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cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]12 <title>ImageMagick: Alpha Compositing</title>
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214
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]215<h1>ImageMagick Image Composition</h1>
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]216<p>This page descibed the Image composition methods that is used to define how
217two images should be merged together in various image operations. For the
218Command Line API it is typically set using the <A
219HREF="../www/command-line-options.html#compose" >-compose</A> setting option. </p>
220
221
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]222<p>The description of composition uses abstract terminology in order to allow
223the description to be more precise, while avoiding constant values which are
224specific to a particular build configuration. Each image pixel is represented
225by red, green, and blue levels (which are equal for a gray pixel). The
226build-dependent value <em class="QR">QuantumRange</em> is the maximum integral
227value which may be stored, per pixel, in the red, green, or blue channels of
228the image. Each image pixel may also optionally (if the image matte channel is
229enabled) have an associated level of opacity, ranging from <em>opaque</em> to
230<em>transparent</em>, which may be used to determine the influence of the pixel
231color when compositing the pixel with another image pixel. If the image matte
232channel is disabled, then all pixels in the image are treated as opaque. The
233color of an opaque pixel is fully visible while the color of a transparent
234pixel color is entirely absent (pixel color is ignored).</p>
235
236<p>By definition, raster images have a rectangular shape. All image rows are of
237equal length, as are all image columns. By treating the alpha channel as a
238visual "mask" the rectangular image may be given a "shape" by treating the
239alpha channel as a cookie-cutter for the image. This is done by setting the
240pixels within the shape to be opaque, with pixels outside the shape set as
241transparent. Pixels on the boundary of the shape may be between opaque and
242transparent in order to provide antialiasing (visually smooth edges). The
243description of the composition operators use this concept of image "shape" in
244order to make the description of the operators easier to understand. While it
245is convenient to describe the operators in terms of "shapes" they are by no
246means limited to mask-style operations since they are based on continuous
247floating-point mathematics rather than simple boolean operations.</p>
248
249<p>The following alpha blending (Duff-Porter) compose methods are available:</p>
250
251<table class="doc">
252 <tbody>
253 <tr valign="top">
254 <th align="left" style="width: 8%">Method</th>
255 <th align="left">Description</th>
256 </tr>
257
258 <tr valign="top">
259 <td valign="top">clear</td>
260 <td valign="top">Both the color and the alpha of the destination are
261 cleared. Neither the source nor the destination are used (except for
262 destinations size and other meta-data which is always preserved.</td>
263 </tr>
264
265 <tr valign="top">
266 <td valign="top">src</td>
267 <td valign="top">The source is copied to the destination. The destination
268 is not used as input, though it is cleared.</td>
269 </tr>
270
271 <tr valign="top">
272 <td valign="top">dst</td>
273 <td valign="top">The destination is left untouched. The source image is
274 completely ignored.</td>
275 </tr>
276
277 <tr valign="top">
278 <td valign="top">src-over</td>
279 <td valign="top">The source is composited over the destination. this is
280 the default alpha blending compose method, when neither the compose
281 setting is set, nor is set in the image meta-data.</td>
282 </tr>
283
284 <tr valign="top">
285 <td valign="top">dst-over</td>
286 <td valign="top">The destination is composited over the source and the
287 result replaces the destination.</td>
288 </tr>
289
290 <tr valign="top">
291 <td valign="top">src-in</td>
292 <td valign="top">The part of the source lying inside of the destination
293 replaces the destination.</td>
294 </tr>
295
296 <tr valign="top">
297 <td valign="top">dst-in</td>
298 <td valign="top">The part of the destination lying inside of the source
299 replaces the destination. Areas not overlaid are cleared.</td>
300 </tr>
301
302 <tr valign="top">
303 <td valign="top">src-out</td>
304 <td valign="top">The part of the source lying outside of the destination
305 replaces the destination.</td>
306 </tr>
307
308 <tr valign="top">
309 <td valign="top">dst-out</td>
310 <td valign="top">The part of the destination lying outside of the source
311 replaces the destination.</td>
312 </tr>
313
314 <tr valign="top">
315 <td valign="top">src-atop</td>
316 <td valign="top">The part of the source lying inside of the destination is
317 composited onto the destination.</td>
318 </tr>
319
320 <tr valign="top">
321 <td valign="top">dst-atop</td>
322 <td valign="top">The part of the destination lying inside of the source is
323 composited over the source and replaces the destination. Areas not
324 overlaid are cleared. </td>
325 </tr>
326
327 <tr valign="top">
328 <td valign="top">xor</td>
329 <td valign="top">The part of the source that lies outside of the
330 destination is combined with the part of the destination that lies
331 outside of the source. Source or Destination, but not both. </td>
332 </tr>
333
334 </tbody>
335</table>
336
337<p>Any of the 'Src-*' methods can also be specified without the 'Src-' part.
