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12 <title>ImageMagick: MagickCore, C API for ImageMagick: Enhance an Image</title>
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18 <meta name="Description" content="ImageMagick® is a software suite to create, edit, and compose bitmap images. It can read, convert and write images in a variety of formats (about 100) including GIF, JPEG, JPEG-2000, PNG, PDF, PhotoCD, TIFF, and DPX. Use ImageMagick to translate, flip, mirror, rotate, scale, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves. ImageMagick is free software delivered as a ready-to-run binary distribution or as source code that you can freely use, copy, modify, and distribute. Its license is compatible with the GPL. It runs on all major operating systems. The functionality of ImageMagick is typically utilized from the command line or you can use the features from programs written in your favorite programming language. Choose from these interfaces: MagickCore (C), MagickWand (C), ChMagick (Ch), Magick++ (C++), JMagick (Java), L-Magick (Lisp), PascalMagick (Pascal), PerlMagick (Perl), MagickWand for PHP (PHP), PythonMagick (Python), RMagick (Ruby), or TclMagick (Tcl/TK). With a language interface, use ImageMagick to modify or create images automagically and dynamically."/>
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153
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157
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]158<p class="navigation-index">[<a href="#AutoGammaImage">AutoGammaImage</a> &bull; <a href="#AutoLevelImage">AutoLevelImage</a> &bull; <a href="#ColorDecisionListImage">ColorDecisionListImage</a> &bull; <a href="#ClutImage">ClutImage</a> &bull; <a href="#ContrastImage">ContrastImage</a> &bull; <a href="#The ContrastStretchImage">The ContrastStretchImage</a> &bull; <a href="#EnhanceImage">EnhanceImage</a> &bull; <a href="#EqualizeImage">EqualizeImage</a> &bull; <a href="#GammaImage">GammaImage</a> &bull; <a href="#HaldClutImage">HaldClutImage</a> &bull; <a href="#LevelImage">LevelImage</a> &bull; <a href="#LevelizeImage">LevelizeImage</a> &bull; <a href="#LevelizeImageChannel">LevelizeImageChannel</a> &bull; <a href="#LevelImageColor">LevelImageColor</a> &bull; <a href="#The LinearStretchImage">The LinearStretchImage</a> &bull; <a href="#ModulateImage">ModulateImage</a> &bull; <a href="#NegateImage">NegateImage</a> &bull; <a href="#The NormalizeImage">The NormalizeImage</a> &bull; <a href="#SigmoidalContrastImage">SigmoidalContrastImage</a>]</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]159
160<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
161_8c.html" target="source" name="AutoGammaImage">AutoGammaImage</a></h2>
162<div class="doc-section">
163
164<p>AutoGammaImage() extract the 'mean' from the image and adjust the image to try make set its gamma appropriatally.</p></ol>
165
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]166<p>The format of the AutoGammaImage method is:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]167
168<pre class="code">
169 MagickBooleanType AutoGammaImage(Image *image)
170 MagickBooleanType AutoGammaImageChannel(Image *image,
171 const ChannelType channel)
172</pre>
173
174<p>A description of each parameter follows:</p></ol>
175
176<h5>image</h5>
177<ol><p>The image to auto-level</p></ol>
178
179<h5>channel</h5>
180<ol><p>The channels to auto-level. If the special 'SyncChannels' flag is set all given channels is adjusted in the same way using the mean average of those channels.</p></ol>
181
182 </div>
183<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
184_8c.html" target="source" name="AutoLevelImage">AutoLevelImage</a></h2>
185<div class="doc-section">
186
187<p>AutoLevelImage() adjusts the levels of a particular image channel by scaling the minimum and maximum values to the full quantum range.</p></ol>
188
189<p>The format of the LevelImage method is:</p>
190
191<pre class="code">
192 MagickBooleanType AutoLevelImage(Image *image)
193 MagickBooleanType AutoLevelImageChannel(Image *image,
194 const ChannelType channel)
195</pre>
196
197<p>A description of each parameter follows:</p></ol>
198
199<h5>image</h5>
200<ol><p>The image to auto-level</p></ol>
201
202<h5>channel</h5>
