The Experts below are selected from a list of 13218 Experts worldwide ranked by ideXlab platform
Robert L. Stevenson - One of the best experts on this subject based on the ideXlab platform.
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A Stochastic Technique for the Removal of Artifacts in Compressed Images and Video
Signal Recovery Techniques for Image and Video Compression and Transmission, 1998Co-Authors: Ramon Llados-bernaus, Mark A. Robertson, Robert L. StevensonAbstract:The perceived quality of images and video sequences reconstructed from low bit rate compressed bit streams is severely degraded by the appearance of coding artifacts. This chapter introduces a technique for the post-processing of compressed images based on a stochastic model for the image data. Quantization Partitions the transform coefficient space and maps all points in a Partition Cell to a representative reconstruction point, usually taken as the centroid of the Cell. The proposed technique selects the reconstruction point within the quantization Partition Cell which results in a reconstructed image that best fits a non-Gaussian Markov Random Field image model. This approach results in a convex constrained optimization problem that can be solved iteratively. Efficient computational algorithms can be used in the minimization. This technique is extended to the post-processing of video sequences. The proposed approach provides a reconstructed image with reduced visibility of transform coding artifacts and superior perceived quality.
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Improved image decompression for reduced transform coding artifacts
IEEE Transactions on Circuits and Systems for Video Technology, 1995Co-Authors: Thomas P. O'rourke, Robert L. StevensonAbstract:The perceived quality of images reconstructed from low bit rate compression is severely degraded by the appearance of transform coding artifacts. This paper proposes a method for producing higher quality reconstructed images based on a stochastic model for the image data. Quantization (scalar or vector) Partitions the transform coefficient space and maps all points in a Partition Cell to a representative reconstruction point, usually taken as the centroid of the Cell. The proposed image estimation technique selects the reconstruction point within the quantization Partition Cell which results in a reconstructed image that best fits a non-Gaussian Markov random field (MRF) image model. This approach results in a convex constrained optimization problem that can be solved iteratively. At each iteration, the gradient projection method is used to update the estimate based on the image model. In the transform domain, the resulting coefficient reconstruction points are projected to the particular quantization Partition Cells defined by the compressed image. Experimental results will be shown for images compressed using scalar quantization of block DCT and using vector quantization of subband wavelet transform. The proposed image decompression provides a reconstructed image with reduced visibility of transform coding artifacts and superior perceived quality.
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Improved image decompression for reduced transform coding artifacts
IEEE Transactions on Circuits and Systems for Video Technology, 1995Co-Authors: Thomas P. O'rourke, Robert L. StevensonAbstract:The perceived quality of images reconstructed from low bit rate compression is severely degraded by the appearance of transform coding artifacts. This paper proposes a method for producing higher quality reconstructed images based on a stochastic model for the image data. Quantization (scalar or vector) Partitions the transform coefficient space and maps all points in a Partition Cell to a representative reconstruction point, usually taken as the centroid of the Cell. The proposed image estimation technique selects the reconstruction point within the quantization Partition Cell which results in a reconstructed image that best fits a non-Gaussian Markov random field (MRF) image model. This approach results in a convex constrained optimization problem that can be solved iteratively. At each iteration, the gradient projection method is used to update the estimate based on the image model. In the transform domain, the resulting coefficient reconstruction points are projected to the particular quantization Partition Cells defined by the compressed image. Experimental results will be shown for images compressed using scalar quantization of block DCT and using vector quantization of subband wavelet transform. The proposed image decompression provides a reconstructed image with reduced visibility of transform coding artifacts and superior perceived quality.
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Improved image decompression for reduced transform coding artifacts
Image and Video Processing II, 1994Co-Authors: Thomas P. O'rourke, Robert L. StevensonAbstract:The perceived quality of images reconstructed from low bit rate compression is severely degraded by the appearance of transform coding artifacts. This paper proposes a method for producing higher quality reconstructed images based on a stochastic model for the image data. Quantization (scalar or vector) Partitions the transform coefficient space and maps all points in a Partition Cell to a representative reconstruction point, usually taken as the centroid of the Cell. The proposed image estimate technique selects the reconstruction point within the quantization Partition Cell which results in a reconstructed image which best fits a non- Gaussian Markov random field image model. The estimation of the best reconstructed image results in a convex constrained optimization problem which can be solved iteratively. Experimental results are shown for images compressed using scalar quantization of block DCT and using vector quantization of subband wavelet transform. The proposed image decompression provides a reconstructed image with reduced visibility of transform coding artifacts and superior perceived quality.
Jean-hugues Renault - One of the best experts on this subject based on the ideXlab platform.
