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190 <h1>ImageMagick Image Composition</h1>
191 <p>This page descibed the Image composition methods that is used to define how
192 two images should be merged together in various image operations. For the
193 Command Line API it is typically set using the <A
194 HREF="../www/command-line-options.html#compose" >-compose</A> setting option. </p>
197 <p>The description of composition uses abstract terminology in order to allow
198 the description to be more precise, while avoiding constant values which are
199 specific to a particular build configuration. Each image pixel is represented
200 by red, green, and blue levels (which are equal for a gray pixel). The
201 build-dependent value <em class="QR">QuantumRange</em> is the maximum integral
202 value which may be stored, per pixel, in the red, green, or blue channels of
203 the image. Each image pixel may also optionally (if the image matte channel is
204 enabled) have an associated level of opacity, ranging from <em>opaque</em> to
205 <em>transparent</em>, which may be used to determine the influence of the pixel
206 color when compositing the pixel with another image pixel. If the image matte
207 channel is disabled, then all pixels in the image are treated as opaque. The
208 color of an opaque pixel is fully visible while the color of a transparent
209 pixel color is entirely absent (pixel color is ignored).</p>
211 <p>By definition, raster images have a rectangular shape. All image rows are of
212 equal length, as are all image columns. By treating the alpha channel as a
213 visual "mask" the rectangular image may be given a "shape" by treating the
214 alpha channel as a cookie-cutter for the image. This is done by setting the
215 pixels within the shape to be opaque, with pixels outside the shape set as
216 transparent. Pixels on the boundary of the shape may be between opaque and
217 transparent in order to provide antialiasing (visually smooth edges). The
218 description of the composition operators use this concept of image "shape" in
219 order to make the description of the operators easier to understand. While it
220 is convenient to describe the operators in terms of "shapes" they are by no
221 means limited to mask-style operations since they are based on continuous
222 floating-point mathematics rather than simple boolean operations.</p>
224 <p>The following alpha blending (Duff-Porter) compose methods are available:</p>
229 <th align="left" style="width: 8%">Method</th>
230 <th align="left">Description</th>
234 <td valign="top">clear</td>
235 <td valign="top">Both the color and the alpha of the destination are
236 cleared. Neither the source nor the destination are used (except for
237 destinations size and other meta-data which is always preserved.</td>
241 <td valign="top">src</td>
242 <td valign="top">The source is copied to the destination. The destination
243 is not used as input, though it is cleared.</td>
247 <td valign="top">dst</td>
248 <td valign="top">The destination is left untouched. The source image is
249 completely ignored.</td>
253 <td valign="top">src-over</td>
254 <td valign="top">The source is composited over the destination. this is
255 the default alpha blending compose method, when neither the compose
256 setting is set, nor is set in the image meta-data.</td>
260 <td valign="top">dst-over</td>
261 <td valign="top">The destination is composited over the source and the
262 result replaces the destination.</td>
266 <td valign="top">src-in</td>
267 <td valign="top">The part of the source lying inside of the destination
268 replaces the destination.</td>
272 <td valign="top">dst-in</td>
273 <td valign="top">The part of the destination lying inside of the source
274 replaces the destination. Areas not overlaid are cleared.</td>
278 <td valign="top">src-out</td>
279 <td valign="top">The part of the source lying outside of the destination
280 replaces the destination.</td>
284 <td valign="top">dst-out</td>
285 <td valign="top">The part of the destination lying outside of the source
286 replaces the destination.</td>
290 <td valign="top">src-atop</td>
291 <td valign="top">The part of the source lying inside of the destination is
292 composited onto the destination.</td>
296 <td valign="top">dst-atop</td>
297 <td valign="top">The part of the destination lying inside of the source is
298 composited over the source and replaces the destination. Areas not
299 overlaid are cleared. </td>
303 <td valign="top">xor</td>
304 <td valign="top">The part of the source that lies outside of the
305 destination is combined with the part of the destination that lies
306 outside of the source. Source or Destination, but not both. </td>
312 <p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
313 For example the default compose method can be specified as just 'Over'.</p>
315 <p>Many of these compose methods will clear the destination image which was
316 not overlaid by the source image. This is to be expected as part of that
317 specific composition methods defintion. You can disable this by setting the
318 special <A HREF="../www/command-line-options.html#define"
319 >-define</A> 'compose:outside-overlay' to a value of 'false' will turn off
322 <p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
323 related method '<kbd>Copy</kbd>' has been provided. This is equivelent to
324 using the '<kbd>Src</kbd>' with the special <A HREF="../www/command-line-options.html#define"
325 >-define</A> option '<kbd>compose:outside-overlay</kbd>' set to
326 '<kbd>false</kbd>', so as to only modify the overlaid area, without clearing
327 the rest of the image outside the overlaid area. </p>
331 <p>The following mathemathical composition methods are also available. </p>
336 <th align="left" style="width: 8%">Method</th>
337 <th align="left">Description</th>
341 <td valign="top">multiply</td>
342 <td valign="top">The source is multiplied by the destination and replaces
343 the destination. The resultant color is always at least as dark as
344 either of the two constituent colors. Multiplying any color with black
345 produces black. Multiplying any color with white leaves the original
346 color unchanged.</td>
350 <td valign="top">screen</td>
351 <td valign="top">The source and destination are complemented and then
352 multiplied and then replace the destination. The resultant color is
353 always at least as light as either of the two constituent colors.