203<ol><p>The channels to auto-level. If the special 'SyncChannels' flag is set the min/max/mean value of all given channels is used for all given channels, to all channels in the same way.</p></ol>
204
205 </div>
206<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
207_8c.html" target="source" name="ColorDecisionListImage">ColorDecisionListImage</a></h2>
208<div class="doc-section">
209
210<p>ColorDecisionListImage() accepts a lightweight Color Correction Collection (CCC) file which solely contains one or more color corrections and applies the correction to the image. Here is a sample CCC file:</p>
211
212<pre class="text">
213 <ColorCorrectionCollection xmlns="urn:ASC:CDL:v1.2">
214 <ColorCorrection id="cc03345">
215 <SOPNode>
216 <Slope> 0.9 1.2 0.5 </Slope>
217 <Offset> 0.4 -0.5 0.6 </Offset>
218 <Power> 1.0 0.8 1.5 </Power>
219 </SOPNode>
220 <SATNode>
221 <Saturation> 0.85 </Saturation>
222 </SATNode>
223 </ColorCorrection>
224 </ColorCorrectionCollection>
225</pre>
226
227<p>which includes the slop, offset, and power for each of the RGB channels as well as the saturation.</p></ol>
228
229<p>The format of the ColorDecisionListImage method is:</p>
230
231<pre class="code">
232 MagickBooleanType ColorDecisionListImage(Image *image,
233 const char *color_correction_collection)
234</pre>
235
236<p>A description of each parameter follows:</p></ol>
237
238<h5>image</h5>
239<ol><p>the image.</p></ol>
240
241<h5>color_correction_collection</h5>
242<ol><p>the color correction collection in XML.</p></ol>
243
244 </div>
245<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
246_8c.html" target="source" name="ClutImage">ClutImage</a></h2>
247<div class="doc-section">
248
249<p>ClutImage() replaces each color value in the given image, by using it as an index to lookup a replacement color value in a Color Look UP Table in the form of an image. The values are extracted along a diagonal of the CLUT image so either a horizontal or vertial gradient image can be used.</p></ol>
250
251<p>Typically this is used to either re-color a gray-scale image according to a color gradient in the CLUT image, or to perform a freeform histogram (level) adjustment according to the (typically gray-scale) gradient in the CLUT image.</p></ol>
252
253<p>When the 'channel' mask includes the matte/alpha transparency channel but one image has no such channel it is assumed that that image is a simple gray-scale image that will effect the alpha channel values, either for gray-scale coloring (with transparent or semi-transparent colors), or a histogram adjustment of existing alpha channel values. If both images have matte channels, direct and normal indexing is applied, which is rarely used.</p></ol>
254
255<p>The format of the ClutImage method is:</p>
256
257<pre class="code">
258 MagickBooleanType ClutImage(Image *image,Image *clut_image)
259 MagickBooleanType ClutImageChannel(Image *image,
260 const ChannelType channel,Image *clut_image)
261</pre>
262
263<p>A description of each parameter follows:</p></ol>
264
265<h5>image</h5>
266<ol><p>the image, which is replaced by indexed CLUT values</p></ol>
267
268<h5>clut_image</h5>
269<ol><p>the color lookup table image for replacement color values.</p></ol>
270
271<h5>channel</h5>
272<ol><p>the channel.</p></ol>
273
274 </div>
275<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
276_8c.html" target="source" name="ContrastImage">ContrastImage</a></h2>
277<div class="doc-section">
278
279<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>
280
281<p>The format of the ContrastImage method is:</p>
282
283<pre class="code">
284 MagickBooleanType ContrastImage(Image *image,
285 const MagickBooleanType sharpen)
286</pre>
287
288<p>A description of each parameter follows:</p></ol>
289
290<h5>image</h5>
291<ol><p>the image.</p></ol>
292
293<h5>sharpen</h5>
294<ol><p>Increase or decrease image contrast.</p></ol>
295
296 </div>
297<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
298_8c.html" target="source" name="The ContrastStretchImage">The ContrastStretchImage</a></h2>
299<div class="doc-section">
300
301<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>
302
303<p>The format of the ContrastStretchImage method is:</p>
304
305<pre class="code">
306 MagickBooleanType ContrastStretchImage(Image *image,
307 const char *levels)