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Intensified separation of steviol glycosides from a crude aqueous extract of Stevia rebaudiana leaves using centrifugal Partition chromatography
Planta Medica, 2015Co-Authors: Jane Hubert, Nicolas Borie, Sébastien Chollet, Joël Perret, Claire Barbet Massin, Monique Berger, Jean Dayde, Jean-hugues RenaultAbstract:Aqueous extracts of Stevia rebaudiana leaves have been approved since 2008 by the Joint Expert Committee for Food Additives as sugar substitutes in many food and beverages in Western and Far East Asian countries. The compounds responsible for the natural sweetness of Stevia leaves include a diversity of diterpenoid glycosides derived from a steviol skeleton. These steviol glycosides also exhibit a low calorific value as well as promising therapeutic applications, particularly for the treatment of sugar metabolism disturbances. In this work, centrifugal Partition chromatography is proposed as an efficient technical alternative to purify steviol glycosides from crude aqueous extracts of Stevia leaves on a multigram scale. Two different commercial instruments, including an ASCPC250 (R) and a FCPE300 (R) made of columns containing 1890 and 231 twin-Cells, respectively, were evaluated and compared. All experiments were performed with a polar biphasic solvent system composed of ethyl acetate, n-butanol, and water in a gradient elution mode. When using the 1890 Partition Cell centrifugal Partition chromatography column of 250 mL, 42 mg of stevioside, 68 mg of dulcoside A, and 172 mg of rebaudioside A, three major constituents of the initial extract were obtained from 1 g of the initial mixture at purities of 81%, 83%, and 99%, respectively. The productivity was further improved by intensifying the procedure on the 231 Partition Cell centrifugal Partition chromatography column of 303 mL with the sample mass loading increased up to 5 g, resulting in the recovery of 1.2 g of stevioside, 100 mg of dulcoside A, and 1.1 g of rebaudioside A at purities of 79%, 62%, and 98%, respectively. The structures of the isolated compounds were validated by HPLC-UV, ESI-MS, H-1, and C-13 NMR analyses. Altogether, the results demonstrate that the column design (i.e., the Partition Cell number) is an important aspect to be considered for a larger scale centrifugal Partition chromatography isolation of Stevia-derived natural sweeteners.
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Strong ion exchange in centrifugal Partition extraction (SIX-CPE): effect of Partition Cell design and dimensions on purification process efficiency.
Journal of chromatography. A, 2012Co-Authors: Mahmoud Hamzaoui, Jane Hubert, Romain Reynaud, Luc Marchal, Alain Foucault, Jean-hugues RenaultAbstract:The aim of this article was to evaluate the influence of the column design of a hydrostatic support-free liquid-liquid chromatography device on the process efficiency when the strong ion-exchange (SIX) development mode is used. The purification of p-hydroxybenzylglucosinolate (sinalbin) from a crude aqueous extract of white mustard seeds (Sinapis alba L.) was achieved on two types of devices: a centrifugal Partition chromatograph (CPC) and a centrifugal Partition extractor (CPE). They differ in the number, volume and geometry of their Partition Cells. The SIX-CPE process was evaluated in terms of productivity and sinalbin purification capability as compared to previously optimized SIX-CPC protocols that were carried out on columns of 200 mL and 5700 mL inner volume, respectively. The objective was to determine whether the decrease in Partition Cell number, the increase in their volume and the use of a "twin Cell" design would induce a significant increase in productivity by applying higher mobile phase flow rate while maintaining a constant separation quality. 4.6g of sinalbin (92% recovery) were isolated from 25 g of a crude white mustard seed extract, in only 32 min and with a purity of 94.7%, thus corresponding to a productivity of 28 g per hour and per liter of column volume (g/h/LV(c)). Therefore, the SIX-CPE process demonstrates promising industrial technology transfer perspectives for the large-scale isolation of ionized natural products.
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partitron 25 a multi purpose industrial centrifugal Partition chromatograph rotor design and preliminary results on efficiency and stationary phase retention
Journal of Liquid Chromatography & Related Technologies, 2005Co-Authors: Rodolphe Margraff, Jean-hugues Renault, Olivier Intes, Pierre GarretAbstract:Abstract A new preparative chromatograph with a capacity of 25 liters has been designed to meet the most rigorous industrial criteria. All parts contacting liquid phases are made of titanium. The rotor, cast in one piece, can be operated up to 150 bars (2,000 psi). Preliminary results on retention of the liquid stationary phases from non‐aqueous and aqueous–aqueous biphasic solvent systems are presented and commented. A special emphasis is made on the theoretical plate number generated by each individual Partition Cell. The results highlight the benefit of a new concept of rotor featuring a better mass transfer than that observed in the stacked disk rotors. Finally, the use of neoteric solvents (ionic liquids, supercritical carbon dioxide) is mentioned.
