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200 <h1>ImageMagick Image Composition</h1>
201 <p>This page descibed the Image composition methods that is used to define how
202 two images should be merged together in various image operations. For the
203 Command Line API it is typically set using the <A
204 HREF="../www/command-line-options.html#compose" >-compose</A> setting option. </p>
207 <p>The description of composition uses abstract terminology in order to allow
208 the description to be more precise, while avoiding constant values which are
209 specific to a particular build configuration. Each image pixel is represented
210 by red, green, and blue levels (which are equal for a gray pixel). The
211 build-dependent value <em class="QR">QuantumRange</em> is the maximum integral
212 value which may be stored, per pixel, in the red, green, or blue channels of
213 the image. Each image pixel may also optionally (if the image matte channel is
214 enabled) have an associated level of opacity, ranging from <em>opaque</em> to
215 <em>transparent</em>, which may be used to determine the influence of the pixel
216 color when compositing the pixel with another image pixel. If the image matte
217 channel is disabled, then all pixels in the image are treated as opaque. The
218 color of an opaque pixel is fully visible while the color of a transparent
219 pixel color is entirely absent (pixel color is ignored).</p>
221 <p>By definition, raster images have a rectangular shape. All image rows are of
222 equal length, as are all image columns. By treating the alpha channel as a
223 visual "mask" the rectangular image may be given a "shape" by treating the
224 alpha channel as a cookie-cutter for the image. This is done by setting the
225 pixels within the shape to be opaque, with pixels outside the shape set as
226 transparent. Pixels on the boundary of the shape may be between opaque and
227 transparent in order to provide antialiasing (visually smooth edges). The
228 description of the composition operators use this concept of image "shape" in
229 order to make the description of the operators easier to understand. While it
230 is convenient to describe the operators in terms of "shapes" they are by no
231 means limited to mask-style operations since they are based on continuous
232 floating-point mathematics rather than simple boolean operations.</p>
234 <p>The following alpha blending (Duff-Porter) compose methods are available:</p>
239 <th align="left" style="width: 8%">Method</th>
240 <th align="left">Description</th>
244 <td valign="top">clear</td>
245 <td valign="top">Both the color and the alpha of the destination are
246 cleared. Neither the source nor the destination are used (except for
247 destinations size and other meta-data which is always preserved.</td>
251 <td valign="top">src</td>
252 <td valign="top">The source is copied to the destination. The destination
253 is not used as input, though it is cleared.</td>
257 <td valign="top">dst</td>
258 <td valign="top">The destination is left untouched. The source image is
259 completely ignored.</td>
263 <td valign="top">src-over</td>
264 <td valign="top">The source is composited over the destination. this is
265 the default alpha blending compose method, when neither the compose
266 setting is set, nor is set in the image meta-data.</td>
270 <td valign="top">dst-over</td>
271 <td valign="top">The destination is composited over the source and the
272 result replaces the destination.</td>
276 <td valign="top">src-in</td>
277 <td valign="top">The part of the source lying inside of the destination
278 replaces the destination.</td>
282 <td valign="top">dst-in</td>
283 <td valign="top">The part of the destination lying inside of the source
284 replaces the destination. Areas not overlaid are cleared.</td>
288 <td valign="top">src-out</td>
289 <td valign="top">The part of the source lying outside of the destination
290 replaces the destination.</td>
294 <td valign="top">dst-out</td>
295 <td valign="top">The part of the destination lying outside of the source
296 replaces the destination.</td>
300 <td valign="top">src-atop</td>
301 <td valign="top">The part of the source lying inside of the destination is
302 composited onto the destination.</td>
306 <td valign="top">dst-atop</td>
307 <td valign="top">The part of the destination lying inside of the source is
308 composited over the source and replaces the destination. Areas not
309 overlaid are cleared. </td>
313 <td valign="top">xor</td>
314 <td valign="top">The part of the source that lies outside of the
315 destination is combined with the part of the destination that lies
316 outside of the source. Source or Destination, but not both. </td>
322 <p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
323 For example the default compose method can be specified as just 'Over'.</p>
325 <p>Many of these compose methods will clear the destination image which was
326 not overlaid by the source image. This is to be expected as part of that
327 specific composition methods defintion. You can disable this by setting the
328 special <A HREF="../www/command-line-options.html#define"
329 >-define</A> 'compose:outside-overlay' to a value of 'false' will turn off
332 <p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
333 related method '<kbd>Copy</kbd>' has been provided. This is equivelent to
334 using the '<kbd>Src</kbd>' with the special <A HREF="../www/command-line-options.html#define"
335 >-define</A> option '<kbd>compose:outside-overlay</kbd>' set to
336 '<kbd>false</kbd>', so as to only modify the overlaid area, without clearing
337 the rest of the image outside the overlaid area. </p>
341 <p>The following mathemathical composition methods are also available. </p>
346 <th align="left" style="width: 8%">Method</th>
347 <th align="left">Description</th>
351 <td valign="top">multiply</td>
352 <td valign="top">The source is multiplied by the destination and replaces
353 the destination. The resultant color is always at least as dark as
354 either of the two constituent colors. Multiplying any color with black
355 produces black. Multiplying any color with white leaves the original
356 color unchanged.</td>
360 <td valign="top">screen</td>
361 <td valign="top">The source and destination are complemented and then
362 multiplied and then replace the destination. The resultant color is
363 always at least as light as either of the two constituent colors.