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]338For example the default compose method can be specified as just 'Over'.</p>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]339
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]340<p>Many of these compose methods will clear the destination image which was
341not overlaid by the source image. This is to be expected as part of that
cristy075ad252010-10-30 21:56:17 +0000[diff] [blame]342specific composition methods defintion. You can disable this by setting the
343special <A HREF="../www/command-line-options.html#define"
344>-define</A> 'compose:outside-overlay' to a value of 'false' will turn off
345this behaviour. </p>
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]346
347<p>On top of the above 12 Duff-Porter Alpha Composition methods, one special
cristybaacd172011-04-30 23:11:03 +0000[diff] [blame]348related method '<kbd>Copy</kbd>' has been provided. This is equivalent to
cristy075ad252010-10-30 21:56:17 +0000[diff] [blame]349using the '<kbd>Src</kbd>' with the special <A HREF="../www/command-line-options.html#define"
350>-define</A> option '<kbd>compose:outside-overlay</kbd>' set to
351'<kbd>false</kbd>', so as to only modify the overlaid area, without clearing
352the rest of the image outside the overlaid area. </p>
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]353
354<br><br>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]355
356<p>The following mathemathical composition methods are also available. </p>
357
358<table class="doc">
359 <tbody>
360 <tr valign="top">
361 <th align="left" style="width: 8%">Method</th>
362 <th align="left">Description</th>
363 </tr>
364
365 <tr valign="top">
366 <td valign="top">multiply</td>
367 <td valign="top">The source is multiplied by the destination and replaces
368 the destination. The resultant color is always at least as dark as
369 either of the two constituent colors. Multiplying any color with black
370 produces black. Multiplying any color with white leaves the original
371 color unchanged.</td>
372 </tr>
373
374 <tr valign="top">
375 <td valign="top">screen</td>
376 <td valign="top">The source and destination are complemented and then
377 multiplied and then replace the destination. The resultant color is
378 always at least as light as either of the two constituent colors.
379 Screening any color with white produces white. Screening any color
380 with black leaves the original color unchanged.</td>
381 </tr>
382
383 <tr valign="top">
384 <td valign="top">plus</td>
385 <td valign="top">The source is added to the destination and replaces the
386 destination. This operator is useful for averaging or a controled
387 merger of two images, rather than a direct overlay.</td>
388 </tr>
389
390 <tr valign="top">
391 <td valign="top">add</td>
392 <td valign="top">As per 'plus' but transparency data is treated as matte
393 values. As such any transparent areas in either image remain
394 transparent. </td>
395 </tr>
396
397 <tr valign="top">
398 <td valign="top">minus</td>
399 <td valign="top">Subtract the colors in the source image from the
400 destination image. When transparency is involved, opaque areas is
401 subtracted from any destination opaque areas. </td>
402 </tr>
403
404 <tr valign="top">
405 <td valign="top">subtract</td>
406 <td valign="top">Subtract the colors in the source image from the
407 destination image. When transparency is involved transparent areas are
408 subtracted, so only the opaque areas in the source remain opaque in
409 the destination image. </td>
410 </tr>
411
412 <tr valign="top">
413 <td valign="top">difference</td>
414 <td valign="top">Subtracts the darker of the two constituent colors from
415 the lighter. Painting with white inverts the destination color.