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Partitron 25, a Multi‐Purpose Industrial Centrifugal Partition Chromatograph: Rotor Design and Preliminary Results on Efficiency and Stationary Phase Retention
Journal of Liquid Chromatography & Related Technologies, 2005Co-Authors: Rodolphe Margraff, Jean-hugues Renault, Olivier Intes, Pierre GarretAbstract:Abstract A new preparative chromatograph with a capacity of 25 liters has been designed to meet the most rigorous industrial criteria. All parts contacting liquid phases are made of titanium. The rotor, cast in one piece, can be operated up to 150 bars (2,000 psi). Preliminary results on retention of the liquid stationary phases from non‐aqueous and aqueous–aqueous biphasic solvent systems are presented and commented. A special emphasis is made on the theoretical plate number generated by each individual Partition Cell. The results highlight the benefit of a new concept of rotor featuring a better mass transfer than that observed in the stacked disk rotors. Finally, the use of neoteric solvents (ionic liquids, supercritical carbon dioxide) is mentioned.
Thomas P. O'rourke - One of the best experts on this subject based on the ideXlab platform.
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Improved image decompression for reduced transform coding artifacts
IEEE Transactions on Circuits and Systems for Video Technology, 1995Co-Authors: Thomas P. O'rourke, Robert L. StevensonAbstract:The perceived quality of images reconstructed from low bit rate compression is severely degraded by the appearance of transform coding artifacts. This paper proposes a method for producing higher quality reconstructed images based on a stochastic model for the image data. Quantization (scalar or vector) Partitions the transform coefficient space and maps all points in a Partition Cell to a representative reconstruction point, usually taken as the centroid of the Cell. The proposed image estimation technique selects the reconstruction point within the quantization Partition Cell which results in a reconstructed image that best fits a non-Gaussian Markov random field (MRF) image model. This approach results in a convex constrained optimization problem that can be solved iteratively. At each iteration, the gradient projection method is used to update the estimate based on the image model. In the transform domain, the resulting coefficient reconstruction points are projected to the particular quantization Partition Cells defined by the compressed image. Experimental results will be shown for images compressed using scalar quantization of block DCT and using vector quantization of subband wavelet transform. The proposed image decompression provides a reconstructed image with reduced visibility of transform coding artifacts and superior perceived quality.
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Improved image decompression for reduced transform coding artifacts
IEEE Transactions on Circuits and Systems for Video Technology, 1995Co-Authors: Thomas P. O'rourke, Robert L. StevensonAbstract:The perceived quality of images reconstructed from low bit rate compression is severely degraded by the appearance of transform coding artifacts. This paper proposes a method for producing higher quality reconstructed images based on a stochastic model for the image data. Quantization (scalar or vector) Partitions the transform coefficient space and maps all points in a Partition Cell to a representative reconstruction point, usually taken as the centroid of the Cell. The proposed image estimation technique selects the reconstruction point within the quantization Partition Cell which results in a reconstructed image that best fits a non-Gaussian Markov random field (MRF) image model. This approach results in a convex constrained optimization problem that can be solved iteratively. At each iteration, the gradient projection method is used to update the estimate based on the image model. In the transform domain, the resulting coefficient reconstruction points are projected to the particular quantization Partition Cells defined by the compressed image. Experimental results will be shown for images compressed using scalar quantization of block DCT and using vector quantization of subband wavelet transform. The proposed image decompression provides a reconstructed image with reduced visibility of transform coding artifacts and superior perceived quality.
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Improved image decompression for reduced transform coding artifacts
Image and Video Processing II, 1994Co-Authors: Thomas P. O'rourke, Robert L. StevensonAbstract:The perceived quality of images reconstructed from low bit rate compression is severely degraded by the appearance of transform coding artifacts. This paper proposes a method for producing higher quality reconstructed images based on a stochastic model for the image data. Quantization (scalar or vector) Partitions the transform coefficient space and maps all points in a Partition Cell to a representative reconstruction point, usually taken as the centroid of the Cell. The proposed image estimate technique selects the reconstruction point within the quantization Partition Cell which results in a reconstructed image which best fits a non- Gaussian Markov random field image model. The estimation of the best reconstructed image results in a convex constrained optimization problem which can be solved iteratively. Experimental results are shown for images compressed using scalar quantization of block DCT and using vector quantization of subband wavelet transform. The proposed image decompression provides a reconstructed image with reduced visibility of transform coding artifacts and superior perceived quality.