364 Screening any color with white produces white. Screening any color
365 with black leaves the original color unchanged.</td>
369 <td valign="top">plus</td>
370 <td valign="top">The source is added to the destination and replaces the
371 destination. This operator is useful for averaging or a controled
372 merger of two images, rather than a direct overlay.</td>
376 <td valign="top">add</td>
377 <td valign="top">As per 'plus' but transparency data is treated as matte
378 values. As such any transparent areas in either image remain
383 <td valign="top">minus</td>
384 <td valign="top">Subtract the colors in the source image from the
385 destination image. When transparency is involved, opaque areas is
386 subtracted from any destination opaque areas. </td>
390 <td valign="top">subtract</td>
391 <td valign="top">Subtract the colors in the source image from the
392 destination image. When transparency is involved transparent areas are
393 subtracted, so only the opaque areas in the source remain opaque in
394 the destination image. </td>
398 <td valign="top">difference</td>
399 <td valign="top">Subtracts the darker of the two constituent colors from
400 the lighter. Painting with white inverts the destination color.
401 Painting with black produces no change.</td>
405 <td valign="top">exclusion</td>
406 <td valign="top">Produces an effect similar to that of 'difference', but
407 appears as lower contrast. Painting with white inverts the
408 destination color. Painting with black produces no change.</td>
412 <td valign="top">darken</td>
413 <td valign="top">Selects the darker of the destination and source colors.
414 The destination is replaced with the source when the source is darker,
415 otherwise it is left unchanged.</td>
419 <td valign="top">lighten</td>
420 <td valign="top">Selects the lighter of the destination and source colors.
421 The destination is replaced with the source when the source is
422 lighter, otherwise it is left unchanged. </td>
428 <p>Typically these use the default 'Over' alpha blending when transparencies
429 are also involved, except for 'Plus' which uses a 'plus' alpha blending. This
430 means the alpha channel of both images will only be used to ensure that any
431 visible input remains visible even in parts not overlaid. It also means that
432 any values are weighted by the alpha channel of the input and output images.
433 This 'Over' alpha blending is also applied to the lighting composition methods
436 <p>As of IM v6.6.1-6, if the special '<kbd>Sync</kbd>' flag is not specified
437 (enabled by default) with the <a href="../www/command-line-options.html#channel"
438 >-channel</a> setting, then the above mathematical compositions will nolonger
439 syncronise its actions with the alpha channel. Instead the math composition
440 will be applied on an individual channel basis as defined by the <a
441 href="../www/command-line-options.html#channel"
442 >-channel</a>. This includes the alpha channel. This special usage
443 allows you to perform true mathematics of the image channels, without alpha
444 compostion effects, becomming involved. </p>
446 <p>This special flag is not applied to the lighting composition methods (see
447 below) even though they are closely related to mathematical composition
452 <p>The following lighting composition methods are also available. </p>
457 <th align="left" style="width: 8%">Method</th>
458 <th align="left">Description</th>
462 <td valign="top">linear-dodge</td>
463 <td valign="top">This is equivelent to 'Plus' in that the color channels
464 are simply added, however it does not 'Plus' the alpha channel, but
465 uses the normal 'Over' alpha blending, which transparencies are
466 involved. Produces a sort of additive multiply-like result. Added
467 ImageMagick version 6.5.4-3. </td>
471 <td valign="top">linear-burn</td>
472 <td valign="top">As 'Linear-Dodge', but also subtract one from the result.
