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182 <h1>ImageMagick Image Composition</h1>
183 <p>This page descibed the Image composition methods that is used to define how
184 two images should be merged together in various image operations. For the
185 Command Line API it is typically set using the <A
186 HREF="../www/command-line-options.html#compose" >-compose</A> setting option. </p>
189 <p>The description of composition uses abstract terminology in order to allow
190 the description to be more precise, while avoiding constant values which are
191 specific to a particular build configuration. Each image pixel is represented
192 by red, green, and blue levels (which are equal for a gray pixel). The
193 build-dependent value <em class="QR">QuantumRange</em> is the maximum integral
194 value which may be stored, per pixel, in the red, green, or blue channels of
195 the image. Each image pixel may also optionally (if the image matte channel is
196 enabled) have an associated level of opacity, ranging from <em>opaque</em> to
197 <em>transparent</em>, which may be used to determine the influence of the pixel
198 color when compositing the pixel with another image pixel. If the image matte
199 channel is disabled, then all pixels in the image are treated as opaque. The
200 color of an opaque pixel is fully visible while the color of a transparent
201 pixel color is entirely absent (pixel color is ignored).</p>
203 <p>By definition, raster images have a rectangular shape. All image rows are of
204 equal length, as are all image columns. By treating the alpha channel as a
205 visual "mask" the rectangular image may be given a "shape" by treating the
206 alpha channel as a cookie-cutter for the image. This is done by setting the
207 pixels within the shape to be opaque, with pixels outside the shape set as
208 transparent. Pixels on the boundary of the shape may be between opaque and
209 transparent in order to provide antialiasing (visually smooth edges). The
210 description of the composition operators use this concept of image "shape" in
211 order to make the description of the operators easier to understand. While it
212 is convenient to describe the operators in terms of "shapes" they are by no
213 means limited to mask-style operations since they are based on continuous
214 floating-point mathematics rather than simple boolean operations.</p>
216 <p>The following alpha blending (Duff-Porter) compose methods are available:</p>
221 <th align="left" style="width: 8%">Method</th>
222 <th align="left">Description</th>
226 <td valign="top">clear</td>
227 <td valign="top">Both the color and the alpha of the destination are
228 cleared. Neither the source nor the destination are used (except for
229 destinations size and other meta-data which is always preserved.</td>
233 <td valign="top">src</td>
234 <td valign="top">The source is copied to the destination. The destination
235 is not used as input, though it is cleared.</td>
239 <td valign="top">dst</td>
240 <td valign="top">The destination is left untouched. The source image is
241 completely ignored.</td>
245 <td valign="top">src-over</td>
246 <td valign="top">The source is composited over the destination. this is
247 the default alpha blending compose method, when neither the compose
248 setting is set, nor is set in the image meta-data.</td>
252 <td valign="top">dst-over</td>
253 <td valign="top">The destination is composited over the source and the
254 result replaces the destination.</td>
258 <td valign="top">src-in</td>
259 <td valign="top">The part of the source lying inside of the destination
260 replaces the destination.</td>
264 <td valign="top">dst-in</td>
265 <td valign="top">The part of the destination lying inside of the source
266 replaces the destination. Areas not overlaid are cleared.</td>
270 <td valign="top">src-out</td>
271 <td valign="top">The part of the source lying outside of the destination
272 replaces the destination.</td>
276 <td valign="top">dst-out</td>
277 <td valign="top">The part of the destination lying outside of the source
278 replaces the destination.</td>
282 <td valign="top">src-atop</td>
283 <td valign="top">The part of the source lying inside of the destination is
284 composited onto the destination.</td>
288 <td valign="top">dst-atop</td>
289 <td valign="top">The part of the destination lying inside of the source is
290 composited over the source and replaces the destination. Areas not
291 overlaid are cleared. </td>
295 <td valign="top">xor</td>
296 <td valign="top">The part of the source that lies outside of the
297 destination is combined with the part of the destination that lies
298 outside of the source. Source or Destination, but not both. </td>
304 <p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
305 For example the default compose method can be specified as just 'Over'.</p>
307 <p>Many of these compose methods will clear the destination image which was
308 not overlaid by the source image. This is to be expected as part of that
309 specific composition methods defintion. You can disable this by setting the
310 special <A HREF="../www/command-line-options.html#define"
311 >-define</A> 'compose:outside-overlay' to a value of 'false' will turn off
314 <p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
315 related method '<kbd>Copy</kbd>' has been provided. This is equivelent to
316 using the '<kbd>Src</kbd>' with the special <A HREF="../www/command-line-options.html#define"
317 >-define</A> option '<kbd>compose:outside-overlay</kbd>' set to
318 '<kbd>false</kbd>', so as to only modify the overlaid area, without clearing
319 the rest of the image outside the overlaid area. </p>
323 <p>The following mathemathical composition methods are also available. </p>
328 <th align="left" style="width: 8%">Method</th>
329 <th align="left">Description</th>
333 <td valign="top">multiply</td>
334 <td valign="top">The source is multiplied by the destination and replaces
335 the destination. The resultant color is always at least as dark as
336 either of the two constituent colors. Multiplying any color with black
337 produces black. Multiplying any color with white leaves the original
338 color unchanged.</td>
342 <td valign="top">screen</td>
343 <td valign="top">The source and destination are complemented and then
344 multiplied and then replace the destination. The resultant color is
345 always at least as light as either of the two constituent colors.