Vivek K Goyal - One of the best experts on this subject based on the ideXlab platform.
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Theoretical foundations of transform coding
IEEE Signal Processing Magazine, 2001Co-Authors: Vivek K GoyalAbstract:Discusses various aspects of transform coding, including: source coding, constrained source coding, the standard theoretical model for transform coding, entropy codes, Huffman codes, quantizers, uniform quantization, bit allocation, optimal transforms, transforms visualization, Partition Cell shapes, autoregressive sources, transform optimization, synthesis transform optimization, orthogonality and independence, and departures form the standard model.
Jane Hubert - One of the best experts on this subject based on the ideXlab platform.
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Intensified separation of steviol glycosides from a crude aqueous extract of Stevia rebaudiana leaves using centrifugal Partition chromatography
Planta Medica, 2015Co-Authors: Jane Hubert, Nicolas Borie, Sébastien Chollet, Joël Perret, Claire Barbet Massin, Monique Berger, Jean Dayde, Jean-hugues RenaultAbstract:Aqueous extracts of Stevia rebaudiana leaves have been approved since 2008 by the Joint Expert Committee for Food Additives as sugar substitutes in many food and beverages in Western and Far East Asian countries. The compounds responsible for the natural sweetness of Stevia leaves include a diversity of diterpenoid glycosides derived from a steviol skeleton. These steviol glycosides also exhibit a low calorific value as well as promising therapeutic applications, particularly for the treatment of sugar metabolism disturbances. In this work, centrifugal Partition chromatography is proposed as an efficient technical alternative to purify steviol glycosides from crude aqueous extracts of Stevia leaves on a multigram scale. Two different commercial instruments, including an ASCPC250 (R) and a FCPE300 (R) made of columns containing 1890 and 231 twin-Cells, respectively, were evaluated and compared. All experiments were performed with a polar biphasic solvent system composed of ethyl acetate, n-butanol, and water in a gradient elution mode. When using the 1890 Partition Cell centrifugal Partition chromatography column of 250 mL, 42 mg of stevioside, 68 mg of dulcoside A, and 172 mg of rebaudioside A, three major constituents of the initial extract were obtained from 1 g of the initial mixture at purities of 81%, 83%, and 99%, respectively. The productivity was further improved by intensifying the procedure on the 231 Partition Cell centrifugal Partition chromatography column of 303 mL with the sample mass loading increased up to 5 g, resulting in the recovery of 1.2 g of stevioside, 100 mg of dulcoside A, and 1.1 g of rebaudioside A at purities of 79%, 62%, and 98%, respectively. The structures of the isolated compounds were validated by HPLC-UV, ESI-MS, H-1, and C-13 NMR analyses. Altogether, the results demonstrate that the column design (i.e., the Partition Cell number) is an important aspect to be considered for a larger scale centrifugal Partition chromatography isolation of Stevia-derived natural sweeteners.
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Strong ion exchange in centrifugal Partition extraction (SIX-CPE): effect of Partition Cell design and dimensions on purification process efficiency.
Journal of chromatography. A, 2012Co-Authors: Mahmoud Hamzaoui, Jane Hubert, Romain Reynaud, Luc Marchal, Alain Foucault, Jean-hugues RenaultAbstract:The aim of this article was to evaluate the influence of the column design of a hydrostatic support-free liquid-liquid chromatography device on the process efficiency when the strong ion-exchange (SIX) development mode is used. The purification of p-hydroxybenzylglucosinolate (sinalbin) from a crude aqueous extract of white mustard seeds (Sinapis alba L.) was achieved on two types of devices: a centrifugal Partition chromatograph (CPC) and a centrifugal Partition extractor (CPE). They differ in the number, volume and geometry of their Partition Cells. The SIX-CPE process was evaluated in terms of productivity and sinalbin purification capability as compared to previously optimized SIX-CPC protocols that were carried out on columns of 200 mL and 5700 mL inner volume, respectively. The objective was to determine whether the decrease in Partition Cell number, the increase in their volume and the use of a "twin Cell" design would induce a significant increase in productivity by applying higher mobile phase flow rate while maintaining a constant separation quality. 4.6g of sinalbin (92% recovery) were isolated from 25 g of a crude white mustard seed extract, in only 32 min and with a purity of 94.7%, thus corresponding to a productivity of 28 g per hour and per liter of column volume (g/h/LV(c)). Therefore, the SIX-CPE process demonstrates promising industrial technology transfer perspectives for the large-scale isolation of ionized natural products.