Three-dimensional remote sensing by optical scanning holography

A pinhole is usually used as the pupil in traditional optical scanning holography (OSH) method. Although such a structure is relatively simple, the in-focus sectional image may be degraded by out-of-focus haze because of its difficulty to be eliminated in sectional image reconstruction. In this paper, a random-phase pupil is employed in OSH system to reduce the impact of defocus image. It is proved by the experimental results that the defocus image trends to be more easily dispersed into speckle-like pattern, and then it can be removed by connected component method in the future. Analysis also focuses on the correlation coefficient between the original image and the reconstructed images under the conditions of adopting a pinhole or a random-phase pupil. From comparison, as the defocus distance increasing, one can find that the correlation coefficient of image by using a random-phase pupil is decreasing faster than using a pinhole pupil.

We introduce a process for optically reconstructing full-color holographic images recorded by optical scanning holography. A complex RGB-color hologram was recorded and converted into a binary hologram using a direct binary search (DBS) algorithm. The generated binary hologram was then optically reconstructed using a spatial light modulator. The discrepancies between the reconstructed object sizes and colors due to chromatic aberration were corrected by adjusting the reconstruction parameters in the DBS algorithm. To the best of our knowledge, this represents the first optical reconstruction of a full-color hologram recorded by optical scanning holography.

Low-complexity compression of holograms based on delta modulation

Inverse imaging is a versatile technique for sectional image reconstruction in optical scanning holography. However, the matrix computation involved in the iterative process imposes a significant constraint on the size of the images. In this work, we develop a fast iterative method that circumvents the problem by taking advantage of the structures in the matrices. Experimental results show that we can handle large-size images about 64 times the previous size with a comparable amount of computation.

Digital holography is an imaging technique offering both sub-wavelength resolution and real-time capabilities to record 3-D objects using the interference between an object wave and a reference wave captured by an image sensor such as a CCD array. The basic advantage of digital holography is that it can quantitatively extract the three-dimensional (3-D) information of the object from the numerical reconstruction of a single digitally recorded hologram [1,2,3]. Since the information of the optically interfering waves is stored in the form of matrices, the numerical reconstruction process enables full digital processing of the holograms and offers many more possibilities than conventional optical processing. It is possible to numerically focus on any section of the 3-D volume object without mechanical focusing adjustment. This opens the field to a variety applications, such as 3-D microscopic investigations and real-time imaging of biological specimens where wavelength-scanning digital interference holography [4] is used to reconstruct the 3-D volume from a set of scanning tomographic images, hybrid holographic microscopy [5], 3-D microscopy by optical scanning holography [6], phase shifting digital holog-

Modified image fusion technique to remove defocus noise in optical scanning holography

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text T-C. Poon, "Three-dimensional Fluorescence Microscopy by Optical Scanning Holography," Optics & Photonics News 8(12), 22_1-23 (1997) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

The advancement of digital holography in the past two decades has enabled precise capturing of three-dimensional (3-D) images of physical objects. This important technology has been widely applied in numerous industrial sectors such as, but not limited to remote sensing, metrology, biomedical imaging, advertising, and entertainment. Most of the hologram acquisition techniques developed to date is employing digital cameras for recording the hologram, hence imposing rigid restrictions on the size and resolution of the captured 3-D image. This limitation, however, is not found in optical scanning holography (OSH). Based on a scanning mechanism and a single pixel sensor, OSH is capable of capturing digital holograms of both macroscopic and microscopic, as well as fluorescent objects with high precision. Since its invention in the late 70s, numerous research works have been conducted to enhance this technology, optimizing important factors such as acquisition speed, precision, data size, and security. The objective of this article is to provide a walkthrough of the state-of-the-art of the OSH technology, from its original principle, to different variants that have been developed over the years with emphasis on their feature extraction capabilities under the incoherent mode of operation. Whenever possible, we shall provide the key formulations of each approach, and experimental outcomes for demonstrating the pros and cons of the method.

We propose a non-cascaded and crosstalk-free multi-image encryption method based on optical scanning holography and 2D orthogonal compressive sensing. This approach enables the simultaneous recording and encryption of multiple plaintext images without mechanical scanning, while allows for independent retrieval of each image with exceptional quality and no crosstalk. Two features would bring about more substantial security and privacy. The one is that, by employing a sequence of pre-designed structural patterns as encryption keys at the pupil, multiple samplings can be achieved and ultimately the holographic cyphertext can be obtained. These patterns are generated using a measurement matrix processed with the generalized orthogonal one. As a result, one can accomplish the differentiation of images prior to the recording and thus neither need to pretreat the pending images nor to suppress the out-of-focus noise in the decrypted image. The other one is that, the non-cascaded architecture ensures that different plaintexts do not share sub-keys. Meanwhile, compared to 1D orthogonal compressive sensing, the 2D counterpart makes the proposed method to synchronously deal with multiple images of more complexity, while acquire significantly high-quality decrypted images and far greater encryption capacity. Further, the regularities of conversion between 1D and 2D orthogonal compressive sensing are identified, which may be instructive when to manufacture a practical multi-image cryptosystem or a single-pixel imaging equipment. A more general method or concept named synthesis pupil encoding is advanced. It may provide an effective way to combine multiple encryption methods together into a non-cascaded one. Our method possesses nonlinearity and it is also promising in multi-image asymmetric or public key cryptosystem as well as multi-user multiplexing.