354 Screening any color with white produces white. Screening any color
355 with black leaves the original color unchanged.</td>
359 <td valign="top">plus</td>
360 <td valign="top">The source is added to the destination and replaces the
361 destination. This operator is useful for averaging or a controled
362 merger of two images, rather than a direct overlay.</td>
366 <td valign="top">add</td>
367 <td valign="top">As per 'plus' but transparency data is treated as matte
368 values. As such any transparent areas in either image remain
373 <td valign="top">minus</td>
374 <td valign="top">Subtract the colors in the source image from the
375 destination image. When transparency is involved, opaque areas is
376 subtracted from any destination opaque areas. </td>
380 <td valign="top">subtract</td>
381 <td valign="top">Subtract the colors in the source image from the
382 destination image. When transparency is involved transparent areas are
383 subtracted, so only the opaque areas in the source remain opaque in
384 the destination image. </td>
388 <td valign="top">difference</td>
389 <td valign="top">Subtracts the darker of the two constituent colors from
390 the lighter. Painting with white inverts the destination color.
391 Painting with black produces no change.</td>
395 <td valign="top">exclusion</td>
396 <td valign="top">Produces an effect similar to that of 'difference', but
397 appears as lower contrast. Painting with white inverts the
398 destination color. Painting with black produces no change.</td>
402 <td valign="top">darken</td>
403 <td valign="top">Selects the darker of the destination and source colors.
404 The destination is replaced with the source when the source is darker,
405 otherwise it is left unchanged.</td>
409 <td valign="top">lighten</td>
410 <td valign="top">Selects the lighter of the destination and source colors.
411 The destination is replaced with the source when the source is
412 lighter, otherwise it is left unchanged. </td>
418 <p>Typically these use the default 'Over' alpha blending when transparencies
419 are also involved, except for 'Plus' which uses a 'plus' alpha blending. This
420 means the alpha channel of both images will only be used to ensure that any
421 visible input remains visible even in parts not overlaid. It also means that
422 any values are weighted by the alpha channel of the input and output images.
423 This 'Over' alpha blending is also applied to the lighting composition methods
426 <p>As of IM v6.6.1-6, if the special '<kbd>Sync</kbd>' flag is not specified
427 (enabled by default) with the <a href="../www/command-line-options.html#channel"
428 >-channel</a> setting, then the above mathematical compositions will nolonger
429 syncronise its actions with the alpha channel. Instead the math composition
430 will be applied on an individual channel basis as defined by the <a
431 href="../www/command-line-options.html#channel"
432 >-channel</a>. This includes the alpha channel. This special usage
433 allows you to perform true mathematics of the image channels, without alpha
434 compostion effects, becomming involved. </p>
436 <p>This special flag is not applied to the lighting composition methods (see
437 below) even though they are closely related to mathematical composition
442 <p>The following lighting composition methods are also available. </p>
447 <th align="left" style="width: 8%">Method</th>
448 <th align="left">Description</th>
452 <td valign="top">linear-dodge</td>
453 <td valign="top">This is equivelent to 'Plus' in that the color channels
454 are simply added, however it does not 'Plus' the alpha channel, but
455 uses the normal 'Over' alpha blending, which transparencies are
456 involved. Produces a sort of additive multiply-like result. Added
457 ImageMagick version 6.5.4-3. </td>
461 <td valign="top">linear-burn</td>
462 <td valign="top">As 'Linear-Dodge', but also subtract one from the result.