416 Painting with black produces no change.</td>
417 </tr>
418
419 <tr valign="top">
420 <td valign="top">exclusion</td>
421 <td valign="top">Produces an effect similar to that of 'difference', but
422 appears as lower contrast. Painting with white inverts the
423 destination color. Painting with black produces no change.</td>
424 </tr>
425
426 <tr valign="top">
427 <td valign="top">darken</td>
428 <td valign="top">Selects the darker of the destination and source colors.
429 The destination is replaced with the source when the source is darker,
430 otherwise it is left unchanged.</td>
431 </tr>
432
433 <tr valign="top">
434 <td valign="top">lighten</td>
435 <td valign="top">Selects the lighter of the destination and source colors.
436 The destination is replaced with the source when the source is
437 lighter, otherwise it is left unchanged. </td>
438 </tr>
439
440 </tbody>
441</table>
442
443<p>Typically these use the default 'Over' alpha blending when transparencies
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]444are also involved, except for 'Plus' which uses a 'plus' alpha blending. This
445means the alpha channel of both images will only be used to ensure that any
446visible input remains visible even in parts not overlaid. It also means that
447any values are weighted by the alpha channel of the input and output images.
448This 'Over' alpha blending is also applied to the lighting composition methods
449below. </p>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]450
451<p>As of IM v6.6.1-6, if the special '<kbd>Sync</kbd>' flag is not specified
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]452(enabled by default) with the <a href="../www/command-line-options.html#channel"
453>-channel</a> setting, then the above mathematical compositions will nolonger
cristy2dcd6822011-06-13 16:21:20 +0000[diff] [blame]454synchronise its actions with the alpha channel. Instead the math composition
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]455will be applied on an individual channel basis as defined by the <a
456href="../www/command-line-options.html#channel"
457>-channel</a>. This includes the alpha channel. This special usage
458allows you to perform true mathematics of the image channels, without alpha
459compostion effects, becomming involved. </p>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]460
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]461<p>This special flag is not applied to the lighting composition methods (see
462below) even though they are closely related to mathematical composition
463methods.</p>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]464
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]465<br><br>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]466
467<p>The following lighting composition methods are also available. </p>
468
469<table class="doc">
470 <tbody>
471 <tr valign="top">
472 <th align="left" style="width: 8%">Method</th>
473 <th align="left">Description</th>
474 </tr>
475
476 <tr valign="top">
477 <td valign="top">linear-dodge</td>
cristybaacd172011-04-30 23:11:03 +0000[diff] [blame]478 <td valign="top">This is equivalent to 'Plus' in that the color channels
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]479 are simply added, however it does not 'Plus' the alpha channel, but
480 uses the normal 'Over' alpha blending, which transparencies are
481 involved. Produces a sort of additive multiply-like result. Added
482 ImageMagick version 6.5.4-3. </td>
483 </tr>
484
485 <tr valign="top">
486 <td valign="top">linear-burn</td>
487 <td valign="top">As 'Linear-Dodge', but also subtract one from the result.
488 Sort of a additive 'Screen' of the images. Added ImageMagick version
489 6.5.4-3. </td>
490 </tr>
491
492 <tr valign="top">
493 <td valign="top">color-dodge</td>
494 <td valign="top">Brightens the destination color to reflect the source
495 color. Painting with black produces no change.</td>
496 </tr>
497
498 <tr valign="top">
499 <td valign="top">color-burn</td>
500 <td valign="top">Darkens the destination color to reflect the source
501 color. Painting with white produces no change. Fixed in ImageMagick
502 version 6.5.4-3. </td>
503 </tr>
504
505 <tr valign="top">
506 <td valign="top">overlay</td>
507 <td valign="top">Multiplies or screens the colors, dependent on the
508 destination color. Source colors overlay the destination whilst
509 preserving its highlights and shadows. The destination color is not
