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218 <h1>ImageMagick Image Composition</h1>
219 <p>This page descibed the Image composition methods that is used to define how
220 two images should be merged together in various image operations. For the
221 Command Line API it is typically set using the <A
222 HREF="../www/command-line-options.html#compose" >-compose</A> setting option. </p>
225 <p>The description of composition uses abstract terminology in order to allow
226 the description to be more precise, while avoiding constant values which are
227 specific to a particular build configuration. Each image pixel is represented
228 by red, green, and blue levels (which are equal for a gray pixel). The
229 build-dependent value <em class="QR">QuantumRange</em> is the maximum integral
230 value which may be stored, per pixel, in the red, green, or blue channels of
231 the image. Each image pixel may also optionally (if the image matte channel is
232 enabled) have an associated level of opacity, ranging from <em>opaque</em> to
233 <em>transparent</em>, which may be used to determine the influence of the pixel
234 color when compositing the pixel with another image pixel. If the image matte
235 channel is disabled, then all pixels in the image are treated as opaque. The
236 color of an opaque pixel is fully visible while the color of a transparent
237 pixel color is entirely absent (pixel color is ignored).</p>
239 <p>By definition, raster images have a rectangular shape. All image rows are of
240 equal length, as are all image columns. By treating the alpha channel as a
241 visual "mask" the rectangular image may be given a "shape" by treating the
242 alpha channel as a cookie-cutter for the image. This is done by setting the
243 pixels within the shape to be opaque, with pixels outside the shape set as
244 transparent. Pixels on the boundary of the shape may be between opaque and
245 transparent in order to provide antialiasing (visually smooth edges). The
246 description of the composition operators use this concept of image "shape" in
247 order to make the description of the operators easier to understand. While it
248 is convenient to describe the operators in terms of "shapes" they are by no
249 means limited to mask-style operations since they are based on continuous
250 floating-point mathematics rather than simple boolean operations.</p>
252 <p>The following alpha blending (Duff-Porter) compose methods are available:</p>
257 <th align="left" style="width: 8%">Method</th>
258 <th align="left">Description</th>
262 <td valign="top">clear</td>
263 <td valign="top">Both the color and the alpha of the destination are
264 cleared. Neither the source nor the destination are used (except for
265 destinations size and other meta-data which is always preserved.</td>
269 <td valign="top">src</td>
270 <td valign="top">The source is copied to the destination. The destination
271 is not used as input, though it is cleared.</td>
275 <td valign="top">dst</td>
276 <td valign="top">The destination is left untouched. The source image is
277 completely ignored.</td>
281 <td valign="top">src-over</td>
282 <td valign="top">The source is composited over the destination. this is
283 the default alpha blending compose method, when neither the compose
284 setting is set, nor is set in the image meta-data.</td>
288 <td valign="top">dst-over</td>
289 <td valign="top">The destination is composited over the source and the
290 result replaces the destination.</td>
294 <td valign="top">src-in</td>
295 <td valign="top">The part of the source lying inside of the destination
296 replaces the destination.</td>
300 <td valign="top">dst-in</td>
301 <td valign="top">The part of the destination lying inside of the source
302 replaces the destination. Areas not overlaid are cleared.</td>
306 <td valign="top">src-out</td>
307 <td valign="top">The part of the source lying outside of the destination
308 replaces the destination.</td>
312 <td valign="top">dst-out</td>
313 <td valign="top">The part of the destination lying outside of the source
314 replaces the destination.</td>
318 <td valign="top">src-atop</td>
319 <td valign="top">The part of the source lying inside of the destination is
320 composited onto the destination.</td>
324 <td valign="top">dst-atop</td>
325 <td valign="top">The part of the destination lying inside of the source is
326 composited over the source and replaces the destination. Areas not
327 overlaid are cleared. </td>
331 <td valign="top">xor</td>
332 <td valign="top">The part of the source that lies outside of the
333 destination is combined with the part of the destination that lies
334 outside of the source. Source or Destination, but not both. </td>
340 <p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
341 For example the default compose method can be specified as just 'Over'.</p>
343 <p>Many of these compose methods will clear the destination image which was
344 not overlaid by the source image. This is to be expected as part of that
345 specific composition methods defintion. You can disable this by setting the
346 special <A HREF="../www/command-line-options.html#define"
347 >-define</A> 'compose:outside-overlay' to a value of 'false' will turn off
350 <p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
351 related method '<kbd>Copy</kbd>' has been provided. This is equivalent to
352 using the '<kbd>Src</kbd>' with the special <A HREF="../www/command-line-options.html#define"
353 >-define</A> option '<kbd>compose:outside-overlay</kbd>' set to
354 '<kbd>false</kbd>', so as to only modify the overlaid area, without clearing
355 the rest of the image outside the overlaid area. </p>
359 <p>The following mathemathical composition methods are also available. </p>
364 <th align="left" style="width: 8%">Method</th>
365 <th align="left">Description</th>
369 <td valign="top">multiply</td>
370 <td valign="top">The source is multiplied by the destination and replaces
371 the destination. The resultant color is always at least as dark as
372 either of the two constituent colors. Multiplying any color with black
373 produces black. Multiplying any color with white leaves the original
374 color unchanged.</td>
378 <td valign="top">screen</td>
379 <td valign="top">The source and destination are complemented and then
380 multiplied and then replace the destination. The resultant color is
381 always at least as light as either of the two constituent colors.