In this paper, we propose a color optical scanning holography (OSH) having common path for Red(R), Green(G) and Blue(B) channels with heterodyne multiplexing. In the proposing color OSH, RGB beams modulated by different heterodyne frequencies follow common path. We record the color complex hologram of an object using the color OSH. To the best of our knowledge, it is the first time to record the color hologram of an object using OSH.

In this paper, we analyze the point spread function of optical scanning holography (OSH) system based on random phase encoding (RPE-OSH) with restricted pupils and compare the lateral resolution of RPE-OSH system with the one of conventional OSH system by the definition of Rayleigh criterion. The results show that the main lobe width of RPE-OSH system is much narrower than that of the conventional OSH system under the same conditions; thus, the reconstructed image in RPE-OSH system has a higher lateral resolution and reserves more detailed information. This conclusion is verified by numerical simulations of the Cymbella cymbiformis image reconstruction.

An accurate measurement of the point spread function (PSF) for the extended depth of field (EDoF) cell phone camera with CMOS sensor is very important for image processing and image restoration. But due to the coarse sampling of the PSF by CMOS sensor, the overall system including the imaging subsystem and sampling subsystem is a shift-variant system with respect to the sample-scene phase parameter within sub-pixel range. In this paper, we present the sub-pixel digital algorithm to estimate the overall camera PSF based on the measurement of a high resolution PSF of the imaging lens. The sub-pixel digital algorithm averages the shifted high resolution PSFs of the lens over one active pixel area with the assumption of uniform random distribution of point source location within one active pixel area. Then the averaged high resolution PSF is down sampled onto Bayer plane to obtain the shift-invariant overall system PSF. We applied this shift-invariant PSF for image restoration of blurred images captured with an extended depth of field camera. The processed images are compared with originally captured images. Improvement of image quality is seen.

The point spread function (PSF) plays a very important part in image post-processing and high-precion astrometry and photometry. It is necessary to analyse the properties of the PSF before we use it to process data. However, in real observations, the PSF is affected by many different factors and the shape of it has inevitable spatial and temporal variations that can be hard to describe. In this paper, we propose a clustering method to evaluate the shape variations of PSFs. We analyse the performance of this method with simulated PSFs under different observation conditions. Then, we process two observational data sets with this method. The PSF clustering results can provide a reference for checking observation conditions and can be used for astrometry based on PSF fitting. In general, our method can reveal the morphologic similarities of different PSFs and can provide a reference for observations. The cluster revealed by our method can provide a reference for the evaluation of observation conditions and for the post-processing of astronomical observation data.

A Kelvin probe force microscopy (KPFM) image is sometimes difficult to interpret because it is a blurred representation of the true surface potential (SP) distribution of the materials under test. The reason for the blurring is that KPFM relies on the detection of electrostatic force, which is a long-range force compared to other surface forces. Usually, KPFM imaging model is described as the convolution of the true SP distribution of the sample with an intrinsic point spread function (PSF) of the measurement system. To restore the true SP signals from the blurred ones, the intrinsic PSF of the system is needed. In this work, we present a way to experimentally calibrate the PSF of the KPFM system. Taking the actual probe shape and experimental parameters into consideration, this calibration method leads to a more accurate PSF than the ones obtained from simulations. Moreover, a nonlinear reconstruction algorithm based on total variation (TV) regularization is applied to KPFM measurement to reverse the blurring caused by PSF during KPFM imaging process; as a result, noises are reduced and the fidelity of SP signals is improved.

Linear systems theory combined with Fourier transform techniques provides a powerful means to characterize electro-optical systems. We present the description and analysis of a particular scanning IR system whose characteristic Point Spread Function (PSF) is space-variant. This peculiarity of the PSF arises from the scanning geometry; the IR sensor spins as it drops toward the ground. A system impulse response, or Point Spread Function (PSF), is derived from effects including diffraction, motion blur, chromatic aberration and detector area. Other effects may be taken into account by cascading PSF's. Once the system PSF is determined, the output of the system is the convolution of the input irradiance with the PSF. Alternatively, the output is the familiar inverse Fourier transform of the product of transforms. However, the space-variance of the PSF makes the latter option impossible and the former difficult. The convolution progresses in a spiral manner, with the PSF width changing continuously. The method is tested using Fortran programs and a digital image processor. The digital images produced show expected results, revealing a marked increase in resolution as the sensor nears the ground.