510 replaced, but is mixed with the source color to reflect the lightness
511 or darkness of the destination.</td>
512 </tr>
513
514 <tr valign="top">
515 <td valign="top">hard-light</td>
516 <td valign="top">Multiplies or screens the colors, dependent on the source
517 color value. If the source color is lighter than 0.5, the destination
518 is lightened as if it were screened. If the source color is darker
519 than 0.5, the destination is darkened, as if it were multiplied. The
520 degree of lightening or darkening is proportional to the difference
521 between the source color and 0.5. If it is equal to 0.5 the
522 destination is unchanged. Painting with pure black or white produces
523 black or white.</td>
524 </tr>
525
526
527 <tr valign="top">
528 <td valign="top">linear-light</td>
529 <td valign="top">Like 'Hard-Light' but using linear-dodge and linear-burn
530 instead. Increases contrast slightly with an impact on the
531 foreground's tonal values.</td>
532 </tr>
533
534 <tr valign="top">
535 <td valign="top">soft-light</td>
536 <td valign="top">Darkens or lightens the colors, dependent on the source
537 color value. If the source color is lighter than 0.5, the destination
538 is lightened. If the source color is darker than 0.5, the destination
539 is darkened, as if it were burned in. The degree of darkening or
540 lightening is proportional to the difference between the source color
541 and 0.5. If it is equal to 0.5, the destination is unchanged. Painting
542 with pure black or white produces a distinctly darker or lighter area,
543 but does not result in pure black or white. Fixed in ImageMagick
544 version 6.5.4-3. </td>
545 </tr>
546
547 <tr valign="top">
548 <td valign="top">pegtop-light</td>
cristybaacd172011-04-30 23:11:03 +0000[diff] [blame]549 <td valign="top">Almost equivalent to 'Soft-Light', but using a
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]550 continuious mathematical formula rather than two conditionally
551 selected formulae. Added ImageMagick version 6.5.4-3. </td>
552 </tr>
553
554 <tr valign="top">
555 <td valign="top">vivid-light</td>
556 <td valign="top">A modified 'Linear-Light' designed to preserve very stong
557 primary and secondary colors in the image. Added ImageMagick version
558 6.5.4-3. </td>
559 </tr>
560
561 <tr valign="top">
562 <td valign="top">pin-light</td>
563 <td valign="top">Similar to 'Hard-Light', but using sharp linear shadings,
564 to similate the effects of a strong 'pinhole' light source. Added
565 ImageMagick version 6.5.4-3. </td>
566 </tr>
567
568 </tbody>
569</table>
570
571
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]572<br><br>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]573
574<p>Also included are these special purpose compose methods:</p>
575
576<table class="doc">
577 <tbody>
578 <tr valign="top">
579 <th align="left" style="width: 8%">Method</th>
580 <th align="left">Description</th>
581 </tr>
582
583 <tr valign="top">
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]584 <td valign="top">copy</td>
cristybaacd172011-04-30 23:11:03 +0000[diff] [blame]585 <td valign="top">This is equivalent to the Duff-Porter composition method
cristy075ad252010-10-30 21:56:17 +0000[diff] [blame]586 '<kbd>Src,</kbd>' but without clearing the parts of the destination
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]587 image that is not overlaid. </td>
588 </tr>
589
590 <tr valign="top">
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]591 <td valign="top">copy-*</td>
592 <td valign="top">Copy the specified channel (Red, Green, Blue, Cyan,
593 Magenta, Yellow, Black, or Opacity) in the source image to the
594 same channel in the destination image. If the channel specified
595 does not exist in the source image, (which can only happen for methods,
596 '<kbd>copy-opacity</kbd>' or '<kbd>copy-black</kbd>') then it is
597 assumed that the source image is a special grayscale channel image
cristy075ad252010-10-30 21:56:17 +0000[diff] [blame]598 of the values that is to be copied. </td>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]599 </tr>
600
601 <tr valign="top">
602 <td valign="top">change-mask</td>
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]603 <td valign="top">Replace any destination pixel that is the similar to the
604 source images pixel (as defined by the current <a
605 href="../www/command-line-options.html#fuzz">-fuzz</a> factor), with transparency.
