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Image Enhancement in Spatial Domain
Published in Vipin Tyagi, Understanding Digital Image Processing, 2018
Unsharp masking is a technique in which a blurred image is subtracted from the original image in order to get a sharper image. This process is adopted from the publishing industry. The process of unsharp masking is represented as: f(x,y)=f(x,y)+∝[f(x,y)-f¯(x,y)],wherefx,yistheoriginalimageandf¯x,yisthecorrespondingblurredimage,∝istheweightfunction $$ \begin{gathered} f(x,y) = f(x,y) + \propto [f(x,y) - \bar{f}(x,y)], \hfill \\ where{\text{ }}f\left( {x,y} \right)is{\text{ }}the{\text{ }}original{\text{ }}image{\text{ }}and\,\,\bar{f}\left( {x,y} \right)is{\text{ }}the{\text{ }}corresponding{\text{ }}blurred{\text{ }} \hfill \\ image, \propto is{\text{ }}the{\text{ }}weight{\text{ }}function \hfill \\ \end{gathered} $$
Analysis of accuracy factor and pre-processing methodology of image compensation for 3D reconstruction using 2D image obtained from unmanned aerial vehicle (UAV)
Published in Journal of Asian Architecture and Building Engineering, 2022
Daeyoon Moon, Kyuhyup Lee, Hyunglyul Ko, Soonwook Kwon, Seojoon Lee, Jinwoo Song
Unsharp masking is a popular image processing technique for image enhancement. With this technique, which is used to sharpen the image, an unsharp mask is created using a different image from the original and a blurred image via filter. Three factors are required for sharpening: threshold, amount, and radius. Threshold means the minimum required contrast for a pixel to be an edge pixel, specified in the scalar range from 0 to 1. Higher values (near 1) allow sharpening only in high-contrast regions, such as strong edges, while leaving low-contrast regions unchanged. Lower values (near 0) allow relatively smoother regions of the image to be sharpened. The strength of the sharpening effect, called amount, is specified as a numeric value. Larger values lead to larger increases in the contrast of the sharpened pixels. Radius is the term used for standard deviation of the Gaussian lowpass filter, also specified as a numeric value that controls the size of the region around the edge pixels that affected by sharpening.