346 Screening any color with white produces white. Screening any color
347 with black leaves the original color unchanged.</td>
351 <td valign="top">plus</td>
352 <td valign="top">The source is added to the destination and replaces the
353 destination. This operator is useful for averaging or a controled
354 merger of two images, rather than a direct overlay.</td>
358 <td valign="top">add</td>
359 <td valign="top">As per 'plus' but transparency data is treated as matte
360 values. As such any transparent areas in either image remain
365 <td valign="top">minus</td>
366 <td valign="top">Subtract the colors in the source image from the
367 destination image. When transparency is involved, opaque areas is
368 subtracted from any destination opaque areas. </td>
372 <td valign="top">subtract</td>
373 <td valign="top">Subtract the colors in the source image from the
374 destination image. When transparency is involved transparent areas are
375 subtracted, so only the opaque areas in the source remain opaque in
376 the destination image. </td>
380 <td valign="top">difference</td>
381 <td valign="top">Subtracts the darker of the two constituent colors from
382 the lighter. Painting with white inverts the destination color.
383 Painting with black produces no change.</td>
387 <td valign="top">exclusion</td>
388 <td valign="top">Produces an effect similar to that of 'difference', but
389 appears as lower contrast. Painting with white inverts the
390 destination color. Painting with black produces no change.</td>
394 <td valign="top">darken</td>
395 <td valign="top">Selects the darker of the destination and source colors.
396 The destination is replaced with the source when the source is darker,
397 otherwise it is left unchanged.</td>
401 <td valign="top">lighten</td>
402 <td valign="top">Selects the lighter of the destination and source colors.
403 The destination is replaced with the source when the source is
404 lighter, otherwise it is left unchanged. </td>
410 <p>Typically these use the default 'Over' alpha blending when transparencies
411 are also involved, except for 'Plus' which uses a 'plus' alpha blending. This
412 means the alpha channel of both images will only be used to ensure that any
413 visible input remains visible even in parts not overlaid. It also means that
414 any values are weighted by the alpha channel of the input and output images.
415 This 'Over' alpha blending is also applied to the lighting composition methods
418 <p>As of IM v6.6.1-6, if the special '<kbd>Sync</kbd>' flag is not specified
419 (enabled by default) with the <a href="../www/command-line-options.html#channel"
420 >-channel</a> setting, then the above mathematical compositions will nolonger
421 syncronise its actions with the alpha channel. Instead the math composition
422 will be applied on an individual channel basis as defined by the <a
423 href="../www/command-line-options.html#channel"
424 >-channel</a>. This includes the alpha channel. This special usage
425 allows you to perform true mathematics of the image channels, without alpha
426 compostion effects, becomming involved. </p>
428 <p>This special flag is not applied to the lighting composition methods (see
429 below) even though they are closely related to mathematical composition
434 <p>The following lighting composition methods are also available. </p>
439 <th align="left" style="width: 8%">Method</th>
440 <th align="left">Description</th>
444 <td valign="top">linear-dodge</td>
445 <td valign="top">This is equivelent to 'Plus' in that the color channels
446 are simply added, however it does not 'Plus' the alpha channel, but
447 uses the normal 'Over' alpha blending, which transparencies are
448 involved. Produces a sort of additive multiply-like result. Added
449 ImageMagick version 6.5.4-3. </td>
453 <td valign="top">linear-burn</td>
454 <td valign="top">As 'Linear-Dodge', but also subtract one from the result.
