Image lightness rescaling using sigmoidal contrast enhancement functions

Braun, Gustav J.; Fairchild, Mark D.

doi:10.1117/1.482706

Cited by 88 publications

(40 citation statements)

References 9 publications

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“…This enables the classification of each pixel yi over an interval [0,1], 0 representing the black tones and 1 the white tones. These curves are often applied to image processing, in particular in histogram equalization (Parker 1997, Braun andFairchild 1999). …”

Section: Analysis Of Aerial Images and Integration Of Pasture Chroniclesmentioning

confidence: 99%

A Contextual Analysis of Land-Use and Vegetation Changes in Two Wooded Pastures in the Swiss Jura Mountains

Chételat¹,

Kalbermatten²,

Lannas³

et al. 2013

E&S

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This study examines the effects of land-use policies and natural events on the evolution of two wooded pastures in the Jura Mountains in Switzerland between 1934 and 2000. The socioeconomic context and the local conditions were seen as major driving forces influencing land management practices which in turn redefined land-use policies. We studied the dynamics of the Jura Mountains' wooded pastures, combining a thorough knowledge of the historic context with aerial image analysis. Besides pointing out general milestones in the evolution of Swiss land policy, we compiled chronicles on the management for both study sites on the basis of archives and interviews. Aerial images taken at time intervals of approximately 15 years were chosen to identify land-cover changes. The method used to analyze them relied on a structural classification of phytocoenoses, thus allowing the determination of four categories of tree-cover densities ranging from unwooded pastures to ungrazed forest. We reported overall aerial changes for each tree density class as well as spatial transitions from one category to another. The combination of spatial statistics with qualitative data depicting the evolution of the historic context gives a better understanding of the land-use changes and their rationale. The most important changes in tree density occurred during World War II and resulted in a more open landscape. The intensive use of wooded pastures during the war was the consequence of a high demand for wood and food resources. Postwar protectionist regulations, agricultural subsidies, and technical improvements maintained considerable pressure on wooded pastures. Storms and drought episodes further exacerbated this process in some areas. The trend then reversed from the 1970s onwards because of the limitations put on milk production and the falling price of wood. This resulted in a more extensive use of pastures, leading to tree encroachment. However, remote sites were more impacted than pastures closer to inhabited areas, which exhibited a trend towards more segregation between grassland and densely wooded pastures. With both extensification and segregation of land use, the complex vegetation mosaic and the landscape diversity that characterize wooded pastures are threatened but still offer good economic opportunities that call for differentiated management strategies

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Section: Analysis Of Aerial Images and Integration Of Pasture Chroniclesmentioning

confidence: 99%

A Contextual Analysis of Land-Use and Vegetation Changes in Two Wooded Pastures in the Swiss Jura Mountains

Chételat¹,

Kalbermatten²,

Lannas³

et al. 2013

E&S

View full text Add to dashboard Cite

show abstract

“…A typical tone mapping function can be logarithmic, a power law (often referred to as a "gamma" function) or a sigmoid, also called an "s shape." More sophisticated global tone mapping methods vary the function parameters depending on global characteristics of the image [8,9,24,25]. The key of the image can be used to determine the exponent of the gamma function [24].…”

Section: Tone Mappingmentioning

confidence: 99%

“…Figures 2(c) and 2(d) show an example of applying our method to a high-dynamic-range image (i.e., containing high contrast and important image details in dark and bright areas). The left image shows the result obtained with standard global tone mapping [8,9] (in this case a gamma operator), and the right image shows the result obtained with our algorithm. Our method successfully enhances detail visibility in the center of the image, the details are well rendered without requiring an additional sharpening operation.…”

Section: Introductionmentioning

confidence: 99%

Model of retinal local adaptation for the tone mapping of color filter array images

2007

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We present a tone mapping algorithm that is derived from a model of retinal processing. Our approach has two major improvements over existing methods. First, tone mapping is applied directly on the mosaic image captured by the sensor, analogous to the human visual system that applies a nonlinearity to the chromatic responses captured by the cone mosaic. This reduces the number of necessary operations by a factor 3. Second, we introduce a variation of the center/surround class of local tone mapping algorithms, which are known to increase the local contrast of images but tend to create artifacts. Our method gives a good improvement in contrast while avoiding halos and maintaining good global appearance. Like traditional center/surround algorithms, our method uses a weighted average of surrounding pixel values. Instead of being used directly, the weighted average serves as a variable in the Naka-Rushton equation, which models the photoreceptors' nonlinearity. Our algorithm provides pleasing results on various images with different scene content and dynamic range.

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“…Previously, contrast enhancement has been performed by linear [1,2,8], quadratic [9], cubic [5,9], sigmoidal [2,10], logarithmic [1], and power law [1,2] functions. Default parameters may be obtained by the optimization of a mathematical criterion [8] or the study of user preference [10]. These simple formulas lack the necessary degrees of freedom to express simultaneous and independent contrast adjustments at different points in the tonal range.…”

Section: Related Workmentioning

confidence: 99%

Automatic Contrast Enhancement by Histogram Warping

Grundland

Dodgson

2006

Computational Imaging and Vision

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Abstract:We present an interactive contrast enhancement technique for the global histogram modification of images. Through direct manipulation, the user adjusts contrast by clicking on the image. Contrast around different key tones can be adjusted simultaneously and independently without altering their luminance. Histogram warping by monotonic splines performs the gray level mapping. User interfaces for contrast correction find application in digital photography, remote sensing, medical imaging, and scientific visualization.

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Image lightness rescaling using sigmoidal contrast enhancement functions

Cited by 88 publications

References 9 publications

A Contextual Analysis of Land-Use and Vegetation Changes in Two Wooded Pastures in the Swiss Jura Mountains

A Contextual Analysis of Land-Use and Vegetation Changes in Two Wooded Pastures in the Swiss Jura Mountains

Model of retinal local adaptation for the tone mapping of color filter array images

Automatic Contrast Enhancement by Histogram Warping

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