Extended depth of field optical systems
View Patent ↗An imaging system is characterized at least by an ambiguity function (“AF”) and a point spread function (“PSF”). The AF is a function of parameters u and v related to a misfocus parameter ψ; the PSF is at least a function of ψ. The system includes (1) an image recording device, (2) an optical arrangement for imaging an object to the image recording device, and (3) a post processor that renders an in-focus electronic image over a range of distances between the object and the optical arrangement. The optical arrangement alters phase such that a main lobe of the AF is broader in v for a specific u. The PSF has a functionally different form for a specific ψ, in comparison to a PSF characterizing the system when the optical arrangement does not alter the phase for those specific values of u and ψ over the range of distances.
1. An imaging system characterized at least by an ambiguity function and a point spread function (PSF), which ambiguity function is a function of a normalized spatial frequency parameter u and a vertical variable v related to a misfocus parameter ψ, and which PSF is at least a function of the misfocus parameter ψ, the imaging system comprising:
an image recording device for converting light imaged thereon into a stored image;
an optical arrangement for imaging light from an object to the image recording device to generate the stored image, which light is characterized by at least phase; and
a post processor for processing the stored image from the image recording device, in accordance with the PSF, to render an in-focus electronic image over a range of object distances between the object and the optical arrangement,
wherein the optical arrangement is configured for altering the phase such that a main lobe of the ambiguity function is broader in v for a given value of u over an optical bandpass of the imaging system, and the PSF has a functionally different form for a given value of ψ, in comparison to a main lobe of an ambiguity function, a PSF and the optical bandpass, respectively, characterizing the imaging system when the optical arrangement does not alter the phase for those given values of u and ψ over the range of object distances.
2. An imaging system of claim 1 , the image recording device comprising a charge-coupled device (CCD).
3. An imaging system of claim 1 , wherein the optical arrangement is formed of an optical material selected from glass and plastic.
4. An imaging system of claim 3 , the optical arrangement having variations in at least a selected one of opaqueness, thickness, diffractive properties and index of refraction to alter the phase of the light.
5. An imaging system of claim 1 , the optical arrangement implementing a cubic phase modulation.
6. An imaging system of claim 1 ,the post processor comprising a digital signal processing algorithm.
7. An imaging system of claim 1 , the post processor comprising an electronic chip.
8. An imaging system of claim 1 , the post processor implementing a function
3
α
u
π
ⅇ
j
α
u
3
4
,
where α is a parameter used to adjust the range of object distances and u is a normalized, unitless spatial frequency parameter, to remove an imaging effect induced by the optical arrangement.
9. An imaging system of claim 1 , the light further including amplitude, and wherein the optical arrangement includes variations in at least a selected one of opaqueness, thickness and index of refraction so as to affect both of the phase and the amplitude.
10. An imaging system of claim 1 , the optical arrangement altering the phase at two different locations in the imaging system.
11. A method for decreasing optical sensitivity to misfocus-related aberrations in an optical system characterized at least by an ambiguity function and a point spread function (PSF), which ambiguity function is a function of a normalized spatial frequency parameter u and a vertical variable v related to a misfocus parameter ψ, and which PSF is at least a function of the misfocus parameter ψ, the method comprising the steps of:
imaging light from an object to form an optical image, which light is characterized by at least phase;
detecting the optical image to generate a stored image; and
post processing the stored image, in accordance with the PSF, to render an in-focus electronic image over a range of object distances between the object and the imaging system,
wherein imaging includes altering at least phase of the light such that a main lobe of the ambiguity function is broader in v for a given value of u over an optical bandpass of the optical system, and the PSF has a functionally different form for a given value of ψ, in comparison to a main lobe of an ambiguity function, a PSF and the optical bandpass, respectively, characterizing the optical system without altering the phase for those given values of u and ψ, over the range of object distances.
12. The method of claim 11 , wherein altering the phase includes altering the phase at two different locations in the optical system.
13. A method for increasing a depth of field of an optical system characterized at least by an ambiguity function and a point spread function (PSF), which ambiguity function is a function of a normalized spatial frequency parameter u and a vertical variable v related to a misfocus parameter ψ, and which PSF is at least a function of the misfocus parameter ψ, the method comprising:
imaging light from an object to form an image, the light being characterized by phase and amplitude;
forming a digital representation of the image; and
electronically processing the digital representation,
wherein imaging includes altering at least the phase while maintaining the amplitude such that a main lobe of the ambiguity function is broader in v for a given value of u over an optical bandpass of the imaging system, and the PSF has a functionally different form in comparison to a main lobe of an ambiguity function, a PSF and the optical bandpass, respectively, characterizing the optical system without altering the phase for those given values of u and ψ, over a range of object distances between the object and the optical system, and
wherein electronically processing includes modifying the digital representation in accordance with the PSF to render an in-focus electronic image over the range of object distances.
14. The method of claim 13 , wherein forming the digital representation of the image includes capturing the image with a charge-coupled device (CCD) array.
15. The method of claim 13 , wherein altering at least the phase comprises modulating the phase with a selected one of a linear phase modulation and a cubic phase modulation.
16. The method of claim 13 , wherein altering at least the phase comprises diffracting the light.
17. The method of claim 13 , further comprising storing the digital representation of the image for use in the electronically processing.
18. The method of claim 13 , wherein electronically processing comprises filtering the image.
19. The method of claim 13 , wherein altering the phase includes altering the phase at two different locations in the optical system.