Image enhancement techniques using selective amplification of spatial frequency components

• US 5,072,314 A
• Filed: 04/04/1990
• Issued: 12/10/1991
• Est. Priority Date: 04/04/1990
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: Rockwell International Corporation
• Inventors: Chang, Tallis Y.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): RYAN, JAY
• Application Number:
  US07/504,519
• Time in Patent Office: 615 Days
• Field of Search: 350/3.64, 350/162.11, 350/162.12, 350/162.13, 350/162.14, 350/401, 364/822, 364/825, 382/31, 382/42
• US Class Current: 359/559
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G06E 3/003 forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions
• CPC Class Codes: G06V 10/88 Image or video recognition using optical means, e.g. reference filters, holographic masks, frequency domain filters or spatial domain filters

Abstract

An optical image enhancer includes a beam of coherent light for carrying an input image and a first lens for receiving the beam and performing a spatial Fourier transform of the input image. A photorefractive crystal at the Fourier plane receives the transformed image, while a coherent pump beam illuminates selected spatial frequency components of the transformed image at the Fourier plane, thereby transferring energy to the selected frequencies by two-beam coupling. A second lens receives the transformed image from the Fourier plane and performs a spatial Fourier transform of the transformed image, thereby reproducing the input image in an output image which contains intensified features corresponding to the selected spatial frequency components. A spatial light modulator may be used to cause the pump beam to illuminate the selected spatial frequency components of the transformed image at the Fourier plane. The pump beam can carry the Fourier transform of a selected portion of the input image, such that the intensity of the selected portion is increased in the output image.

Claims

1. An optical image enhancer, comprising:

a beam of coherent light for carrying an input image;

a first lens for receiving the beam and performing a spatial Fourier transform of the input image;

a photorefractive crystal at the Fourier plane for receiving the transformed image;

a coherent pump beam directed toward the Fourier plane;

means for causing the coherent pump beam to illuminate selected spatial frequency components of the transformed image at the Fourier plane, thereby leaving a portion of the spatial frequency components unilluminated by the coherent pump beam and transferring energy only to the selected frequencies by two-beam coupling; and

a second lens for receiving the transformed image from the Fourier plane and performing a spatial Fourier transform of the transformed image, thereby reproducing the input image in an output image which contains intensified features corresponding to the selected spatial frequency components.

2. The enhancer of claim 1, wherein the illuminated spatial frequency components are selected to increase the intensity of horizontal edges in the output image.

3. The enhancer of claim 1, wherein the illuminated spatial frequency components are selected to increase the intensity of vertical edges in the output image.

4. The enhancer of claim 1, wherein the illuminated spatial frequency components are selected to increase the intensity of diagonal edges in the output image.

5. The enhancer of claim 1, wherein the illuminated spatial frequency components are selected to increase the intensity of all the edges in the output image.

6. The enhancer of claim 1, wherein the means for causing the coherent pump beam to illuminate selected spatial frequency components of the transformed image at the Fourier plane further comprises a spatial light modulator.

7. The enhancer of claim 1, wherein the pump beam carries the Fourier transform of a selected portion of the input image, such that the intensity of the selected portion is increased in the output image.

8. The enhancer of claim 1, further comprising:

an optical element between the first lens and the photorefractive crystal for separating the DC component of the transformed image from the remainder of the transformed image, such that the DC component of the transformed image is directed at the photorefractive crystal to act as the coherent beam and transfer energy to the higher order Fourier components of the transformed image.

9. The enhancer of claim 8, wherein the optical element further comprises:

a birefringent plate for rotating the polarization of the DC component of the transformed image by 90°

; and

a polarizing beam splitter between the birefringent plate and the photorefractive crystal.

