Nitesh Pandey | Graphic Era University (original) (raw)
Papers by Nitesh Pandey
Optics Letters, 2010
In this Letter, we study the reconstruction of digital holograms of microscopic objects using a f... more In this Letter, we study the reconstruction of digital holograms of microscopic objects using a fixed-point representation of the numercial-reconstruction process. For different bit levels in our fixed-point reconstruction algorithm, we investigate the errors introduced to both the reconstructed image intensity and the unwrapped quantitative phase information. Experimental results based on a microscopic lens array are provided.
We discuss some common sources of noise which affect the quality of reconstruction in digital hol... more We discuss some common sources of noise which affect the quality of reconstruction in digital holography. We show that by using holograms obtained with independent illumination patterns, we can suppress these noise sources in a unified manner and improve the image quality while reducing the memory usage.
Digital Holography is an imaging modality made up of two parts: (1) using a digital camera to rec... more Digital Holography is an imaging modality made up of two parts: (1) using a digital camera to record the interference pattern between a field scattered from an object and a known reference field so that the complex object wavefield can be obtained and (2) replaying or reconstructing the hologram on a computer by simulating the propagation of the object wavefield back to the object plane. Thus an image is obtained. The most commonly used algorithms for the reconstruction algorithm are the so-called direct method and the spectral method of calculating the Fresnel Transform, which describes free space propagation in the paraxial approximation. These algorithms differ in the output range that they display. For the direct method, the output image size is proportional to the distance making it more appropriate for large objects at large distances. The spectral method has an output image size equal to the size of the CCD. We show how to adapt this latter algorithm in a simple way to allow it to generate any output range and in any location making it far more versatile for zooming in on specific regions of our reconstructed image.
The presence of a residual sphericity in a reference beam causes magnification in the reconstruct... more The presence of a residual sphericity in a reference beam causes magnification in the reconstructed image in digital holography. We discuss a method to estimate the relative sphericities in a multi-perspective multi-camera digital hologram recording unit. The digital holograms can then be compensated with numerical quadratic phase factors so that the object appears with the same magnification in all the reconstructions.
We show how the reconstruction of digital holograms can be speeded up on ordinary computers by pr... more We show how the reconstruction of digital holograms can be speeded up on ordinary computers by precomputing the chirp factor in the Fresnel transform for a given detector array size. The speedup in time is shown for various hologram sizes. We also run the same algorithm on a Nvidia GPU. The speedup and the error introduced due to quantizing to different levels is investigated. Additionally a variance based
International Journal of Digital Multimedia Broadcasting, 2010
The application of digital holography as a viable solution to 3D capture and display technology i... more The application of digital holography as a viable solution to 3D capture and display technology is examined. A review of the current state of the field is presented in which some of the major challenges involved in a digital holographic solution are highlighted. These challenges include (i) the removal of the DC and conjugate image terms, which are features of the holographic recording process, (ii) the reduction of speckle noise, a characteristic of a coherent imaging process, (iii) increasing the angular range of perspective of digital holograms (iv) and replaying captured and/or processed digital holograms using spatial light modulators. Each of these challenges are examined theoretically and several solutions are put forward. Experimental results are presented that demonstrate the validity of the theoretical solutions.
Optics Letters, 2009
A method to numerically remove the twin image for inline digital holography, using multiple digit... more A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing specklereduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.
3d Research, 2011
Digital holographic microscopy is a quantitative phase measurement technique that can provide nan... more Digital holographic microscopy is a quantitative phase measurement technique that can provide nanometer resolution of the thickness or surface profile of an object. We analyze the influence of additive noise in the hologram plane on the accuracy of phase measurement. We analyze Gaussian distributed and Poisson distributed shot noise in the camera plane and we develop a model for quantifying the phase error in the reconstructed phase.
Optics Letters, 2009
A method to numerically remove the twin image for inline digital holography, using multiple digit... more A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing specklereduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.
Applied Optics, 2011
Digital holography is an imaging technique that enables recovery of topographic 3D information ab... more Digital holography is an imaging technique that enables recovery of topographic 3D information about an object under investigation. In digital holography, an interference pattern is recorded on a digital camera. Therefore, quantization of the recorded hologram is an integral part of the imaging process. We study the influence of quantization error in the recorded holograms on the fidelity of both the intensity and phase of the reconstructed image. We limit our analysis to the case of lensless Fourier off-axis digital holograms. We derive a theoretical model to predict the effect of quantization noise and we validate this model using experimental results. Based on this, we also show how the resultant noise in the reconstructed image, as well as the speckle that is inherent in digital holography, can be conveniently suppressed by standard speckle reduction techniques. We show that high-quality images can be obtained from binary holograms when speckle reduction is performed.
