ENVI Tutorial
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E N V I T u t o r i a l : M o s a i c k i n gi n E N V IM o s a i c k i n g i n E N V I 2F i l e s U s e d i n t h i s T u t o r i a l 2T h e M o s a i c k i n g P r o c e s s i n E N V I 3F e a t h e r i n g 3V i r t u a l M o s a i c s 4P i x e l - B a s e d M o s a i c k i n g E x a m p l e 5O t h e r M e t h o d s f o r P o s i t i o n i n g I m a g e s 6M a p - B a s e d M o s a i c k i n g E x a m p l e 9V i e w t h e T o p I m a g e , C u t - l i n e a n d V i r t u a l , N o n - F e a t h e r e d M o s a i c 9C r e a t e t h e O u t p u t F e a t h e r e d M o s a i c 1 0C o l o r B a l a n c i n g D u r i n g M o s a i c k i n g 1 1C r e a t e t h e M o s a i c I m a g e w i t h o u t C o l o r B a l a n c i n g 1 1R G B M o s a i c P r e v i e w 1 2O u t p u t t h e M o s a i c W i t h o u t C o l o r B a l a n c i n g 1 2O u t p u t t h e M o s a i c W i t h C o l o r B a l a n c i n g 1 21E N V I T u t o r i a l : M o sa i cki n g i n E N V IM o s a i c k i n g i n E N V IThis tutorial is designed to give you a working knowledge of ENVI’s image mosaicking capabilities. Foradditional details, please see ENVI Help.F i l e s U s e d i n t h i s T u t o r i a lENVI Resource DVD: D a t a / a v m o s a i cFile Descriptiond v 0 6 _ 2 . i m g ( . h d r ) AVIRIS Scene 02d v 0 6 _ 3 . i m g ( . h d r ) AVIRIS Scene 03d v 0 6 a . m o s Mosaic template for end-to-end AVIRIS mosaicd v 0 6 b . m o s Mosaic template for feathered overlapping ...
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ENVI Tutorial: Mosaicking in ENVI
Mosaicking in ENVI Files Used in this Tutorial The Mosaicking Process in ENVI Feathering Virtual Mosaics Pixel-Based Mosaicking Example Other Methods for Positioning Images Map-Based Mosaicking Example View the Top Image, Cut-line and Virtual, Non-Feathered Mosaic Create the Output Feathered Mosaic Color Balancing During Mosaicking Create the Mosaic Image without Color Balancing RGB Mosaic Preview Output the Mosaic Without Color Balancing Output the Mosaic With Color Balancing
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ENVI Tutorial: Mosaicking in ENVI
Mosaicking in ENVI This tutorial is designed to give you a working knowledge of ENVI’s image mosaicking capabilities. For additional details, please see ENVI Help. Files Used in this Tutorial ENVI Resource DVD: Data/avmosaic File Description _ dv06 2.img (.hdr) AVIRIS Scene 02 _ dv06 3.img (.hdr) AVIRIS Scene 03 dv06a.mos Mosaic template for end-to-end AVIRIS mosaic dv06b.mos Mosaic template for feathered overlapping AVIRIS mosaic _ dv06 fea.img (.hdr) Feathered mosaic File Description _ lch 01w.img (.hdr) Warped, histogram-matched image lch_01w.ann Cut-line feathering annotation for above _ lch 02w.img (.hdr) Warped, histogram matched image _ lch a.mos Mosaic template for georeferenced image mosaicking _ lch mos1.img (.hdr) Georeferenced mosaic result File Description _ mosaic1 equal.dat (.hdr) Subset of a Landsat-7 ETM image with a histogram equalization stretch independently applied to each band Another subset from the same Landsat-7 ETM image, without any stretching applied
mosaic 2.dat (.hdr) _
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ENVI Tutorial: Mosaicking in ENVI
The Mosaicking Process in ENVI Mosaicking involves combining multiple images into a single composite image. ENVI provides interactive capabilities for placing non-georeferenced images within a mosaic, and automated placement of georeferenced images within a georeferenced output mosaic. ENVI also provides transparency, histogram matching, and automated color balancing. ENVI’s Virtual Mosaic allows you to create and display mosaics without creating large output files. The following sections provide useful information about mosaics in ENVI before you start the exercises. The actual exercises are in "Pixel-Based Mosaicking Example" on page 5. Feathering To blend or blur the seams between mosaicked images, you can feather the edges of overlapping areas using either edge feathering or cut-line feathering over a specified distance. To use feathering when mosaicking images, import the bottom image without feathering. Then import the overlapping images with edge or cut-line feathering. Edge Feathering Edge Feathering uses a pixel distance you specify to blend the seams along the edges of the mosaicked image. The edge is blended using a linear ramp that averages the two images across the specified distance. For example, if the specified distance is 20 pixels, 0% of the top image is used in the blending at the edge and 100% of the bottom image is used to make the output image. At 20 pixels from the edge, 100% of the top image is used to make the output image and 0% of the bottom image is used. At 10 pixels from the edge, 50% of each image is used to make the output image.
