January 1, 2013 Making a Landsat Image in Adobe Photoshop Please note: All the Landsat data you want to work with should be downloaded before you begin this tutorial. To learn how to download Landsat data from U.S. Geological Survey’s GloVIS, see a separate tutorial, Finding and Downloading Landsat Data from the U.S. Geological Survey’s Global Visualization Viewer Website. Core Concept Landsat scenes are made of separate layers or files (bands) of data. Each band represents a section of the electromagnetic spectrum that has been chosen for Landsat because it happens to be useful for looking at land cover and land use. That is Landsat’s job. More about Landsat bands appears on page 6 of this tutorial. More about using ImageJ can be found on the program website, Eyes in the Sky II, as indicated in the section below, “Going Further with ImageJ.” Before starting this tutorial you should have all the Landsat data you will want to work with. To download Landsat data from U.S. Geological Survey’s GloVIS or Earth Explorer websites, see that tutorial. Tutorial Summary Step 1. Open Photoshop. Step 2. Open three bands of data. Step 3. Merge the bands of data (channels). Step 4. Choose which channels (bands) should appear in your final image in tones of red, green, and blue. Step 5. Adjust color levels. Step 6. Set white and black points in your image. Step 7. Sharpen the image. Step 8. Save the image as a .tiff file. Before you begin: Landsat scenes are large files. Unzipped Landsat 5 scenes are about 404 megabytes (MB), and Landsat 7 scenes are about 654 MB. This is an important consideration when downloading or manipulating them1 Step 1. Open Photoshop. To learn how to download Landsat data, see the NASA tutorial, “Finding and Downloading Landsat Data from the U.S. Geological Survey’s Global Visualization Viewer and Earth Explorer Websites.” To learn what makes up a Landsat scene, see the NASA presentation, “More than a Pretty Picture,” at: [Need URL] Step 2. Open three bands of data: Open Band 1. The file name ends with B10. Open Band 2. The file name ends with B20. Open Band 3. The file name ends with B30. Please note: Bands 1, 2, and 3 show visible light: blue, green, and red wavelengths. Bands 4, 5, 6, and 7 show infrared light. You can make Landsat images of any combination of those bands that you wish. Common band combinations are 3,2,1; 5,4,2; and 7,4,2. It’s the convention to list bands with higher numbers first, indicating what will appear red in the image, what will appear green, and then what will appear blue. Please note: In this tutorial, “Channel” and “Band” are equivalent terms. ________________ Step 3. Merge the bands of data (channels). a. Go to the "Window" menu and select "Channels." In the Channels box, click on the very small menu icon (four horizontal lines) in the upper right corner.  b. Select "Merge Channels” from that pull-down menu. c. Set Mode to RGB Color d. Set Channels to 3, and click “OK.” A window titled, “Merge RGB Channels” will appear. Step 4. Choose which channels (bands) should appear in your final image in tones of red, green, and blue. To make your final image appear as close as possible to its appearance if seen with our own eyes, you will use Landsat’s visible wavelength ranges (bands, or channels). Select Band 3 (with a file name that ends in B30) for the red channel, Select Band 2 (with a file name that ends in B20) for the green channel, and Select Band 1 (with a file name that ends in B10) for the blue channel. Click “OK.” Don’t worry if the resulting colors don’t appear exactly as you want them! There’s a little more work yet to do that will fix the color balance. Step 5. Adjust color levels. a. Go to the Image menu in the top navigation bar and select “Adjustments” and then “Levels.” In the Levels box under “Channel,” select “Red.” Grab the far left arrow under the histogram with your cursor and slide the arrow so it touches the left side of the bulk of the data as shown by the curve. Example below. ________________ Slide the far right arrow under the histogram so it touches the right side of the bulk of the data. (Ignore the central arrow.) b. Under “Channel,” select “Green,” and repeat the adjustment by arrows; then do the same for the Blue Channel. Click “OK.” Step 6. Set white (lightest) and black (darkest) points in your image. a. Go to the Image menu at top and pull down to select “Adjustments,” then “Curves.” This box will open: b. Go to the Window menu in the top navigation and select Info. The Info box will open. c. In the Curves box under the graph, select the third eye dropper. (If you hover over it, it will say "Sample in image to set white point.") Place the eyedropper over a white point, such as a cloud, in the image. As you do so, watch the Info box. The