GEOG474/666
 Contrast Enhancment

In-Class Exercise

    Image enhancement is the process of making an image more interpretable for a particular application.  Enhancement can make important features of raw remotely sensed data more interpretable to the human eye.  For this exercise, we'll examine the  contrast enhancement techniques available in ArcView's Image Analysis.   Remember that Image Analysis extension is only available on the PCs in Pearson Hall Training Center.

Imagery found under ~tracyd/Geog474/images directory:
landsat_tm_delmarva.img


Start ArcView.

Examine the Online Help to see where the image contrast enhancements are found.

Under the Help menu.  Select Help topics and click on the Contents tab.

Under the Image Analysis extension, select "Working with Image Analysis Themes" and you'll see:

"Adjusting brightness and contrast"
"Stretching histogram to improve image display"

Questions:

  • What are the contrast enhancement techniques available in ArcView Image Analysis?
  • What does stretch - none - indicate?
  • When you initially load an image, is there a default stretch applied to it?
  • When the stretch window is defined as current, what does this indicate?
Apply each of the enhancement techniques available in ArcView.  For each technique note how the image brightness and contrast have changed and if particular features are more readily identifiable.
Question:  Discuss very briefly how the image has changed when you apply each enhancement technique.
Next, apply a piecewise linear contrast stretch by clicking on the Advanced tab.  Perform a piecewise stretch on 1 band and note its affect.
Questions:
  • What's the difference between the black and colored histograms?
  • Sketch the histogram.  How many peaks does it have?  What is the range of BVs.
  • How many piecewise linear stretches are appropriate?
  • What's the overall effect of the piecewise stretch
That's it.  Please turn in your brief answers to the questions above by Tuesday, November 16, 1999.
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Last revised on November 9, 1999 by Tracy DeLiberty.