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94
95<p class="lead magick-description">This page descibed the Image composition methods that is used to define how
96two images should be merged together in various image operations.  For the
97Command Line API it is typically set using the <a
98href="../www/command-line-options.html#compose" >-compose</a> setting option. </p>
99
100
101<p>The description of composition uses abstract terminology in order to allow
102the description to be more precise, while avoiding constant values which are
103specific to a particular build configuration. Each image pixel is represented
104by red, green, and blue levels (which are equal for a gray pixel). The
105build-dependent value <var>QuantumRange</var> is the maximum integral
106value which may be stored, per pixel, in the red, green, or blue channels of
107the image. Each image pixel may also optionally (if the image matte channel is
108enabled) have an associated level of opacity, ranging from <var>opaque</var> to
109<var>transparent</var>, which may be used to determine the influence of the pixel
110color when compositing the pixel with another image pixel. If the image matte
111channel is disabled, then all pixels in the image are treated as opaque. The
112color of an opaque pixel is fully visible while the color of a transparent
113pixel color is entirely absent (pixel color is ignored).</p>
114
115<p>By definition, raster images have a rectangular shape. All image rows are of
116equal length, as are all image columns. By treating the alpha channel as a
117visual "mask" the rectangular image may be given a "shape" by treating the
118alpha channel as a cookie-cutter for the image. This is done by setting the
119pixels within the shape to be opaque, with pixels outside the shape set as
120transparent. Pixels on the boundary of the shape may be between opaque and
121transparent in order to provide antialiasing (visually smooth edges). The
122description of the composition operators use this concept of image "shape" in
123order to make the description of the operators easier to understand. While it
124is convenient to describe the operators in terms of "shapes" they are by no
125means limited to mask-style operations since they are based on continuous
126floating-point mathematics rather than simple boolean operations.</p>
127
128<p>The following alpha blending (Duff-Porter) compose methods are available:</p>
129
130<table class="table table-sm table-hover">
131  <tbody>
132  <tr>
133    <th align="left" style="width: 8%">Method</th>
134    <th align="left">Description</th>
135  </tr>
136
137  <tr>
138    <td>clear</td>
139    <td>Both the color and the alpha of the destination are
140        cleared. Neither the source nor the destination are used (except for
141        destinations size and other meta-data which is always preserved.</td>
142  </tr>
143
144  <tr>
145    <td>src</td>
146    <td>The source is copied to the destination. The destination
147        is not used as input, though it is cleared.</td>
148  </tr>
149
150  <tr>
151    <td>dst</td>
152    <td>The destination is left untouched. The source image is
153        completely ignored.</td>
154  </tr>
155
156  <tr>
157    <td>src-over</td>
158    <td>The source is composited over the destination. this is
159       the default alpha blending compose method, when neither the compose
160       setting is set, nor is set in the image meta-data.</td>
161  </tr>
162
163  <tr>
164    <td>dst-over</td>
165    <td>The destination is composited over the source and the
166        result replaces the destination.</td>
167  </tr>
168
169  <tr>
170    <td>src-in</td>
171    <td>The part of the source lying inside of the destination
172        replaces the destination.</td>
173  </tr>
174
175  <tr>
176    <td>dst-in</td>
177    <td>The part of the destination lying inside of the source
178        replaces the destination. Areas not overlaid are cleared.</td>
179  </tr>
180
181  <tr>
182    <td>src-out</td>
183    <td>The part of the source lying outside of the destination
184        replaces the destination.</td>
185  </tr>
186
187  <tr>
188    <td>dst-out</td>
189    <td>The part of the destination lying outside of the source
190        replaces the destination.</td>
191  </tr>
192
193  <tr>
194    <td>src-atop</td>
195    <td>The part of the source lying inside of the destination is
196        composited onto the destination.</td>
197  </tr>
198
199  <tr>
200    <td>dst-atop</td>
201    <td>The part of the destination lying inside of the source is
202        composited over the source and replaces the destination. Areas not
203        overlaid are cleared. </td>
204  </tr>
205
206  <tr>
207    <td>xor</td>
208    <td>The part of the source that lies outside of the
209        destination is combined with the part of the destination that lies
210        outside of the source.  Source or Destination, but not both. </td>
211  </tr>
212
213  </tbody>
214</table>
215
216<p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
217For example the default compose method can be specified as just 'Over'.</p>
218
219<p>Many of these compose methods will clear the destination image which was
220not overlaid by the source image.  This is to be expected as part of that
