Steps - How to start? - Step 3

VISUALIZING AN IMAGE

We will start talking about satellite images, in this example they are identified by the Category: TM_Image.

An image is similar to a photograph, which is obtained by a sensor on board of the satellite. The "Thematic Mapper or TM" sensor on board of the LANDSAT 5 satellite can get seven different images from the same region, each image is named a band and they are enumerated 1 through 7. Each band has information about the amount of radiation reflected by the earth surface, in the electromagnetic spectrum band. The TM-1 band corresponds to the blue color wave length, the TM-2 band corresponds to the green color wave length, the TM-3 band corresponds to the red color wave length, and TM-4, TM-5, TM-6, and TM-7 are related to different wave length in the infrared spectrum, which are not visible by the human eye. The SPRING manual describes in more details the image features. You will have the opportunity to access these information during this training.

Each image corresponds to an independent layer of information. The layers can be combined, thus the name Information Layer or IL, which translates this idea where each layer carries a certain type of information.

In this project there are several images taken from the LANDSAT TM, with a 30 meters resolution. These images can be displayed in the drawing display either in color or in black and white. When a band is visualized in black and white we say the image is displayed in gray levels, or in its monochromatic form.

In order to visualize a color image we need to combine three bands and associate, each of them, to the basic color system (Red, Green, and Blue). In order to facilitate an image visualization in color the IL ComposicaoR4G5B3 was generated in a single band, artificially, using the composition of the three band (TM_3, TM_4 and TM-5), creating what is called a synthetic image.

This color composition is denominated false color, because it does not reproduce the natural colors of the objects, associating the LANDSAT bands 5, 4 and 3 to the Red, Green and Blue colors, respectively.

 To Visualize an Image:

  • click on Show in the main menu and allow the Control Panel, or in the button atalho_painel.gif - 967 Bytesin the toolbar.;
  • click on the category Imagen_TM (figure below);

  • select the IL ComposicaoR4G5B3, and click on Synthetic.
  • click on the button Draw  to visualize the desired image in the Main Display, which is enabled.

 


VISUALIZING A SINGLE BAND

In order to visualize a single band (IL) in gray level we can use any of the bands obtained by the satellite sensor.

To visualize a single band:

  • select the TM_3 band from the Information Layer list;
  • click on M (monochromatic) and on the Draw button in the toolbar;
  • the same procedure can be used for the other images, TM_4 and TM_5.

 


VISUALIZING THREE BANDS IN A SINGLE display

To activate a Project:

  • select the TM_3 band and click in B (blue);
  • select the TM_5 band and click in G (green);
  • select the TM_4 band and click in R (red);

  • click on the Draw button in the toolbar.

VISUALIZING IMAGES IN SEPARATED display

To visualize several images in separated display:

  • after visualizing the three bands in the main display, click on the tab of the display 2, then select the ComposícaoR4G5B3 and select Synthetic Image
  • click in the Draw button;
  • compare the images drawn in the main display and in display 2. Notice that there is a difference between the compositions, the colored and the synthetic images. The image in the main display is darker because the image is raw, while the image in display 2 was already processed.

 


ACTIVATING A PROJECT    HIGHLIGHTING AN IMAGE


 
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