455 Sort of a additive 'Screen' of the images. Added ImageMagick version
460 <td valign="top">color-dodge</td>
461 <td valign="top">Brightens the destination color to reflect the source
462 color. Painting with black produces no change.</td>
466 <td valign="top">color-burn</td>
467 <td valign="top">Darkens the destination color to reflect the source
468 color. Painting with white produces no change. Fixed in ImageMagick
469 version 6.5.4-3. </td>
473 <td valign="top">overlay</td>
474 <td valign="top">Multiplies or screens the colors, dependent on the
475 destination color. Source colors overlay the destination whilst
476 preserving its highlights and shadows. The destination color is not
477 replaced, but is mixed with the source color to reflect the lightness
478 or darkness of the destination.</td>
482 <td valign="top">hard-light</td>
483 <td valign="top">Multiplies or screens the colors, dependent on the source
484 color value. If the source color is lighter than 0.5, the destination
485 is lightened as if it were screened. If the source color is darker
486 than 0.5, the destination is darkened, as if it were multiplied. The
487 degree of lightening or darkening is proportional to the difference
488 between the source color and 0.5. If it is equal to 0.5 the
489 destination is unchanged. Painting with pure black or white produces
495 <td valign="top">linear-light</td>
496 <td valign="top">Like 'Hard-Light' but using linear-dodge and linear-burn
497 instead. Increases contrast slightly with an impact on the
498 foreground's tonal values.</td>
502 <td valign="top">soft-light</td>
503 <td valign="top">Darkens or lightens the colors, dependent on the source
504 color value. If the source color is lighter than 0.5, the destination
505 is lightened. If the source color is darker than 0.5, the destination
506 is darkened, as if it were burned in. The degree of darkening or
507 lightening is proportional to the difference between the source color
508 and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
509 with pure black or white produces a distinctly darker or lighter area,
510 but does not result in pure black or white. Fixed in ImageMagick
511 version 6.5.4-3. </td>
515 <td valign="top">pegtop-light</td>
516 <td valign="top">Almost equivelent to 'Soft-Light', but using a
517 continuious mathematical formula rather than two conditionally
518 selected formulae. Added ImageMagick version 6.5.4-3. </td>
522 <td valign="top">vivid-light</td>
523 <td valign="top">A modified 'Linear-Light' designed to preserve very stong
524 primary and secondary colors in the image. Added ImageMagick version
529 <td valign="top">pin-light</td>
530 <td valign="top">Similar to 'Hard-Light', but using sharp linear shadings,
531 to similate the effects of a strong 'pinhole' light source. Added
532 ImageMagick version 6.5.4-3. </td>
541 <p>Also included are these special purpose compose methods:</p>
546 <th align="left" style="width: 8%">Method</th>
547 <th align="left">Description</th>
551 <td valign="top">copy</td>
552 <td valign="top">This is equivelent to the Duff-Porter composition method
553 '<kbd>Src,</kbd>' but without clearing the parts of the destination
554 image that is not overlaid. </td>
558 <td valign="top">copy-*</td>
559 <td valign="top">Copy the specified channel (Red, Green, Blue, Cyan,
560 Magenta, Yellow, Black, or Opacity) in the source image to the
561 same channel in the destination image. If the channel specified
562 does not exist in the source image, (which can only happen for methods,
563 '<kbd>copy-opacity</kbd>' or '<kbd>copy-black</kbd>') then it is
564 assumed that the source image is a special grayscale channel image
565 of the values that is to be copied. </td>
569 <td valign="top">change-mask</td>
570 <td valign="top">Replace any destination pixel that is the similar to the
571 source images pixel (as defined by the current <a
572 href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
580 <p>On top of these composed methods are a few special ones that not only require
581 the two images that are being merged or overlaid, but have some extra numerical
582 arguments, which are tabled below. </p>
584 <p>In the "<code>composite</code>" command these composition methods are
585 selected using special options with the arguments needed. They are usually,
586 but not always, the same name as the composte 'method' they use, and replaces
587 the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
588 setting in the "<code>composite</code>" command. For example... </p>
590 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>composite ... -blend 50x50 ...</span></p>
591 <p>As of IM v6.5.3-4 the "<code>convert</code>" command can now also supply
592 these extra arguments to its <a href="../www/command-line-options.html#composite"
593 >-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
594 attribute of '<kbd class="arg">compose:args</kbd>'. This means you can now
595 make use of these special argumented <a href="../www/command-line-options.html#compose"
596 >-compose</a> methods, those the argument and the method both need to be set
597 separatally. For example... </p>
599 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert ... -compose blend -define compose:args=50,50 -composite ...</span></p>
600 <p>The following is a table of these special 'argumented' compose methods,
601 with a brief summary of what they do. For more details see the equivalent
602 "composite" command option name. </p>
607 <th align="left" style="width: 8%">Method</th>
608 <th align="left">Description</th>
612 <td valign="top">dissolve</td>
613 <td valign="top">Arguments:
614 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
615 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
616 <br>Dissolve the 'source' image by the percentage given before overlaying
617 'over' the 'destination' image. If <em class="arg">src_percent</em> is
618 greater than 100, it starts dissolving the main image so it will
619 become transparent at a value of '<kbd class="arg">200</kbd>'. If
620 both percentages are given, each image are dissolved to the
626 <td valign="top">blend</td>
627 <td valign="top">Arguments:
628 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
629 <br>Equivalent to "<code>composite</code>" <a
630 href="../www/command-line-options.html#blend">-blend</a>
631 <br>Average the images together ('plus') according to the percentages
632 given and each pixels transparency. If only a single percentage value
633 is given it sets the weight of the composite or 'source' image, while
634 the background image is weighted by the exact opposite amount. That is
635 a <kbd>-blend 30</kbd> merges 30% of the 'source' image with 70% of
636 the 'destination' image. Thus it is equivalent to <kbd>-blend
642 <td valign="top">mathematics</td>
643 <td valign="top">Arguments: <em class="arg">A, B, C, D</em>
644 <br>Not available in "<code>composite</code>" at this time.