RGB values will change as you move the eyedropper. Look for a point for which all three values approach (but aren't at) 255. Once you've identified such a point, click to select it. d. Select the first eyedropper. Place the eyedropper on a black point in the image. A shadow is a good candidate for this black point. In the Info box, the RGB values should approach, but not reach, zero. Click on the point to set the black point. e. If you wish, you can also adjust the brightness of the image by going to the Image menu, select Adjustments, then Brightness. Step 7. Sharpen the image. Go to “Filter,” and pull down to “Sharpen.” Step 8. Save the image as a .tiff file. You’re done! LEARNING MORE More about Landsat Spectral Bands Landsat Bands in microns (millionths of a meter or micrometers, µm) 1 0.45-0.52 µm Blue-Green 2 0.52-0.60 µm Green 3 0.63-0.69 µm Red 4 0.76-0.90 µm Near-infrared 5 1.55-1.75 µm Mid-infrared 7 2.08-2.35 µm Mid-infrared 6 10.40-12.50 µm Far-infrared (thermal infrared) You may find it peculiar that Band 6 appears after Band 7 in this list. That sequence is purely a factor of the special way in which the Landsat engineers and scientists designed the system. About Band Combinations True Color, or 3, 2, 1: For the true color rendition, band 1 is displayed in the blue color, band 2 is displayed in the green color, and band 3 is displayed in the red color. The resulting image is fairly close to realistic - as though you took the picture with your camera and were riding in the satellite. False-Color, also called Near Infrared or NIR, or 4, 3, 2: In this image, band 2 is displayed in blue, band 3 is displayed in green, and band 4 is displayed in red. In this rendition, vegetation is bright red because green vegetation readily reflects infrared light energy. It is frequently used for studying vegetation. Short-Wavelength Infrared (SWIR), or 7, 4, 2: In this SWIR image, band 2 is displayed in blue, band 4 is displayed in green, and band 7 (or 5) is displayed in red. Like a true-color image, vegetation is green, but cities and bare soil are purple and pink. This band combination is often used to detect burn scars, which are dark red in short wave infrared, and water, which is black or dark blue. Ground Cover Type: In Natural Color (3,2,1), appears: In False Color: (4,3,2), appears: In Pseudo Natural Color (7,4,2), appears: Trees and bushes Olive Green Red Shades of green Crops Medium to light green Pink to red Shades of green Wetland Vegetation Dark green to black Dark red Shades of green Water Shades of blue, green, and brown Shades of blue Black to dark blue Urban areas White to light blue Blue to gray Lavender Bare soil White to light gray Blue to gray Magenta, Lavender, or pale pink Uses of Landsat Spectral Bands Band 1: 0.45 - 0.52 µm (Blue). Mapping coastal waters, differentiating between soil and plants, classifying forests, and identifying manmade objects such as roads and buildings Band 2: 0.52 - 0.60 µm (Green). Spans the region between the blue and red chlorophyll absorption bands, so shows the green reflectance of healthy vegetation. Useful for differentiating between types of plants, determining the health of plants, and identifying manmade objects Band 3: 0.63 - 0.69 µm (Red). One of the most important bands for discriminating among different kinds of vegetation. Also useful for mapping boundaries of soil types and geological formations. Band 4: 0.76 - 0.90 µm (Near infrared). Especially responsive to the amount of vegetation biomass present in a scene, so useful for crop identification, for distinguishing between crops and soil, and for seeing the boundaries of bodies of water Band 5: 1.55 - 1.75 µm (Mid-Infrared). Sensitive to the amount of water in plants (turgidity), so useful for studies of drought and plant vigor. Also useful for discriminating among clouds, snow, and ice Band 6: 10.4 - 12.5 µm (Thermal infrared). Measures the amount of heat (part of infrared radiation) emitted from surfaces, so helps to locate geothermal activity, classify vegetation, and analyze vegetation stress Band 7: 2.08 - 2.35 µm (Mid-infrared). Particularly helpful for discriminating among types of rock formations and for observing vegetation moisture content To learn more about Landsat scenes, study one or more of these tutorials: An Introductory Landsat Tutorial http://zulu.ssc.nasa.gov/mrsid/tutorial/Landsat%20Tutorial-V1.html Fundamentals of Remote Sensing http://www.nrcan.gc.ca/earth-sciences/geography-boundary/remote-sensing/fundamentals/1430 If you are an educator and you have any questions, you may contact – Jeannie Allen, Sigma Space Corp. Hydrospheric and Biospheric Sciences NASA Goddard Space Flight Center Organization Code 618; US Mail Code 610.9 Greenbelt, MD 20770 E-mail: Jeannette.E.Allen@nasa.gov