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175 <p>This page descibed the Image composition methods that is used to define how
176 two images should be merged together in various image operations. For the
177 Command Line API it is typically set using the <A
178 HREF="../www/command-line-options.html#compose" >-compose</A> setting option. </p>
181 <p>The description of composition uses abstract terminology in order to allow
182 the description to be more precise, while avoiding constant values which are
183 specific to a particular build configuration. Each image pixel is represented
184 by red, green, and blue levels (which are equal for a gray pixel). The
185 build-dependent value <em class="QR">QuantumRange</em> is the maximum integral
186 value which may be stored, per pixel, in the red, green, or blue channels of
187 the image. Each image pixel may also optionally (if the image matte channel is
188 enabled) have an associated level of opacity, ranging from <em>opaque</em> to
189 <em>transparent</em>, which may be used to determine the influence of the pixel
190 color when compositing the pixel with another image pixel. If the image matte
191 channel is disabled, then all pixels in the image are treated as opaque. The
192 color of an opaque pixel is fully visible while the color of a transparent
193 pixel color is entirely absent (pixel color is ignored).</p>
195 <p>By definition, raster images have a rectangular shape. All image rows are of
196 equal length, as are all image columns. By treating the alpha channel as a
197 visual "mask" the rectangular image may be given a "shape" by treating the
198 alpha channel as a cookie-cutter for the image. This is done by setting the
199 pixels within the shape to be opaque, with pixels outside the shape set as
200 transparent. Pixels on the boundary of the shape may be between opaque and
201 transparent in order to provide antialiasing (visually smooth edges). The
202 description of the composition operators use this concept of image "shape" in
203 order to make the description of the operators easier to understand. While it
204 is convenient to describe the operators in terms of "shapes" they are by no
205 means limited to mask-style operations since they are based on continuous
206 floating-point mathematics rather than simple boolean operations.</p>
208 <p>The following alpha blending (Duff-Porter) compose methods are available:</p>
213 <th align="left" style="width: 8%">Method</th>
214 <th align="left">Description</th>
218 <td valign="top">clear</td>
219 <td valign="top">Both the color and the alpha of the destination are
220 cleared. Neither the source nor the destination are used (except for
221 destinations size and other meta-data which is always preserved.</td>
225 <td valign="top">src</td>
226 <td valign="top">The source is copied to the destination. The destination
227 is not used as input, though it is cleared.</td>
231 <td valign="top">dst</td>
232 <td valign="top">The destination is left untouched. The source image is
233 completely ignored.</td>
237 <td valign="top">src-over</td>
238 <td valign="top">The source is composited over the destination. this is
239 the default alpha blending compose method, when neither the compose
240 setting is set, nor is set in the image meta-data.</td>
244 <td valign="top">dst-over</td>
245 <td valign="top">The destination is composited over the source and the
246 result replaces the destination.</td>
250 <td valign="top">src-in</td>
251 <td valign="top">The part of the source lying inside of the destination
252 replaces the destination.</td>
256 <td valign="top">dst-in</td>
257 <td valign="top">The part of the destination lying inside of the source
258 replaces the destination. Areas not overlaid are cleared.</td>
262 <td valign="top">src-out</td>
263 <td valign="top">The part of the source lying outside of the destination
264 replaces the destination.</td>
268 <td valign="top">dst-out</td>
269 <td valign="top">The part of the destination lying outside of the source
270 replaces the destination.</td>
274 <td valign="top">src-atop</td>
275 <td valign="top">The part of the source lying inside of the destination is
276 composited onto the destination.</td>
280 <td valign="top">dst-atop</td>
281 <td valign="top">The part of the destination lying inside of the source is
282 composited over the source and replaces the destination. Areas not
283 overlaid are cleared. </td>
287 <td valign="top">xor</td>
288 <td valign="top">The part of the source that lies outside of the
289 destination is combined with the part of the destination that lies
290 outside of the source. Source or Destination, but not both. </td>
296 <p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
297 For example the default compose method can be specified as just 'Over'.</p>
299 <p>Many of these compose methods will clear the destination image which was
300 not overlaid by the source image. This is to be expected as part of that
301 specific composition methods defintion. You can disable this by setting the
302 special <A HREF="../www/command-line-options.html#define"
303 >-define</A> 'compose:outside-overlay' to a value of 'false' will turn off
306 <p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
307 related method '<kbd>Copy</kbd>' has been provided. This is equivelent to
308 using the '<kbd>Src</kbd>' with the special <A HREF="../www/command-line-options.html#define"
309 >-define</A> option '<kbd>compose:outside-overlay</kbd>' set to
310 '<kbd>false</kbd>', so as to only modify the overlaid area, without clearing
311 the rest of the image outside the overlaid area. </p>
315 <p>The following mathemathical composition methods are also available. </p>
320 <th align="left" style="width: 8%">Method</th>
321 <th align="left">Description</th>
325 <td valign="top">multiply</td>
326 <td valign="top">The source is multiplied by the destination and replaces
327 the destination. The resultant color is always at least as dark as
328 either of the two constituent colors. Multiplying any color with black
329 produces black. Multiplying any color with white leaves the original
330 color unchanged.</td>
334 <td valign="top">screen</td>
335 <td valign="top">The source and destination are complemented and then
336 multiplied and then replace the destination. The resultant color is
337 always at least as light as either of the two constituent colors.