382 Screening any color with white produces white. Screening any color
383 with black leaves the original color unchanged.</td>
387 <td valign="top">plus</td>
388 <td valign="top">The source is added to the destination and replaces the
389 destination. This operator is useful for averaging or a controled
390 merger of two images, rather than a direct overlay.</td>
394 <td valign="top">add</td>
395 <td valign="top">As per 'plus' but transparency data is treated as matte
396 values. As such any transparent areas in either image remain
401 <td valign="top">minus</td>
402 <td valign="top">Subtract the colors in the source image from the
403 destination image. When transparency is involved, opaque areas is
404 subtracted from any destination opaque areas. </td>
408 <td valign="top">subtract</td>
409 <td valign="top">Subtract the colors in the source image from the
410 destination image. When transparency is involved transparent areas are
411 subtracted, so only the opaque areas in the source remain opaque in
412 the destination image. </td>
416 <td valign="top">difference</td>
417 <td valign="top">Subtracts the darker of the two constituent colors from
418 the lighter. Painting with white inverts the destination color.
419 Painting with black produces no change.</td>
423 <td valign="top">exclusion</td>
424 <td valign="top">Produces an effect similar to that of 'difference', but
425 appears as lower contrast. Painting with white inverts the
426 destination color. Painting with black produces no change.</td>
430 <td valign="top">darken</td>
431 <td valign="top">Selects the darker of the destination and source colors.
432 The destination is replaced with the source when the source is darker,
433 otherwise it is left unchanged.</td>
437 <td valign="top">lighten</td>
438 <td valign="top">Selects the lighter of the destination and source colors.
439 The destination is replaced with the source when the source is
440 lighter, otherwise it is left unchanged. </td>
446 <p>Typically these use the default 'Over' alpha blending when transparencies
447 are also involved, except for 'Plus' which uses a 'plus' alpha blending. This
448 means the alpha channel of both images will only be used to ensure that any
449 visible input remains visible even in parts not overlaid. It also means that
450 any values are weighted by the alpha channel of the input and output images.
451 This 'Over' alpha blending is also applied to the lighting composition methods
454 <p>As of IM v6.6.1-6, if the special '<kbd>Sync</kbd>' flag is not specified
455 (enabled by default) with the <a href="../www/command-line-options.html#channel"
456 >-channel</a> setting, then the above mathematical compositions will nolonger
457 synchronise its actions with the alpha channel. Instead the math composition
458 will be applied on an individual channel basis as defined by the <a
459 href="../www/command-line-options.html#channel"
460 >-channel</a>. This includes the alpha channel. This special usage
461 allows you to perform true mathematics of the image channels, without alpha
462 compostion effects, becomming involved. </p>
464 <p>This special flag is not applied to the lighting composition methods (see
465 below) even though they are closely related to mathematical composition
470 <p>The following lighting composition methods are also available. </p>
475 <th align="left" style="width: 8%">Method</th>
476 <th align="left">Description</th>
480 <td valign="top">linear-dodge</td>
481 <td valign="top">This is equivalent to 'Plus' in that the color channels
482 are simply added, however it does not 'Plus' the alpha channel, but
483 uses the normal 'Over' alpha blending, which transparencies are
484 involved. Produces a sort of additive multiply-like result. Added
485 ImageMagick version 6.5.4-3. </td>
489 <td valign="top">linear-burn</td>
490 <td valign="top">As 'Linear-Dodge', but also subtract one from the result.
