Create Color Composites
Lesson content
Lesson 1 of 1
Create Color Composites
In this quick guide, you will:
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Open and display a Sentinel-2 multispectral image. * •
Use the Data Manager to assign spectral bands to red/green/blue color channels. * •
Use the Predefined Band Combinations button to create quick color composites.
Sample Data
Download sample data below. Then extract the contents of the .zip file to a local directory.
[GettingStarted.zip
116 MB
DownloadArrow down with horizontal line beneath it](assets/GettingStarted.zip)
Open and Display an Image
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Select File > Open from the Menu bar. An Open dialog appears. 2. 2
Go to the location where you saved the sample data. Select Sentinel2_Venice_LayerStack.dat and click Open. The center of the image is displayed at full (100%) resolution in the view. 3. 3
Press the F12 key on your keyboard to view the full extent of the image. This Sentinel-2 multispectral image is centered around Porto Marghera in eastern Italy. The small island to the east is Venice. This image was acquired on August 13, 2015. Sentinel-2 images are available from the Copernicus Data Space Ecosystem(opens in a new tab) website.
The Layer Manager shows which bands are assigned to the Red, Green, and Blue channels. The display channels are represented by colored boxes, and the band names are listed to the right of the colored boxes.
In this case, the Red band is assigned to the Red color channel. The Green band is assigned to the Green color channel. The Blue band is assigned to the Blue color channel. The result is a true-color composite. The image is displayed in colors that are natural to our eyes, with blue water, green vegetation, etc.
Sentinel-2 imagery contain more than three bands. Next, you will use the Data Manager to see the full list of bands and to create a color-infrared composite.
Use the Data Manager to Assign Bands to Colors
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Click the Data Manager button in the Toolbar. The Data Manager appears.
The Data Manager shows that the Sentinel-2 image contains 11 bands. The values in parentheses are wavelengths, in nanometers. Sentinel-2 Level-1C images are originally distributed in three multispectral band groups, each with different spatial resolutions. The image you are working with is a layer stack that combines all of the bands into a single image. Refer to the Create Band and Layer Stacks quick guide for more information.
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In the Data Manager, right-click on Sentinel2_Venice_LayerStack.dat and select Load CIR.
The result is a color-infrared (CIR) or false-color composite. Healthy vegetation reflects strongly in the near-infrared wavelengths. With the near-infrared band (B8) assigned to the red color channel, healthy vegetation appears red in the composite. This is a common standard for displaying healthy vegetation in multispectral remote sensing. Urban areas and bare-earth areas are colored cyan.
The Layer Manager shows an additional layer: [1] Sentinel2_Venice_LayerStack.dat. The [1] indicates a variation of the original layer; in this case, a CIR composite.
The default stretch type is Optimized Linear. To display color composites with higher contrast, click the stretch type drop-down list in the Toolbar and select Linear 1%.
You can also use the Data Manager to create a custom color composite, which you will do next.
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Click the arrow next to Band Selection to expand that section. When you click on band names, color assignments will cycle through red, green, and blue (in that order). 2. 4
Click SWIR (B12) to assign that band to the red color channel. A red icon appears next to the band. 3. 5
Click SWIR (B11) to assign that band to the green color channel. A green icon appears next to the band. 4. 6
Click Red (B4) to assign that band to the blue color channel. A blue icon appears next to the band.
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Click the Load Data button to display the new band combination. This color composite emphasizes urban areas and man-made features with light grey and purple colors.
Interactively Assign Bands to Colors
A quicker way to assign bands to color channels is to use the interactive slider below the Property Sheet.
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Click the Predefined Band Combinations drop-down list to the left of the slider, and select Agriculture. 2. 2
Move your cursor over the red, green, and blue slider bars. What bands are assigned to each color channel?
This color composite uses shortwave-infrared (SWIR) and red-edge bands to highlight vegetated and agricultural areas. Bright and dark green areas represent healthy, green vegetation. Brown and orange areas on land represent dormant or fallowed crops. On the island of Venice, those colors correspond to brownish-red rooftops. Urban areas are colored light purple.
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Click the Predefined Band Combinations drop-down list and select Bathymetric. This is a true-color composite that uses the Coastal aerosol (B1) band instead of Blue (B2) to reveal suspended sediment in water. This composite is useful for coastal studies.
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Click and drag the blue, green, and red sliders to different bands to create your own custom color composite. 2. 5
To save a custom color composite for future use (in the current ENVI session), click the drop-down list and select Add Band Combination. A small popup window appears. 3. 6
Accept the default name by clicking the green check box, or enter a different name and click the green check box.
The band combination is added to the list of composites in the drop-down menu.
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This concludes the quick guide.
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