Contrast: Difference between revisions
From Glossary of Meteorology
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<div class="definition"><div class="short_definition">In meteorological usage, contrast ''C'' is defined by <div class="display-formula"><blockquote>[[File:ams2001glos-Ce29.gif|link=|center|ams2001glos-Ce29]]</blockquote></div> where ''L''<sub>0</sub> is the [[luminance]] of a [[target]] object and ''L''<sub>''s''</sub> is that of its immediate visual surroundings.</div><br/> <div class="paragraph">Both luminances may include [[airlight]] or reflected [[glare]], and ''L''<sub>''s''</sub> is always assumed to be greater than zero. Because [[detection]] outdoors often depends on luminance rather than chromaticity differences, ''C'' is usually calculated from spectrally integrated luminances. Contrast for a perfectly black target is | <div class="definition"><div class="short_definition">In meteorological usage, contrast ''C'' is defined by <div class="display-formula"><blockquote>[[File:ams2001glos-Ce29.gif|link=|center|ams2001glos-Ce29]]</blockquote></div> where ''L''<sub>0</sub> is the [[luminance]] of a [[target]] object and ''L''<sub>''s''</sub> is that of its immediate visual surroundings.</div><br/> <div class="paragraph">Both luminances may include [[airlight]] or reflected [[glare]], and ''L''<sub>''s''</sub> is always assumed to be greater than zero. Because [[detection]] outdoors often depends on luminance rather than chromaticity differences, ''C'' is usually calculated from spectrally integrated luminances. Contrast for a perfectly black target is -1 but, in principle, ''C'' has no upper limit for a self-luminous target. If <div class="inline-formula">[[File:ams2001glos-Cex06.gif|link=|ams2001glos-Cex06]]</div> is less than a variable threshold contrast, the target is visually indistinguishable from its surroundings.</div><br/> </div> | ||
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Latest revision as of 14:58, 20 February 2012
contrast
In meteorological usage, contrast C is defined by where L0 is the luminance of a target object and Ls is that of its immediate visual surroundings.
Both luminances may include airlight or reflected glare, and Ls is always assumed to be greater than zero. Because detection outdoors often depends on luminance rather than chromaticity differences, C is usually calculated from spectrally integrated luminances. Contrast for a perfectly black target is -1 but, in principle, C has no upper limit for a self-luminous target. If is less than a variable threshold contrast, the target is visually indistinguishable from its surroundings.