606 </td>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]607 </tr>
608 </tbody>
609</table>
610
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]611<br><br>
612
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]613<p>On top of these composed methods are a few special ones that not only require
614the two images that are being merged or overlaid, but have some extra numerical
615arguments, which are tabled below. </p>
616
617<p>In the "<code>composite</code>" command these composition methods are
618selected using special options with the arguments needed. They are usually,
619but not always, the same name as the composte 'method' they use, and replaces
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]620the normal use of the <a href="../www/command-line-options.html#compose" >-compose</a>
621setting in the "<code>composite</code>" command. For example... </p>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]622
623<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>composite ... -blend 50x50 ...</span></p>
624<p>As of IM v6.5.3-4 the "<code>convert</code>" command can now also supply
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]625these extra arguments to its <a href="../www/command-line-options.html#composite"
cristy075ad252010-10-30 21:56:17 +0000[diff] [blame]626>-composite</a> operator, using the special <a href="../www/command-line-options.html#define">-define</a>
627attribute of '<kbd class="arg">compose:args</kbd>'. This means you can now
628make use of these special argumented <a href="../www/command-line-options.html#compose"
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]629>-compose</a> methods, those the argument and the method both need to be set
630separatally. For example... </p>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]631
cristy075ad252010-10-30 21:56:17 +0000[diff] [blame]632<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert ... -compose blend -define compose:args=50,50 -composite ...</span></p>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]633<p>The following is a table of these special 'argumented' compose methods,
634with a brief summary of what they do. For more details see the equivalent
635"composite" command option name. </p>
636
637<table class="doc">
638 <tbody>
639 <tr valign="top">
640 <th align="left" style="width: 8%">Method</th>
641 <th align="left">Description</th>
642 </tr>
643
644 <tr valign="top">
645 <td valign="top">dissolve</td>
646 <td valign="top">Arguments:
647 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]648 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#dissolve">-dissolve</a>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]649 <br>Dissolve the 'source' image by the percentage given before overlaying
650 'over' the 'destination' image. If <em class="arg">src_percent</em> is
651 greater than 100, it starts dissolving the main image so it will
652 become transparent at a value of '<kbd class="arg">200</kbd>'. If
653 both percentages are given, each image are dissolved to the
654 percentages given.
655 </td>
656 </tr>
657
658 <tr valign="top">
659 <td valign="top">blend</td>
660 <td valign="top">Arguments:
661 <em class="arg">src_percent</em>[x<em class="arg">dst_percent</em>]
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]662 <br>Equivalent to "<code>composite</code>" <a
663 href="../www/command-line-options.html#blend">-blend</a>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]664 <br>Average the images together ('plus') according to the percentages
665 given and each pixels transparency. If only a single percentage value
666 is given it sets the weight of the composite or 'source' image, while
667 the background image is weighted by the exact opposite amount. That is
668 a <kbd>-blend 30</kbd> merges 30% of the 'source' image with 70% of
669 the 'destination' image. Thus it is equivalent to <kbd>-blend
670 30x70</kbd>.
671 </td>
672 </tr>
673
674 <tr valign="top">
675 <td valign="top">mathematics</td>
676 <td valign="top">Arguments: <em class="arg">A, B, C, D</em>
677 <br>Not available in "<code>composite</code>" at this time.
678 <br>Merge the source and destination images according to the formula
679 <br>&nbsp; &nbsp; &nbsp;<code>A*Sc*Dc + B*Sc + C*Dc + D</code>
680 <br>Can be used to generate a custom composition method that would
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]681 otherwise need to be implemented using the slow <a
682 href="../www/command-line-options.html#fx">-fx</a> DIY image operator. Added
683 to ImageMagick version 6.5.4-3.
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]684 <br>As of IM v6.6.1-6 this method will do per-channel math compositions
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]685 if the 'Sync' flag is removed from <a
686 href="../www/command-line-options.html#channel" >-channel</a>, just like all
687 the other mathematical compostion methods above.
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]688 </td>
689 </tr>
690
691 <tr valign="top">
692 <td valign="top">modulate</td>
693 <td valign="top">Arguments:
694 <em class="arg">brightness</em>[x<em class="arg">saturation</em>]
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]695 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#watermark">-watermark</a>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]696 <br>Take a grayscale image (with alpha mask) and modify the destination
697 image's brightness according to watermark image's grayscale value and
698 the <em class="arg">brightness</em> percentage. The destinations
699 color saturation attribute is just direct modified by the <em
700 class="arg">saturation</em> percentage, which defaults to 100 percent
701 (no color change).
