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.
It is
accessible through:
Raster
Processing >
Contrast...(list
of all
raster layers will be available)
This
wizard consists of the
following steps:
Wizard Page 1 - Selection
of the layer to apply the contrast (Layer Search)
On the List
of Layers select the raster layer to apply the contrast.
Optionally use Filter By Name
field
giving part of the layer name to help find the layer in the list.
Press Next
to go to next step or Cancel to close the
dialog.
Wizard Page 2 - Contrast parameters
Select the Type of contrast to
be used (Linear, Histogram or Mean and Standard deviation).
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.
On the Preview tab
click on to have a preview of the contrast with the parameters
informed.
The Histogramtab presents the histogram to help
in the contrast operation.
The Input histogram represents the
histogram of the selected band.
The Outputisasthe histogramwould be ifthe
contrastwas applied.
Usingthe mouse buttonsyou
can purchasethe pixel valuefromthe histogram, helping to definetheparametersof each type ofcontrast.
Press Next to apply the
contrast or Back to go to the previous wizard page.
Wizard Page 3 - Output
information
Raster Info
- First press and inform the folder where the resulting
file will be saved.
Name - inform
the raster name.
Extra
Parameters - if there are some, see the details on how to inform
then here.
Press Finish
to save the resulting contrasted raster or Back
to go to the previous wizard page.
Hint: The contrasted image will be added as a new layer at the
TerraView project.