Digital holography is a growing field that owes its success to the provided three-dimensional imaging representation. This is achieved by encoding the wave field transmitted or scattered by an object in the form of an interference pattern with a reference beam. While in conventional imaging systems it is usually impossible to recover the correct focused image from a defocused one, with digital holography the image can be numerically retrieved at any distance from the hologram. Digital holography also allows the reconstruction of multiple objects at different depths. In a previous study, the benchmark of the main available image coding standard solutions JPEG, JPEG-XT, JPEG 2000 and the HEVC intra mode was performed for digital holographic data represented on the object plane. The HEVC intra main coding profile outperforms the other standards while JPEG 2000 results in very similar compression performance. In the current work, a scheme based on the HEVC intra mode codec for holographic information compression on the object plane is proposed. In the base layer, a 2D version of the object (amplitude information on object plane) is coded with HEVC intra main coding profile. Previously was observed that the phase information requires much higher bit rates than the amplitude information, as standardized codecs are not adapted for the compression of this type of information. In this paper we propose a model where the amplitude information is encoded with the HEVC intra mode codec, while the phase is represented by encoding the real information and the signal of the imaginary information. The real information is also encoded using the HEVC intra mode as it already revealed appropriate for compression of this type of information. The imaginary information signal is encoded with JBIG. The advantage of this scheme is that the amplitude information provides a direct 2D representation of the hologram while the phase information can be considered as a 3D enhancement layer. The results show that the proposed scheme outperforms the state of the art in holography compression, while allowing compatibility with the current standards and direct 2D visualization.
Pseudo-sequence based light field image compression methods use state-of-the-art video codecs like HEVC. Although video codecs have been designed to compress video sequences, they have good performance for light field images compression. Considering the light field images represented by their multi-views representation, a sequence with different image views is aligned following an appropriate strategy. However, there are some differences between video sequences and light field pseudo videos that can be utilized to improve the codec adaptation to the different view images compression. The pseudo-sequence images have spatial distances and predictable behaviors when compared to video sequences that have temporal distance and unpredictable behavior respectively. Considering these differences unnecessary operations can be avoided, while its performance can be improved. The video codecs compute the motion vectors using block matching motion estimation algorithms, which is computationally the most complex operation of any video codec. To reduce the motion estimation complexity many codecs use prediction models. In this paper, HEVC motion vectors search models are applied to the light field image views aligned as pseudo-sequences to analyze and find their repetitive and predictable patterns. These new patterns are then utilized for changing the HEVC motion estimation algorithm for codec complexity reduction using a state-of-the-art pseudo sequence compression method. Moreover, the use of parallel computing for the pseudo sequence compression method is addressed.
Point clouds have been gaining importance as a solution to the problem of efficient representation of 3D geometric and visual information. They are commonly represented by large amounts of data, and compression schemes are important for their manipulation transmission and storing. However, the selection of appropriate compression schemes requires effective quality evaluation. In this work a subjective quality evaluation of point clouds using a surface representation is analyzed. Using a set of point cloud data objects encoded with the popular octree pruning method with different qualities, a subjective evaluation was designed. The point cloud geometry was presented to observers in the form of a movie showing the 3D Poisson reconstructed surface without textural information with the point of view changing in time. Subjective evaluations were performed in three different laboratories. Scores obtained from each test were correlated and no statistical differences were observed. Scores were also correlated with previous subjective tests and a good correlation was obtained when compared with mesh rendering in 2D monitors. Moreover, the results were correlated with state of the art point cloud objective metrics revealing poor correlation. Likewise, the correlation with a subjective test using a different representation of the point cloud data also showed poor correlation. These results suggest the need for more reliable objective quality metrics and further studies on adequate point cloud data representations.