645 <br>Merge the source and destination images according to the formula
646 <br> <code>A*Sc*Dc + B*Sc + C*Dc + D</code>
647 <br>Can be used to generate a custom composition method that would
648 otherwise need to be implemented using the slow <a
649 href="../www/command-line-options.html#fx">-fx</a> DIY image operator. Added
650 to ImageMagick version 6.5.4-3.
651 <br>As of IM v6.6.1-6 this method will do per-channel math compositions
652 if the 'Sync' flag is removed from <a
653 href="../www/command-line-options.html#channel" >-channel</a>, just like all
654 the other mathematical compostion methods above.
659 <td valign="top">modulate</td>
660 <td valign="top">Arguments:
661 <em class="arg">brightness</em>[x<em class="arg">saturation</em>]
662 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
663 <br>Take a grayscale image (with alpha mask) and modify the destination
664 image's brightness according to watermark image's grayscale value and
665 the <em class="arg">brightness</em> percentage. The destinations
666 color saturation attribute is just direct modified by the <em
667 class="arg">saturation</em> percentage, which defaults to 100 percent
674 <td valign="top">displace</td>
675 <td valign="top">Arguments:
676 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em>][!][%]
677 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
678 <br>With this option, the 'overlay' image, and optionally the 'mask'
679 image, is used as a relative displacement map, which is used to
680 displace the lookup of what part of the destination image is seen at
681 each point of the overlaid area. Much like the displacement map is a
682 'lens' that distorts the original 'background' image behind it.
684 The X-scale is modilated by the 'red' channel of the overlay image
685 while the Y-scale is modulated by the green channel, (the mask image
686 if given is rolled into green channel of the overlay image. This
687 separation allows you to modulate the X and Y lookup displacement
688 separatally allowing you to di 2 dimentional displacements, rather
689 than 1 dimentional verctored displacements (using grayscale image).
691 If the overlay image contains transparency this is used as a mask
692 of the resulting image to remove 'invalid' pixels.
694 The '%' flag makes the displacement scale relative to the size of the
695 overlay image (100% = half width/height of image). Using '!' switches
696 percentage arguments to refer to the destination image size instead.
698 Special flags were added Added to ImageMagick version 6.5.3-5.
703 <td valign="top">distort</td>
704 <td valign="top">Arguments:
705 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em
706 >[+<em class="arg">X-center</em>+<em class="arg">Y-center</em>]][!][%]
707 <br>Not available in "<code>composite</code>" at this time.
708 <br>Exactly as per 'Displace' (above), but using absolute coordinates,
709 relative to the center of the overlay (or that given). Basically
710 allows you to generate absolute distortion maps where 'black' will
711 look up the left/top edge, and 'white' looks up the bottom/right
712 edge of the destination image, according to the scale given.
714 The '!' flag not only switches percentage scaling, to use the
715 destination image, but also the image the center offset of the lookup.
716 This means the overlay can lookup a completely different region of the
719 Added to ImageMagick version 6.5.3-5.
724 <td valign="top">blur</td>
725 <td valign="top">Arguments:
726 <em class="arg">Width</em>[x<em class="arg">Height</em
727 >[+<em class="arg">Angle</em>][+<em class="arg">Angle2</em>]]
728 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
729 <br>A Variable Blur Mapping Composition method, where each pixel in the
730 overlaid region is replaced with an Elliptical Weighted Average (EWA),
731 with an ellipse (typically a circle) of the given sigma size, scaled
732 according to overlay (source image) grayscale mapping.
734 As per 'Displace' and 'Distort', the red channel will modulate the
735 width of the ellipse, while the green channel will modulate the height
736 of the ellipse. If a single Angle value is given in the arguments,
737 then the ellipse will then be rotated by the angle specifed.
739 Normally the blue channel of the mapping overlay image is ignored.
740 However if a second ellipse angle is given, then it is assumed that
741 the blue channel defines a variable angle for the ellipse ranging from
742 the first angle to the second angle given. This allows to generate
743 radial blurs, or a rough approximation for rotational blur. Or any mix
746 Added to ImageMagick version 6.5.4-0.
753 <p>To print a complete list of all the available compose operators, use <a
754 href="../www/command-line-options.html#list">-list compose</a>.</p>
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