221specific composition methods defintion. You can disable this by setting the
222special <a href="../www/command-line-options.html#define"
223>-define</a> 'compose:outside-overlay' to a value of 'false' will turn off
224this behavior. </p>
225
226<p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
227related method '<code>Copy</code>' has been provided. This is equivalent to
228using the '<code>Src</code>'  with the special <a href="../www/command-line-options.html#define"
229>-define</a> option '<code>compose:outside-overlay</code>' set to
230'<code>false</code>', so as to only modify the overlaid area, without clearing
231the rest of the image outside the overlaid area.  </p>
232
233<p>The following mathematical composition methods are also available. </p>
234
235<table class="table table-sm table-hover">
236  <tbody>
237  <tr>
238    <th align="left" style="width: 8%">Method</th>
239    <th align="left">Description</th>
240  </tr>
241
242  <tr>
243    <td>multiply</td>
244    <td>The source is multiplied by the destination and replaces
245        the destination. The resultant color is always at least as dark as
246        either of the two constituent colors. Multiplying any color with black
247        produces black. Multiplying any color with white leaves the original
248        color unchanged.</td>
249  </tr>
250
251  <tr>
252    <td>screen</td>
253    <td>The source and destination are complemented and then
254        multiplied and then replace the destination. The resultant color is
255        always at least as light as either of the two constituent colors.
256        Screening any color with white produces white. Screening any color
257        with black leaves the original color unchanged.</td>
258  </tr>
259
260  <tr>
261    <td>plus</td>
262    <td>The source is added to the destination and replaces the
263        destination. This operator is useful for averaging or a controlled
264        merger of two images, rather than a direct overlay.</td>
265  </tr>
266
267  <tr>
268    <td>add</td>
269    <td>As per 'plus' but transparency data is treated as matte
270        values. As such any transparent areas in either image remain
271        transparent. </td>
272  </tr>
273
274  <tr>
275    <td>minus</td>
276    <td>Subtract the colors in the source image from the
277        destination image. When transparency is involved, opaque areas is
278        subtracted from any destination opaque areas. </td>
279  </tr>
280
281  <tr>
282    <td>subtract</td>
283    <td>Subtract the colors in the source image from the
284        destination image. When transparency is involved transparent areas are
285        subtracted, so only the opaque areas in the source remain opaque in
286        the destination image. </td>
287  </tr>
288
289  <tr>
290    <td>difference</td>
291    <td>Subtracts the darker of the two constituent colors from
292        the lighter. Painting with white inverts the destination color.
293        Painting with black produces no change.</td>
294  </tr>
295
296  <tr>
297    <td>exclusion</td>
298    <td>Produces an effect similar to that of 'difference', but
299        appears as lower contrast.  Painting with white inverts the
300        destination color. Painting with black produces no change.</td>
301  </tr>
302
303  <tr>
304    <td>darken</td>
305    <td>Selects the darker of the destination and source colors.
306        The destination is replaced with the source when the source is darker,
307        otherwise it is left unchanged.</td>
308  </tr>
309
310  <tr>
311    <td>lighten</td>
312    <td>Selects the lighter of the destination and source colors.
313        The destination is replaced with the source when the source is
314        lighter, otherwise it is left unchanged. </td>
315  </tr>
316
317  <tr>
318    <td>negate</td>
319    <td>The "opposite" of difference mode. Note that it is not difference mode inverted, because black and white return the same result, but colors between become brighter instead of darker. </td>
320  </tr>
321
322  <tr>
323    <td>reflect</td>
324    <td>This mode is useful when adding shining objects or light zones to images. The formula is similar to color dodge, but the result is not that bright in most cases. The result looks a bit like soft light. </td>
325  </tr>
326
327  <tr>
328    <td>freeze</td>
329    <td>Another variation of reflect mode (base and blend color inverted, the result inverted again). </td>
330  </tr>
331
332  <tr>
333    <td>stamp</td>
334    <td>This mode somehow is similar to average mode. It is helpful when applying relief or bump textures to images. </td>
335  </tr>
336
337  <tr>
338    <td>interpolate</td>
339    <td>This mode somehow combines multiply and screen mode (looks very similar for very dark or bright colors). </td>
340  </tr>
341</table>
342
343<p>Typically these use the default 'Over' alpha blending when transparencies
344are also involved, except for 'Plus' which uses a 'plus' alpha blending.  This
345means the alpha channel  of both images will only be used to ensure that any
346visible input remains visible even in parts not overlaid. It also means that
347any values are weighted by the alpha channel of the input and output images.
