title: Retinal vessel segmentation using the 2-D Gabor wavelet and supervised classification

authors: Soares, J.V.B.

abstract: We present a method for automated segmentation of the vasculature in retinal images. The method produces segmentations by classifying each image pixel as vessel or nonvessel, based on the pixel's feature vector. Feature vectors are composed of the pixel's intensity and two-dimensional Gabor wavelet transform responses taken at multiple scales. The Gabor wavelet is capable of tuning to specific frequencies, thus allowing noise filtering and vessel enhancement in a single step. We use a Bayesian classifier with class-conditional probability density functions (likelihoods) described as Gaussian mixtures, yielding a fast classification, while being able to model complex decision surfaces. The probability distributions are estimated based on a training set of labeled pixels obtained from manual segmentations. The method's performance is evaluated on publicly available DRIVE (Staal et al.,2004) and STARE (Hoover et al.,2000) databases of manually labeled images. On the DRIVE database, it achieves an area under the receiver operating characteristic curve of 0.9614, being slightly superior than that presented by state-of-the-art approaches. We are making our implementation available as open source MATLAB scripts for researchers interested in implementation details, evaluation, or development of methods.

text: Retinal vessel segmentation using the 2-D Gabor wavelet and supervised classification We present a method for automated segmentation of the vasculature in retinal images. The method produces segmentations by classifying each image pixel as vessel or nonvessel, based on the pixel's feature vector. Feature vectors are composed of the pixel's intensity and two-dimensional Gabor wavelet transform responses taken at multiple scales. The Gabor wavelet is capable of tuning to specific frequencies, thus allowing noise filtering and vessel enhancement in a single step. We use a Bayesian classifier with class-conditional probability density functions (likelihoods) described as Gaussian mixtures, yielding a fast classification, while being able to model complex decision surfaces. The probability distributions are estimated based on a training set of labeled pixels obtained from manual segmentations. The method's performance is evaluated on publicly available DRIVE (Staal et al.,2004) and STARE (Hoover et al.,2000) databases of manually labeled images. On the DRIVE database, it achieves an area under the receiver operating characteristic curve of 0.9614, being slightly superior than that presented by state-of-the-art approaches. We are making our implementation available as open source MATLAB scripts for researchers interested in implementation details, evaluation, or development of methods.

year: 2006-09

title: Peat humification records from Restionaceae bogs in northern New Zealand as potential indicators of Holocene precipitation, seasonality, and ENSO

authors: Newnham, Rewi M.

subjects: Science & Technology

abstract: In comparison with temperature reconstructions, New Zealand proxy records for paleo-precipitation are rare, despite the importance of precipitation in contemporary climate variability and for projected climate impacts. In this study, records of mid-late Holocene palaeomoisture variation were derived for two hydrologically separate ombrotrophic Restionaceae bogs in northern New Zealand, based on peat humification analysis. At each site, three cores were analysed for peat humification, facilitating both intra- and inter-site comparisons. Age models for the six sequences were developed using radiocarbon dating and tephrochronology. Twelve tephras (including six cryptotephras) were recognised, four of which were used to precisely link the two sites and to define start and end points for the records at 7027 ± 170 (Tuhua tephra) and 1718 ± 10 cal yr BP (Taupo tephra) (2σ-age ranges), respectively. We find individual differences between the six peat humification records at short-term timescales that are presumably due to local site factors, in particular changing vegetation and microtopography, or to changes in the composition of the material analysed. Stronger longer-term coherence is observed between all six records but is attributed to slow anaerobic decay over time because the implied trend towards wetter summers in the late Holocene cannot be corroborated by independent climate proxies. Despite these confounding factors, centennial scale shifts in bog surface wetness are a pervasive feature of all six records with varying degrees of overlap in time that show strong correspondence with El Niño-Southern Oscillation reconstructions from the eastern equatorial Pacific. These results indicate the potential for peat humification records from New Zealand's ombrotrophic bogs to elucidate past climate variability and also demonstrate the importance of developing multiple well-dated profiles from more than one site.