491 Sort of a additive 'Screen' of the images. Added ImageMagick version
496 <td valign="top">color-dodge</td>
497 <td valign="top">Brightens the destination color to reflect the source
498 color. Painting with black produces no change.</td>
502 <td valign="top">color-burn</td>
503 <td valign="top">Darkens the destination color to reflect the source
504 color. Painting with white produces no change. Fixed in ImageMagick
505 version 6.5.4-3. </td>
509 <td valign="top">overlay</td>
510 <td valign="top">Multiplies or screens the colors, dependent on the
511 destination color. Source colors overlay the destination whilst
512 preserving its highlights and shadows. The destination color is not
513 replaced, but is mixed with the source color to reflect the lightness
514 or darkness of the destination.</td>
518 <td valign="top">hard-light</td>
519 <td valign="top">Multiplies or screens the colors, dependent on the source
520 color value. If the source color is lighter than 0.5, the destination
521 is lightened as if it were screened. If the source color is darker
522 than 0.5, the destination is darkened, as if it were multiplied. The
523 degree of lightening or darkening is proportional to the difference
524 between the source color and 0.5. If it is equal to 0.5 the
525 destination is unchanged. Painting with pure black or white produces
531 <td valign="top">linear-light</td>
532 <td valign="top">Like 'Hard-Light' but using linear-dodge and linear-burn
533 instead. Increases contrast slightly with an impact on the
534 foreground's tonal values.</td>
538 <td valign="top">soft-light</td>
539 <td valign="top">Darkens or lightens the colors, dependent on the source
540 color value. If the source color is lighter than 0.5, the destination
541 is lightened. If the source color is darker than 0.5, the destination
542 is darkened, as if it were burned in. The degree of darkening or
543 lightening is proportional to the difference between the source color
544 and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
545 with pure black or white produces a distinctly darker or lighter area,
546 but does not result in pure black or white. Fixed in ImageMagick
547 version 6.5.4-3. </td>
551 <td valign="top">pegtop-light</td>
552 <td valign="top">Almost equivalent to 'Soft-Light', but using a
553 continuious mathematical formula rather than two conditionally
554 selected formulae. Added ImageMagick version 6.5.4-3. </td>
558 <td valign="top">vivid-light</td>
559 <td valign="top">A modified 'Linear-Light' designed to preserve very stong
560 primary and secondary colors in the image. Added ImageMagick version
565 <td valign="top">pin-light</td>
566 <td valign="top">Similar to 'Hard-Light', but using sharp linear shadings,
567 to similate the effects of a strong 'pinhole' light source. Added
568 ImageMagick version 6.5.4-3. </td>
577 <p>Also included are these special purpose compose methods:</p>
582 <th align="left" style="width: 8%">Method</th>
583 <th align="left">Description</th>
587 <td valign="top">copy</td>
588 <td valign="top">This is equivalent to the Duff-Porter composition method
589 '<kbd>Src,</kbd>' but without clearing the parts of the destination
590 image that is not overlaid. </td>
594 <td valign="top">copy-*</td>
595 <td valign="top">Copy the specified channel (Red, Green, Blue, Cyan,
596 Magenta, Yellow, Black, or Opacity) in the source image to the
597 same channel in the destination image. If the channel specified
598 does not exist in the source image, (which can only happen for methods,
599 '<kbd>copy-opacity</kbd>' or '<kbd>copy-black</kbd>') then it is
600 assumed that the source image is a special grayscale channel image
601 of the values that is to be copied. </td>
605 <td valign="top">change-mask</td>
606 <td valign="top">Replace any destination pixel that is the similar to the
607 source images pixel (as defined by the current <a
608 href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
616 <p>On top of these composed methods are a few special ones that not only require
617 the two images that are being merged or overlaid, but have some extra numerical
618 arguments, which are tabled below. </p>
620 <p>In the "<code>composite</code>" command these composition methods are
621 selected using special options with the arguments needed. They are usually,
622 but not always, the same name as the composte 'method' they use, and replaces
623 the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
624 setting in the "<code>composite</code>" command. For example... </p>
626 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>composite ... -blend 50x50 ...</span></p>
627 <p>As of IM v6.5.3-4 the "<code>convert</code>" command can now also supply
628 these extra arguments to its <a href="../www/command-line-options.html#composite"
629 >-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
630 attribute of '<kbd class="arg">compose:args</kbd>'. This means you can now
631 make use of these special argumented <a href="../www/command-line-options.html#compose"
632 >-compose</a> methods, those the argument and the method both need to be set
633 separately. For example... </p>
635 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert ... -compose blend -define compose:args=50,50 -composite ...</span></p>
636 <p>The following is a table of these special 'argumented' compose methods,
637 with a brief summary of what they do. For more details see the equivalent
638 "composite" command option name. </p>
643 <th align="left" style="width: 8%">Method</th>
644 <th align="left">Description</th>
648 <td valign="top">dissolve</td>
649 <td valign="top">Arguments:
650 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
651 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
652 <br>Dissolve the 'source' image by the percentage given before overlaying
653 'over' the 'destination' image. If <em class="arg">src_percent</em> is
654 greater than 100, it starts dissolving the main image so it will
655 become transparent at a value of '<kbd class="arg">200</kbd>'. If
656 both percentages are given, each image are dissolved to the
662 <td valign="top">blend</td>
663 <td valign="top">Arguments:
664 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
665 <br>Equivalent to "<code>composite</code>" <a
666 href="../www/command-line-options.html#blend">-blend</a>
667 <br>Average the images together ('plus') according to the percentages
668 given and each pixels transparency. If only a single percentage value
669 is given it sets the weight of the composite or 'source' image, while
670 the background image is weighted by the exact opposite amount. That is
671 a <kbd>-blend 30</kbd> merges 30% of the 'source' image with 70% of
672 the 'destination' image. Thus it is equivalent to <kbd>-blend
678 <td valign="top">mathematics</td>
679 <td valign="top">Arguments: <em class="arg">A, B, C, D</em>
680 <br>Not available in "<code>composite</code>" at this time.
