Steps - How to start? - Step 4

HIGHLIGHTING A COLOR COMPOSITION

To highlight an image, like the one presented in Display 2, we need to change (highlight) the contrast over the original images.

  • Activate Display 1 with a color composition presented in the previous step;
  • To access the contrast window click on Image in the toolbar and then Contrast....

 

Notice that there is a chart that shows a histogram, which defines the number of points with the same color intensity in the image. The color intensity, named gray level, can take values from 0 to 255, creating a "degrade", as presented in the bar below the histogram. Slide the cursor over the histogram and notice the variation in the Input Level.


To highlight a color composition:

  • click in Operation and choose the Linear option.
  • click in Channel and choose the Red color (R);
  • click in View and check In/New;
  • click using the mouse left button (LB) over the histogram (figure below), immediately before starting the chart, which should correspond to the input level 10, approximately;

  • click using the mouse right button (RB) over the histogram (figure above), immediately after finishing the chart, which should correspond to the input level 160, approximately;
  • click on Apply.

Notice that the image got a kind of reddish color. Looking at the output histogram, shown in the chart area, we notice that this histogram shows a higher number of points where the red color intensity is higher, closer to the 255 value in gray level. Even more, you can check that the output histogram has a better distribution over all gray levels, this fact will help to increase the image contrast.

·        execute the same procedure for the Blue and Green colors. Notice that the histograms are different and the maximum and minimum values will be different. The final result is close to the image presented in Canvas 2.

·        click on Execute and Reset, to change the contrast back to its original values before going to the next tasks.

Change the band color association for each band in the same way that we did to visualize the current image.

  • select the TM-5 band and click in B (blue)
  • select the TM-4 band and click in G (green)
  • select the TM-3 band and click in R (red)
  • click on the Draw button   in the toolbar

This color combination is one of the most frequently used.
 


VISUALIZING AN IMAGE    OTHER VISUALIZATION RESOURCES


 
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