE, KG , KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, YU, ZW (71) Applicant 3101 Iris Avenue, Suite 250, Boulder, Colorado 80301, United States Statesofos America (72) Inventor Dowski Edward Earl. Junior United States 80026 La Fayette, Colorado East Clelandland Street 307

Claims (74)

[Claims] 1. An apparatus for increasing the depth of field of an optical system for processing incoherent light, said optical system having an optical transfer function, wherein said optical system images incoherent light provided by an object. An optical mask having means for focusing on a plane, and storing means for storing an electrical depiction of the light image incident on the image plane; an optical mask positioned between the object and the storage means; Created and deployed to modulate the optical transfer function of the system, such that the modulated optical transfer function between the object and the optical system over a wider object distance range than given by the unmodulated optical transfer function. Becomes substantially independent of an unknown distance, and the mask acts on the modulation of the optical transfer function substantially by acting on the phase of light transmitted through the mask; and Depth-of-field post-processing means for restoring the electrical depiction of the stored light image by reversing the modulation of the optical transfer function made by the mask. 2. The apparatus of claim 1 wherein said focusing means comprises a plastic lens. 3. The apparatus of claim 1 wherein said focusing means comprises an infrared lens. 4. The apparatus of claim 1, wherein said focusing means comprises a self-focusing fiber. 5. The apparatus of claim 1, wherein said mask is bonded to a color filter. 6. The apparatus of claim 1, wherein said focusing means comprises a lens cemented with a mask. 7. The apparatus of claim 1, wherein said mask is bonded to a diffractive element. 8. The apparatus of claim 1, wherein said focusing means includes defocus aberration. 9. The method of claim 8, wherein the means for focusing includes at least one of the following defocus aberrations: spherical aberration, astigmatism, field curvature, chromatic aberration, and temperature-dependent focal shift. apparatus. 10. The apparatus of claim 1, wherein said phase mask is a three-dimensional PM phase mask. 11. The apparatus of claim 10, wherein the three-dimensional PM mask is symmetric and separably orthogonal. 12. The apparatus of claim 10, wherein said focusing means comprises a plastic lens. 13. The apparatus of claim 10, wherein said focusing means comprises an infrared lens.
Equipment. 14. The method of claim 1, wherein the focusing means comprises a self-focusing element.
0 device. 15. The mask according to claim 1, wherein the mask is bonded to a color filter.
0 device. 16. The apparatus of claim 10, wherein said focusing means comprises a lens cemented with a mask. 17. The apparatus of claim 10, wherein said mask is joined with a diffractive element. 18. The method according to claim 1, wherein the focusing means includes defocus aberration.
0 device. 19. An apparatus for increasing the depth of field of an optical system for processing incoherent light, said optical system having an optical transfer function, wherein said optical system images incoherent light provided by an object. Two optical masks having means for focusing on a plane and having storage means for storing an electrical depiction of the light image incident on the image plane, said two optical masks being located between the object and the storage means; Are created and deployed to modulate the optical transfer function of the optical system, so that the modulated optical transfer function can be transmitted between the object and the optical system over a wider object distance range than given by the unmodulated optical transfer function. Become substantially independent of the unknown distance between them,
The mask acts on the phase of light transmitted through the mask,
Depth-of-field post-processing means for restoring the electrical depiction of the stored light image by substantially effecting said modulation on the optical transfer function and reversing the modulation of the optical transfer function made by the mask. A device with and. 20. An optical mask for use in an optical system for imaging an object, the optical mask comprising: a body of optical material-created to effect a change in a wavefront of light passing through the body according to a preselected phase transfer function. Deployed to provide a modulated optical transfer function of the optical system by changing the wavefront, wherein the modulated optical transfer function is more dependent on the distance between the object and the optical system than the optical transfer function of the unfiltered optical system. An optical mask having substantially less. 21. The mask of claim 20, which is created and deployed to satisfy a three-dimensional phase modulation function. 22. The method of claim 21 wherein the phase modulation function is created and deployed to satisfy ax ³ + by ³ , wherein a and b are constants and x and y represent the optical area of the mask through which light passes. mask. 23. The mask of claim 22, wherein the change in wavefront is caused by a change in thickness of the mask. 24. The mask of claim 22, wherein the change in wavefront is caused by a change in the refractive index of the mask. 25. Created and deployed to satisfy a phase modulation function ax ³ + by ³ + cx ² y + dxy ² , where a, b, c and d are constants and x and y
22. The mask of claim 21 wherein represents the optical area of the mask through which light passes. 26. The mask of claim 25, wherein the change in wavefront is effected by a change in mask thickness. 27. The mask of claim 25, wherein the change in wavefront is caused by a change in the refractive index of the mask. 28. An optical mask comprising: means for collecting light from an object; means for modulating a wavefront of the collected light according to a three-dimensional phase modulation function; and means for emitting modulated light. 29. means for modulating satisfies the phase modulation function ax ³ + by ^3, where a and b are constants, x and y are the mask of claim 28 which represents the optical area of the mask through which light passes. 30. The method of claim 2, wherein the modulating means comprises a change in mask thickness.
