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172 <p>This page descibed the Image composition methods that is used to define how
173 two images should be merged together in various image operations. For the
174 Command Line API it is typically set using the <A
175 HREF="../www/command-line-options.html#compose" >-compose</A> setting option. </p>
178 <p>The description of composition uses abstract terminology in order to allow
179 the description to be more precise, while avoiding constant values which are
180 specific to a particular build configuration. Each image pixel is represented
181 by red, green, and blue levels (which are equal for a gray pixel). The
182 build-dependent value <em class="QR">QuantumRange</em> is the maximum integral
183 value which may be stored, per pixel, in the red, green, or blue channels of
184 the image. Each image pixel may also optionally (if the image matte channel is
185 enabled) have an associated level of opacity, ranging from <em>opaque</em> to
186 <em>transparent</em>, which may be used to determine the influence of the pixel
187 color when compositing the pixel with another image pixel. If the image matte
188 channel is disabled, then all pixels in the image are treated as opaque. The
189 color of an opaque pixel is fully visible while the color of a transparent
190 pixel color is entirely absent (pixel color is ignored).</p>
192 <p>By definition, raster images have a rectangular shape. All image rows are of
193 equal length, as are all image columns. By treating the alpha channel as a
194 visual "mask" the rectangular image may be given a "shape" by treating the
195 alpha channel as a cookie-cutter for the image. This is done by setting the
196 pixels within the shape to be opaque, with pixels outside the shape set as
197 transparent. Pixels on the boundary of the shape may be between opaque and
198 transparent in order to provide antialiasing (visually smooth edges). The
199 description of the composition operators use this concept of image "shape" in
200 order to make the description of the operators easier to understand. While it
201 is convenient to describe the operators in terms of "shapes" they are by no
202 means limited to mask-style operations since they are based on continuous
203 floating-point mathematics rather than simple boolean operations.</p>
205 <p>The following alpha blending (Duff-Porter) compose methods are available:</p>
210 <th align="left" style="width: 8%">Method</th>
211 <th align="left">Description</th>
215 <td valign="top">clear</td>
216 <td valign="top">Both the color and the alpha of the destination are
217 cleared. Neither the source nor the destination are used (except for
218 destinations size and other meta-data which is always preserved.</td>
222 <td valign="top">src</td>
223 <td valign="top">The source is copied to the destination. The destination
224 is not used as input, though it is cleared.</td>
228 <td valign="top">dst</td>
229 <td valign="top">The destination is left untouched. The source image is
230 completely ignored.</td>
234 <td valign="top">src-over</td>
235 <td valign="top">The source is composited over the destination. this is
236 the default alpha blending compose method, when neither the compose
237 setting is set, nor is set in the image meta-data.</td>
241 <td valign="top">dst-over</td>
242 <td valign="top">The destination is composited over the source and the
243 result replaces the destination.</td>
247 <td valign="top">src-in</td>
248 <td valign="top">The part of the source lying inside of the destination
249 replaces the destination.</td>
253 <td valign="top">dst-in</td>
254 <td valign="top">The part of the destination lying inside of the source
255 replaces the destination. Areas not overlaid are cleared.</td>
259 <td valign="top">src-out</td>
260 <td valign="top">The part of the source lying outside of the destination
261 replaces the destination.</td>
265 <td valign="top">dst-out</td>
266 <td valign="top">The part of the destination lying outside of the source
267 replaces the destination.</td>
271 <td valign="top">src-atop</td>
272 <td valign="top">The part of the source lying inside of the destination is
273 composited onto the destination.</td>
277 <td valign="top">dst-atop</td>
278 <td valign="top">The part of the destination lying inside of the source is
279 composited over the source and replaces the destination. Areas not
280 overlaid are cleared. </td>
284 <td valign="top">xor</td>
285 <td valign="top">The part of the source that lies outside of the
286 destination is combined with the part of the destination that lies
287 outside of the source. Source or Destination, but not both. </td>
293 <p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
294 For example the default compose method can be specified as just 'Over'.</p>
296 <p>Many of these compose methods will clear the destination image which was
297 not overlaid by the source image. This is to be expected as part of that
298 specific composition methods defintion. You can disable this by setting the
299 special <A HREF="../www/command-line-options.html#define"
300 >-define</A> 'compose:outside-overlay' to a value of 'false' will turn off
303 <p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
304 related method '<kbd>Copy</kbd>' has been provided. This is equivelent to
305 using the '<kbd>Src</kbd>' with the special <A HREF="../www/command-line-options.html#define"
306 >-define</A> option '<kbd>compose:outside-overlay</kbd>' set to
307 '<kbd>false</kbd>', so as to only modify the overlaid area, without clearing
308 the rest of the image outside the overlaid area. </p>
312 <p>The following mathemathical composition methods are also available. </p>
317 <th align="left" style="width: 8%">Method</th>
318 <th align="left">Description</th>
322 <td valign="top">multiply</td>
323 <td valign="top">The source is multiplied by the destination and replaces
324 the destination. The resultant color is always at least as dark as
325 either of the two constituent colors. Multiplying any color with black
326 produces black. Multiplying any color with white leaves the original
327 color unchanged.</td>
331 <td valign="top">screen</td>
332 <td valign="top">The source and destination are complemented and then
333 multiplied and then replace the destination. The resultant color is
334 always at least as light as either of the two constituent colors.