338 Screening any color with white produces white. Screening any color
339 with black leaves the original color unchanged.</td>
343 <td valign="top">plus</td>
344 <td valign="top">The source is added to the destination and replaces the
345 destination. This operator is useful for averaging or a controled
346 merger of two images, rather than a direct overlay.</td>
350 <td valign="top">add</td>
351 <td valign="top">As per 'plus' but transparency data is treated as matte
352 values. As such any transparent areas in either image remain
357 <td valign="top">minus</td>
358 <td valign="top">Subtract the colors in the source image from the
359 destination image. When transparency is involved, opaque areas is
360 subtracted from any destination opaque areas. </td>
364 <td valign="top">subtract</td>
365 <td valign="top">Subtract the colors in the source image from the
366 destination image. When transparency is involved transparent areas are
367 subtracted, so only the opaque areas in the source remain opaque in
368 the destination image. </td>
372 <td valign="top">difference</td>
373 <td valign="top">Subtracts the darker of the two constituent colors from
374 the lighter. Painting with white inverts the destination color.
375 Painting with black produces no change.</td>
379 <td valign="top">exclusion</td>
380 <td valign="top">Produces an effect similar to that of 'difference', but
381 appears as lower contrast. Painting with white inverts the
382 destination color. Painting with black produces no change.</td>
386 <td valign="top">darken</td>
387 <td valign="top">Selects the darker of the destination and source colors.
388 The destination is replaced with the source when the source is darker,
389 otherwise it is left unchanged.</td>
393 <td valign="top">lighten</td>
394 <td valign="top">Selects the lighter of the destination and source colors.
395 The destination is replaced with the source when the source is
396 lighter, otherwise it is left unchanged. </td>
402 <p>Typically these use the default 'Over' alpha blending when transparencies
403 are also involved, except for 'Plus' which uses a 'plus' alpha blending. This
404 means the alpha channel of both images will only be used to ensure that any
405 visible input remains visible even in parts not overlaid. It also means that
406 any values are weighted by the alpha channel of the input and output images.
407 This 'Over' alpha blending is also applied to the lighting composition methods
410 <p>As of IM v6.6.1-6, if the special '<kbd>Sync</kbd>' flag is not specified
411 (enabled by default) with the <a href="../www/command-line-options.html#channel"
412 >-channel</a> setting, then the above mathematical compositions will nolonger
413 syncronise its actions with the alpha channel. Instead the math composition
414 will be applied on an individual channel basis as defined by the <a
415 href="../www/command-line-options.html#channel"
416 >-channel</a>. This includes the alpha channel. This special usage
417 allows you to perform true mathematics of the image channels, without alpha
418 compostion effects, becomming involved. </p>
420 <p>This special flag is not applied to the lighting composition methods (see
421 below) even though they are closely related to mathematical composition
426 <p>The following lighting composition methods are also available. </p>
431 <th align="left" style="width: 8%">Method</th>
432 <th align="left">Description</th>
436 <td valign="top">linear-dodge</td>
437 <td valign="top">This is equivelent to 'Plus' in that the color channels
438 are simply added, however it does not 'Plus' the alpha channel, but
439 uses the normal 'Over' alpha blending, which transparencies are
440 involved. Produces a sort of additive multiply-like result. Added
441 ImageMagick version 6.5.4-3. </td>
445 <td valign="top">linear-burn</td>
446 <td valign="top">As 'Linear-Dodge', but also subtract one from the result.