9 masks. 31. The mask of claim 29, wherein the modulating means comprises a change in the refractive index of the mask. 32. The means for modulating satisfies ax ³ + by ³ + cx ² y + dxy ² , wherein a, b, c and d are constants, and x and y represent the optical area of the mask through which light passes. 28 masks. 33. The method of claim 3, wherein the modulating means comprises a change in mask thickness.
2 mask. 34. The mask of claim 32, wherein the modulating means comprises a change in the refractive index of the mask. 35. An optical mask for reducing contrast in an imaging optical system, wherein the optical mask is made and deployed to effect a change in a wavefront of light passing through the body according to a three-dimensional phase modulation function. An optical mask comprising 36. The method of claim 35, wherein the phase modulation function is created and deployed to satisfy ax ³ + by ³ , where a and b are constants and x and y represent the optical area of the mask through which light passes. mask. 37. The mask of claim 36, wherein the change in wavefront is effected by a change in mask thickness. 38. The mask of claim 36, wherein the change in wavefront is caused by a change in the refractive index of the mask. 39. Created and deployed to satisfy the phase modulation function ax ³ + by ³ + cx ² y + dxy ² , where a, b, c and d are constants and x and y
36. The mask of claim 35, wherein represents the optical area of the mask through which light passes. 40. The mask of claim 39, wherein the change in wavefront is effected by a change in mask thickness. 41. The mask of claim 39, wherein the change in wavefront is caused by a change in the refractive index of the mask. 42. An optical low-pass filter comprising a body of optical material-created and deployed to effect a change in the wavefront of light passing through the body according to a three-dimensional phase modulation function. 43. The method of claim 42, wherein the phase modulation function is created and deployed to satisfy ax ³ + by ³ , wherein a and b are constants and x and y represent the optical area of the mask through which light passes. mask. 44. The mask of claim 43, wherein the change in wavefront is effected by a change in mask thickness. 45. The mask of claim 43, wherein the change in wavefront is caused by a change in the refractive index of the mask. 46. Created and deployed to satisfy a phase modulation function ax ³ + by ³ + cx ² y + dxy ² , where a, b, c and d are constants and x and y
43. The mask of claim 42, wherein represents the optical area of the mask through which light passes. 47. The mask of claim 46, wherein the change in wavefront is caused by a change in mask thickness. 48. The mask of claim 46, wherein the change in wavefront is caused by a change in the refractive index of the mask. 49. An optical mask comprising a body of optical material having a thickness change substantially according to a three-dimensional function: 50. The mask of claim 49 used as an optical low pass filter in an imaging system. 51. The mask of claim 49, used to reduce contrast in an imaging system. 52. The mask of claim 49 used to increase the depth of field in an imaging system. 53. The mask of claim 49, wherein the three-dimensional function is of the form ax ³ + by ³ , wherein a and b are constants and x and y are spatial coordinates across the mask surface. 54. The mask of claim 49, wherein the three-dimensional function is of the form r ³ cos (3q), where r and q are polar coordinates across the mask surface. 55. The three-dimensional function is of the form ax ³ + by ³ + cx ² y + dxy ² , where a, b, c and d are constants and x and y are spatial coordinates across the mask surface. 49 masks. 56. An optical mask comprising a body of optical material-created and arranged to effect a change in the wavefront of light passing through the body substantially according to a three-dimensional phase modulation function. 57. The mask of claim 56 used as an optical low pass filter in an imaging system. 58. The mask of claim 56, used to reduce contrast in an imaging system. 59. The mask of claim 56 used to extend the depth of field in an imaging system. 60. The mask of claim 56, wherein the mask is constructed and deployed to satisfy a phase modulation function ax ³ + by ³ , where a and b are constants and x and y are spatial coordinates across the mask surface. 61. A mask constructed and deployed to substantially satisfy a phase modulation function r ³ cos (3q), wherein r and q are polar coordinates across the mask surface.