308 MagickBooleanType ContrastStretchImageChannel(Image *image,
309 const unsigned long channel,const double black_point,
310 const double white_point)
311</pre>
312
313<p>A description of each parameter follows:</p></ol>
314
315<h5>image</h5>
316<ol><p>the image.</p></ol>
317
318<h5>channel</h5>
319<ol><p>the channel.</p></ol>
320
321<h5>black_point</h5>
322<ol><p>the black point.</p></ol>
323
324<h5>white_point</h5>
325<ol><p>the white point.</p></ol>
326
327<h5>levels</h5>
328<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>
329
330 </div>
331<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
332_8c.html" target="source" name="EnhanceImage">EnhanceImage</a></h2>
333<div class="doc-section">
334
335<p>EnhanceImage() applies a digital filter that improves the quality of a noisy image.</p></ol>
336
337<p>The format of the EnhanceImage method is:</p>
338
339<pre class="code">
340 Image *EnhanceImage(const Image *image,ExceptionInfo *exception)
341</pre>
342
343<p>A description of each parameter follows:</p></ol>
344
345<h5>image</h5>
346<ol><p>the image.</p></ol>
347
348<h5>exception</h5>
349<ol><p>return any errors or warnings in this structure.</p></ol>
350
351 </div>
352<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
353_8c.html" target="source" name="EqualizeImage">EqualizeImage</a></h2>
354<div class="doc-section">
355
356<p>EqualizeImage() applies a histogram equalization to the image.</p></ol>
357
358<p>The format of the EqualizeImage method is:</p>
359
360<pre class="code">
361 MagickBooleanType EqualizeImage(Image *image)
362 MagickBooleanType EqualizeImageChannel(Image *image,
363 const ChannelType channel)
364</pre>
365
366<p>A description of each parameter follows:</p></ol>
367
368<h5>image</h5>
369<ol><p>the image.</p></ol>
370
371<h5>channel</h5>
372<ol><p>the channel.</p></ol>
373
374 </div>
375<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
376_8c.html" target="source" name="GammaImage">GammaImage</a></h2>
377<div class="doc-section">
378
379<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>
380
381<p>You can also reduce the influence of a particular channel with a gamma value of 0.</p></ol>
382
383<p>The format of the GammaImage method is:</p>
384
385<pre class="code">
386 MagickBooleanType GammaImage(Image *image,const double gamma)
387 MagickBooleanType GammaImageChannel(Image *image,
388 const ChannelType channel,const double gamma)
389</pre>
390
391<p>A description of each parameter follows:</p></ol>
392
393<h5>image</h5>
394<ol><p>the image.</p></ol>
395
396<h5>channel</h5>
397<ol><p>the channel.</p></ol>
398
399<h5>gamma</h5>
400<ol><p>the image gamma.</p></ol>
401
402 </div>
403<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
404_8c.html" target="source" name="HaldClutImage">HaldClutImage</a></h2>
405<div class="doc-section">
406
407<p>HaldClutImage() applies a Hald color lookup table to the image. A Hald color lookup table is a 3-dimensional color cube mapped to 2 dimensions. Create it with the HALD coder. You can apply any color transformation to the Hald image and then use this method to apply the transform to the image.</p></ol>
408
409<p>The format of the HaldClutImage method is:</p>
410
411<pre class="code">
412 MagickBooleanType HaldClutImage(Image *image,Image *hald_image)
413 MagickBooleanType HaldClutImageChannel(Image *image,
414 const ChannelType channel,Image *hald_image)
415</pre>
416
417<p>A description of each parameter follows:</p></ol>
418
419<h5>image</h5>
420<ol><p>the image, which is replaced by indexed CLUT values</p></ol>
421
422<h5>hald_image</h5>
423<ol><p>the color lookup table image for replacement color values.</p></ol>
424
425<h5>channel</h5>
426<ol><p>the channel.</p></ol>
427
428 </div>
429<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
430_8c.html" target="source" name="LevelImage">LevelImage</a></h2>
431<div class="doc-section">
432
433<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>
434
435<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>
436
437<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>
438
439<p>Gamma specifies a gamma correction to apply to the image.</p></ol>
440
441<p>The format of the LevelImage method is:</p>
442
443<pre class="code">
444 MagickBooleanType LevelImage(Image *image,const char *levels)
445</pre>