447 Sort of a additive 'Screen' of the images. Added ImageMagick version
452 <td valign="top">color-dodge</td>
453 <td valign="top">Brightens the destination color to reflect the source
454 color. Painting with black produces no change.</td>
458 <td valign="top">color-burn</td>
459 <td valign="top">Darkens the destination color to reflect the source
460 color. Painting with white produces no change. Fixed in ImageMagick
461 version 6.5.4-3. </td>
465 <td valign="top">overlay</td>
466 <td valign="top">Multiplies or screens the colors, dependent on the
467 destination color. Source colors overlay the destination whilst
468 preserving its highlights and shadows. The destination color is not
469 replaced, but is mixed with the source color to reflect the lightness
470 or darkness of the destination.</td>
474 <td valign="top">hard-light</td>
475 <td valign="top">Multiplies or screens the colors, dependent on the source
476 color value. If the source color is lighter than 0.5, the destination
477 is lightened as if it were screened. If the source color is darker
478 than 0.5, the destination is darkened, as if it were multiplied. The
479 degree of lightening or darkening is proportional to the difference
480 between the source color and 0.5. If it is equal to 0.5 the
481 destination is unchanged. Painting with pure black or white produces
487 <td valign="top">linear-light</td>
488 <td valign="top">Like 'Hard-Light' but using linear-dodge and linear-burn
489 instead. Increases contrast slightly with an impact on the
490 foreground's tonal values.</td>
494 <td valign="top">soft-light</td>
495 <td valign="top">Darkens or lightens the colors, dependent on the source
496 color value. If the source color is lighter than 0.5, the destination
497 is lightened. If the source color is darker than 0.5, the destination
498 is darkened, as if it were burned in. The degree of darkening or
499 lightening is proportional to the difference between the source color
500 and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
501 with pure black or white produces a distinctly darker or lighter area,
502 but does not result in pure black or white. Fixed in ImageMagick
503 version 6.5.4-3. </td>
507 <td valign="top">pegtop-light</td>
508 <td valign="top">Almost equivelent to 'Soft-Light', but using a
509 continuious mathematical formula rather than two conditionally
510 selected formulae. Added ImageMagick version 6.5.4-3. </td>
514 <td valign="top">vivid-light</td>
515 <td valign="top">A modified 'Linear-Light' designed to preserve very stong
516 primary and secondary colors in the image. Added ImageMagick version
521 <td valign="top">pin-light</td>
522 <td valign="top">Similar to 'Hard-Light', but using sharp linear shadings,
523 to similate the effects of a strong 'pinhole' light source. Added
524 ImageMagick version 6.5.4-3. </td>
533 <p>Also included are these special purpose compose methods:</p>
538 <th align="left" style="width: 8%">Method</th>
539 <th align="left">Description</th>
543 <td valign="top">copy</td>
544 <td valign="top">This is equivelent to the Duff-Porter composition method
545 '<kbd>Src,</kbd>' but without clearing the parts of the destination
546 image that is not overlaid. </td>
550 <td valign="top">copy-*</td>
551 <td valign="top">Copy the specified channel (Red, Green, Blue, Cyan,
552 Magenta, Yellow, Black, or Opacity) in the source image to the
553 same channel in the destination image. If the channel specified
554 does not exist in the source image, (which can only happen for methods,
555 '<kbd>copy-opacity</kbd>' or '<kbd>copy-black</kbd>') then it is
556 assumed that the source image is a special grayscale channel image
557 of the values that is to be copied. </td>
561 <td valign="top">change-mask</td>
562 <td valign="top">Replace any destination pixel that is the similar to the
563 source images pixel (as defined by the current <a
564 href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
572 <p>On top of these composed methods are a few special ones that not only require
573 the two images that are being merged or overlaid, but have some extra numerical
574 arguments, which are tabled below. </p>
576 <p>In the "<code>composite</code>" command these composition methods are
577 selected using special options with the arguments needed. They are usually,
578 but not always, the same name as the composte 'method' they use, and replaces
579 the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
580 setting in the "<code>composite</code>" command. For example... </p>
582 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>composite ... -blend 50x50 ...</span></p>
583 <p>As of IM v6.5.3-4 the "<code>convert</code>" command can now also supply
584 these extra arguments to its <a href="../www/command-line-options.html#composite"
585 >-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
586 attribute of '<kbd class="arg">compose:args</kbd>'. This means you can now
587 make use of these special argumented <a href="../www/command-line-options.html#compose"
588 >-compose</a> methods, those the argument and the method both need to be set
589 separatally. For example... </p>
591 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert ... -compose blend -define compose:args=50,50 -composite ...</span></p>
592 <p>The following is a table of these special 'argumented' compose methods,
593 with a brief summary of what they do. For more details see the equivalent
594 "composite" command option name. </p>
599 <th align="left" style="width: 8%">Method</th>
600 <th align="left">Description</th>
604 <td valign="top">dissolve</td>
605 <td valign="top">Arguments:
606 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
607 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
608 <br>Dissolve the 'source' image by the percentage given before overlaying
609 'over' the 'destination' image. If <em class="arg">src_percent</em> is
610 greater than 100, it starts dissolving the main image so it will
611 become transparent at a value of '<kbd class="arg">200</kbd>'. If
612 both percentages are given, each image are dissolved to the
618 <td valign="top">blend</td>
619 <td valign="top">Arguments:
620 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
621 <br>Equivalent to "<code>composite</code>" <a
622 href="../www/command-line-options.html#blend">-blend</a>
623 <br>Average the images together ('plus') according to the percentages
624 given and each pixels transparency. If only a single percentage value
625 is given it sets the weight of the composite or 'source' image, while
626 the background image is weighted by the exact opposite amount. That is
627 a <kbd>-blend 30</kbd> merges 30% of the 'source' image with 70% of
628 the 'destination' image. Thus it is equivalent to <kbd>-blend
634 <td valign="top">mathematics</td>
635 <td valign="top">Arguments: <em class="arg">A, B, C, D</em>
636 <br>Not available in "<code>composite</code>" at this time.