10. The enhancer of claim 8, wherein the optical element further comprises a prism.

11. The enhancer of claim 8, wherein the optical element further comprises an optical fiber.

12. An optical image enhancer, comprising:

a beam of coherent light for carrying an input image;

a first lens for receiving the beam and performing a spatial Fourier transform of the input image;

a photorefractive crystal at the Fourier plane for receiving the transformed image;

a coherent pump beam for carrying the Fourier transform of a selected portion of the imput image and illuminating the corresponding spatial frequency components of the transformed image a the Fourier plane, thereby transferring energy to the corresponding frequencies by two beam coupling; and

a second lens for receiving the transformed image from the Fourier plane and performing a spatial Fourier transform of the transformed image, thereby reproducing the input image in an output image in which the intensity of the selected portion is increased.

13. An optical image enhancer, comprising:

a beam of coherent light for carrying an input image;

a first lens for receiving the beam and performing a spatial Fourier transform of the input image;

an optical element at the Fourier plane for receiving the transformed image and separating the DC component of the transformed image from the remainder of the transformed image;

a photorefractive crystal for receiving the transformed image, the DC component of the transformed image illuminating selected spatial frequency components of the transformed image at the Fourier plane, thereby transferring energy to the higher order Fourier components by two-beam coupling; and

a second lens for receiving the transformed image from the crystal and performing a spatial Fourier transform of the transformed image, thereby reproducing the input image in an output image which contains intensified features corresponding to the selected spatial frequency components.

14. A method of enhancing an optical image, comprising the steps of:

providing a beam of coherent light for carrying an input image;

performing a spatial Fourier transform of the input image;

directing the transformed image into a photorefractive crystal at the Fourier plane;

directing a coherent pump beam toward the Fourier plane;

causing the coherent pump beam to illuminate selected spatial frequency components of the transformed image in the crystal, thereby leaving a portion of the spatial frequency components unilluminated by the coherent pump beam and causing energy to transfer only to the selected frequencies by two-beam coupling; and

performing a spatial Fourier transform of the transformed image, thereby reproducing the input image in an output image which contains intensified features corresponding to the selected spatial frequency components.

15. The method of claim 14, wherein the step of illuminating selected spatial frequency components further comprises illuminating selected frequencies to increase the intensity of horizontal edges in the output image.

16. The method of claim 14, wherein the step of illuminating selected spatial frequency components further comprises illuminating selected frequencies to increase the intensity of vertical edges in the output image.

17. The method of claim 14, wherein the step of illuminating selected spatial frequency components further comprises illuminating selected frequencies to increase the intensity of diagonal edges in the output image.

18. The method of claim 14, wherein the step of illuminating selected spatial frequency components further comprises illuminating selected frequencies to increase the intensity of all the edges in the output image.

19. The method of claim 14, wherein the step of illuminating selected spatial frequency components of the transformed image in the crystal with a coherent pump beam further comprises imposing the Fourier transform of a selected portion of the input image on the pump beam, thereby increasing the intensity of the selected portion in the output image.

20. The method of claim 14, further comprising the step of:

separating the DC component of the transformed image from the remainder of the transformed image, such that the DC component of the transformed image is directed at the photorefractive crystal to act as the coherent beam and transfer energy to the higher order Fourier components of the transformed image.

21. A method of enhancing an optical image, comprising the steps of:

providing a beam of coherent light for carrying an input image;

performing a spatial Fourier transform of the input image;

directing the transformed image into a photorefractive crystal at the Fourier plane;

illuminating the transformed image in the crystal with a coherent pump beam carrying the Fourier transform of a selected portion of the imput image, thereby transferring energy to the corresponding frequencies by two-beam coupling; and

performing a spatial Fourier transform of the transformed image, thereby reproducing the input image in an output image in which the intensity of the selected portion is increased.

22. A method of enhancing an optical image, comprising the steps of:

providing a beam of coherent light for carrying an input image;

performing a spatial Fourier transform of the input image;

separating the DC component of the transformed image from the remainder of the transformed image;

directing the remainder of the transformed image into a photorefractive crystal;

illuminating the transformed image in the crystal with the DC component of the transformed image, the DC component acting as a coherent pump beam to cause energy to transfer to the higher order Fourier components of the transformed image by two-beam coupling; and

performing a spatial Fourier transform of the transformed image, thereby reproducing the input image in an output image which contains intensified features corresponding to the selected spatial frequency components.