F. t. s. Yu

Speckle Reduction in Holography by Means of Random Spatial Sampling

In this paper, we will illustrate a new technique by which the hologram image speckle can be reduced by spatially random sampling of the hologram aperture. The sampling procedure can be performed by a movable random mask. If the sampling function is made to be uncorrelated in subsequent spatial sampling, the speckle effect in the hologram image can be eliminated. However, an optimum sampling function may be difficult to obtain, which remains to be seen. This speckle reduction technique can be achieved only by some trade-off of the holographic resolution. A simple experimental confirmation of this technique is illustrated. Since one of the most severely limiting factors in applications of holography may be the speckle effect, this proposed technique should be added, together with the other existent techniques, to remedy this limiting factor.

Incoherent image addition and subtraction: a technique

A technique of incoherent image addition and subtraction is described. The basic advantage of this technique is its use of white light processing, in which case the unavoidable artifact noise in the coherent optical processor may be removed. Although the incoherent processing technique that we have proposed is effective only in a 1-D operation, it also works for 2-D image addition and subtraction.

Spatial filtered pseudocolor holographic imaging

A technique of spatial filtered pseudocolor holographic imaging is described. The encoding process takes place at the spatial frequency plane together with the one-step rainbow holographic process. The pseudocolor hologram imaging is obtained by the white light reconstruction of the multiplexed rainbow hologram. This technique provides a simple encoding procedure and offers a wide range of pseudocolor holographic images. The potential applications of this pseudocolor holographic imaging can range from aerial photography for remote sensing to X-ray transparencies for medical diagnosis. Experimental setup of this pseudocolor encoding process is illustrated. Some experimental demonstrations of the pseudocolor encoding hologram images are also provided.

White-light pseudocolor density encoder

A simple technique utilizing a white-light processing system for the pseudocolor encoding of photographic materials by density is presented. Pseudocolored output of many different color codes is obtained by selectively spatial filtering the dispersed colors of the various high-diffraction orders of a halftone input. Besides permitting a large variety of color codes, this white-light technique would also eliminate all coherent artifact noises that plague coherent systems. Experimental results are presented, and comparison with the coherent technique is provided.

White light processing technique for archival storage of color films

The method of archival storage of color films utilizing a spatial color encoding process and a white light color image retrieval technique is described. This archival technique offers several advantages as compared with all the other existing archival techniques: It employs a white light source for the encoding and decoding processes, so that the coherent artifact noise can be avoided. Since the technique does not utilize a slit aperture and a narrow spatial filter, the reproduced color image causes no marginal loss in resolution. The storage volume by this technique is also reduced to one-third of that needed with the traditional technique. This technique offers the advantage of direct viewing, which may be important for library applications. We also stress that this archival storage technique is simple and economical to implement. A simple experimental demonstration is also presented.

White-light pseudocolor density encoding through contrast reversal.

A simple technique of pseudocolor density encoding of photographic image by white-light processing is described. Spatial encodings are made through positive and negative photographic-image transparencies, and the pseudocoloring is obtained by color filtering of the smeared Fourier spectra. The technique is simple, versatile, and economical to operate. Since coherent sources are not used, annoying coherent artifact noise can be eliminated. Spatial color encoding uses the entire Fourier spectrum; therefore, this technique offers no apparent resolution loss. Simple experimental demonstrations of this technique are provided.

Optical logarithmic filtering using inherent film nonlinearity

Linear optical spatial filtering cannot be effectively applied to multiplied and convolved signals. One approach is to first perform a logarithmic transformation to produce a signal in additive form suitable for linear filtering processes [A. V. Oppenheim et al., Proc. IEEE 56, 1264 (1968)]. It was first suggested that a halftone screen be used to perform such a transformation [H. Kato and J. W. Goodman, Appl. Opt. 14, 1813 (1975)]. However, the maximum spatial resolution of this halftone screen technique is limited by the resolution of the screen. In this paper, we shall propose a different technique using the inherent film nonlinearity for the logarithmic transformation. Such a technique would enable the transformation of signals of very high spatial resolution, limited only by the resolution limit of the photographic film. This technique is applied to the spatial filtering and detection of signals in multiplicative noise. Experimental comparisons between linear and logarithmic filtering are presented.

Effect of Emulsion Thickness Variations on Wavefront Reconstruction

In this paper an approach will be developed for wavefront recording and reconstruction with a photographic plate when emulsion thickness is not uniform. It is shown that in a first approximation an emulsion thickness variation will not affect the wavefront recording. However, thickness variation does affect the hologram image reconstruction. It is found that a first-order thickness variation (wedge-shaped), except for a lateral translation of image coordinates, will not affect the precision of the reconstruction. However, a second-order variation not only affects the precise dimension of the image reconstruction but also causes an astigmatic effect in the hologram image.

Polychromatic processing technique for color image transparencies

A technique of spatial encoding color photographic image in a black and white tran-sparency for coherent polychromatic processing is presented. The applications of this technique to color image signal detection, restoration of color blurred images, and color image addition and subtraction are provided. We note that this polychromatic processing technique is capable of processing color images similar to monochromatic coherent pro-cessing technique. Although there is a disadvantage of this technique, it requires an en-coding step for image processing, however this technique may open a new dimension in color image processing. We also note that the application of this technique is not res-tricted only to color images, it may apply to some problems in gray level transparencies.

Archival storage of color films by rainbow holographic technique

Abstract A technique of generating color holographic images with a one-step rainbow holographic process is described. This technique offers the capability of archival storage of color materials on a single black and white photographic film. The process is very simple to implement and it allows the reconstruction of the color image with a white light source. Although some degree of color blur is inherent with the rainbow holographic process, it can be minimized by the proper design of the optical system. A simple experimental result is also presented.