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216 <h1>ImageMagick Image Composition</h1>
217 <p>This page descibed the Image composition methods that is used to define how
218 two images should be merged together in various image operations. For the
219 Command Line API it is typically set using the <A
220 HREF="../www/command-line-options.html#compose" >-compose</A> setting option. </p>
223 <p>The description of composition uses abstract terminology in order to allow
224 the description to be more precise, while avoiding constant values which are
225 specific to a particular build configuration. Each image pixel is represented
226 by red, green, and blue levels (which are equal for a gray pixel). The
227 build-dependent value <em class="QR">QuantumRange</em> is the maximum integral
228 value which may be stored, per pixel, in the red, green, or blue channels of
229 the image. Each image pixel may also optionally (if the image matte channel is
230 enabled) have an associated level of opacity, ranging from <em>opaque</em> to
231 <em>transparent</em>, which may be used to determine the influence of the pixel
232 color when compositing the pixel with another image pixel. If the image matte
233 channel is disabled, then all pixels in the image are treated as opaque. The
234 color of an opaque pixel is fully visible while the color of a transparent
235 pixel color is entirely absent (pixel color is ignored).</p>
237 <p>By definition, raster images have a rectangular shape. All image rows are of
238 equal length, as are all image columns. By treating the alpha channel as a
239 visual "mask" the rectangular image may be given a "shape" by treating the
240 alpha channel as a cookie-cutter for the image. This is done by setting the
241 pixels within the shape to be opaque, with pixels outside the shape set as
242 transparent. Pixels on the boundary of the shape may be between opaque and
243 transparent in order to provide antialiasing (visually smooth edges). The
244 description of the composition operators use this concept of image "shape" in
245 order to make the description of the operators easier to understand. While it
246 is convenient to describe the operators in terms of "shapes" they are by no
247 means limited to mask-style operations since they are based on continuous
248 floating-point mathematics rather than simple boolean operations.</p>
250 <p>The following alpha blending (Duff-Porter) compose methods are available:</p>
255 <th align="left" style="width: 8%">Method</th>
256 <th align="left">Description</th>
260 <td valign="top">clear</td>
261 <td valign="top">Both the color and the alpha of the destination are
262 cleared. Neither the source nor the destination are used (except for
263 destinations size and other meta-data which is always preserved.</td>
267 <td valign="top">src</td>
268 <td valign="top">The source is copied to the destination. The destination
269 is not used as input, though it is cleared.</td>
273 <td valign="top">dst</td>
274 <td valign="top">The destination is left untouched. The source image is
275 completely ignored.</td>
279 <td valign="top">src-over</td>
280 <td valign="top">The source is composited over the destination. this is
281 the default alpha blending compose method, when neither the compose
282 setting is set, nor is set in the image meta-data.</td>
286 <td valign="top">dst-over</td>
287 <td valign="top">The destination is composited over the source and the
288 result replaces the destination.</td>
292 <td valign="top">src-in</td>
293 <td valign="top">The part of the source lying inside of the destination
294 replaces the destination.</td>
298 <td valign="top">dst-in</td>
299 <td valign="top">The part of the destination lying inside of the source
300 replaces the destination. Areas not overlaid are cleared.</td>
304 <td valign="top">src-out</td>
305 <td valign="top">The part of the source lying outside of the destination
306 replaces the destination.</td>
310 <td valign="top">dst-out</td>
311 <td valign="top">The part of the destination lying outside of the source
312 replaces the destination.</td>
316 <td valign="top">src-atop</td>
317 <td valign="top">The part of the source lying inside of the destination is
318 composited onto the destination.</td>
322 <td valign="top">dst-atop</td>
323 <td valign="top">The part of the destination lying inside of the source is
324 composited over the source and replaces the destination. Areas not
325 overlaid are cleared. </td>
329 <td valign="top">xor</td>
330 <td valign="top">The part of the source that lies outside of the
331 destination is combined with the part of the destination that lies
332 outside of the source. Source or Destination, but not both. </td>
338 <p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
339 For example the default compose method can be specified as just 'Over'.</p>
341 <p>Many of these compose methods will clear the destination image which was
342 not overlaid by the source image. This is to be expected as part of that
343 specific composition methods defintion. You can disable this by setting the
344 special <A HREF="../www/command-line-options.html#define"
345 >-define</A> 'compose:outside-overlay' to a value of 'false' will turn off
348 <p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
349 related method '<kbd>Copy</kbd>' has been provided. This is equivalent to
350 using the '<kbd>Src</kbd>' with the special <A HREF="../www/command-line-options.html#define"
351 >-define</A> option '<kbd>compose:outside-overlay</kbd>' set to
352 '<kbd>false</kbd>', so as to only modify the overlaid area, without clearing
353 the rest of the image outside the overlaid area. </p>
357 <p>The following mathemathical composition methods are also available. </p>
362 <th align="left" style="width: 8%">Method</th>
363 <th align="left">Description</th>
367 <td valign="top">multiply</td>
368 <td valign="top">The source is multiplied by the destination and replaces
369 the destination. The resultant color is always at least as dark as
370 either of the two constituent colors. Multiplying any color with black
371 produces black. Multiplying any color with white leaves the original
372 color unchanged.</td>
376 <td valign="top">screen</td>
377 <td valign="top">The source and destination are complemented and then
378 multiplied and then replace the destination. The resultant color is
379 always at least as light as either of the two constituent colors.