473 Sort of a additive 'Screen' of the images. Added ImageMagick version
478 <td valign="top">color-dodge</td>
479 <td valign="top">Brightens the destination color to reflect the source
480 color. Painting with black produces no change.</td>
484 <td valign="top">color-burn</td>
485 <td valign="top">Darkens the destination color to reflect the source
486 color. Painting with white produces no change. Fixed in ImageMagick
487 version 6.5.4-3. </td>
491 <td valign="top">overlay</td>
492 <td valign="top">Multiplies or screens the colors, dependent on the
493 destination color. Source colors overlay the destination whilst
494 preserving its highlights and shadows. The destination color is not
495 replaced, but is mixed with the source color to reflect the lightness
496 or darkness of the destination.</td>
500 <td valign="top">hard-light</td>
501 <td valign="top">Multiplies or screens the colors, dependent on the source
502 color value. If the source color is lighter than 0.5, the destination
503 is lightened as if it were screened. If the source color is darker
504 than 0.5, the destination is darkened, as if it were multiplied. The
505 degree of lightening or darkening is proportional to the difference
506 between the source color and 0.5. If it is equal to 0.5 the
507 destination is unchanged. Painting with pure black or white produces
513 <td valign="top">linear-light</td>
514 <td valign="top">Like 'Hard-Light' but using linear-dodge and linear-burn
515 instead. Increases contrast slightly with an impact on the
516 foreground's tonal values.</td>
520 <td valign="top">soft-light</td>
521 <td valign="top">Darkens or lightens the colors, dependent on the source
522 color value. If the source color is lighter than 0.5, the destination
523 is lightened. If the source color is darker than 0.5, the destination
524 is darkened, as if it were burned in. The degree of darkening or
525 lightening is proportional to the difference between the source color
526 and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
527 with pure black or white produces a distinctly darker or lighter area,
528 but does not result in pure black or white. Fixed in ImageMagick
529 version 6.5.4-3. </td>
533 <td valign="top">pegtop-light</td>
534 <td valign="top">Almost equivelent to 'Soft-Light', but using a
535 continuious mathematical formula rather than two conditionally
536 selected formulae. Added ImageMagick version 6.5.4-3. </td>
540 <td valign="top">vivid-light</td>
541 <td valign="top">A modified 'Linear-Light' designed to preserve very stong
542 primary and secondary colors in the image. Added ImageMagick version
547 <td valign="top">pin-light</td>
548 <td valign="top">Similar to 'Hard-Light', but using sharp linear shadings,
549 to similate the effects of a strong 'pinhole' light source. Added
550 ImageMagick version 6.5.4-3. </td>
559 <p>Also included are these special purpose compose methods:</p>
564 <th align="left" style="width: 8%">Method</th>
565 <th align="left">Description</th>
569 <td valign="top">copy</td>
570 <td valign="top">This is equivelent to the Duff-Porter composition method
571 '<kbd>Src,</kbd>' but without clearing the parts of the destination
572 image that is not overlaid. </td>
576 <td valign="top">copy-*</td>
577 <td valign="top">Copy the specified channel (Red, Green, Blue, Cyan,
578 Magenta, Yellow, Black, or Opacity) in the source image to the
579 same channel in the destination image. If the channel specified
580 does not exist in the source image, (which can only happen for methods,
581 '<kbd>copy-opacity</kbd>' or '<kbd>copy-black</kbd>') then it is
582 assumed that the source image is a special grayscale channel image
583 of the values that is to be copied. </td>
587 <td valign="top">change-mask</td>
588 <td valign="top">Replace any destination pixel that is the similar to the
589 source images pixel (as defined by the current <a
590 href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
598 <p>On top of these composed methods are a few special ones that not only require
599 the two images that are being merged or overlaid, but have some extra numerical
600 arguments, which are tabled below. </p>
602 <p>In the "<code>composite</code>" command these composition methods are
603 selected using special options with the arguments needed. They are usually,
604 but not always, the same name as the composte 'method' they use, and replaces
605 the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
606 setting in the "<code>composite</code>" command. For example... </p>
608 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>composite ... -blend 50x50 ...</span></p>
609 <p>As of IM v6.5.3-4 the "<code>convert</code>" command can now also supply
610 these extra arguments to its <a href="../www/command-line-options.html#composite"
611 >-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
612 attribute of '<kbd class="arg">compose:args</kbd>'. This means you can now
613 make use of these special argumented <a href="../www/command-line-options.html#compose"
614 >-compose</a> methods, those the argument and the method both need to be set
615 separatally. For example... </p>
617 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert ... -compose blend -define compose:args=50,50 -composite ...</span></p>
618 <p>The following is a table of these special 'argumented' compose methods,
619 with a brief summary of what they do. For more details see the equivalent
620 "composite" command option name. </p>
625 <th align="left" style="width: 8%">Method</th>
626 <th align="left">Description</th>
630 <td valign="top">dissolve</td>
631 <td valign="top">Arguments:
632 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
633 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
634 <br>Dissolve the 'source' image by the percentage given before overlaying
635 'over' the 'destination' image. If <em class="arg">src_percent</em> is
636 greater than 100, it starts dissolving the main image so it will
637 become transparent at a value of '<kbd class="arg">200</kbd>'. If
638 both percentages are given, each image are dissolved to the
644 <td valign="top">blend</td>
645 <td valign="top">Arguments:
646 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
647 <br>Equivalent to "<code>composite</code>" <a
648 href="../www/command-line-options.html#blend">-blend</a>
649 <br>Average the images together ('plus') according to the percentages
650 given and each pixels transparency. If only a single percentage value
651 is given it sets the weight of the composite or 'source' image, while
652 the background image is weighted by the exact opposite amount. That is
653 a <kbd>-blend 30</kbd> merges 30% of the 'source' image with 70% of
654 the 'destination' image. Thus it is equivalent to <kbd>-blend
660 <td valign="top">mathematics</td>
661 <td valign="top">Arguments: <em class="arg">A, B, C, D</em>
662 <br>Not available in "<code>composite</code>" at this time.
