Remote Sensing and GIS Application Lecturer Ruba Yousif

Remote Sensing and GIS Application Lecturer Ruba Yousif Hussain Third Year 1

Remote Sensing and GIS Application Lecturer Third Year Ruba Yousif Hussain Image Enhancement The goal of image enhancement is to improve the visual interpretability of an image by increasing the apparent distinction between the features in the scene. Enhancement operations are normally applied to image data after the appropriate restoration procedures have been performed. Digital enhancement techniques can be categorized as 1 - Contrast Manipulation - Gray level thresholding - level slicing - contrast stretching 2 - Spatial feature manipulation - Spatial filtering - edge enhancement - Fourier analysis 3 - Multi-image manipulation - Multispectral band ratioing and differencing - principal components - canonical components - vegetation components - intensity-hue-saturation ( IHS ) color space transformation - decorrelation stretching 2

Remote Sensing and GIS Application Lecturer Third Year Ruba Yousif Hussain The visual quality of an image is related to the range of brightness in the image , known as contrast. A high contrast image has a narrow range of brightness mainly blacks and whites. A low contrast image has a wide range of brightness. Three most important enhancement techniques 1 - Radiometric Enhancement Enhancing image based on the values of individual pixels 2 - Spectral Enhancement Enhancing image by transforming the values of each pixel on a multiband basis ( Band Ratios , Vegetation Indices , Tasseled Cap ) 3 - Spatial Enhancement Enhancing image based on the values of individual and neighboring pixels. 3

Remote Sensing and GIS Application Lecturer Third Year Ruba Yousif Hussain Laboratory Radiometric Enhancement of Imagery Purpose Enhancing image based on the values of individual pixels. Application Arc. GIS Tutorial Using Arc. GIS as a Viewer for Radiometric Enhancement Image Analysis Window Contrast Brightness Transparency Gamma Dynamic Range Adjustment Background Zoom To raster Resolution Image Analysis Window changes the image on display but does not change the file (original image). 4

Remote Sensing and GIS Application Lecturer Third Year Ruba Yousif Hussain Contrast changes the range of differences between the darkest and lightness objects Brightness will make the image appear lighter or darker Transparency display the image so you can see the image below it Gamma controls relationships between the brightness of original scene and that on the display For example Gamma = 1 , the two images will use the same scale of brightnesses Gamma = 0. 5 or 1. 5 , the display shows , respectively , either compressed , or expanded, scale of brightness relative to the original. Background eliminates the no data value in the display. Histograms plot the frequency values of the digital numbers ( DNs ) ( x-axis ) against the number of pixels with that value ( y-axis ). Remember , the shape of the histogram is determined by the features represented in the image , and their brightnesses ). Arc. Map displays histograms in two ways First : Layer Properties / Symbology tab. 5