463 Sort of a additive 'Screen' of the images. Added ImageMagick version
468 <td valign="top">color-dodge</td>
469 <td valign="top">Brightens the destination color to reflect the source
470 color. Painting with black produces no change.</td>
474 <td valign="top">color-burn</td>
475 <td valign="top">Darkens the destination color to reflect the source
476 color. Painting with white produces no change. Fixed in ImageMagick
477 version 6.5.4-3. </td>
481 <td valign="top">overlay</td>
482 <td valign="top">Multiplies or screens the colors, dependent on the
483 destination color. Source colors overlay the destination whilst
484 preserving its highlights and shadows. The destination color is not
485 replaced, but is mixed with the source color to reflect the lightness
486 or darkness of the destination.</td>
490 <td valign="top">hard-light</td>
491 <td valign="top">Multiplies or screens the colors, dependent on the source
492 color value. If the source color is lighter than 0.5, the destination
493 is lightened as if it were screened. If the source color is darker
494 than 0.5, the destination is darkened, as if it were multiplied. The
495 degree of lightening or darkening is proportional to the difference
496 between the source color and 0.5. If it is equal to 0.5 the
497 destination is unchanged. Painting with pure black or white produces
503 <td valign="top">linear-light</td>
504 <td valign="top">Like 'Hard-Light' but using linear-dodge and linear-burn
505 instead. Increases contrast slightly with an impact on the
506 foreground's tonal values.</td>
510 <td valign="top">soft-light</td>
511 <td valign="top">Darkens or lightens the colors, dependent on the source
512 color value. If the source color is lighter than 0.5, the destination
513 is lightened. If the source color is darker than 0.5, the destination
514 is darkened, as if it were burned in. The degree of darkening or
515 lightening is proportional to the difference between the source color
516 and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
517 with pure black or white produces a distinctly darker or lighter area,
518 but does not result in pure black or white. Fixed in ImageMagick
519 version 6.5.4-3. </td>
523 <td valign="top">pegtop-light</td>
524 <td valign="top">Almost equivelent to 'Soft-Light', but using a
525 continuious mathematical formula rather than two conditionally
526 selected formulae. Added ImageMagick version 6.5.4-3. </td>
530 <td valign="top">vivid-light</td>
531 <td valign="top">A modified 'Linear-Light' designed to preserve very stong
532 primary and secondary colors in the image. Added ImageMagick version
537 <td valign="top">pin-light</td>
538 <td valign="top">Similar to 'Hard-Light', but using sharp linear shadings,
539 to similate the effects of a strong 'pinhole' light source. Added
540 ImageMagick version 6.5.4-3. </td>
549 <p>Also included are these special purpose compose methods:</p>
554 <th align="left" style="width: 8%">Method</th>
555 <th align="left">Description</th>
559 <td valign="top">copy</td>
560 <td valign="top">This is equivelent to the Duff-Porter composition method
561 '<kbd>Src,</kbd>' but without clearing the parts of the destination
562 image that is not overlaid. </td>
566 <td valign="top">copy-*</td>
567 <td valign="top">Copy the specified channel (Red, Green, Blue, Cyan,
568 Magenta, Yellow, Black, or Opacity) in the source image to the
569 same channel in the destination image. If the channel specified
570 does not exist in the source image, (which can only happen for methods,
571 '<kbd>copy-opacity</kbd>' or '<kbd>copy-black</kbd>') then it is
572 assumed that the source image is a special grayscale channel image
573 of the values that is to be copied. </td>
577 <td valign="top">change-mask</td>
578 <td valign="top">Replace any destination pixel that is the similar to the
579 source images pixel (as defined by the current <a
580 href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
588 <p>On top of these composed methods are a few special ones that not only require
589 the two images that are being merged or overlaid, but have some extra numerical
590 arguments, which are tabled below. </p>
592 <p>In the "<code>composite</code>" command these composition methods are
593 selected using special options with the arguments needed. They are usually,
594 but not always, the same name as the composte 'method' they use, and replaces
595 the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
596 setting in the "<code>composite</code>" command. For example... </p>
598 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>composite ... -blend 50x50 ...</span></p>
599 <p>As of IM v6.5.3-4 the "<code>convert</code>" command can now also supply
600 these extra arguments to its <a href="../www/command-line-options.html#composite"
601 >-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
602 attribute of '<kbd class="arg">compose:args</kbd>'. This means you can now
603 make use of these special argumented <a href="../www/command-line-options.html#compose"
604 >-compose</a> methods, those the argument and the method both need to be set
605 separatally. For example... </p>
607 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert ... -compose blend -define compose:args=50,50 -composite ...</span></p>
608 <p>The following is a table of these special 'argumented' compose methods,
609 with a brief summary of what they do. For more details see the equivalent
610 "composite" command option name. </p>
615 <th align="left" style="width: 8%">Method</th>
616 <th align="left">Description</th>
620 <td valign="top">dissolve</td>
621 <td valign="top">Arguments:
622 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
623 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
624 <br>Dissolve the 'source' image by the percentage given before overlaying
625 'over' the 'destination' image. If <em class="arg">src_percent</em> is
626 greater than 100, it starts dissolving the main image so it will
627 become transparent at a value of '<kbd class="arg">200</kbd>'. If
628 both percentages are given, each image are dissolved to the
634 <td valign="top">blend</td>
635 <td valign="top">Arguments:
636 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
637 <br>Equivalent to "<code>composite</code>" <a
638 href="../www/command-line-options.html#blend">-blend</a>
639 <br>Average the images together ('plus') according to the percentages
640 given and each pixels transparency. If only a single percentage value
641 is given it sets the weight of the composite or 'source' image, while
642 the background image is weighted by the exact opposite amount. That is
643 a <kbd>-blend 30</kbd> merges 30% of the 'source' image with 70% of
644 the 'destination' image. Thus it is equivalent to <kbd>-blend
650 <td valign="top">mathematics</td>
651 <td valign="top">Arguments: <em class="arg">A, B, C, D</em>
652 <br>Not available in "<code>composite</code>" at this time.