335 Screening any color with white produces white. Screening any color
336 with black leaves the original color unchanged.</td>
340 <td valign="top">plus</td>
341 <td valign="top">The source is added to the destination and replaces the
342 destination. This operator is useful for averaging or a controled
343 merger of two images, rather than a direct overlay.</td>
347 <td valign="top">add</td>
348 <td valign="top">As per 'plus' but transparency data is treated as matte
349 values. As such any transparent areas in either image remain
354 <td valign="top">minus</td>
355 <td valign="top">Subtract the colors in the source image from the
356 destination image. When transparency is involved, opaque areas is
357 subtracted from any destination opaque areas. </td>
361 <td valign="top">subtract</td>
362 <td valign="top">Subtract the colors in the source image from the
363 destination image. When transparency is involved transparent areas are
364 subtracted, so only the opaque areas in the source remain opaque in
365 the destination image. </td>
369 <td valign="top">difference</td>
370 <td valign="top">Subtracts the darker of the two constituent colors from
371 the lighter. Painting with white inverts the destination color.
372 Painting with black produces no change.</td>
376 <td valign="top">exclusion</td>
377 <td valign="top">Produces an effect similar to that of 'difference', but
378 appears as lower contrast. Painting with white inverts the
379 destination color. Painting with black produces no change.</td>
383 <td valign="top">darken</td>
384 <td valign="top">Selects the darker of the destination and source colors.
385 The destination is replaced with the source when the source is darker,
386 otherwise it is left unchanged.</td>
390 <td valign="top">lighten</td>
391 <td valign="top">Selects the lighter of the destination and source colors.
392 The destination is replaced with the source when the source is
393 lighter, otherwise it is left unchanged. </td>
399 <p>Typically these use the default 'Over' alpha blending when transparencies
400 are also involved, except for 'Plus' which uses a 'plus' alpha blending. This
401 means the alpha channel of both images will only be used to ensure that any
402 visible input remains visible even in parts not overlaid. It also means that
403 any values are weighted by the alpha channel of the input and output images.
404 This 'Over' alpha blending is also applied to the lighting composition methods
407 <p>As of IM v6.6.1-6, if the special '<kbd>Sync</kbd>' flag is not specified
408 (enabled by default) with the <a href="../www/command-line-options.html#channel"
409 >-channel</a> setting, then the above mathematical compositions will nolonger
410 syncronise its actions with the alpha channel. Instead the math composition
411 will be applied on an individual channel basis as defined by the <a
412 href="../www/command-line-options.html#channel"
413 >-channel</a>. This includes the alpha channel. This special usage
414 allows you to perform true mathematics of the image channels, without alpha
415 compostion effects, becomming involved. </p>
417 <p>This special flag is not applied to the lighting composition methods (see
418 below) even though they are closely related to mathematical composition
423 <p>The following lighting composition methods are also available. </p>
428 <th align="left" style="width: 8%">Method</th>
429 <th align="left">Description</th>
433 <td valign="top">linear-dodge</td>
434 <td valign="top">This is equivelent to 'Plus' in that the color channels
435 are simply added, however it does not 'Plus' the alpha channel, but
436 uses the normal 'Over' alpha blending, which transparencies are
437 involved. Produces a sort of additive multiply-like result. Added
438 ImageMagick version 6.5.4-3. </td>
442 <td valign="top">linear-burn</td>
443 <td valign="top">As 'Linear-Dodge', but also subtract one from the result.