348This 'Over' alpha blending is also applied to the lighting composition methods
349below. </p>
350
351<p> The math composition is applied on an individual channel basis as defined by the <a href="../www/command-line-options.html#channel" >-channel</a>.  This includes the alpha channel. This special usage allows you to perform true mathematics of the image channels, without alpha
352composition effects, becoming involved. </p>
353
354<p>The following lighting composition methods are also available. </p>
355
356<table class="table table-sm table-hover">
357  <tbody>
358  <tr>
359    <th align="left" style="width: 8%">Method</th>
360    <th align="left">Description</th>
361  </tr>
362
363  <tr>
364    <td>linear-dodge</td>
365    <td>This is equivalent to 'Plus' in that the color channels
366        are simply added, however it does not 'Plus' the alpha channel, but
367        uses the normal 'Over' alpha blending, which transparencies are
368        involved.  Produces a sort of additive multiply-like result.  </td>
369  </tr>
370
371  <tr>
372    <td>linear-burn</td>
373    <td>As 'Linear-Dodge', but also subtract one from the result.
374        Sort of a additive 'Screen' of the images. </td>
375  </tr>
376
377  <tr>
378    <td>color-dodge</td>
379    <td>Brightens the destination color to reflect the source
380        color. Painting with black produces no change.</td>
381  </tr>
382
383  <tr>
384    <td>color-burn</td>
385    <td>Darkens the destination color to reflect the source
386        color.  Painting with white produces no change.  </td>
387  </tr>
388
389  <tr>
390    <td>overlay</td>
391    <td>Multiplies or screens the colors, dependent on the
392        destination color. Source colors overlay the destination whilst
393        preserving its highlights and shadows. The destination color is not
394        replaced, but is mixed with the source color to reflect the lightness
395        or darkness of the destination.</td>
396  </tr>
397
398  <tr>
399    <td>hard-light</td>
400    <td>Multiplies or screens the colors, dependent on the source
401        color value. If the source color is lighter than 0.5, the destination
402        is lightened as if it were screened. If the source color is darker
403        than 0.5, the destination is darkened, as if it were multiplied. The
404        degree of lightening or darkening is proportional to the difference
405        between the source color and 0.5. If it is equal to 0.5 the
406        destination is unchanged.  Painting with pure black or white produces
407        black or white.</td>
408  </tr>
409
410
411  <tr>
412    <td>linear-light</td>
413    <td>Like 'Hard-Light' but using linear-dodge and linear-burn
414        instead.  Increases contrast slightly with an impact on the
415        foreground's tonal values.</td>
416  </tr>
417
418  <tr>
419    <td>soft-burn</td>
420    <td>A combination of color burn and inverse color dodge mode, but a lot smoother than both of them. The base image is lightened a bit, but very dark blend colors are "burned" in. </td>
421  </tr>
422
423  <tr>
424    <td>soft-dodge</td>
425    <td> Combination of color dodge and inverse color burn mode, but a lot smoother than both of them. The base image is darkened a bit, but very bright blend colors are "dodged" in. </td>
426  </tr>
427
428  <tr>
429    <td>soft-light</td>
430    <td>Darkens or lightens the colors, dependent on the source
431        color value. If the source color is lighter than 0.5, the destination
432        is lightened. If the source color is darker than 0.5, the destination
433        is darkened, as if it were burned in. The degree of darkening or
434        lightening is proportional to the difference between the source color
435        and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
436        with pure black or white produces a distinctly darker or lighter area,
437        but does not result in pure black or white. </td>
438  </tr>
439
440  <tr>
441    <td>pegtop-light</td>
442    <td>Almost equivalent to 'Soft-Light', but using a
443        continuous mathematical formula rather than two conditionally
444        selected formulae. </td>
445  </tr>
446
447  <tr>
448    <td>vivid-light</td>
449    <td>A modified 'Linear-Light' designed to preserve very stong
450        primary and secondary colors in the image.  </td>
451  </tr>
452
453  <tr>
454    <td>pin-light</td>
455    <td>Similar to 'Hard-Light', but using sharp linear shadings,
456        to simulate the effects of a strong 'pinhole' light source. </td>
457  </tr>
458
459  </tbody>
460</table>
461
