Extended depth of field using a multi-focal length lens with a controlled range of spherical aberration and a centrally obscured aperture
View Patent ↗An extended depth of field is achieved by a computational imaging system that combines a multifocal imaging subsystem for producing a purposefully blurred intermediate image with a digital processing subsystem for producing a recovered image having an extended depth of field. The multifocal imaging system preferably exhibits spherical aberration as the dominant feature of the purposeful blur. A central obscuration of the multifocal imaging subsystem renders point-spread functions of object points more uniform over a range of object distances. An iterative digital deconvolution algorithm for converting the intermediate image into the recovered image contains a metric parameter that speeds convergence, avoids stagnations, and enhances image quality.
1. A method of recovering an image based on an intermediate image, comprising steps of:
accessing the intermediate image; and performing an iterative digital deconvolution of the intermediate image using a maximum entropy algorithm including the sub-steps of:
estimating a new image containing a combination of directional images that include a metric parameter; and altering the directional images using the metric parameter to speed convergence toward a recovered image while avoiding points of stagnation.
2. The method of claim 1 in which the metric parameter has a non-integer value.
3. The method of claim 2 in which the metric parameter has a value between 0.2 and 0.6.
4. The method of claim 1 in which the directional images include pixel values, and the metric parameter adjusts weights among the pixel values.
5. The method of claim 4 in which the metric parameter is adjusted above zero to give larger pixel values more weight.
6. The method of claim 1 in which the metric parameter has a value that results in a modulation transfer function having a shape that increases contrast at high spatial frequencies approaching a Nyquist limit.
7. The method of claim 1 including a further step of producing the intermediate image using a multifocal imaging system.
8. The method of claim 7 in which the intermediate image produced by the multifocal imaging system exhibits a point spread function having side lobe rings, and the metric parameter is adjustable within a range that reduces side lobe rings of the point spread function in the intermediate image.
9. The method of claim 7 in which the multifocal imaging system includes third-order spherical aberration.
10. The method of claim 7 in which the multifocal imaging system includes a central obscuration.