lab2CoastalMappingTutorial110113

lab2CoastalMappingTutorial110113 - Digital Image Analysis...

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Unformatted text preview: Digital Image Analysis - Lab 3 Page 1 of 12 GISC 4037C and 5033C: Digital Image Analysis Name___________________________________ Score ____/25 LAB 3 CONTRAST ENHANCEMENT TOOLS To start set your ERDAS Session Preferences: Default drives should be X: drive, IMPORTANT: Be sure to set the Viewer preference to “No Stretch.” Viewer preferences can be found in the Session Preferences. Copy all data from the Lab 3 folder to your X: drive. Lab 3A: Histogram Equalization In this lab we will explore several contrast enhancement tools in Imagine. Start by opening a SPOT scene called greatriftvalley.img , gathered by SPOT 1 in the late 1980s. This image features a horst and graben feature in Kenya. The agriculture shown is mostly coffee plantations and the soils are of volcanic origin. Now look at the layer information to get the minimum and maximum values for each band (you should remember this step from previous labs). Question 1 : Band 1: Min______ Max_______ Band 2: Min_______ Max_______ Band 3: Min_______ Max_______ What we are doing in this exercise is enhancing the contrast of images in various ways to better visually interpret them. Most of the time, raw imagery does not occupy the full range of grey scales in an 8 bit system, like the MSS from Lab 1 was a 6 bit satellite. Simple stretches such as the histogram equalization will solve the problem. Today we will experiment with several contrast stretch procedures. Digital Image Analysis - Lab 3 Page 2 of 12 Examine the graphic histogram of the raw data for all the bands. Notice that the maximum values are less than halfway up the scale of 0-255; thus, the image is dark and dingy. Also notice that at the lower end, they do not take up the full range of values. Instead of a spread of 255 gray scale values, the spread is more like 100. Thus, the image is dark and not very contrasty. What we can do is increase the contrast without losing any of the information by performing contrast stretches to the image. We will start with the simplest one, the Histogram Equalization. Digital Image Analysis - Lab 3 Page 3 of 12 Go into the viewer dropdown menu and select RASTER/CONTRAST/GENERAL CONTRAST/HISTOGRAM EQUALIZATION Apply the stretch to the Image file. Keep the Number of Bins (Gray Scales) at 256. This will use 256 grey scales per band. Then click Apply. Next, save the file by going to File/Save/Top Layer As. Use herift_(lastnamefirstname).img as the file name. Save all of your original work files to your X: drive. Remember to include your directory path to your files in the “Comments” field of your Blackboard Lab Assignment submission. Look at the graphic histogram again to see the affect it had on the data. Notice that the data is nicely spread out and there are empty gray scales between ones with pixels in them. This increases the contrast....
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lab2CoastalMappingTutorial110113 - Digital Image Analysis...

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