380 Screening any color with white produces white. Screening any color
381 with black leaves the original color unchanged.</td>
385 <td valign="top">plus</td>
386 <td valign="top">The source is added to the destination and replaces the
387 destination. This operator is useful for averaging or a controled
388 merger of two images, rather than a direct overlay.</td>
392 <td valign="top">add</td>
393 <td valign="top">As per 'plus' but transparency data is treated as matte
394 values. As such any transparent areas in either image remain
399 <td valign="top">minus</td>
400 <td valign="top">Subtract the colors in the source image from the
401 destination image. When transparency is involved, opaque areas is
402 subtracted from any destination opaque areas. </td>
406 <td valign="top">subtract</td>
407 <td valign="top">Subtract the colors in the source image from the
408 destination image. When transparency is involved transparent areas are
409 subtracted, so only the opaque areas in the source remain opaque in
410 the destination image. </td>
414 <td valign="top">difference</td>
415 <td valign="top">Subtracts the darker of the two constituent colors from
416 the lighter. Painting with white inverts the destination color.
417 Painting with black produces no change.</td>
421 <td valign="top">exclusion</td>
422 <td valign="top">Produces an effect similar to that of 'difference', but
423 appears as lower contrast. Painting with white inverts the
424 destination color. Painting with black produces no change.</td>
428 <td valign="top">darken</td>
429 <td valign="top">Selects the darker of the destination and source colors.
430 The destination is replaced with the source when the source is darker,
431 otherwise it is left unchanged.</td>
435 <td valign="top">lighten</td>
436 <td valign="top">Selects the lighter of the destination and source colors.
437 The destination is replaced with the source when the source is
438 lighter, otherwise it is left unchanged. </td>
444 <p>Typically these use the default 'Over' alpha blending when transparencies
445 are also involved, except for 'Plus' which uses a 'plus' alpha blending. This
446 means the alpha channel of both images will only be used to ensure that any
447 visible input remains visible even in parts not overlaid. It also means that
448 any values are weighted by the alpha channel of the input and output images.
449 This 'Over' alpha blending is also applied to the lighting composition methods
452 <p>As of IM v6.6.1-6, if the special '<kbd>Sync</kbd>' flag is not specified
453 (enabled by default) with the <a href="../www/command-line-options.html#channel"
454 >-channel</a> setting, then the above mathematical compositions will nolonger
455 synchronise its actions with the alpha channel. Instead the math composition
456 will be applied on an individual channel basis as defined by the <a
457 href="../www/command-line-options.html#channel"
458 >-channel</a>. This includes the alpha channel. This special usage
459 allows you to perform true mathematics of the image channels, without alpha
460 compostion effects, becomming involved. </p>
462 <p>This special flag is not applied to the lighting composition methods (see
463 below) even though they are closely related to mathematical composition
468 <p>The following lighting composition methods are also available. </p>
473 <th align="left" style="width: 8%">Method</th>
474 <th align="left">Description</th>
478 <td valign="top">linear-dodge</td>
479 <td valign="top">This is equivalent to 'Plus' in that the color channels
480 are simply added, however it does not 'Plus' the alpha channel, but
481 uses the normal 'Over' alpha blending, which transparencies are
482 involved. Produces a sort of additive multiply-like result. Added
483 ImageMagick version 6.5.4-3. </td>
487 <td valign="top">linear-burn</td>
488 <td valign="top">As 'Linear-Dodge', but also subtract one from the result.