446
447<p>A description of each parameter follows:</p></ol>
448
449<h5>image</h5>
450<ol><p>the image.</p></ol>
451
452<h5>levels</h5>
453<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>
454
455 </div>
456<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]457_8c.html" target="source" name="LevelizeImage">LevelizeImage</a></h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]458<div class="doc-section">
459
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]460<p>LevelizeImage() applies the normal level operation to the image, 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]461
462<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>
463
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]464<p>The format of the LevelizeImage method is:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]465
466<pre class="code">
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]467 MagickBooleanType LevelizeImage(Image *image,const double black_point,
468 const double white_point,const double gamma)
469 MagickBooleanType LevelizeImageChannel(Image *image,
470 const ChannelType channel,const double black_point,
471 const double white_point,const double gamma)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]472</pre>
473
474<p>A description of each parameter follows:</p></ol>
475
476<h5>image</h5>
477<ol><p>the image.</p></ol>
478
479<h5>channel</h5>
480<ol><p>the channel.</p></ol>
481
482<h5>black_point</h5>
483<ol><p>The level which is to be mapped to zero (black)</p></ol>
484
485<h5>white_point</h5>
486<ol><p>The level which is to be mapped to QuantiumRange (white)</p></ol>
487
488<h5>gamma</h5>
489<ol><p>adjust gamma by this factor before mapping values. use 1.0 for purely linear stretching of image color values</p></ol>
490
491 </div>
492<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
493_8c.html" target="source" name="LevelizeImageChannel">LevelizeImageChannel</a></h2>
494<div class="doc-section">
495
496<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>
497
498<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>
499
500<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>
501
502<p>The format of the LevelizeImageChannel method is:</p>
503
504<pre class="code">
505 MagickBooleanType LevelizeImageChannel(Image *image,
506 const ChannelType channel,const char *levels)
507</pre>
508
509<p>A description of each parameter follows:</p></ol>
510
511<h5>image</h5>
512<ol><p>the image.</p></ol>
513
514<h5>channel</h5>
515<ol><p>the channel.</p></ol>
516
517<h5>black_point</h5>
518<ol><p>The level to map zero (black) to.</p></ol>
519
520<h5>white_point</h5>
521<ol><p>The level to map QuantiumRange (white) to.</p></ol>
522
523<h5>gamma</h5>
524<ol><p>adjust gamma by this factor before mapping values.</p></ol>
525
526 </div>
527<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
528_8c.html" target="source" name="LevelImageColor">LevelImageColor</a></h2>
529<div class="doc-section">
530
cristye7f8fdd2009-09-20 14:43:12 +0000[diff] [blame]531<p>LevelImageColor() maps the given color to "black" and "white" values, linearly 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]532
533<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>
534
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]535<p>The format of the LevelColorsImageChannel method is:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]536
537<pre class="code">
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]538 MagickBooleanType LevelColorsImage(Image *image,
cristye7f8fdd2009-09-20 14:43:12 +0000[diff] [blame]539 const MagickPixelPacket *black_color,
540 const MagickPixelPacket *white_color,const MagickBooleanType invert)
cristy5cadd612009-09-21 19:33:41 +0000[diff] [blame]541 MagickBooleanType LevelColorsImageChannel(Image *image,
542 const ChannelType channel,const MagickPixelPacket *black_color,
543 const MagickPixelPacket *white_color,const MagickBooleanType invert)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]544</pre>
545
546<p>A description of each parameter follows:</p></ol>
547
548<h5>image</h5>
549<ol><p>the image.</p></ol>
550
551<h5>channel</h5>
552<ol><p>the channel.</p></ol>
553
554<h5>black_color</h5>
555<ol><p>The color to map black to/from</p></ol>
556
557<h5>white_point</h5>
