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214 var script = document.getElementsByTagName('offline-script')[0]; 215 script.parentNode.insertBefore(po, script); 216 })(); 217 var gplusone = document.getElementById("gplusone"); 218 gplusone.setAttribute("data-size","medium"); 219 gplusone.setAttribute("data-count","true"); 220 /* ]]> */ 221 </script> 222</div> 223 224<div class="main"> 225 226<h1>Apply Special Effects to an Image with an Fx Expression</h1> 227<p class="navigation-index">[<a href="fx.html#fx">The Fx Special Effects Image Operator</a> • <a href="fx.html#anatomy">The Anatomy of an Fx Expression</a>]</p> 228 229<a id="fx"></a> 230<div class="doc-section"> 231 232<p>Use the Fx special effects image operator to apply a mathematical expression to an image or image channels. Use Fx to:</p> 233 234<ul> 235 <li>create canvases, gradients, mathematical colormaps</li> 236 <li>move color values between images and channels</li> 237 <li>translate, flip, mirror, rotate, scale, shear and generally distort images</li> 238 <li>merge or composite multiple images together</li> 239 <li>convolve or merge neighboring pixels together</li> 240 <li>generate image metrics or 'fingerprints'</li> 241</ul> 242 243<p>The expression can be simple:</p> 244 245<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert -size 64x64 canvas:black -channel blue -fx "1/2" fx_navy.png</span></p> 246<p>Here, we convert a black to a navy blue image:</p> 247 248<p class="image"> 249 <a href="/images/black.png"><img src="/images/black.png" width="64" height="64" alt="black" /></a> 250 <img style="margin-top:22px; margin-bottom:22px;" src="/images/right.gif" width="20" height="20" alt="==>" /> 251 <a href="/images/navy.png"><img src="/images/navy.png" width="64" height="64" alt="navy" /></a> 252</p> 253 254<p>Or the expression can be complex:</p> 255 256<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert rose.jpg \ <br/> 257 -fx "(1.0/(1.0+exp(10.0*(0.5-u)))-0.006693)*1.0092503" \ <br/> 258 rose-sigmoidal.png</span></p> 259<p>This expression results in a high contrast version of the image:</p> 260 261<p class="image"> 262 <a href="/images/rose.jpg"><img src="/images/rose.jpg" width="70" height="46" alt="rose" /></a> 263 <img style="margin-top:13px; margin-bottom:13px;" src="/images/right.gif" width="20" height="20" alt="==>" /> 264 <a href="/images/rose-sigmoidal.png"><img src="/images/rose-sigmoidal.png" width="70" height="46" alt="rose-sigmoidal" /></a> 265</p> 266 267<p>The expression can include variable assignments. Assignments, in most cases, reduce the complexity of an expression and permit some operations that might not be possible any other way. For example, lets create a radial gradient:</p> 268 269<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert -size 70x70 canvas: \ <br/> 270 -fx "Xi=i-w/2; Yj=j-h/2; 1.2*(0.5-hypot(Xi,Yj)/70.0)+0.5" \ <br/> 271 radial-gradient.png</span></p> 272<p>The command above returns this image:</p> 273 274<p class="image"> 275 <a href="/images/radial-gradient.png"><img src="/images/radial-gradient.png" width="70" height="70" alt="radial-gradient" /></a> 276</p> 277 278<p>This FX expression adds random noise to an image:</p> 279 280<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert photo.jpg -fx 'iso=32; rone=rand(); rtwo=rand(); \<br /> 281 myn=sqrt(-2*ln(rone))*cos(2*Pi*rtwo); myntwo=sqrt(-2*ln(rtwo))* \<br /> 282 cos(2*Pi*rone); pnoise=sqrt(p)*myn*sqrt(iso)* \ <br /> 283 channel(4.28,3.86,6.68,0)/255; max(0,p+pnoise)' noisy.png</span></p> 284<p>See <a href="http://www.imagemagick.org/Usage/transform/index.html#fx">Using FX, The Special Effects Image Operator</a> for more examples.</p> 285 286<p>The next section discusses the Fx expression language.