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<title>ImageMagick: MagickCore, C API for ImageMagick: Enhance an Image</title>
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<p class="navigation-index">[ <a href="#ClutImage">ClutImage</a> | <a href="#ContrastImage">ContrastImage</a> | <a href="#The ContrastStretchImage">The ContrastStretchImage</a> | <a href="#EnhanceImage">EnhanceImage</a> | <a href="#EqualizeImage">EqualizeImage</a> | <a href="#GammaImage">GammaImage</a> | <a href="#LevelImage">LevelImage</a> | <a href="#The LinearStretchImage">The LinearStretchImage</a> | <a href="#ModulateImage">ModulateImage</a> | <a href="#NegateImage">NegateImage</a> | <a href="#The NormalizeImage">The NormalizeImage</a> | <a href="#SigmoidalContrastImage">SigmoidalContrastImage</a> ]</p>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="ClutImage">ClutImage</a></h2>
</div>
<p>ClutImage() replaces colors in the image from a color lookup table.</p></ol>
<p>The format of the ClutImage method is:</p>
<pre class="code">
MagickBooleanType ClutImage(Image *image,Image *clut_image)
MagickBooleanType ClutImageChannel(Image *image,
const ChannelType channel,Image *clut_image)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>channel</h5>
<ol><p>the channel.</p></ol>
<h5>clut_image</h5>
<ol><p>the color lookup.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="ContrastImage">ContrastImage</a></h2>
</div>
<p>ContrastImage() enhances the intensity differences between the lighter and darker elements of the image. Set sharpen to a MagickTrue to increase the image contrast otherwise the contrast is reduced.</p></ol>
<p>The format of the ContrastImage method is:</p>
<pre class="code">
MagickBooleanType ContrastImage(Image *image,
const MagickBooleanType sharpen)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>sharpen</h5>
<ol><p>Increase or decrease image contrast.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="The ContrastStretchImage">The ContrastStretchImage</a></h2>
</div>
<p>The ContrastStretchImage() is a simple image enhancement technique that attempts to improve the contrast in an image by `stretching' the range of intensity values it contains to span a desired range of values. It differs from the more sophisticated histogram equalization in that it can only apply a linear scaling function to the image pixel values. As a result the `enhancement' is less harsh.</p></ol>
<p>The format of the ContrastStretchImage method is:</p>
<pre class="code">
MagickBooleanType ContrastStretchImage(Image *image,
const char *levels)
MagickBooleanType ContrastStretchImageChannel(Image *image,
const unsigned long channel,const double black_point,
const double white_point)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>channel</h5>
<ol><p>the channel.</p></ol>
<h5>black_point</h5>
<ol><p>the black point.</p></ol>
<h5>white_point</h5>
<ol><p>the white point.</p></ol>
<h5>levels</h5>
<ol><p>Specify the levels where the black and white points have the range of 0 to number-of-pixels (e.g. 1, 10x90, etc.).</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="EnhanceImage">EnhanceImage</a></h2>
</div>
<p>EnhanceImage() applies a digital filter that improves the quality of a noisy image.</p></ol>
<p>The format of the EnhanceImage method is:</p>
<pre class="code">
Image *EnhanceImage(const Image *image,ExceptionInfo *exception)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>exception</h5>
<ol><p>Return any errors or warnings in this structure.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="EqualizeImage">EqualizeImage</a></h2>
</div>
<p>EqualizeImage() applies a histogram equalization to the image.</p></ol>
<p>The format of the EqualizeImage method is:</p>
<pre class="code">
MagickBooleanType EqualizeImage(Image *image)
MagickBooleanType EqualizeImageChannel(Image *image,
const ChannelType channel)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>channel</h5>
<ol><p>the channel.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="GammaImage">GammaImage</a></h2>
</div>
<p>GammaImage() gamma-corrects a particular image channel. The same image viewed on different devices will have perceptual differences in the way the image's intensities are represented on the screen. Specify individual gamma levels for the red, green, and blue channels, or adjust all three with the gamma parameter. Values typically range from 0.8 to 2.3.</p></ol>
<p>You can also reduce the influence of a particular channel with a gamma value of 0.</p></ol>
<p>The format of the GammaImage method is:</p>
<pre class="code">
MagickBooleanType GammaImage(Image *image,const double gamma)
MagickBooleanType GammaImageChannel(Image *image,
const ChannelType channel,const double gamma)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>channel</h5>
<ol><p>the channel.</p></ol>
<h5>gamma</h5>
<ol><p>the image gamma.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="LevelImage">LevelImage</a></h2>
</div>