663 <br>Merge the source and destination images according to the formula
664 <br> <code>A*Sc*Dc + B*Sc + C*Dc + D</code>
665 <br>Can be used to generate a custom composition method that would
666 otherwise need to be implemented using the slow <a
667 href="../www/command-line-options.html#fx">-fx</a> DIY image operator. Added
668 to ImageMagick version 6.5.4-3.
669 <br>As of IM v6.6.1-6 this method will do per-channel math compositions
670 if the 'Sync' flag is removed from <a
671 href="../www/command-line-options.html#channel" >-channel</a>, just like all
672 the other mathematical compostion methods above.
677 <td valign="top">modulate</td>
678 <td valign="top">Arguments:
679 <em class="arg">brightness</em>[x<em class="arg">saturation</em>]
680 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
681 <br>Take a grayscale image (with alpha mask) and modify the destination
682 image's brightness according to watermark image's grayscale value and
683 the <em class="arg">brightness</em> percentage. The destinations
684 color saturation attribute is just direct modified by the <em
685 class="arg">saturation</em> percentage, which defaults to 100 percent
692 <td valign="top">displace</td>
693 <td valign="top">Arguments:
694 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em>][!][%]
695 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
696 <br>With this option, the 'overlay' image, and optionally the 'mask'
697 image, is used as a relative displacement map, which is used to
698 displace the lookup of what part of the destination image is seen at
699 each point of the overlaid area. Much like the displacement map is a
700 'lens' that distorts the original 'background' image behind it.
702 The X-scale is modilated by the 'red' channel of the overlay image
703 while the Y-scale is modulated by the green channel, (the mask image
704 if given is rolled into green channel of the overlay image. This
705 separation allows you to modulate the X and Y lookup displacement
706 separatally allowing you to di 2 dimentional displacements, rather
707 than 1 dimentional verctored displacements (using grayscale image).
709 If the overlay image contains transparency this is used as a mask
710 of the resulting image to remove 'invalid' pixels.
712 The '%' flag makes the displacement scale relative to the size of the
713 overlay image (100% = half width/height of image). Using '!' switches
714 percentage arguments to refer to the destination image size instead.
716 Special flags were added Added to ImageMagick version 6.5.3-5.
721 <td valign="top">distort</td>
722 <td valign="top">Arguments:
723 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em
724 >[+<em class="arg">X-center</em>+<em class="arg">Y-center</em>]][!][%]
725 <br>Not available in "<code>composite</code>" at this time.
726 <br>Exactly as per 'Displace' (above), but using absolute coordinates,
727 relative to the center of the overlay (or that given). Basically
728 allows you to generate absolute distortion maps where 'black' will
729 look up the left/top edge, and 'white' looks up the bottom/right
730 edge of the destination image, according to the scale given.
732 The '!' flag not only switches percentage scaling, to use the
733 destination image, but also the image the center offset of the lookup.
734 This means the overlay can lookup a completely different region of the
737 Added to ImageMagick version 6.5.3-5.
742 <td valign="top">blur</td>
743 <td valign="top">Arguments:
744 <em class="arg">Width</em>[x<em class="arg">Height</em
745 >[+<em class="arg">Angle</em>][+<em class="arg">Angle2</em>]]
746 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
747 <br>A Variable Blur Mapping Composition method, where each pixel in the
748 overlaid region is replaced with an Elliptical Weighted Average (EWA),
749 with an ellipse (typically a circle) of the given sigma size, scaled
750 according to overlay (source image) grayscale mapping.
752 As per 'Displace' and 'Distort', the red channel will modulate the
753 width of the ellipse, while the green channel will modulate the height
754 of the ellipse. If a single Angle value is given in the arguments,
755 then the ellipse will then be rotated by the angle specifed.
757 Normally the blue channel of the mapping overlay image is ignored.
758 However if a second ellipse angle is given, then it is assumed that
759 the blue channel defines a variable angle for the ellipse ranging from
760 the first angle to the second angle given. This allows to generate
761 radial blurs, or a rough approximation for rotational blur. Or any mix
764 Added to ImageMagick version 6.5.4-0.
771 <p>To print a complete list of all the available compose operators, use <a
772 href="../www/command-line-options.html#list">-list compose</a>.</p>
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