444 Sort of a additive 'Screen' of the images. Added ImageMagick version
449 <td valign="top">color-dodge</td>
450 <td valign="top">Brightens the destination color to reflect the source
451 color. Painting with black produces no change.</td>
455 <td valign="top">color-burn</td>
456 <td valign="top">Darkens the destination color to reflect the source
457 color. Painting with white produces no change. Fixed in ImageMagick
458 version 6.5.4-3. </td>
462 <td valign="top">overlay</td>
463 <td valign="top">Multiplies or screens the colors, dependent on the
464 destination color. Source colors overlay the destination whilst
465 preserving its highlights and shadows. The destination color is not
466 replaced, but is mixed with the source color to reflect the lightness
467 or darkness of the destination.</td>
471 <td valign="top">hard-light</td>
472 <td valign="top">Multiplies or screens the colors, dependent on the source
473 color value. If the source color is lighter than 0.5, the destination
474 is lightened as if it were screened. If the source color is darker
475 than 0.5, the destination is darkened, as if it were multiplied. The
476 degree of lightening or darkening is proportional to the difference
477 between the source color and 0.5. If it is equal to 0.5 the
478 destination is unchanged. Painting with pure black or white produces
484 <td valign="top">linear-light</td>
485 <td valign="top">Like 'Hard-Light' but using linear-dodge and linear-burn
486 instead. Increases contrast slightly with an impact on the
487 foreground's tonal values.</td>
491 <td valign="top">soft-light</td>
492 <td valign="top">Darkens or lightens the colors, dependent on the source
493 color value. If the source color is lighter than 0.5, the destination
494 is lightened. If the source color is darker than 0.5, the destination
495 is darkened, as if it were burned in. The degree of darkening or
496 lightening is proportional to the difference between the source color
497 and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
498 with pure black or white produces a distinctly darker or lighter area,
499 but does not result in pure black or white. Fixed in ImageMagick
500 version 6.5.4-3. </td>
504 <td valign="top">pegtop-light</td>
505 <td valign="top">Almost equivelent to 'Soft-Light', but using a
506 continuious mathematical formula rather than two conditionally
507 selected formulae. Added ImageMagick version 6.5.4-3. </td>
511 <td valign="top">vivid-light</td>
512 <td valign="top">A modified 'Linear-Light' designed to preserve very stong
513 primary and secondary colors in the image. Added ImageMagick version
518 <td valign="top">pin-light</td>
519 <td valign="top">Similar to 'Hard-Light', but using sharp linear shadings,
520 to similate the effects of a strong 'pinhole' light source. Added
521 ImageMagick version 6.5.4-3. </td>
530 <p>Also included are these special purpose compose methods:</p>
535 <th align="left" style="width: 8%">Method</th>
536 <th align="left">Description</th>
540 <td valign="top">copy</td>
541 <td valign="top">This is equivelent to the Duff-Porter composition method
542 '<kbd>Src,</kbd>' but without clearing the parts of the destination
543 image that is not overlaid. </td>
547 <td valign="top">copy-*</td>
548 <td valign="top">Copy the specified channel (Red, Green, Blue, Cyan,
549 Magenta, Yellow, Black, or Opacity) in the source image to the
550 same channel in the destination image. If the channel specified
551 does not exist in the source image, (which can only happen for methods,
552 '<kbd>copy-opacity</kbd>' or '<kbd>copy-black</kbd>') then it is
553 assumed that the source image is a special grayscale channel image
554 of the values that is to be copied. </td>
558 <td valign="top">change-mask</td>
559 <td valign="top">Replace any destination pixel that is the similar to the
560 source images pixel (as defined by the current <a
561 href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
569 <p>On top of these composed methods are a few special ones that not only require
570 the two images that are being merged or overlaid, but have some extra numerical
571 arguments, which are tabled below. </p>
573 <p>In the "<code>composite</code>" command these composition methods are
574 selected using special options with the arguments needed. They are usually,
575 but not always, the same name as the composte 'method' they use, and replaces
576 the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
577 setting in the "<code>composite</code>" command. For example... </p>
579 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>composite ... -blend 50x50 ...</span></p>
580 <p>As of IM v6.5.3-4 the "<code>convert</code>" command can now also supply
581 these extra arguments to its <a href="../www/command-line-options.html#composite"
582 >-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
583 attribute of '<kbd class="arg">compose:args</kbd>'. This means you can now
584 make use of these special argumented <a href="../www/command-line-options.html#compose"
585 >-compose</a> methods, those the argument and the method both need to be set
586 separatally. For example... </p>
588 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert ... -compose blend -define compose:args=50,50 -composite ...</span></p>
589 <p>The following is a table of these special 'argumented' compose methods,
590 with a brief summary of what they do. For more details see the equivalent
591 "composite" command option name. </p>
596 <th align="left" style="width: 8%">Method</th>
597 <th align="left">Description</th>
601 <td valign="top">dissolve</td>
602 <td valign="top">Arguments:
603 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
604 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
605 <br>Dissolve the 'source' image by the percentage given before overlaying
606 'over' the 'destination' image. If <em class="arg">src_percent</em> is
607 greater than 100, it starts dissolving the main image so it will
608 become transparent at a value of '<kbd class="arg">200</kbd>'. If
609 both percentages are given, each image are dissolved to the
615 <td valign="top">blend</td>
616 <td valign="top">Arguments:
617 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
618 <br>Equivalent to "<code>composite</code>" <a
619 href="../www/command-line-options.html#blend">-blend</a>
620 <br>Average the images together ('plus') according to the percentages
621 given and each pixels transparency. If only a single percentage value
622 is given it sets the weight of the composite or 'source' image, while
623 the background image is weighted by the exact opposite amount. That is
624 a <kbd>-blend 30</kbd> merges 30% of the 'source' image with 70% of
625 the 'destination' image. Thus it is equivalent to <kbd>-blend
631 <td valign="top">mathematics</td>
632 <td valign="top">Arguments: <em class="arg">A, B, C, D</em>
633 <br>Not available in "<code>composite</code>" at this time.
