Noriaki Miura

ITERATIVE RECONSTRUCTION METHOD IN PHASE-DIVERSITY IMAGING

An object is iteratively reconstructed from two atmospherically degraded images, one of which is detected by shifting of a known amount of phase with respect to the other. The iterative reconstruction scheme is based on the ideas of the blind-deconvolution method and the error-reduction algorithm. An optical system to do phase shifting is proposed in which a deformable mirror is employed. Several computer simulations are conducted to exemplify the usefulness of our method.

Extended-object reconstruction with sequential use of the iterative blind deconvolution method

Abstract A new algorithm for speckle imaging with sequential use of the iterative blind deconvolution method is described. The algorithm allows reconstruction of an extended object from several noisy speckle frames without reference star data, and calculation of a function to evaluate the reconstructed image. Some results of computer simulations are presented.

Parallel scheme of the iterative blind deconvolution method for stellar object reconstruction

An algorithm for stellar object reconstruction without a reference star is described. The algorithm is based on parallel application of the iterative blind deconvolution method to several speckle frames, and it permits reconstruction of an object that satisfies the convolution relation in all the frames used. Computer simulations with noisy speckle images are carried out to demonstrate performances of the algorithm. The algorithm is applied to observational data of binary stars, and high-resolution images are clearly reconstructed. Binary parameters extracted from the images show good consistency with those obtained both with the power spectrum analysis and with the shift-and-add method.

Single-frame blind deconvolution by means of frame segmentation.

For restoration of an image degraded with a shift-invariant point-spread function (PSF), partial images segmented from the degraded image are blind deconvolved in parallel for estimation of the common PSF in each partial image. An object function is reconstructed by deconvolution of the whole image with the PSF. A technique for calibrating contamination caused by the segmentation is developed. Results for a computer-generated image and an atmospherically degraded solar image are presented.

Superresolution for a nonnegative band-limited image

A superresolution method is presented with a conjugate-gradient procedure under a nonnegativity constraint. The method is based on the property of a nonnegative object that its band-limited spectrum is the autoconvolution of a spectrum with a half-band limit, and the method is capable of doubling the band limit of an image. Computer simulations are conducted to investigate the performance of the present method.

Segmentation-based multiframe blind deconvolution of solar images

A blind deconvolution method is applied to the recovery of atmospherically degraded solar images. The method consists of an iterative deconvolution algorithm that uses several partial images segmented from each of multiple frames. It is shown that the algorithm decreases a specified error metric, allows a unique solution, and reduces contamination originally existing in solar images observed with a limited field of view. Artificial contamination introduced into the partial images by segmentation is calibrated with the use of estimates of an object and a point-spread function at the previous iteration. Computer simulation demonstrates successful reconstruction for a low-contrast degraded image and the expected behavior of an error metric. High-resolution images are reconstructed from observed solar images.

Binary star reconstruction with use of the blind deconvolution method

Abstract The iterative blind deconvolution method and a modified auto-correlation method are applied to reconstruct a binary star from a speckle interferogram. The results of two methods are compared to evaluate reconstructed images. For successful reconstruction, a method of frame selection of speckle interferograms is also proposed. A suitable frame selection improves the efficiency of the reconstruction. Some results of the binary star reconstruction are demonstrated to show the usefulness of our method.

Toward high-resolution imaging with a simple adaptive-optics system.

High-resolution imaging with reference to a widely separated star is examined. Peak tracking of the specklegram in the reference channel results in a high-resolution image in the observational channel. A binary star with angular separation of 30.5 arcsec is examined in white light, and the resultant image of the primary star obtained with reference to the secondary star is shown to have better resolution than the centroid tracking image by a factor of 3.

Stellar speckle imaging by reference to different-colored specklegrams.

Stellar specklegrams at different wavelengths are examined. The position of the brightest speckle at one wavelength is shown to coincide nearly with that at a widely separated wavelength. The shift-and-add operation for specklegrams at one wavelength produces a high-resolution stellar image at the other wavelength. We show that the shift-and-add operation at 450 nm results in a high-resolution image at 800 nm by use of observational speckle data from which specklegrams at these wavelengths are taken simultaneously.

Speckle spectroscopy with tip–tilt operation

A stellar speckle spectrometer with tip-tilt operation is proposed for high-spatial-resolution spectroscopy under atmospheric turbulence. A specklegram is used to drive a tip-tilt mirror for real-time shift-and-add operation to its dispersed specklegram. The proposed speckle spectroscopy attains a long exposure for the spectrum and a slit spectrometer. Several simulation experiments confirm the effectiveness of our method.