text: Peat humification records from Restionaceae bogs in northern New Zealand as potential indicators of Holocene precipitation, seasonality, and ENSO In comparison with temperature reconstructions, New Zealand proxy records for paleo-precipitation are rare, despite the importance of precipitation in contemporary climate variability and for projected climate impacts. In this study, records of mid-late Holocene palaeomoisture variation were derived for two hydrologically separate ombrotrophic Restionaceae bogs in northern New Zealand, based on peat humification analysis. At each site, three cores were analysed for peat humification, facilitating both intra- and inter-site comparisons. Age models for the six sequences were developed using radiocarbon dating and tephrochronology. Twelve tephras (including six cryptotephras) were recognised, four of which were used to precisely link the two sites and to define start and end points for the records at 7027 ± 170 (Tuhua tephra) and 1718 ± 10 cal yr BP (Taupo tephra) (2σ-age ranges), respectively. We find individual differences between the six peat humification records at short-term timescales that are presumably due to local site factors, in particular changing vegetation and microtopography, or to changes in the composition of the material analysed. Stronger longer-term coherence is observed between all six records but is attributed to slow anaerobic decay over time because the implied trend towards wetter summers in the late Holocene cannot be corroborated by independent climate proxies. Despite these confounding factors, centennial scale shifts in bog surface wetness are a pervasive feature of all six records with varying degrees of overlap in time that show strong correspondence with El Niño-Southern Oscillation reconstructions from the eastern equatorial Pacific. These results indicate the potential for peat humification records from New Zealand's ombrotrophic bogs to elucidate past climate variability and also demonstrate the importance of developing multiple well-dated profiles from more than one site.

year: 2019

title: Te whakaihonga: He tikanga tapahi makawe i te ao Māori

authors: McDonald, Rangihurihia Ann

subjects: Tapahi makawe

abstract: E ai ki te Māori, mai anō i a Māui Pōtiki, kua tapahia e te pouaru, e te kirimate, ngō rātou makawe i te tangihanga. He reureu, he tiotio, he pakipaki taha ngētehi o ngā tohu weriweri nei, i tauawhi, i whakaū i te aroha ki te mate. I ngētehi wā, he whakamaumahara, he take whakariri i te ngākau, he utu i te tangi kino o te manawa. Mutu kau ana te tangihanga, ko te heuenga hoki i te whare tauā, ki te wai whakaika. Ko ngētehi take ngēnei o te tapahi makawe a te kirimate, otirā, ko te tino whāinga o tēnei tuhinga whakapae. He whakapono makawe anō i whakaemingia, nā te rangahau mātātuhi, ko ngā pūrākau, ngā mōteatea, ngā whakataukī anō hoki a ngā tūpuna. He tirohanga kaumātua i kohikohingia nā roto mai o te uiui. Waiho mai ana ko ngā tikanga tawhito mō te tapahi i te uru tapu o te tangata, ki te ao tūroa.

text: Te whakaihonga: He tikanga tapahi makawe i te ao Māori E ai ki te Māori, mai anō i a Māui Pōtiki, kua tapahia e te pouaru, e te kirimate, ngō rātou makawe i te tangihanga. He reureu, he tiotio, he pakipaki taha ngētehi o ngā tohu weriweri nei, i tauawhi, i whakaū i te aroha ki te mate. I ngētehi wā, he whakamaumahara, he take whakariri i te ngākau, he utu i te tangi kino o te manawa. Mutu kau ana te tangihanga, ko te heuenga hoki i te whare tauā, ki te wai whakaika. Ko ngētehi take ngēnei o te tapahi makawe a te kirimate, otirā, ko te tino whāinga o tēnei tuhinga whakapae. He whakapono makawe anō i whakaemingia, nā te rangahau mātātuhi, ko ngā pūrākau, ngā mōteatea, ngā whakataukī anō hoki a ngā tūpuna. He tirohanga kaumātua i kohikohingia nā roto mai o te uiui. Waiho mai ana ko ngā tikanga tawhito mō te tapahi i te uru tapu o te tangata, ki te ao tūroa.

year: 2011