462<p>Also included are these special purpose compose methods:</p>
463
464<table class="table table-sm table-hover">
465  <tbody>
466  <tr>
467    <th align="left" style="width: 8%">Method</th>
468    <th align="left">Description</th>
469  </tr>
470
471  <tr>
472    <td>copy</td>
473    <td>This is equivalent to the Duff-Porter composition method
474        '<code>Src,</code>' but without clearing the parts of the destination
475        image that is not overlaid.  </td>
476    </tr>
477
478  <tr>
479    <td>copy-*</td>
480    <td>Copy the specified channel (Red, Green, Blue, Cyan,
481        Magenta, Yellow, Black, or Opacity) in the source image to the
482        same channel in the destination image.  If the channel specified
483        does not exist in the source image, (which can only happen for methods,
484        '<code>copy-opacity</code>' or '<code>copy-black</code>') then it is
485        assumed that the source image is a special grayscale channel image
486        of the values that is to be copied. </td>
487    </tr>
488
489  <tr>
490    <td>change-mask</td>
491    <td>Replace any destination pixel that is the similar to the
492    source images pixel (as defined by the current <a
493    href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
494    </td>
495  </tr>
496
497  <tr>
498    <td>stereo</td>
499    <td>create a stereo anaglyph</td>
500  </tr>
501  </tbody>
502</table>
503
504<p>On top of these composed methods are a few special ones that not only require
505the two images that are being merged or overlaid, but have some extra numerical
506arguments, which are tabled below. </p>
507
508<p>In the "<code>composite</code>" command these composition methods are
509selected using special options with the arguments needed. They are usually,
510but not always, the same name as the composite 'method' they use, and replaces
511the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
512setting in the "<code>composite</code>" command.  For example... </p>
513
514<pre class="highlight"><code>composite ... -blend 50x50 ...
515</code></pre>
516
517<p>The "<code>magick</code>" command can accept these extra arguments to its <a href="../www/command-line-options.html#composite"
518>-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
519attribute of '<code class="arg">compose:args</code>'.  This means you can now
520make use of these special augmented <a href="../www/command-line-options.html#compose"
521>-compose</a> methods, those the argument and the method both need to be set
522separately.  For example... </p>
523
524<pre class="highlight"><code>magick ... -compose blend  -define compose:args=50,50 -composite ...
525</code></pre>
526
527<p>The following is a table of these special 'argumented' compose methods,
528with a brief summary of what they do. For more details see the equivalent
529"composite" command option name.  </p>
530
531<table class="table table-sm table-hover">
532  <tbody>
533  <tr>
534    <th align="left" style="width: 8%">Method</th>
535    <th align="left">Description</th>
536  </tr>
537
538  <tr>
539    <td>dissolve</td>
540    <td>Arguments:
541        <var>src_percent</var>[x<var>dst_percent</var>]
542    <br/>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
543    <br/>Dissolve the 'source' image by the percentage given before overlaying
544        'over' the 'destination' image. If <var>src_percent</var> is
545        greater than 100, it starts dissolving the main image so it will
546        become transparent at a value of '<code class="arg">200</code>'.  If
547        both percentages are given, each image are dissolved to the
548        percentages given.
549    </td>
550  </tr>
551
552  <tr>
553    <td>blend</td>
554    <td>Arguments:
555        <var>src_percent</var>[x<var>dst_percent</var>]
556    <br/>Equivalent to "<code>composite</code>" <a
557        href="../www/command-line-options.html#blend">-blend</a>
558    <br/>Average the images together ('plus') according to the percentages
559        given and each pixels transparency.  If only a single percentage value
560        is given it sets the weight of the composite or 'source' image, while
561        the background image is weighted by the exact opposite amount. That is
562        a <code>-blend 30</code> merges 30% of the 'source' image with 70% of
563        the 'destination' image.  Thus it is equivalent to <code>-blend
564        30x70</code>.
565    </td>
566  </tr>
567
568  <tr>
569    <td>mathematics</td>
570    <td>Arguments: <var>A, B, C, D</var>
571    <br/>Not available in "<code>composite</code>" at this time.