702
703 </td>
704 </tr>
705
706 <tr valign="top">
707 <td valign="top">displace</td>
708 <td valign="top">Arguments:
709 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em>][!][%]
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]710 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#displace">-displace</a>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]711 <br>With this option, the 'overlay' image, and optionally the 'mask'
712 image, is used as a relative displacement map, which is used to
713 displace the lookup of what part of the destination image is seen at
714 each point of the overlaid area. Much like the displacement map is a
715 'lens' that distorts the original 'background' image behind it.
716 <br><br>
717 The X-scale is modilated by the 'red' channel of the overlay image
718 while the Y-scale is modulated by the green channel, (the mask image
719 if given is rolled into green channel of the overlay image. This
720 separation allows you to modulate the X and Y lookup displacement
721 separatally allowing you to di 2 dimentional displacements, rather
722 than 1 dimentional verctored displacements (using grayscale image).
723 <br><br>
724 If the overlay image contains transparency this is used as a mask
725 of the resulting image to remove 'invalid' pixels.
726 <br><br>
727 The '%' flag makes the displacement scale relative to the size of the
728 overlay image (100% = half width/height of image). Using '!' switches
729 percentage arguments to refer to the destination image size instead.
730 <br><br>
731 Special flags were added Added to ImageMagick version 6.5.3-5.
732 </td>
733 </tr>
734
735 <tr valign="top">
736 <td valign="top">distort</td>
737 <td valign="top">Arguments:
738 <em class="arg">X-scale</em>[x<em class="arg">Y-scale</em
739 >[+<em class="arg">X-center</em>+<em class="arg">Y-center</em>]][!][%]
740 <br>Not available in "<code>composite</code>" at this time.
741 <br>Exactly as per 'Displace' (above), but using absolute coordinates,
742 relative to the center of the overlay (or that given). Basically
743 allows you to generate absolute distortion maps where 'black' will
744 look up the left/top edge, and 'white' looks up the bottom/right
745 edge of the destination image, according to the scale given.
746 <br><br>
747 The '!' flag not only switches percentage scaling, to use the
748 destination image, but also the image the center offset of the lookup.
749 This means the overlay can lookup a completely different region of the
750 destination image.
751 <br><br>
752 Added to ImageMagick version 6.5.3-5.
753 </td>
754 </tr>
755
756 <tr valign="top">
757 <td valign="top">blur</td>
758 <td valign="top">Arguments:
759 <em class="arg">Width</em>[x<em class="arg">Height</em
cristy075ad252010-10-30 21:56:17 +0000[diff] [blame]760 >[+<em class="arg">Angle</em>][+<em class="arg">Angle2</em>]]
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]761 <br>Equivalent to "<code>composite</code>" <a href="../www/command-line-options.html#blur-composite">-blur</a>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]762 <br>A Variable Blur Mapping Composition method, where each pixel in the
763 overlaid region is replaced with an Elliptical Weighted Average (EWA),
764 with an ellipse (typically a circle) of the given sigma size, scaled
765 according to overlay (source image) grayscale mapping.
766 <br><br>
767 As per 'Displace' and 'Distort', the red channel will modulate the
768 width of the ellipse, while the green channel will modulate the height
cristy075ad252010-10-30 21:56:17 +0000[diff] [blame]769 of the ellipse. If a single Angle value is given in the arguments,
770 then the ellipse will then be rotated by the angle specifed.
771 <br><br>
772 Normally the blue channel of the mapping overlay image is ignored.
773 However if a second ellipse angle is given, then it is assumed that
774 the blue channel defines a variable angle for the ellipse ranging from
775 the first angle to the second angle given. This allows to generate
776 radial blurs, or a rough approximation for rotational blur. Or any mix
777 of the two.
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]778 <br><br>
779 Added to ImageMagick version 6.5.4-0.
780 </td>
781 </tr>
782
783 </tbody>
784</table>
785
786<p>To print a complete list of all the available compose operators, use <a
cristyabd337d2010-08-17 01:06:59 +0000[diff] [blame]787href="../www/command-line-options.html#list">-list compose</a>.</p>
cristybc9539a2010-08-16 18:06:20 +0000[diff] [blame]788
789
790
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