<p>LevelImage() adjusts the levels of a particular image channel by scaling the colors falling between specified white and black points to the full available quantum range. The parameters provided represent the black, mid, and white points. The black point specifies the darkest color in the image. Colors darker than the black point are set to zero. Gamma specifies a gamma correction to apply to the image. White point specifies the lightest color in the image. Colors brighter than the white point are set to the maximum quantum value.</p></ol>
<p>The format of the LevelImage method is:</p>
<pre class="code">
MagickBooleanType LevelImage(Image *image,const char *levels)
MagickBooleanType LevelImageChannel(Image *image,
const ChannelType channel,const char *levels)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>channel</h5>
<ol><p>the channel.</p></ol>
<h5>levels</h5>
<ol><p>Specify the levels where the black and white points have the range of 0-QuantumRange, and gamma has the range 0-10 (e.g. 10x90+2).</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="The LinearStretchImage">The LinearStretchImage</a></h2>
</div>
<p>The LinearStretchImage() discards any pixels below the black point and above the white point and levels the remaining pixels.</p></ol>
<p>The format of the LinearStretchImage method is:</p>
<pre class="code">
MagickBooleanType LinearStretchImage(Image *image,
const double black_point,const double white_point)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>black_point</h5>
<ol><p>the black point.</p></ol>
<h5>white_point</h5>
<ol><p>the white point.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="ModulateImage">ModulateImage</a></h2>
</div>
<p>ModulateImage() lets you control the brightness, saturation, and hue of an image. Modulate represents the brightness, saturation, and hue as one parameter (e.g. 90,150,100). If the image colorspace is HSL, the modulation is luminosity, saturation, and hue. And if the colorspace is HWB, use blackness, whiteness, and hue.</p></ol>
<p>The format of the ModulateImage method is:</p>
<pre class="code">
MagickBooleanType ModulateImage(Image *image,const char *modulate)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>modulate</h5>
<ol><p>Define the percent change in brightness, saturation, and hue.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="NegateImage">NegateImage</a></h2>
</div>
<p>NegateImage() negates the colors in the reference image. The grayscale option means that only grayscale values within the image are negated.</p></ol>
<p>The format of the NegateImageChannel method is:</p>
<pre class="code">
MagickBooleanType NegateImage(Image *image,
const MagickBooleanType grayscale)
MagickBooleanType NegateImageChannel(Image *image,
const ChannelType channel,const MagickBooleanType grayscale)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>channel</h5>
<ol><p>the channel.</p></ol>
<h5>grayscale</h5>
<ol><p>If MagickTrue, only negate grayscale pixels within the image.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="The NormalizeImage">The NormalizeImage</a></h2>
</div>
<p>The NormalizeImage() method enhances the contrast of a color image by mapping the darkest 2 percent of all pixel to black and the brightest 1 percent to white.</p></ol>
<p>The format of the NormalizeImage method is:</p>
<pre class="code">
MagickBooleanType NormalizeImage(Image *image)
MagickBooleanType NormalizeImageChannel(Image *image,
const ChannelType channel)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>channel</h5>
<ol><p>the channel.</p></ol>
<div style="margin: auto;">
<h2><a href="http://magick.imagemagick.org/viewvc/bin/cgi/viewvc.cgi/svn/ImageMagick/trunk/magick/enhance.c
?view=markup" target="source" name="SigmoidalContrastImage">SigmoidalContrastImage</a></h2>
</div>
<p>SigmoidalContrastImage() adjusts the contrast of an image with a non-linear sigmoidal contrast algorithm. Increase the contrast of the image using a sigmoidal transfer function without saturating highlights or shadows. Contrast indicates how much to increase the contrast (0 is none; 3 is typical; 20 is pushing it); mid-point indicates where midtones fall in the resultant image (0 is white; 50 is middle-gray; 100 is black). Set sharpen to MagickTrue to increase the image contrast otherwise the contrast is reduced.</p></ol>
<p>The format of the SigmoidalContrastImage method is:</p>
<pre class="code">
MagickBooleanType SigmoidalContrastImage(Image *image,
const MagickBooleanType sharpen,const char *levels)
MagickBooleanType SigmoidalContrastImageChannel(Image *image,
const ChannelType channel,const MagickBooleanType sharpen,
const double contrast,const double midpoint)
</pre>
<p>A description of each parameter follows:</p></ol>
<h5>image</h5>
<ol><p>the image.</p></ol>
<h5>channel</h5>
<ol><p>the channel.</p></ol>
<h5>sharpen</h5>
<ol><p>Increase or decrease image contrast.</p></ol>
<h5>contrast</h5>
<ol><p>control the "shoulder" of the contast curve.</p></ol>
<h5>midpoint</h5>
<ol><p>control the "toe" of the contast curve.</p></ol>
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