1. Purpose of the experiment
Familiar with basic image processing operations, including: image display, color synthesis, multi-band image overlay, viewing header files, editing header file information, image cropping, image comparison between two periods, and closing files.
2. Experimental requirements
Master the basic operations of image processing
3. Experimental content
Content 1: Open the image and perform color synthesis: true color, standard false color, arbitrary false color;
1. Open the image
Data: Data_s1>Data_s1>y1988, seven bands
Operation steps: File→Open image file→Enter data filenames window→Select band→load band
a) Introduction to the image display window (as shown in Figure 1)
Figure 1 Three windows used to display images in ENVI
Display of windows in ENVI:
(1) Scroll window: Panoramic window, which displays the global information of the image, which is the result of resampling of the original image;
(2) Image window: Image window, which displays images in a 1:1 pixel mode (one point on the screen represents one pixel in the image), and can only display partial range images in the Scroll window;
(3) Zoom window: Enlarge the window, zoom in and display some areas in the Image, and the multiple is displayed in the title of the window, and the picture is 4 times enlarged.
b) Monochrome display: click "Gray Scale", click the band, such as band1 of band 1, click "Load Band" (Figure 2)
Figure 2 Monochrome display of Band 1
c) RGB composite display: Click "RGB Color", click the three bands in turn as the bands or files corresponding to the R, G, and B channels, and click "Load Band". For example: synthesize and display the loaded bands according to (3,2,1) method: click "RGB Color", click "R", click band1 of bands 3, 2, 1 in sequence, and click "Load Band" to display the image synthesis result .
If you want to adjust ( R,G,B ) sequence, for example, change the band corresponding to G to band 4 , then: click " G ", click band1 of band 4 , and then click " load band " to load the image.
When opening a new window, click " New Display " after selecting the band, click " load band " to load the new window, and display the new image in #2 after opening the new window .
2. Color synthesis
(1) True color synthesis
3, 2, and 1 of the TM image correspond to the three band ranges of (R, G, B) respectively, and the synthesis of (3, 2, 1) is true color synthesis, and the window number is #1. (as shown in Figure 5).
Data: Data_s1>Data_s1>y1988>1,2,3 bands
Operation steps: File→Open image file→load data of all bands (7)→select RGB Color→assign (3,2,1) bands to (R,G,B) channels in turn (by clicking the Band 1)→New Display→load band
Figure 5 ( 3,2,1 ) true color composite display
It is found from the figure that the image obtained by true color synthesis is similar to the color of the actual ground features, such as: water is blue, vegetation is green, buildings are gray, etc.
(2) Standard false color composite
The standard false color composition selects (4,3,2) bands to assign to (R, G, B) channels respectively, and the window number is #2. (Figure 6).
Data: Data_s1>Data_s1>y1988>2,3,4 bands
Steps: (Based on (1)) sequentially assign (3,2,1) bands to (R,G,B) channels (by clicking Band 1 under the respective bands)→New Display→load band
Figure 6 ( 4,3,2 ) Standard false color composite display
It is found from the figure that the vegetation in the standard false-color composite image is displayed in red, with obvious features, which is of great significance for the human eye to intuitively recognize the vegetation.
(3) Arbitrary false color synthesis
Any three-band synthesis display, except for the combination of (3,2,1) bands, is a standard false-color synthesis, here select (5,4,3) synthesis, and the window number is #3. (Figure 7)
Data: Data_s1>Data_s1>y1988>3,4,5 bands
Operation steps: (Based on (1)) sequentially assign (5,4,3) bands to (R,G,B) channels (by clicking Band 1 under the respective bands)→New Display→load band
Figure 7 ( 5,4,3 ) false color composite display
It can be found from Figure 7 that in the ( 5,4,3 ) false color synthesis scheme, the blue of the water body is prominent, while the vegetation is displayed as green, and the buildings are displayed as an approximate earth color, which contributes significantly to the distinction between woodland and water.
Content 2: Overlay of multi-band images;
Requirements: superimpose the seven band data in the y1988 folder, and output a new file AA.
Data: Data: Data_s1>Data_s1>y1988 (data of seven bands)
Steps: Basic Tools → layer stacking → Import files, adjust the order, the output file name is AA
The obtained AA file contains seven bands, and the header file " AA.HDR " about the AA file is obtained , which can be viewed through a text editor.
Task 3: Open the header file, take a screenshot, explain the following problems, and edit the header file:
1. Open the header file
Open the AA.HDR file in Notepad to view the file information
Data: Data_s1>Data_s1>AA
Edit the header file:
Band name: b1,b2,b3,b4,b5,b6,b7;
Wavelength: Take the center wavelength value of the band. They are 478.700, 561.000, 661.400, 834.600, 1650.000, 1500.000, 2208.000, the unit is nm;
Pixel size: 30m.
Operation steps: main menu File→Edit ENVI Header→select file AA→click OK to edit interface, click edit attribute, modify band name, wavelength, pixel size in turn, as shown in Figure 9.
Figure 9 Edit header file steps
Open the header file after editing
Task 4: Image cropping
① Subset using Image in Spatial Subset;
Data: Band 3 data in AA file
Steps:
a. Main menu File→Save files as→ENVI Standard→Import file→select the file AA→Spatial Subset→Image.
b. Select the clipping range (in this example, band 3 is clipped), and the clipping range falls within the red frame ( as shown in Figure 12 ).
Figure 12 Manually check the cropping range in the Image window (the red box is the cropping range)
c. After checking the cropping range, click OK to return to the editing interface, select the output file location, and display the cropped image in the new interface, as shown in Figure 13:
Figure 13 Cropping result (right picture)
From the figure, the image interface obtained is the range in the red frame, and the method is simple.
(2) Subset using File in Spectral Subset
data:
Cropped image file: AA
Cropped image file: mask_2000
Steps:
a. Main menu File→Save files as→ENVI Standard→Import file→Select the clipped data (AA)→Spatial Subset→File→Crop image file (mask_2000),
b. Click OK, and click Choose to select the location to save the file, and click OK to complete the cropping
c. Display the cropped image in monochrome, as shown in Figure 17.
Figure 17 cropped image display
Thinking: For the cropping of regular images, if the cropping range is known, that is, when the cropping range can be manually selected, the Image cropping method is simple and convenient; you can further explore the method of image cropping, and learn how to use vector files to crop remote sensing images (whether feasible?).
Task 5: Comparison of images from the two periods;
When comparing images in two periods, you need to use window connection tools. Window connection refers to connecting multiple image display windows to display image data synchronously.
Data: Remote sensing images of land use in China (30m resolution)
CLCD_v01_1990_albert.tif
CLCD_v01_1995_albert.tif
Steps:
a. Display the above two images in the window respectively (1990 image is displayed in #1 window, 1995 image is displayed in #2 window)
b. Window connection: click #1 window Tools → Link → Link Displays
c. After the windows are connected, select the red frame to a certain position in the #1 window, and the #2 window will change accordingly, and the two images can be compared for analysis, as shown in Figure 20 .
Figure 20 Comparison of images in the two periods (left picture in 1990 and right picture in 1995 )
From Figure 20 , it is found that in 1990 and 1995 , compared with 1995, the change of China's land use change is not very large. This may be because the selected area falls in the area with small change, or it may be the two periods of the image The time difference is relatively short, and further statistical analysis is needed.
Task 6: Close a single file; close all files (but do not close the ENVI main interface);
(1) Close a single file: right click on the band list → select Close Selected File or the band display window File → Close Selected File
(2) Close all files: Band display window File→Close All Files as shown in Figure 21 .
Figure 21 Close the file