Cutline Feathering Cut-line Feathering uses a pixel distance and annotation file you specify to blend the image boundaries. You must define cut-lines using the annotation tools prior to mosaicking. The annotation file must contain a polyline defining the cut-line that is drawn from edge-to-edge, and you must place a symbol in the region of the image that will be cut off. The cut-line distance is used to create a linear ramp that averages the two images across that distance from the cut-line outwards. For example, if the specified distance is 20 pixels, 100% of the top image is used in the blending at the cut-line and 0% of the bottom
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ENVI Tutorial: Mosaicking in ENVI
image is used to make the output image. At 20 pixels from the cutline, 0% of the top image is used to make the output image and 100% of the bottom image is used. At 10 pixels from the cutline, 50% of each image is used to make the output image.
Virtual Mosaics You can use a mosaic template file to construct a “Virtual Mosaic,” one that can be displayed and used by ENVI without actually creating a mosaic output file. You cannot use feathering when creating a Virtual Mosaic in ENVI. After creating a mosaic, save the template file by selecting File > Save Template from the Image Mosaicking dialog menu bar. This creates a small text file describing the mosaic layout. To use the Virtual Mosaic, select File > Open Image File from the ENVI main menu bar and open the mosaic template file. All of the images used in the mosaic are opened and their bands are listed in the Available Bands List. Display or process any of the bands in the Virtual Mosaic, and ENVI treats the individual images as if they were an actual mosaic output file. The new processed file has the specified size of the mosaic, and the input files are in their specified positions within the mosaic.
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ENVI Tutorial: Mosaicking in ENVI
Pixel-Based Mosaicking Example 1. From the ENVI main menu bar, select Map > Mosaicking > Pixel Based . The Pixel Based Mosaic dialog appears. 2. From the Pixel Based Mosaic dialog menu bar, select Import > Import Files . The Mosaic Input Files dialog appears. 3. Select Open > New File . Navigate to Data\avmosaic and select dv06 2.img . _ Click Open . _ 4. Repeat Step 3 for dv06 3.img . 5. In the Mosaic Input Files dialog, click Shift to select both images. Click OK . The Select Mosaic Size dialog appears. 6. In the Mosaic Xsize field, enter 614 . In the Mosaic Ysize field, enter 1024 . Click OK . A Pixel Mosaic dialog appears:
_ 7. The bottom of the Pixel Mosaic dialog lists the current position of the images. Select dv06 3.img , enter 513 in the Y0 field, and press Enter . The file dv06 3.img is placed directly _ below dv06 2.img . _
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ENVI Tutorial: Mosaicking in ENVI
8. From the Pixel Mosaic dialog menu bar, select File > Apply . A Mosaic Parameters dialog appears. 9. In the Enter Output Filename field, enter dv06.img and click OK to create the mosaic. 10. To create a Virtual Mosaic instead of a new mosaic file, select File > Save Template from the Pixel Based Mosaic dialog menu bar. When the Output Mosaic Template dialog appears, enter the output filename dv06a.mos . 11. In the Available Bands List, select Mosaic (Band 1) under dv06.mos (or dv06a.mos from Step 9) and click Load Band . Other Methods for Positioning Images The second part of this example shows you how to position the two images into a composite mosaic image by entering X0 and Y0 values, or by dragging the images to the desired locations within the Pixel Mosaic dialog. The example also includes edge feathering. 1. In the Pixel Mosaic dialog, select Options > Change Mosaic Size . The Select Mosaic Size dialog appears. 2. In the Mosaic Xsize and Mosaic Ysize fields, enter 768 . Click OK . 3. In the Pixel Mosaic dialog, click the image surrounded by a green box ( dv06 2.img ) and drag _ it to the lower-right corner of the dialog. 4. Right-click inside this image and select Edit Entry . An Entry: dialog appears.
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ENVI Tutorial: Mosaicking in ENVI
5. In the Data Value to Ignore field, enter 0 . 6. In the Feathering Distance field, enter 25 . 7. Leave the default values for other fields and click OK . _ 8. Click the image surrounded by a red box ( dv06 3.img ) and drag it to the upper-left corner of the dialog. Then, repeat steps 4-7 for this image.
