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Fix sigmoidal contrast calculation #3328

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Dec 29, 2020
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Fix sigmoidal contrast calculation #3328

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
### Changed
- Remove explicit unused Scaffeine dependency from projects [#3314](https://github.com/locationtech/geotrellis/pull/3314)
- Remove an excessive close after the abort call in S3RangeReader [#3324](https://github.com/locationtech/geotrellis/pull/3324)
- Fix sigmoidal contrast calculation [#3328](https://github.com/locationtech/geotrellis/pull/3328)

## [3.5.1] - 2020-11-23

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4 changes: 3 additions & 1 deletion raster/src/main/scala/geotrellis/raster/sigmoidal/SigmoidalContrast.scala
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Expand Up @@ -44,7 +44,9 @@ object SigmoidalContrast {
(intensity + (1<<(bits-1))) / ((1<<bits)-1)
}

val numer = 1/(1+math.exp(beta*(alpha-u))) - 1/(1+math.exp(beta))
// see https://legacy.imagemagick.org/Usage/color_mods/#sigmoidal
// and https://github.com/locationtech/geotrellis/issues/3326
val numer = 1/(1+math.exp(beta*(alpha-u))) - 1/(1+math.exp(beta*alpha))
val denom = 1/(1+math.exp(beta*(alpha-1))) - 1/(1+math.exp(beta*alpha))
val gu = math.max(0.0, math.min(1.0, numer / denom))

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