489 Sort of a additive 'Screen' of the images. Added ImageMagick version
494 <td valign="top">color-dodge</td>
495 <td valign="top">Brightens the destination color to reflect the source
496 color. Painting with black produces no change.</td>
500 <td valign="top">color-burn</td>
501 <td valign="top">Darkens the destination color to reflect the source
502 color. Painting with white produces no change. Fixed in ImageMagick
503 version 6.5.4-3. </td>
507 <td valign="top">overlay</td>
508 <td valign="top">Multiplies or screens the colors, dependent on the
509 destination color. Source colors overlay the destination whilst
510 preserving its highlights and shadows. The destination color is not
511 replaced, but is mixed with the source color to reflect the lightness
512 or darkness of the destination.</td>
516 <td valign="top">hard-light</td>
517 <td valign="top">Multiplies or screens the colors, dependent on the source
518 color value. If the source color is lighter than 0.5, the destination
519 is lightened as if it were screened. If the source color is darker
520 than 0.5, the destination is darkened, as if it were multiplied. The
521 degree of lightening or darkening is proportional to the difference
522 between the source color and 0.5. If it is equal to 0.5 the
523 destination is unchanged. Painting with pure black or white produces
529 <td valign="top">linear-light</td>
530 <td valign="top">Like 'Hard-Light' but using linear-dodge and linear-burn
531 instead. Increases contrast slightly with an impact on the
532 foreground's tonal values.</td>
536 <td valign="top">soft-light</td>
537 <td valign="top">Darkens or lightens the colors, dependent on the source
538 color value. If the source color is lighter than 0.5, the destination
539 is lightened. If the source color is darker than 0.5, the destination
540 is darkened, as if it were burned in. The degree of darkening or
541 lightening is proportional to the difference between the source color
542 and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
543 with pure black or white produces a distinctly darker or lighter area,
544 but does not result in pure black or white. Fixed in ImageMagick
545 version 6.5.4-3. </td>
549 <td valign="top">pegtop-light</td>
550 <td valign="top">Almost equivalent to 'Soft-Light', but using a
551 continuious mathematical formula rather than two conditionally
552 selected formulae. Added ImageMagick version 6.5.4-3. </td>
556 <td valign="top">vivid-light</td>
557 <td valign="top">A modified 'Linear-Light' designed to preserve very stong
558 primary and secondary colors in the image. Added ImageMagick version
563 <td valign="top">pin-light</td>
564 <td valign="top">Similar to 'Hard-Light', but using sharp linear shadings,
565 to similate the effects of a strong 'pinhole' light source. Added
566 ImageMagick version 6.5.4-3. </td>
575 <p>Also included are these special purpose compose methods:</p>
580 <th align="left" style="width: 8%">Method</th>
581 <th align="left">Description</th>
585 <td valign="top">copy</td>
586 <td valign="top">This is equivalent to the Duff-Porter composition method
587 '<kbd>Src,</kbd>' but without clearing the parts of the destination
588 image that is not overlaid. </td>
592 <td valign="top">copy-*</td>
593 <td valign="top">Copy the specified channel (Red, Green, Blue, Cyan,
594 Magenta, Yellow, Black, or Opacity) in the source image to the
595 same channel in the destination image. If the channel specified
596 does not exist in the source image, (which can only happen for methods,
597 '<kbd>copy-opacity</kbd>' or '<kbd>copy-black</kbd>') then it is
598 assumed that the source image is a special grayscale channel image
599 of the values that is to be copied. </td>
603 <td valign="top">change-mask</td>
604 <td valign="top">Replace any destination pixel that is the similar to the
605 source images pixel (as defined by the current <a
606 href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
614 <p>On top of these composed methods are a few special ones that not only require
615 the two images that are being merged or overlaid, but have some extra numerical
616 arguments, which are tabled below. </p>
618 <p>In the "<code>composite</code>" command these composition methods are
619 selected using special options with the arguments needed. They are usually,
620 but not always, the same name as the composte 'method' they use, and replaces
621 the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
622 setting in the "<code>composite</code>" command. For example... </p>
624 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>composite ... -blend 50x50 ...</span></p>
625 <p>As of IM v6.5.3-4 the "<code>convert</code>" command can now also supply
626 these extra arguments to its <a href="../www/command-line-options.html#composite"
627 >-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
628 attribute of '<kbd class="arg">compose:args</kbd>'. This means you can now
629 make use of these special argumented <a href="../www/command-line-options.html#compose"
630 >-compose</a> methods, those the argument and the method both need to be set
631 separately. For example... </p>
633 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert ... -compose blend -define compose:args=50,50 -composite ...</span></p>
634 <p>The following is a table of these special 'argumented' compose methods,
635 with a brief summary of what they do. For more details see the equivalent
636 "composite" command option name. </p>
641 <th align="left" style="width: 8%">Method</th>
642 <th align="left">Description</th>
646 <td valign="top">dissolve</td>
647 <td valign="top">Arguments:
648 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
649 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
650 <br>Dissolve the 'source' image by the percentage given before overlaying
651 'over' the 'destination' image. If <em class="arg">src_percent</em> is
652 greater than 100, it starts dissolving the main image so it will
653 become transparent at a value of '<kbd class="arg">200</kbd>'. If
654 both percentages are given, each image are dissolved to the
660 <td valign="top">blend</td>
661 <td valign="top">Arguments:
662 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
663 <br>Equivalent to "<code>composite</code>" <a
664 href="../www/command-line-options.html#blend">-blend</a>
665 <br>Average the images together ('plus') according to the percentages
666 given and each pixels transparency. If only a single percentage value
667 is given it sets the weight of the composite or 'source' image, while
668 the background image is weighted by the exact opposite amount. That is
669 a <kbd>-blend 30</kbd> merges 30% of the 'source' image with 70% of
670 the 'destination' image. Thus it is equivalent to <kbd>-blend
676 <td valign="top">mathematics</td>
677 <td valign="top">Arguments: <em class="arg">A, B, C, D</em>
678 <br>Not available in "<code>composite</code>" at this time.