637 <br>Merge the source and destination images according to the formula
638 <br> <code>A*Sc*Dc + B*Sc + C*Dc + D</code>
639 <br>Can be used to generate a custom composition method that would
640 otherwise need to be implemented using the slow <a
641 href="../www/command-line-options.html#fx">-fx</a> DIY image operator. Added
642 to ImageMagick version 6.5.4-3.
643 <br>As of IM v6.6.1-6 this method will do per-channel math compositions
644 if the 'Sync' flag is removed from <a
645 href="../www/command-line-options.html#channel" >-channel</a>, just like all
646 the other mathematical compostion methods above.
651 <td valign="top">modulate</td>
652 <td valign="top">Arguments:
653 <em class="arg">brightness</em>[x<em class="arg">saturation</em>]
654 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
655 <br>Take a grayscale image (with alpha mask) and modify the destination
656 image's brightness according to watermark image's grayscale value and
657 the <em class="arg">brightness</em> percentage. The destinations
658 color saturation attribute is just direct modified by the <em
659 class="arg">saturation</em> percentage, which defaults to 100 percent
666 <td valign="top">displace</td>
667 <td valign="top">Arguments:
668 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em>][!][%]
669 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
670 <br>With this option, the 'overlay' image, and optionally the 'mask'
671 image, is used as a relative displacement map, which is used to
672 displace the lookup of what part of the destination image is seen at
673 each point of the overlaid area. Much like the displacement map is a
674 'lens' that distorts the original 'background' image behind it.
676 The X-scale is modilated by the 'red' channel of the overlay image
677 while the Y-scale is modulated by the green channel, (the mask image
678 if given is rolled into green channel of the overlay image. This
679 separation allows you to modulate the X and Y lookup displacement
680 separatally allowing you to di 2 dimentional displacements, rather
681 than 1 dimentional verctored displacements (using grayscale image).
683 If the overlay image contains transparency this is used as a mask
684 of the resulting image to remove 'invalid' pixels.
686 The '%' flag makes the displacement scale relative to the size of the
687 overlay image (100% = half width/height of image). Using '!' switches
688 percentage arguments to refer to the destination image size instead.
690 Special flags were added Added to ImageMagick version 6.5.3-5.
695 <td valign="top">distort</td>
696 <td valign="top">Arguments:
697 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em
698 >[+<em class="arg">X-center</em>+<em class="arg">Y-center</em>]][!][%]
699 <br>Not available in "<code>composite</code>" at this time.
700 <br>Exactly as per 'Displace' (above), but using absolute coordinates,
701 relative to the center of the overlay (or that given). Basically
702 allows you to generate absolute distortion maps where 'black' will
703 look up the left/top edge, and 'white' looks up the bottom/right
704 edge of the destination image, according to the scale given.
706 The '!' flag not only switches percentage scaling, to use the
707 destination image, but also the image the center offset of the lookup.
708 This means the overlay can lookup a completely different region of the
711 Added to ImageMagick version 6.5.3-5.
716 <td valign="top">blur</td>
717 <td valign="top">Arguments:
718 <em class="arg">Width</em>[x<em class="arg">Height</em
719 >[+<em class="arg">Angle</em>][+<em class="arg">Angle2</em>]]
720 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
721 <br>A Variable Blur Mapping Composition method, where each pixel in the
722 overlaid region is replaced with an Elliptical Weighted Average (EWA),
723 with an ellipse (typically a circle) of the given sigma size, scaled
724 according to overlay (source image) grayscale mapping.
726 As per 'Displace' and 'Distort', the red channel will modulate the
727 width of the ellipse, while the green channel will modulate the height
728 of the ellipse. If a single Angle value is given in the arguments,
729 then the ellipse will then be rotated by the angle specifed.
731 Normally the blue channel of the mapping overlay image is ignored.
732 However if a second ellipse angle is given, then it is assumed that
733 the blue channel defines a variable angle for the ellipse ranging from
734 the first angle to the second angle given. This allows to generate
735 radial blurs, or a rough approximation for rotational blur. Or any mix
738 Added to ImageMagick version 6.5.4-0.
745 <p>To print a complete list of all the available compose operators, use <a
746 href="../www/command-line-options.html#list">-list compose</a>.</p>
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