Digital holography is a growing field that owes its success to the provided three-dimensional imaging representation. This is achieved by encoding the wave field transmitted or scattered by an object in the form of an interference pattern with a reference beam. While in conventional imaging systems it is usually impossible to recover the correct focused image from a defocused one, with digital holography the image can be numerically retrieved at any distance from the hologram. Digital holography also allows the reconstruction of multiple objects at different depths.<p> </p> The complex object field at the hologram plane can be separated on real and imaginary, or amplitude and phase components for further compression. It could be inferred that more inter-component redundancies exist in real and imaginary information than in the amplitude and phase information. Also, several compression schemes, like lossless compression, lossy compression, based on subsampling, quantization, and transformation, mainly using wavelets were considered. The benchmark of the main available image coding standard solutions like JPEG, JPEG 2000, and the intra coding modes available on MPEG-2, H264/AVC and HEVC video codecs were also analyzed for digital holographic data compression on the hologram plane.<p> </p> In the current work, the benchmark of the main available image coding standard solutions JPEG, JPEG-XT, JPEG 2000 and the intra mode of HEVC, are performed for digital holographic data represented on the object plane, instead of the hologram plane. This study considers Real-Imaginary and Amplitude-Phase representations. As expected Real, Imaginary and Amplitude information present very similar compression performance and are coded very efficiently with the different standards. However, the phase information requires much higher bitrates (3/4 bpp more) to reach similar quality levels. Moreover, the Amplitude information results in slightly larger bitrates for the same quality level than real or imaginary information.<p> </p> Comparing the different standards, the HEVC intra main coding profile is a very efficient model and outperforms the other standards. Furthermore, JPEG 2000 results in very similar compression performance. A comparison with studies where coding was performed on the hologram plane will reveal the advantages of coding on the object plane. Hence, becomes evident that future representation standards should consider the representation of digital holograms on the object plane instead of the hologram plane.
Proc. SPIE. 9138, Optics, Photonics, and Digital Technologies for Multimedia Applications III
KEYWORDS: Facial recognition systems, Detection and tracking algorithms, Visualization, Imaging systems, Cameras, Databases, High dynamic range imaging, Associative arrays, Information visualization, Time multiplexed optical shutter
The gaining popularity of the new High Dynamic Range (HDR) imaging systems is raising new privacy issues caused by the methods used for visualization. HDR images require tone mapping methods for an appropriate visualization on conventional and non-expensive LDR displays. These visualization methods might result in completely different visualization raising several issues on privacy intrusion. In fact, some visualization methods result in a perceptual recognition of the individuals, while others do not even show any identity. Although perceptual recognition might be possible, a natural question that can rise is how computer based recognition will perform using tone mapping generated images? In this paper, a study where automatic face recognition using sparse representation is tested with images that result from common tone mapping operators applied to HDR images. Its ability for the face identity recognition is described. Furthermore, typical LDR images are used for the face recognition training.
In this paper we present novel results on the reconstruction of stereoscopic information from a single phase-shift hologram captured using a 2:2 μm pixel-pitch CMOS camera in a holographic interferometer configuration. The low pixel-pitch camera allows the digitizing of holograms with a higher spatial-frequency than what has been reported in the literature, allowing the recording of macroscopic objects closer to the camera sensor. The reconstructed information can be visualized using 3D stereo glasses. From the perceived 3D we could identify several depth cues, including the occlusion effect which has not been easy to produce from single-aperture holography. The occlusion effect is also known to be difficult to produce from stereoscopic sources.
A novel approach for the mammary gland region segmentation of Breast Ultrasound exams is proposed. This
method is important because the mammary gland is the Region of Interest for pathological diagnosis.
Five different pre-processing methods that enhance the transition areas or remove the speckle of the ultrasound
images were selected: Non-linear diffusion, Speckle Reducing Anisotropic Diffusion, Entropy filter, Laplacian filter
and Homomorphic filter. The results of these processing methods define the features that are used as descriptors
for a K-Means and SVM classifier or as weak classifiers by an Adaboost classifier. The pixel classification results
in a rough tissue segmentation. A new method is proposed to interpolate the classification results into an accurate
tissue separation line, using graph theory. This step overcomes the problem of the discontinuities between the
different classified areas.
The developed segmentation method was applied to a database with 61 images, 34 without masses and 27
with masses collected using digital support, and segmented by an experienced medical oncologist in Centro
Hospitalar da Cova da Beira in Portugal. The presented results were obtained using cross-validation.
In this paper we present a new method to produce low overhead redundant bits used to detect transmission errors
of J2K streams on noisy communication channels. This method takes advantage of algorithms already existing
on the JPEG 2000 standard and does not require any intrusive alterations on the coder. We will show that it
is possible to improve standard JPEG 2000 error resilience in exchange for null resource footprint. Remark that
this capability can be very important, for example in wireless communications that are mainly used by mobile
devices with small processing capabilities.