9. From the Pixel Mosaic menu bar, select File > Save Template . An Output Mosaic Template dialog appears. 10. In the Enter Output Filename field, enter dv06b.mos . Click OK . 11. In the Available Bands List, select Virtual Mosaic (Band 1) and click Load Band . No feathering is performed with a Virtual Mosaic. 12. Make the same image as a feathered mosaic by creating an output file. From the Pixel Mosaic dialog menu bar, select File > Apply . A Mosaic Parameters dialog appears. 13. In the Enter Output Filename field, enter dv06f.img . 14. In the Background Value field, enter 255 . Click OK . 15. In the Available Bands List, click Display #1 and select New Display . 16. Select Mosaic (Band 1) under dv06f.img and click Load Band . If you cannot see the entire image in the Image window, click and drag a corner of the Image window to resize it.
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ENVI Tutorial: Mosaicking in ENVI
17. Compare the Virtual Mosaic and the feathered mosaic using image linking and dynamic overlays. The following figure shows the feathered output mosaic produced by overlapping the two AVIRIS scenes.
18. From the Available Bands List menu bar, select File > Close All Files . 19. Close the Pixel Mosaic dialog and all display groups.
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ENVI Tutorial: Mosaicking in ENVI
Map-Based Mosaicking Example Follow these steps to create a map-based mosaic image: 1. From the ENVI main menu bar, select Map > Mosaicking > Georeferenced . A Map Based Mosaic dialog appears. 2. From the Map Based Mosaic dialog menu bar, select File > Restore Template . A file selection dialog appears. 3. Navigate to Data\avmosaic and select lch a.mos . Click Open . This opens the files _ associated with the mosaic template and restores the mosaic parameters necessary for a georeferenced, feathered mosaic. You can also individually import georeferenced images and set the feathering options by selecting Import > Import Files from the Map Based Mosaic dialog menu bar. Images will automatically be placed in their correct geographic locations. The location and size of the georeferenced images will determine the size of the output mosaic. View the Top Image, Cut-line and Virtual, Non-Feathered Mosaic _ 1. In the Available Bands List, select Warp under lch 01w.img and click Load Band . 2. Right-click in the Image window and select Toggle > Display Scroll Bars . Click the horizontal scroll bar until a good portion of the image is visible. 3. From the Display group menu bar, select Overlay > Annotation . An Annotation dialog appears. 4. From the Annotation dialog menu bar, select File > Restore Annotation . A file selection dialog appears. 5. Select lch 01w.ann and click OK . The display group shows a red cut-line used to blend the _ two images in this mosaic. 6. In the Available Bands List, click Display #1 and select New Display . _ 7. Select Warp under lch 02w.img and click Load Band . 8. Can you identify the relationship between the cut-line and this image? 9. From the ENVI main menu bar, select File > Open Image File . A file selection dialog appears. _ 10. Select lch a.mos and click Open . 11. In the Available Bands List, click Display #2 and select New Display . _ 12. Select Virtual Mosaic under lch a.mos and click Load Band .
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ENVI Tutorial: Mosaicking in ENVI
13. Examine the non-feathered edge between the two images that were used to create the mosaic:
Create the Output Feathered Mosaic 1. From the Mosaic dialog menu bar, select File > Apply . A Mosaic Parameters dialog appears. 2. In the Enter Output Filename field, enter lch mos.img and click OK to create the feathered _ mosaic. _ _ 3. Close Display #1 ( lch 01w.img ) and Display #2 ( lch 02w.img ). 4. In the Available Bands List, click Display #3 and select New Display . _ 5. Select Warp under lch 01w.img and click Load Band . 6. Compare the feathered mosaic to the non-feathered mosaic using image linking and dynamic overlays.
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ENVI Tutorial: Mosaicking in ENVI
Color Balancing During Mosaicking This tutorial describes the procedure for creating a georeferenced mosaic using automated color balancing. For this exercise, you will use two overlapping subsets from a Landsat-7 ETM image. Create the Mosaic Image without Color Balancing First, you will create a mosaic without color balancing. You will start by importing both of the images without any feathering so you can clearly see the seams between the images. 1. From the ENVI main menu bar, select Map > Mosaicking > Georeferenced . A Map Based Mosaic dialog appears. 2. From the Map Based Mosaic dialog menu bar, select Import > Import Files . A Mosaic Input Files dialog appears. 3. In the Mosaic Input Files dialog, click Open and select New File . Navigate to _ Data\avmosaic and select mosaic1 equal.dat . Click Open . A histogram equalization stretch was independently applied to each band in this image. _ 4. Repeat Step 3 for mosaic 2.dat . _ _ 5. In the Mosaic Input Files dialog, Click Shift to select mosaic 2.dat and mosaic1 equal.dat . Click OK . The two images are automatically placed in their correct geographic locations in the Mosaic dialog. By default, a 2% contrast stretch is applied to the images.
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