Optics Letters, 2009
A method to numerically remove the twin image for inline digital holography, using multiple digit... more A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing specklereduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.
Optical Engineering, 2009
We examine some fundamental theoretical limits on the ability of practical digital holography ͑DH... more We examine some fundamental theoretical limits on the ability of practical digital holography ͑DH͒ systems to resolve detail in an image. Unlike conventional diffraction-limited imaging systems, where a projected image of the limiting aperture is used to define the system performance, there are at least three major effects that determine the performance of a DH system: ͑i͒ The spacing between adjacent pixels on the CCD, ͑ii͒ an averaging effect introduced by the finite size of these pixels, and ͑iii͒ the finite extent of the camera face itself. Using a theoretical model, we define a single expression that accounts for all these physical effects. With this model, we explore several different DH recording techniques: off-axis and inline, considering both the dc terms, as well as the real and twin images that are features of the holographic recording process. Our analysis shows that the imaging operation is shift variant and we demonstrate this using a simple example. We examine how our theoretical model can be used to optimize CCD design for lensless DH capture. We present a series of experimental results to confirm the validity of our theoretical model, demonstrating recovery of super-Nyquist frequencies for the first time. © 2009 Society of Photo-Optical Instrumentation Engineers.
Optics Letters, 2009
A method to numerically remove the twin image for inline digital holography, using multiple digit... more A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing specklereduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.
Optical Engineering, 2009
We examine some fundamental theoretical limits on the ability of practical digital holography ͑DH... more We examine some fundamental theoretical limits on the ability of practical digital holography ͑DH͒ systems to resolve detail in an image. Unlike conventional diffraction-limited imaging systems, where a projected image of the limiting aperture is used to define the system performance, there are at least three major effects that determine the performance of a DH system: ͑i͒ The spacing between adjacent pixels on the CCD, ͑ii͒ an averaging effect introduced by the finite size of these pixels, and ͑iii͒ the finite extent of the camera face itself. Using a theoretical model, we define a single expression that accounts for all these physical effects. With this model, we explore several different DH recording techniques: off-axis and inline, considering both the dc terms, as well as the real and twin images that are features of the holographic recording process. Our analysis shows that the imaging operation is shift variant and we demonstrate this using a simple example. We examine how our theoretical model can be used to optimize CCD design for lensless DH capture. We present a series of experimental results to confirm the validity of our theoretical model, demonstrating recovery of super-Nyquist frequencies for the first time. © 2009 Society of Photo-Optical Instrumentation Engineers.
Optics Letters, 2010
In this Letter, we study the reconstruction of digital holograms of microscopic objects using a f... more In this Letter, we study the reconstruction of digital holograms of microscopic objects using a fixed-point representation of the numercial-reconstruction process. For different bit levels in our fixed-point reconstruction algorithm, we investigate the errors introduced to both the reconstructed image intensity and the unwrapped quantitative phase information. Experimental results based on a microscopic lens array are provided.
We discuss some common sources of noise which affect the quality of reconstruction in digital hol... more We discuss some common sources of noise which affect the quality of reconstruction in digital holography. We show that by using holograms obtained with independent illumination patterns, we can suppress these noise sources in a unified manner and improve the image quality while reducing the memory usage.
Digital Holography is an imaging modality made up of two parts: (1) using a digital camera to rec... more Digital Holography is an imaging modality made up of two parts: (1) using a digital camera to record the interference pattern between a field scattered from an object and a known reference field so that the complex object wavefield can be obtained and (2) replaying or reconstructing the hologram on a computer by simulating the propagation of the object wavefield back to the object plane. Thus an image is obtained. The most commonly used algorithms for the reconstruction algorithm are the so-called direct method and the spectral method of calculating the Fresnel Transform, which describes free space propagation in the paraxial approximation. These algorithms differ in the output range that they display. For the direct method, the output image size is proportional to the distance making it more appropriate for large objects at large distances. The spectral method has an output image size equal to the size of the CCD. We show how to adapt this latter algorithm in a simple way to allow it to generate any output range and in any location making it far more versatile for zooming in on specific regions of our reconstructed image.
The presence of a residual sphericity in a reference beam causes magnification in the reconstruct... more The presence of a residual sphericity in a reference beam causes magnification in the reconstructed image in digital holography. We discuss a method to estimate the relative sphericities in a multi-perspective multi-camera digital hologram recording unit. The digital holograms can then be compensated with numerical quadratic phase factors so that the object appears with the same magnification in all the reconstructions.