634 <br>Merge the source and destination images according to the formula
635 <br> <code>A*Sc*Dc + B*Sc + C*Dc + D</code>
636 <br>Can be used to generate a custom composition method that would
637 otherwise need to be implemented using the slow <a
638 href="../www/command-line-options.html#fx">-fx</a> DIY image operator. Added
639 to ImageMagick version 6.5.4-3.
640 <br>As of IM v6.6.1-6 this method will do per-channel math compositions
641 if the 'Sync' flag is removed from <a
642 href="../www/command-line-options.html#channel" >-channel</a>, just like all
643 the other mathematical compostion methods above.
648 <td valign="top">modulate</td>
649 <td valign="top">Arguments:
650 <em class="arg">brightness</em>[x<em class="arg">saturation</em>]
651 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
652 <br>Take a grayscale image (with alpha mask) and modify the destination
653 image's brightness according to watermark image's grayscale value and
654 the <em class="arg">brightness</em> percentage. The destinations
655 color saturation attribute is just direct modified by the <em
656 class="arg">saturation</em> percentage, which defaults to 100 percent
663 <td valign="top">displace</td>
664 <td valign="top">Arguments:
665 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em>][!][%]
666 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
667 <br>With this option, the 'overlay' image, and optionally the 'mask'
668 image, is used as a relative displacement map, which is used to
669 displace the lookup of what part of the destination image is seen at
670 each point of the overlaid area. Much like the displacement map is a
671 'lens' that distorts the original 'background' image behind it.
673 The X-scale is modilated by the 'red' channel of the overlay image
674 while the Y-scale is modulated by the green channel, (the mask image
675 if given is rolled into green channel of the overlay image. This
676 separation allows you to modulate the X and Y lookup displacement
677 separatally allowing you to di 2 dimentional displacements, rather
678 than 1 dimentional verctored displacements (using grayscale image).
680 If the overlay image contains transparency this is used as a mask
681 of the resulting image to remove 'invalid' pixels.
683 The '%' flag makes the displacement scale relative to the size of the
684 overlay image (100% = half width/height of image). Using '!' switches
685 percentage arguments to refer to the destination image size instead.
687 Special flags were added Added to ImageMagick version 6.5.3-5.
692 <td valign="top">distort</td>
693 <td valign="top">Arguments:
694 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em
695 >[+<em class="arg">X-center</em>+<em class="arg">Y-center</em>]][!][%]
696 <br>Not available in "<code>composite</code>" at this time.
697 <br>Exactly as per 'Displace' (above), but using absolute coordinates,
698 relative to the center of the overlay (or that given). Basically
699 allows you to generate absolute distortion maps where 'black' will
700 look up the left/top edge, and 'white' looks up the bottom/right
701 edge of the destination image, according to the scale given.
703 The '!' flag not only switches percentage scaling, to use the
704 destination image, but also the image the center offset of the lookup.
705 This means the overlay can lookup a completely different region of the
708 Added to ImageMagick version 6.5.3-5.
713 <td valign="top">blur</td>
714 <td valign="top">Arguments:
715 <em class="arg">Width</em>[x<em class="arg">Height</em
716 >[+<em class="arg">Angle</em>][+<em class="arg">Angle2</em>]]
717 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
718 <br>A Variable Blur Mapping Composition method, where each pixel in the
719 overlaid region is replaced with an Elliptical Weighted Average (EWA),
720 with an ellipse (typically a circle) of the given sigma size, scaled
721 according to overlay (source image) grayscale mapping.
723 As per 'Displace' and 'Distort', the red channel will modulate the
724 width of the ellipse, while the green channel will modulate the height
725 of the ellipse. If a single Angle value is given in the arguments,
726 then the ellipse will then be rotated by the angle specifed.
728 Normally the blue channel of the mapping overlay image is ignored.
729 However if a second ellipse angle is given, then it is assumed that
730 the blue channel defines a variable angle for the ellipse ranging from
731 the first angle to the second angle given. This allows to generate
732 radial blurs, or a rough approximation for rotational blur. Or any mix
735 Added to ImageMagick version 6.5.4-0.
742 <p>To print a complete list of all the available compose operators, use <a
743 href="../www/command-line-options.html#list">-list compose</a>.</p>
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