681 <br>Merge the source and destination images according to the formula
682 <br> <code>A*Sc*Dc + B*Sc + C*Dc + D</code>
683 <br>Can be used to generate a custom composition method that would
684 otherwise need to be implemented using the slow <a
685 href="../www/command-line-options.html#fx">-fx</a> DIY image operator. Added
686 to ImageMagick version 6.5.4-3.
687 <br>As of IM v6.6.1-6 this method will do per-channel math compositions
688 if the 'Sync' flag is removed from <a
689 href="../www/command-line-options.html#channel" >-channel</a>, just like all
690 the other mathematical compostion methods above.
695 <td valign="top">modulate</td>
696 <td valign="top">Arguments:
697 <em class="arg">brightness</em>[x<em class="arg">saturation</em>]
698 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
699 <br>Take a grayscale image (with alpha mask) and modify the destination
700 image's brightness according to watermark image's grayscale value and
701 the <em class="arg">brightness</em> percentage. The destinations
702 color saturation attribute is just direct modified by the <em
703 class="arg">saturation</em> percentage, which defaults to 100 percent
710 <td valign="top">displace</td>
711 <td valign="top">Arguments:
712 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em>][!][%]
713 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
714 <br>With this option, the 'overlay' image, and optionally the 'mask'
715 image, is used as a relative displacement map, which is used to
716 displace the lookup of what part of the destination image is seen at
717 each point of the overlaid area. Much like the displacement map is a
718 'lens' that distorts the original 'background' image behind it.
720 The X-scale is modulated by the 'red' channel of the overlay image
721 while the Y-scale is modulated by the green channel, (the mask image
722 if given is rolled into green channel of the overlay image. This
723 separation allows you to modulate the X and Y lookup displacement
724 separately allowing you to do 2-dimensional displacements, rather
725 than 1-dimensional verctored displacements (using grayscale image).
727 If the overlay image contains transparency this is used as a mask
728 of the resulting image to remove 'invalid' pixels.
730 The '%' flag makes the displacement scale relative to the size of the
731 overlay image (100% = half width/height of image). Using '!' switches
732 percentage arguments to refer to the destination image size instead.
734 Special flags were added Added to ImageMagick version 6.5.3-5.
739 <td valign="top">distort</td>
740 <td valign="top">Arguments:
741 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em
742 >[+<em class="arg">X-center</em>+<em class="arg">Y-center</em>]][!][%]
743 <br>Not available in "<code>composite</code>" at this time.
744 <br>Exactly as per 'Displace' (above), but using absolute coordinates,
745 relative to the center of the overlay (or that given). Basically
746 allows you to generate absolute distortion maps where 'black' will
747 look up the left/top edge, and 'white' looks up the bottom/right
748 edge of the destination image, according to the scale given.
750 The '!' flag not only switches percentage scaling, to use the
751 destination image, but also the image the center offset of the lookup.
752 This means the overlay can lookup a completely different region of the
755 Added to ImageMagick version 6.5.3-5.
760 <td valign="top">blur</td>
761 <td valign="top">Arguments:
762 <em class="arg">Width</em>[x<em class="arg">Height</em
763 >[+<em class="arg">Angle</em>][+<em class="arg">Angle2</em>]]
764 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
765 <br>A Variable Blur Mapping Composition method, where each pixel in the
766 overlaid region is replaced with an Elliptical Weighted Average (EWA),
767 with an ellipse (typically a circle) of the given sigma size, scaled
768 according to overlay (source image) grayscale mapping.
770 As per 'Displace' and 'Distort', the red channel will modulate the
771 width of the ellipse, while the green channel will modulate the height
772 of the ellipse. If a single Angle value is given in the arguments,
773 then the ellipse will then be rotated by the angle specifed.
775 Normally the blue channel of the mapping overlay image is ignored.
776 However if a second ellipse angle is given, then it is assumed that
777 the blue channel defines a variable angle for the ellipse ranging from
778 the first angle to the second angle given. This allows to generate
779 radial blurs, or a rough approximation for rotational blur. Or any mix
782 Added to ImageMagick version 6.5.4-0.
789 <p>To print a complete list of all the available compose operators, use <a
790 href="../www/command-line-options.html#list">-list compose</a>.</p>
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