We show how the reconstruction of digital holograms can be speeded up on ordinary computers by pr... more We show how the reconstruction of digital holograms can be speeded up on ordinary computers by precomputing the chirp factor in the Fresnel transform for a given detector array size. The speedup in time is shown for various hologram sizes. We also run the same algorithm on a Nvidia GPU. The speedup and the error introduced due to quantizing to different levels is investigated. Additionally a variance based
International Journal of Digital Multimedia Broadcasting, 2010
The application of digital holography as a viable solution to 3D capture and display technology i... more The application of digital holography as a viable solution to 3D capture and display technology is examined. A review of the current state of the field is presented in which some of the major challenges involved in a digital holographic solution are highlighted. These challenges include (i) the removal of the DC and conjugate image terms, which are features of the holographic recording process, (ii) the reduction of speckle noise, a characteristic of a coherent imaging process, (iii) increasing the angular range of perspective of digital holograms (iv) and replaying captured and/or processed digital holograms using spatial light modulators. Each of these challenges are examined theoretically and several solutions are put forward. Experimental results are presented that demonstrate the validity of the theoretical solutions.
Optics Letters, 2009
A method to numerically remove the twin image for inline digital holography, using multiple digit... more A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing specklereduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.
3d Research, 2011
Digital holographic microscopy is a quantitative phase measurement technique that can provide nan... more Digital holographic microscopy is a quantitative phase measurement technique that can provide nanometer resolution of the thickness or surface profile of an object. We analyze the influence of additive noise in the hologram plane on the accuracy of phase measurement. We analyze Gaussian distributed and Poisson distributed shot noise in the camera plane and we develop a model for quantifying the phase error in the reconstructed phase.
Optics Letters, 2009
A method to numerically remove the twin image for inline digital holography, using multiple digit... more A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing specklereduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.
Applied Optics, 2011
Digital holography is an imaging technique that enables recovery of topographic 3D information ab... more Digital holography is an imaging technique that enables recovery of topographic 3D information about an object under investigation. In digital holography, an interference pattern is recorded on a digital camera. Therefore, quantization of the recorded hologram is an integral part of the imaging process. We study the influence of quantization error in the recorded holograms on the fidelity of both the intensity and phase of the reconstructed image. We limit our analysis to the case of lensless Fourier off-axis digital holograms. We derive a theoretical model to predict the effect of quantization noise and we validate this model using experimental results. Based on this, we also show how the resultant noise in the reconstructed image, as well as the speckle that is inherent in digital holography, can be conveniently suppressed by standard speckle reduction techniques. We show that high-quality images can be obtained from binary holograms when speckle reduction is performed.
Optics Letters, 2009
A method to numerically remove the twin image for inline digital holography, using multiple digit... more A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing specklereduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.
Optical Engineering, 2009
We examine some fundamental theoretical limits on the ability of practical digital holography ͑DH... more We examine some fundamental theoretical limits on the ability of practical digital holography ͑DH͒ systems to resolve detail in an image. Unlike conventional diffraction-limited imaging systems, where a projected image of the limiting aperture is used to define the system performance, there are at least three major effects that determine the performance of a DH system: ͑i͒ The spacing between adjacent pixels on the CCD, ͑ii͒ an averaging effect introduced by the finite size of these pixels, and ͑iii͒ the finite extent of the camera face itself. Using a theoretical model, we define a single expression that accounts for all these physical effects. With this model, we explore several different DH recording techniques: off-axis and inline, considering both the dc terms, as well as the real and twin images that are features of the holographic recording process. Our analysis shows that the imaging operation is shift variant and we demonstrate this using a simple example. We examine how our theoretical model can be used to optimize CCD design for lensless DH capture. We present a series of experimental results to confirm the validity of our theoretical model, demonstrating recovery of super-Nyquist frequencies for the first time. © 2009 Society of Photo-Optical Instrumentation Engineers.
Optics Letters, 2009
A method to numerically remove the twin image for inline digital holography, using multiple digit... more A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing specklereduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.
Optical Engineering, 2009
We examine some fundamental theoretical limits on the ability of practical digital holography ͑DH... more We examine some fundamental theoretical limits on the ability of practical digital holography ͑DH͒ systems to resolve detail in an image. Unlike conventional diffraction-limited imaging systems, where a projected image of the limiting aperture is used to define the system performance, there are at least three major effects that determine the performance of a DH system: ͑i͒ The spacing between adjacent pixels on the CCD, ͑ii͒ an averaging effect introduced by the finite size of these pixels, and ͑iii͒ the finite extent of the camera face itself. Using a theoretical model, we define a single expression that accounts for all these physical effects. With this model, we explore several different DH recording techniques: off-axis and inline, considering both the dc terms, as well as the real and twin images that are features of the holographic recording process. Our analysis shows that the imaging operation is shift variant and we demonstrate this using a simple example. We examine how our theoretical model can be used to optimize CCD design for lensless DH capture. We present a series of experimental results to confirm the validity of our theoretical model, demonstrating recovery of super-Nyquist frequencies for the first time. © 2009 Society of Photo-Optical Instrumentation Engineers.