mask of. 62. Created and deployed to satisfy a phase modulation function ax ³ + by ³ + cx ² y + dxy ² , where a, b, c and d are constants and x and y
57. The mask of claim 56, wherein is a spatial coordinate across the mask surface. 63. An optical low-pass filter for use in an optical system having an object and an image capture device, comprising: means for collecting light from the object; and a wavefront of light collected from the object in a curved asymmetric manner. Means for modulating, and means for emitting modulated light captured by the image capture device, wherein the means for modulating the wavefront is constructed and arranged to modulate the wavefront so that the captured image is in a predetermined space. An optical low pass filter that is constrained to have an optical output below a selected output limit outside the frequency band limit. 64. The means for modulating the wavefront of light comprises a transmission element formed from an optical material having a variable thickness, said element being disposed in an optical path from an object through which light from the object passes. The low-pass filter according to claim 63, which modulates the phase of light from the object. 65. The means for modulating the wavefront of light comprises a transmission element formed of an optical material having a varying index of refraction, said element being disposed in an optical path from an object, wherein the light from the object reflects the element. 64. The low pass filter of claim 63, wherein the low pass filter modulates the phase of light from the object when passed. 66. A means for modulating the wavefront of light is a transmission element formed of an element made of an optical material having a varying thickness and an element made of an optical material having a varying refractive index. 64. The low pass filter of claim 63, comprising: 67. An optical low-pass filter for reducing the spatial resolution of an optical image formed from light passing through a filter, comprising: a body formed from optical material, said body receiving light passing therethrough. The thickness of the light passing through the body depends on the area of the body through which the light passes, and the change in thickness is An optical low-pass filter created and deployed to reduce the optical power of an image that is outside a predetermined band limit below a predetermined power level. 68. The phase function of the filter is proportional to the thickness of the filter, and the phase function of the filter has the form: p (x, y) = y ³ (a + b) + yx ² (3a-b), here ^{x 2 + y 2 £ 1 a} , b low-pass filter according to claim 67 represented by a real number. 69. A method for reducing the spatial resolution of an image formed from light transmitted from an object through an incoherent optical system to an image location, the method comprising transmitting light from the object through the optical system to the image location. Operating on the phase of the light wavefront in a curved, asymmetric manner; and capturing the image at the image location, wherein the phase operating step operates on the phase, so that the image formed is A method that is constrained to have an optical power below a selected power limit outside a predetermined spatial frequency band limit. 70. The phase actuating step comprises passing light through a transmission element that modulates the phase of the light, thereby modulating the wavefront.
the method of. 71. The method of claim 70, wherein the phase acting step acts on the phase substantially according to a three-dimensional function. 72. An optical imaging system disposed between an object and an image plane comprising a lens, a low-pass filter, and means for capturing an image formed in the image plane, the system comprising: a low-pass filter; Comprises means for modulating the phase front of the light from the object in a curved, asymmetric manner, so that the captured image has an optical output below a selected output limit outside a predetermined spatial frequency band limit. Is suppressed. 73. The means for modulating light comprises a body formed from an optical material, the body varying in thickness in a curved, asymmetric manner in the direction of light passing through the body, thereby passing through the body. 73. The optical system of claim 72, wherein the phase of the incident light depends on the area of the body through which the light passes. 74. The optical system of claim 73, wherein the thickness of the body varies substantially according to a three-dimensional function.