Contrast
The
Contrast
operation is used
to enhance the
visual quality of the image represented by a raster file. The
available methods in TerraLib
are:
- Decorrelation
Enhancement: Uses the principal components to contrast the
raster.
- Histogram
Equalization:
Using this method, the histogram of the image will be equalized
automatically.
- Linear:
The user defines
a new minimum and maximum values for the pixels in the image. The
algorithm then applies a linear function over the pixels using this 2
values.
- Mean
and Standard Deviation:
The contrasted image will have a predefined mean and standard
deviation, defined by the user.
- Log:
The contrasted image will be created by using a log function.
- Square:
The contrasted image will be created by using a square function.
- Square
Root: he contrasted image will be created by using a square root
function.
Click on the layer
in the layer explorer and select PROCESSING → RASTER PROCESSING
→ CONTRAST in the main menu.
- Select the type of
contrast to be used, for instance: Linear.
- In Raster Bands
check the desired bands and set the specific parameters which will
varies depending on the contrast type chosen. Double click over the
cell of each parameter to make the cell editable and then change the
value and press enter:
- If Linear, Square, Square
Root or Log: set the
new value for Minimum and/or Maximum,
- If Histogram Equalization:
set the new value for Maximum,
- If Mean and Standard Deviation:
set the new value for Mean and/or Std Dev.
- If Decorrelation
Enhancement: none extra parameters will be necessary.
- Check the Preview
box to have a preview of the contrast with the parameters informed in
the visualization area.
- The Histogram tab presents the histogram to help
in the contrast operation.
- The Input histogram represents the
histogram of the selected band.
- The Output is
as the histogram would be if the contrast was applied..
- Using
the mouse buttons you
can purchase the pixel value from the histogram, helping to define
the parameters
of each type of contrast.
- Histogram Area:
select which area will be used as reference to do the contrast: Use
all image, use visible area showed in the visualization area or a new
region of interest created by the user (click on the New ROI
button to mark the region on the visualization area).
- Repository -
Select one type of repository by
clicking on the
button to save the output layer as a file or on the
button to save it in the database.
- Layer Name -
inform the raster name.
- Press the OK
button to save the resulting contrasted raster.
Hint: The contrasted image will be added as a new layer at the
TerraView project.