遥感数字图像增强课件.pptxVIP

遥感数字图像增强;概念：单波段黑白遥感图像可按亮度分层，对每层赋予不同的色彩，使之成为一幅彩色图像。这种方法又叫密度分割。

分层方案的确定：分层方案与地物光谱差异对应合适，可以较好地区分地物类别。

处理过程

效果分析;处理过程;以不同的色彩表示图像的色调变化，增强了图像的显示能力

同一地物或现象可能被分割成两种不同密度并以不同的颜色显示出来，或同一色彩却表示两种以上不同的地物，造成判读错误。

;2、多波段色彩变换;ColourComposites;;TM1;TM

7,4,1;ERDAS彩色合成演示;3、HLS变换;二、对比度变换;二、对比度变换;Alinearstretchinvolvesidentifyinglowerandupperboundsfromthehistogram(usuallytheminimumandmaximumbrightnessvaluesintheimage)andapplyingatransformationtostretchthisrangetofillthefullrange.

;Thisgraphicillustratestheincreaseincontrastinanimagebefore(left)andafter(right)alinearcontraststretch.

;Iftheinputrangeisnotuniformlydistributed.Inthiscase,ahistogram-equalisedstretchmaybebetter.Thisstretchassignsmoredisplayvalues(range)tothefrequentlyoccurringportionsofthehistogram.Inthisway,thedetailintheseareaswillbebetterenhancedrelativetothoseareasoftheoriginalhistogramwherevaluesoccurlessfrequently;Thisgraphicillustratestheratherunevenincreaseincontrastinanimagebefore(left)andafter(right)ahistogramequalisedstretch.;三、空间滤波;三、空间滤波;SpatialFiltering;Acommonfilteringinvolvesmovinga‘window’（活动窗口）ofafewpixelsindimension(e.g.3x3,5x5,etc.)overeachpixelintheimage,applyingamathematicalcalculationusingthepixelvaluesunderthatwindow,andreplacingthecentralpixelwiththenewvalue.;ImageofCHURNFarm

Daedalus1268ATMChannel3;Alow-passfilter（低通滤波）isdesignedtoemphasiselarger,homogeneousareasofsimilartoneandreducethesmallerdetailinanimage.Thus,low-passfiltersgenerallyservetosmooth（平滑）theappearanceofanimage.;;Directionaloredgedetectingfiltershighlightlinearfeatures,suchasroadsorfieldboundaries.;Horizontaledges;1、平滑--图像中出现某些亮度值过大的区域，或出现不该有的亮点时，采用平滑方法可以减小变化，使亮度平缓或去掉不必要的亮点。;2、锐化—突出图像的边缘、线性目标或某些亮度变化率大的部分。;Low-andHigh-PassFiltering

Whenwelookatspatialstructure,wecanusuallyseeacharacteristiclen