679 <br>Merge the source and destination images according to the formula
680 <br> <code>A*Sc*Dc + B*Sc + C*Dc + D</code>
681 <br>Can be used to generate a custom composition method that would
682 otherwise need to be implemented using the slow <a
683 href="../www/command-line-options.html#fx">-fx</a> DIY image operator. Added
684 to ImageMagick version 6.5.4-3.
685 <br>As of IM v6.6.1-6 this method will do per-channel math compositions
686 if the 'Sync' flag is removed from <a
687 href="../www/command-line-options.html#channel" >-channel</a>, just like all
688 the other mathematical compostion methods above.
693 <td valign="top">modulate</td>
694 <td valign="top">Arguments:
695 <em class="arg">brightness</em>[x<em class="arg">saturation</em>]
696 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
697 <br>Take a grayscale image (with alpha mask) and modify the destination
698 image's brightness according to watermark image's grayscale value and
699 the <em class="arg">brightness</em> percentage. The destinations
700 color saturation attribute is just direct modified by the <em
701 class="arg">saturation</em> percentage, which defaults to 100 percent
708 <td valign="top">displace</td>
709 <td valign="top">Arguments:
710 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em>][!][%]
711 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
712 <br>With this option, the 'overlay' image, and optionally the 'mask'
713 image, is used as a relative displacement map, which is used to
714 displace the lookup of what part of the destination image is seen at
715 each point of the overlaid area. Much like the displacement map is a
716 'lens' that distorts the original 'background' image behind it.
718 The X-scale is modulated by the 'red' channel of the overlay image
719 while the Y-scale is modulated by the green channel, (the mask image
720 if given is rolled into green channel of the overlay image. This
721 separation allows you to modulate the X and Y lookup displacement
722 separately allowing you to do 2-dimensional displacements, rather
723 than 1-dimensional verctored displacements (using grayscale image).
725 If the overlay image contains transparency this is used as a mask
726 of the resulting image to remove 'invalid' pixels.
728 The '%' flag makes the displacement scale relative to the size of the
729 overlay image (100% = half width/height of image). Using '!' switches
730 percentage arguments to refer to the destination image size instead.
732 Special flags were added Added to ImageMagick version 6.5.3-5.
737 <td valign="top">distort</td>
738 <td valign="top">Arguments:
739 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em
740 >[+<em class="arg">X-center</em>+<em class="arg">Y-center</em>]][!][%]
741 <br>Not available in "<code>composite</code>" at this time.
742 <br>Exactly as per 'Displace' (above), but using absolute coordinates,
743 relative to the center of the overlay (or that given). Basically
744 allows you to generate absolute distortion maps where 'black' will
745 look up the left/top edge, and 'white' looks up the bottom/right
746 edge of the destination image, according to the scale given.
748 The '!' flag not only switches percentage scaling, to use the
749 destination image, but also the image the center offset of the lookup.
750 This means the overlay can lookup a completely different region of the
753 Added to ImageMagick version 6.5.3-5.
758 <td valign="top">blur</td>
759 <td valign="top">Arguments:
760 <em class="arg">Width</em>[x<em class="arg">Height</em
761 >[+<em class="arg">Angle</em>][+<em class="arg">Angle2</em>]]
762 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
763 <br>A Variable Blur Mapping Composition method, where each pixel in the
764 overlaid region is replaced with an Elliptical Weighted Average (EWA),
765 with an ellipse (typically a circle) of the given sigma size, scaled
766 according to overlay (source image) grayscale mapping.
768 As per 'Displace' and 'Distort', the red channel will modulate the
769 width of the ellipse, while the green channel will modulate the height
770 of the ellipse. If a single Angle value is given in the arguments,
771 then the ellipse will then be rotated by the angle specifed.
773 Normally the blue channel of the mapping overlay image is ignored.
774 However if a second ellipse angle is given, then it is assumed that
775 the blue channel defines a variable angle for the ellipse ranging from
776 the first angle to the second angle given. This allows to generate
777 radial blurs, or a rough approximation for rotational blur. Or any mix
780 Added to ImageMagick version 6.5.4-0.
787 <p>To print a complete list of all the available compose operators, use <a
788 href="../www/command-line-options.html#list">-list compose</a>.</p>
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