558<ol><p>The color to map white to/from</p></ol>
559
560<h5>invert</h5>
561<ol><p>if true map the colors (levelize), rather than from (level)</p></ol>
562
563 </div>
564<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
565_8c.html" target="source" name="The LinearStretchImage">The LinearStretchImage</a></h2>
566<div class="doc-section">
567
568<p>The LinearStretchImage() discards any pixels below the black point and above the white point and levels the remaining pixels.</p></ol>
569
570<p>The format of the LinearStretchImage method is:</p>
571
572<pre class="code">
573 MagickBooleanType LinearStretchImage(Image *image,
574 const double black_point,const double white_point)
575</pre>
576
577<p>A description of each parameter follows:</p></ol>
578
579<h5>image</h5>
580<ol><p>the image.</p></ol>
581
582<h5>black_point</h5>
583<ol><p>the black point.</p></ol>
584
585<h5>white_point</h5>
586<ol><p>the white point.</p></ol>
587
588 </div>
589<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
590_8c.html" target="source" name="ModulateImage">ModulateImage</a></h2>
591<div class="doc-section">
592
593<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>
594
595<p>The format of the ModulateImage method is:</p>
596
597<pre class="code">
598 MagickBooleanType ModulateImage(Image *image,const char *modulate)
599</pre>
600
601<p>A description of each parameter follows:</p></ol>
602
603<h5>image</h5>
604<ol><p>the image.</p></ol>
605
606<h5>modulate</h5>
607<ol><p>Define the percent change in brightness, saturation, and hue.</p></ol>
608
609 </div>
610<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
611_8c.html" target="source" name="NegateImage">NegateImage</a></h2>
612<div class="doc-section">
613
614<p>NegateImage() negates the colors in the reference image. The grayscale option means that only grayscale values within the image are negated.</p></ol>
615
616<p>The format of the NegateImageChannel method is:</p>
617
618<pre class="code">
619 MagickBooleanType NegateImage(Image *image,
620 const MagickBooleanType grayscale)
621 MagickBooleanType NegateImageChannel(Image *image,
622 const ChannelType channel,const MagickBooleanType grayscale)
623</pre>
624
625<p>A description of each parameter follows:</p></ol>
626
627<h5>image</h5>
628<ol><p>the image.</p></ol>
629
630<h5>channel</h5>
631<ol><p>the channel.</p></ol>
632
633<h5>grayscale</h5>
634<ol><p>If MagickTrue, only negate grayscale pixels within the image.</p></ol>
635
636 </div>
637<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
638_8c.html" target="source" name="The NormalizeImage">The NormalizeImage</a></h2>
639<div class="doc-section">
640
641<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>
642
643<p>The format of the NormalizeImage method is:</p>
644
645<pre class="code">
646 MagickBooleanType NormalizeImage(Image *image)
647 MagickBooleanType NormalizeImageChannel(Image *image,
648 const ChannelType channel)
649</pre>
650
651<p>A description of each parameter follows:</p></ol>
652
653<h5>image</h5>
654<ol><p>the image.</p></ol>
655
656<h5>channel</h5>
657<ol><p>the channel.</p></ol>
658
659 </div>
660<h2><a href="http://www.imagemagick.org/api/MagickCore/enhance
661_8c.html" target="source" name="SigmoidalContrastImage">SigmoidalContrastImage</a></h2>
662<div class="doc-section">
663
664<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>
665
666<p>The format of the SigmoidalContrastImage method is:</p>
667
668<pre class="code">
669 MagickBooleanType SigmoidalContrastImage(Image *image,
670 const MagickBooleanType sharpen,const char *levels)
671 MagickBooleanType SigmoidalContrastImageChannel(Image *image,
672 const ChannelType channel,const MagickBooleanType sharpen,
673 const double contrast,const double midpoint)
674</pre>
675
676<p>A description of each parameter follows:</p></ol>
677
678<h5>image</h5>
679<ol><p>the image.</p></ol>
680
681<h5>channel</h5>
682<ol><p>the channel.</p></ol>
683
684<h5>sharpen</h5>
685<ol><p>Increase or decrease image contrast.</p></ol>
686
687<h5>contrast</h5>
688<ol><p>control the "shoulder" of the contast curve.</p></ol>
689
690<h5>midpoint</h5>
691<ol><p>control the "toe" of the contast curve.</p></ol>
692
693 </div>
cristyf3bb4782009-09-08 13:10:04 +0000[diff] [blame]694
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