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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="#LevelImageChannel">LevelImageChannel</a> | <a href="#LevelizeImageChannel">LevelizeImageChannel</a> | <a href="#LevelImageColor">LevelImageColor</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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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.</p></ol>
<p>The parameters provided represent the black, and white points. The black point specifies the darkest color in the image. Colors darker than the black point are set to zero. 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>If a '!' flag is given, map black and white colors to the given levels rather than mapping those levels to black and white. See LevelizeImageChannel() and LevelizeImageChannel(), below.</p></ol>
<p>Gamma specifies a gamma correction to apply to the image.</p></ol>
<p>The format of the LevelImage method is:</p>
<pre class="code">
MagickBooleanType LevelImage(Image *image,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). A '!' flag inverts the re-mapping.</p></ol>
<div style="margin: auto;">
<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
_8c.html" target="source" name="LevelImageChannel">LevelImageChannel</a></h2>
</div>
<p>LevelImageChannel() applies the normal LevelImage() operation to just the Specific channels specified, spreading out the values between the black and white points over the entire range of values. Gamma correction is also applied after the values has been mapped.</p></ol>
<p>It is typically used to improve image contrast, or to provide a controlled linear threshold for the image. If the black and white points are set to the minimum and maximum values found in the image, the image can be normalized. or by swapping black and white values, negate the image.</p></ol>
<p>The format of the LevelizeImageChannel method is:</p>
<pre class="code">
MagickBooleanType LevelImageChannel(Image *image,
const ChannelType channel,black_point,white_point,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>black_point</h5>
<ol><p>The level which is to be mapped to zero (black)</p></ol>
<h5>white_point</h5>
<ol><p>The level which is to be mapped to QuantiumRange (white)</p></ol>
<h5>gamma</h5>
<ol><p>adjust gamma by this factor before mapping values.</p></ol>
<div style="margin: auto;">
<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
_8c.html" target="source" name="LevelizeImageChannel">LevelizeImageChannel</a></h2>
</div>
<p>LevelizeImageChannel() applies the reversed LevelImage() operation to just the specific channels specified. It compresses the full range of color values, so that they lie between the given black and white points. Gamma is applied before the values are mapped.</p></ol>
<p>LevelizeImageChannel() can be called with by using a +level command line API option, or using a '!' on a -level or LevelImage() geometry string.</p></ol>
<p>It can be used for example de-contrast a greyscale image to the exact levels specified. Or by using specific levels for each channel of an image you can convert a gray-scale image to any linear color gradient, according to those levels.</p></ol>
<p>The format of the LevelizeImageChannel method is:</p>
<pre class="code">
MagickBooleanType LevelizeImageChannel(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>black_point</h5>
<ol><p>The level to map zero (black) to.</p></ol>
<h5>white_point</h5>
<ol><p>The level to map QuantiumRange (white) to.</p></ol>
<h5>gamma</h5>
<ol><p>adjust gamma by this factor before mapping values.</p></ol>
<div style="margin: auto;">
<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
_8c.html" target="source" name="LevelImageColor">LevelImageColor</a></h2>
</div>
<p>LevelImageColor() will map the given color to "black" and "white" values, limearly spreading out the colors, and level values on a channel by channel bases, as per LevelImage(). The given colors allows you to specify different level ranges for each of the color channels seperatally.</p></ol>
<p>If the boolean 'invert' is set true the image values will modifyed in the reverse direction. That is any existing "black" and "white" colors in the image will become the color values given, with all other values compressed appropriatally. This effectivally maps a greyscale gradient into the given color gradient.</p></ol>
<p>The format of the LevelImageColors method is:</p>
<pre class="code">
MagickBooleanType LevelImageColors(Image *image,const ChannelType channel,
const MagickPixelPacket *black_color,const MagickPixelPacket *white_color,
const MagickBooleanType invert)
</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_color</h5>
<ol><p>The color to map black to/from</p></ol>
<h5>white_point</h5>
<ol><p>The color to map white to/from</p></ol>
<h5>invert</h5>
<ol><p>if true map the colors (levelize), rather than from (level)</p></ol>
<div style="margin: auto;">
<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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 lightness, 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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://www.imagemagick.org/api/MagickCore/enhance
_8c.html" 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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