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penumbra |
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penumbra [pĕ-num´brah]
1. the part of a shadow in which there is a small amount of illumination from a light source. 2. blurring at the edges of a structure on a radiograph.
penumbra a blurred edge to an image, a halo effect, in an x-ray film caused usually by an overlarge focal spot exacerbated by a long object-to-film distance.
penumbra 1. Region of very low illumination on a dark background. 2. Zone in which the brightness varies from some illumination to zero (umbra) in the shadow cast by an opaque object intercepting light from an extensive light source. See shadow. How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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