2011-2012 (Spring Semester)

11.02.2012

ICE-02 Digital Image Processing (For Group A1 & A2 ONLY) Practical 3 Title: Preprocessing of digital data through (i) atmospheric correction; (ii) Geometric correction; (iii) radiometric correction. I.

ATMOSPHERIC CORRECTIONS A. Atmospheric Corrections by Haze Reduction Salient Steps to conduct practical: 1. Open ERDAS Imagine. 2. Click to “Interpreter” icon window. 3. Select “Radiometric Enhancement” from the pull down menu of “Interpreter. 4. Select “Haze Reduction” from the pull down menu of “Radiometric Enhancement”. 5. In “Haze Reduction”, after providing the input & output file names, click OK. 6. Display output file in img format using Viewer icon window (Practical -1). 7. Compare the output image histogram with that of input image histogram i.e. using ImageInfo icon (Practical -2) B. Replace bad lines Salient Steps to conduct practical: 1. Click to “Interpreter” menu window. 2. Select “Utilities” from the pull down menu of “Interpreter. 3. Select “Replace Bad lines” from the pull down menu of “Utilities”. 4. In “Replace Bad lines”, after providing the input & output file names, click OK. 5. Display output file in img format using Viewer icon window (Practical -1) C. Dark Pixel Reduction Salient Steps to conduct practical: 1. Write a program using the spatial modeler that subtracts the dark object. 2. The program will include input and output rasters connected by a function of the form {image} - {Global Minimum(Image)} (if there are no pixels of zero value) or {image} - {Global Minimum(Image) Ignore (0)} (if there are background pixels assigned zero value; note that this will work even if there are no pixels of zero value). 3. Compare the initial image with your dark-pixel-subtracted image as it appears in the viewer. (Practical -1) 4. Now compare the histograms of the two images using ImageInfo. (Practical -2)

II.

GEOMETRIC CORRECTION: The geometric correction model, ground control points - their geographical locations and descriptions, resampling strategy, Outputs geometrically rectified (before and after) images. A. Image Geometric Correction Salient Steps to conduct practical : 1. Click to “Data Preparation” icon window.

2. Select “Image Geometric Correction” from the pull down menu of “Data Preparation” 3. Provide input file through “Set Geo Correction Input file” and click OK. 4. Display output file in img format [optional using Viewer icon window (Practical -1)]. B. Reproject Images Salient Steps to conduct practical : 1. Click to “Data Preparation” icon window. 2. Select “Reproject Images” from the pull down menu of “Data Preparation” 3. Provide input file and out file names through “Reproject Images” and click OK. 4. Display output file in img format using Viewer icon window (Practical -1). III.

RADIOMETRIC CORRECTION A. Destriping Striping is usually caused by some sensors that are out of alignment, defective or not calibrated correctly. The destriping algorithms is used to correct it. Salient Steps to conduct practical: 1. Click to “Interpreter” 2. Go to Radiometric Enhancement Destripe TM Data. 3. Select input file. Provide output file name. 4. Open both images in separate Viewer. 5. Go to Raster Profile Tools Select Spatial profile tool. Click OK. 6. Compare spatial profile for both images. B. Histogram Equalization Salient Steps to conduct practical: 1. Click to “Interpreter” 2. Go to Radiometric Enhancement Histogram Equalization. 3. Enter input file name. Provide output file name. 4. Click Ok. 5. Open both input and output files in separate viewer. 6. Compute statistics for both. 7. Compare histogram for both images. Haze removal and atmospheric effect is given in Part I. Further works: Navigate through different options in the selection windows to generate different option outputs and study thoroughly the outputs.

J.K.Ghosh (Practical Instructor for Group A1 & A2)