653 <br>Merge the source and destination images according to the formula
654 <br> <code>A*Sc*Dc + B*Sc + C*Dc + D</code>
655 <br>Can be used to generate a custom composition method that would
656 otherwise need to be implemented using the slow <a
657 href="../www/command-line-options.html#fx">-fx</a> DIY image operator. Added
658 to ImageMagick version 6.5.4-3.
659 <br>As of IM v6.6.1-6 this method will do per-channel math compositions
660 if the 'Sync' flag is removed from <a
661 href="../www/command-line-options.html#channel" >-channel</a>, just like all
662 the other mathematical compostion methods above.
667 <td valign="top">modulate</td>
668 <td valign="top">Arguments:
669 <em class="arg">brightness</em>[x<em class="arg">saturation</em>]
670 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
671 <br>Take a grayscale image (with alpha mask) and modify the destination
672 image's brightness according to watermark image's grayscale value and
673 the <em class="arg">brightness</em> percentage. The destinations
674 color saturation attribute is just direct modified by the <em
675 class="arg">saturation</em> percentage, which defaults to 100 percent
682 <td valign="top">displace</td>
683 <td valign="top">Arguments:
684 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em>][!][%]
685 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
686 <br>With this option, the 'overlay' image, and optionally the 'mask'
687 image, is used as a relative displacement map, which is used to
688 displace the lookup of what part of the destination image is seen at
689 each point of the overlaid area. Much like the displacement map is a
690 'lens' that distorts the original 'background' image behind it.
692 The X-scale is modilated by the 'red' channel of the overlay image
693 while the Y-scale is modulated by the green channel, (the mask image
694 if given is rolled into green channel of the overlay image. This
695 separation allows you to modulate the X and Y lookup displacement
696 separatally allowing you to di 2 dimentional displacements, rather
697 than 1 dimentional verctored displacements (using grayscale image).
699 If the overlay image contains transparency this is used as a mask
700 of the resulting image to remove 'invalid' pixels.
702 The '%' flag makes the displacement scale relative to the size of the
703 overlay image (100% = half width/height of image). Using '!' switches
704 percentage arguments to refer to the destination image size instead.
706 Special flags were added Added to ImageMagick version 6.5.3-5.
711 <td valign="top">distort</td>
712 <td valign="top">Arguments:
713 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em
714 >[+<em class="arg">X-center</em>+<em class="arg">Y-center</em>]][!][%]
715 <br>Not available in "<code>composite</code>" at this time.
716 <br>Exactly as per 'Displace' (above), but using absolute coordinates,
717 relative to the center of the overlay (or that given). Basically
718 allows you to generate absolute distortion maps where 'black' will
719 look up the left/top edge, and 'white' looks up the bottom/right
720 edge of the destination image, according to the scale given.
722 The '!' flag not only switches percentage scaling, to use the
723 destination image, but also the image the center offset of the lookup.
724 This means the overlay can lookup a completely different region of the
727 Added to ImageMagick version 6.5.3-5.
732 <td valign="top">blur</td>
733 <td valign="top">Arguments:
734 <em class="arg">Width</em>[x<em class="arg">Height</em
735 >[+<em class="arg">Angle</em>][+<em class="arg">Angle2</em>]]
736 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
737 <br>A Variable Blur Mapping Composition method, where each pixel in the
738 overlaid region is replaced with an Elliptical Weighted Average (EWA),
739 with an ellipse (typically a circle) of the given sigma size, scaled
740 according to overlay (source image) grayscale mapping.
742 As per 'Displace' and 'Distort', the red channel will modulate the
743 width of the ellipse, while the green channel will modulate the height
744 of the ellipse. If a single Angle value is given in the arguments,
745 then the ellipse will then be rotated by the angle specifed.
747 Normally the blue channel of the mapping overlay image is ignored.
748 However if a second ellipse angle is given, then it is assumed that
749 the blue channel defines a variable angle for the ellipse ranging from
750 the first angle to the second angle given. This allows to generate
751 radial blurs, or a rough approximation for rotational blur. Or any mix
754 Added to ImageMagick version 6.5.4-0.
761 <p>To print a complete list of all the available compose operators, use <a
762 href="../www/command-line-options.html#list">-list compose</a>.</p>
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