Showing papers on "Iterative reconstruction published in 1973"

Method for Computing Kinoforms that Reduces Image Reconstruction Error.

Abstract: An analysis of kinoform image reconstruction error is presented. This analysis considers the effects of the error introduced by the kinoform approximation and the quantization effects of plotting. The error measure developed is applied to a proposed method for computing kinoforms. Numerical results indicate that images produced by this method offer considerable reduction in the error when compared with images produced from kinoforms made with the random phase method.

Image reconstruction from finite numbers of projections

Abstract: Several results are obtained appertaining to the reconstruction of a two- dimensional image from a finite number of projections. Several schemes are considered for interpolating between the given data. When a trigonometrical Fourier series is used for angular interpolation then one finds, firstly, a consistency condition whereby a posteriori estimates can be made of the errors in the given data, and secondly, a basic image which contains only that information common to all physically permissible interpolation schemes. This basic image is necessarily free of misleading artefacts but it is computationally slow. Several computationally rapid interpolation schemes (based on the fast Fourier transform algorithm) are found to give good quality images, provided the given number of projections is sufficient to resolve the major details of the true image. A computational example is presented showing that a contrived image can be accurately reconstructed from a single projection.

Holographic System for Automatic Surface Mapping

Abstract: The surfaces of large (approximately 1-m) diffusely reflecting objects can be mapped by automatic following of the holographic real image of the object. Large aperture, low f number holograms give the shallow depth of focus required for this method. The ability to apply the technique to situations requiring a pulsed laser is demonstrated. Unity magnification real images from holograms made with a Q-switched ruby laser have a measured metric fidelity of at least one part in 104 over an object field of 60 deg. A sinusoidal optical interference pattern projected onto the object when the hologram is taken provides the type of contrast pattern necessary for unambiguous determination of the location of the focused image surface and facilitates automatic focus detection. The image is scanned by an image dissector that is moved about the image by a 3-axis slide system. A computer analyzes the video signals, directs the machine motions to follow the image, and provides an output of surface dimensions in digital form. A prototype machine using cw helium–neon lasers for object illumination and image reconstruction is described and performance data presented.

On the Numerical Reconstruction of Images from a Microwave Hologram

Abstract: A new technique for the numerical reconstruction of images from a long-wavelength hologram is proposed. The technique is to calculate images by the fast Fourier transform (FFT) algorithm with the hologram data sampled by a straight line approximation. This sampling technique is convenient to reduce the number of the sampling points, and the image can be reconstructed with less data than the conventional equally spaced sampling method. A one-dimensional hologram is constructed at S band and an image is reconstructed by the proposed method. These results are discussed and compared with the results of the conventional numerical reconstruction.

Apparent image enhancement through coherent defocusing

Abstract: Defocusing effects for amplitude-modulated targets, in coherent imaging systems such as an electron microscope, are theoretically and experimentally studied. A mathematical model is developed that adequately predicts experimental observations. Of specific interest in this study is the apparent image enhancement that occurs with small amounts of change of defocus. It is shown that certain spatial frequencies of an image are selectively destroyed as a function of the amount of defocus and, consequently, that an apparent image enhancement results for certain image details.