| The ContrastEnhancement object defines contrast enhancement for a channel of
a false-color image or for a color image. Its format is:
<xs:element name="ContrastEnhancement">
<xs:complexType>
<xs:sequence>
<xs:choice minOccurs="0">
<xs:element ref="sld:Normalize"/>
<xs:element ref="sld:Histogram"/>
</xs:choice>
<xs:element ref="sld:GammaValue" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="Normalize">
<xs:complexType/>
</xs:element>
<xs:element name="Histogram">
<xs:complexType/>
</xs:element>
<xs:element name="GammaValue" type="xs:double"/>
In the case of a color image, the relative grayscale brightness of a pixel
color is used. ?Normalize? means to stretch the contrast so that the
dimmest color is stretched to black and the brightest color is stretched to
white, with all colors in between stretched out linearly. ?Histogram? means
to stretch the contrast based on a histogram of how many colors are at each
brightness level on input, with the goal of producing equal number of
pixels in the image at each brightness level on output. This has the
effect of revealing many subtle ground features. A ?GammaValue? tells how
much to brighten (value greater than 1.0) or dim (value less than 1.0) an
image. The default GammaValue is 1.0 (no change). If none of Normalize,
Histogram, or GammaValue are selected in a ContrastEnhancement, then no
enhancement is performed.
author:
iant |