572    <br/>Merge the source and destination images according to the formula
573    <br/>     <code>A*Sc*Dc + B*Sc + C*Dc + D</code>
574    <br/>Can be used to generate a custom composition method that would
575        otherwise need to be implemented using the slow <a
576        href="../www/command-line-options.html#fx">-fx</a> DIY image operator.
577    </td>
578  </tr>
579
580  <tr>
581    <td>modulate</td>
582    <td>Arguments:
583        <var>brightness</var>[x<var>saturation</var>]
584    <br/>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
585    <br/>Take a grayscale image (with alpha mask) and modify the destination
586        image's brightness according to watermark image's grayscale value and
587        the <var>brightness</var> percentage.  The destinations
588        color saturation attribute is just direct modified by the <var>saturation</var> percentage, which defaults to 100 percent
589        (no color change).
590
591    </td>
592  </tr>
593
594  <tr>
595    <td>displace</td>
596    <td>Arguments:
597        <var>X-scale</var>[x<var>Y-scale</var>][!][%]
598    <br/>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
599    <br/>With this option, the 'overlay' image, and optionally the 'mask'
600        image, is used as a relative displacement map, which is used to
601        displace the lookup of what part of the destination image is seen at
602        each point of the overlaid area.  Much like the displacement map is a
603        'lens' that distorts the original 'background' image behind it.
604    <br/><br/>
605        The X-scale is modulated by the 'red' channel of the overlay image
606        while the Y-scale is modulated by the green channel, (the mask image
607        if given is rolled into green channel of the overlay image. This
608        separation allows you to modulate the X and Y lookup displacement
609        separately allowing you to do 2-dimensional displacements, rather
610        than 1-dimensional vectored displacements (using grayscale image).
611    <br/><br/>
612        If the overlay image contains transparency this is used as a mask
613        of the resulting image to remove 'invalid' pixels.
614    <br/><br/>
615        The '%' flag makes the displacement scale relative to the size of the
616        overlay image (100% = half width/height of image). Using '!' switches
617        percentage arguments to refer to the destination image size instead.
618    <br/><br/>
619    </td>
620  </tr>
621
622  <tr>
623    <td>distort</td>
624    <td>Arguments:
625        <var>X-scale</var>[x<var>Y-scale</var>[+<var>X-center</var>+<var>Y-center</var>]][!][%]
626    <br/>Not available in "<code>composite</code>" at this time.
627    <br/>Exactly as per 'Displace' (above), but using absolute coordinates,
628        relative to the center of the overlay (or that given).  Basically
629        allows you to generate absolute distortion maps where 'black' will
630        look up the left/top edge, and 'white' looks up the bottom/right
631        edge of the destination image, according to the scale given.
632    <br/><br/>
633        The '!' flag not only switches percentage scaling, to use the
634        destination image, but also the image the center offset of the lookup.
635        This means the overlay can lookup a completely different region of the
636        destination image.
637    <br/><br/>
638    </td>
639  </tr>
640
641  <tr>
642    <td>blur</td>
643    <td>Arguments:
644        <var>Width</var>[x<var>Height</var>[+<var>Angle</var>][+<var>Angle2</var>]]
645    <br/>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
646    <br/>A Variable Blur Mapping Composition method, where each pixel in the
647        overlaid region is replaced with an Elliptical Weighted Average (EWA),
648        with an ellipse (typically a circle) of the given sigma size, scaled
649        according to overlay (source image) grayscale mapping.
650    <br/><br/>
651        As per 'Displace' and 'Distort', the red channel will modulate the
652        width of the ellipse, while the green channel will modulate the height
653        of the ellipse. If a single Angle value is given in the arguments,
654        then the ellipse will then be rotated by the angle specified.
655    <br/><br/>
656        Normally the blue channel of the mapping overlay image is ignored.
657        However if a second ellipse angle is given, then it is assumed that
658        the blue channel defines a variable angle for the ellipse ranging from
659        the first angle to the second angle given.  This allows to generate
660        radial blurs, or a rough approximation for rotational blur. Or any mix
661        of the two.
662    <br/><br/>
663    </td>
664  </tr>
665
666  </tbody>
667</table>
668
669<p>To print a complete list of all the available compose operators, use <a
670href="../www/command-line-options.html#list">-list compose</a>.</p>
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