</p> 287 288</div> 289 290<h2><a id="anatomy"></a>The Anatomy of an Fx Expression</h2> 291<div class="doc-section"> 292 293<h3>The Fx Expression Language</h3> 294<div class="doc-section"> 295 296<p>The formal Fx expression language is defined here:</p> 297 298<dl class="doc"> 299 <dt class="doc"> numbers:</dt> 300 <dd> integer, floating point, scientfic notation (+/- required, e.g. 3.81469e-06), International System number postfixes (.e.g KB, Mib, GB, etc.)</dd> 301 <dt class="doc"> constants: </dt> 302 <dd> E (Euler's number), Epsilon, QuantumRange, QuantumScale, Opaque, Phi (golden ratio), Pi, Transparent</dd> 303 <dt class="doc"> Fx operators (in order of precedence): </dt> 304 <dd> ^ (power), unary -, *, /, % (modulo), +, -, 305 <<, >>, <, <=, >, >=, ==, !=, 306 & (bitwise AND), | (bitwise OR), 307 && (logical AND), || (logical OR), 308 ~ (logical NOT), ?: (ternary conditional)</dd> 309 <dt class="doc"> math functions: </dt> 310 <dd> abs(), acos(), acosh(), airy(), alt(), asin(), asinh(), atan(), atanh(), atan2(), ceil(), cos(), cosh(), debug(), drc(), exp(), floor(), gauss(), gcd(), hypot(), int(), isnan(), j0(), j1(), jinc(), ln(), log(), logtwo(), max(), min(), mod(), not(), pow(), rand(), round(), sign(), sin(), sinc(), sinh(), sqrt(), squish(), tan(), tanh(), trunc()</dd> 311 <dt class="doc"> channel functions: </dt> 312 <dd> channel(r,g,b,a), channel(c,m,y,k,a)</dd> 313 <dt class="doc"> color names:</dt> 314 <dd> red, cyan, black, etc.</dd> 315 <dt class="doc"> color functions:</dt> 316 <dd> srgb(), srgba(), rgb(), rgba(), cmyk(), cmyka(), hsl(), hsla(), etc.</dd> 317 <dt class="doc"> color hex values:</dt> 318 <dd> #ccc, #cbfed0, #b9e1cc00, etc.</dd> 319 <dt class="doc"> symbols:</dt> 320 <dd style="white-space:pre"> 321 u = first image in list 322 v = second image in list 323 s = current image in list (for %[fx:] otherwise = u) 324 t = index of current image (s) in list 325 n = number of images in list 326 327 i = column offset 328 j = row offset 329 p = pixel to use (absolute or relative to current pixel) 330 331 w = width of this image 332 h = height of this image 333 z = channel depth 334 335 r = red value (from RGBA), of a specific or current pixel 336 g = green '' 337 b = blue '' 338 a = alpha '' 339 o = opacity '' 340 341 c = cyan value of CMYK color of pixel 342 y = yellow '' 343 m = magenta '' 344 k = black '' 345 346 intensity = pixel intensity 347 348 hue = pixel hue 349 saturation = pixel saturation 350 lightness = pixel lightness 351 luminance = pixel luminance 352 353 page.width = page width 354 page.height = page height 355 page.x = page x offset 356 page.y = page y offset 357 358 resolution.x = x resolution 359 resolution.y = y resolution 360 361 depth = image depth 362 minima = image minima 363 maxima = image maxima 364 mean = image mean 365 standard_deviation = image standard deviation 366 kurtosis = image kurtosis 367 skewness = image skewness 368 (add a channel specifier to compute a statistic for that channel, e.g. depth.r) 369 </dd> 370 <dt class="doc"> iterators:</dt> 371 <dd> while()</dd> 372</dl> 373 374</div> 375 376<h3>The Fx Expression</h3> 377<div class="doc-section"> 378 379<p>An Fx expression may include any combination of the following:</p> 380<ul> 381<li> <em>x</em> <code>^</code> <em>y</em>: exponentiation (<em>x<sup>y</sup></em>)</li> 382<li> <code>(</code> ... <code>)</code>: grouping</li> 383<li> <em>x</em> <code>*</code> <em>y</em>: multiplication (the asterisk <code>*</code> is optional, for example, <code>2u</code> or <code>2(x+y)</code> are acceptable)</li> 384<li> <em>x</em> <code>/</code> <em>y</em>: division</li> 385<li> <em>x</em> <code>%</code> <em>y</em>: modulo</li> 386<li> <em>x</em> <code>+</code> <em>y</em>: addition</li> 387<li> <em>x</em> <code>-</code> <em>y</em>: subtraction</li> 388<li> <em>x</em> <code><<</code> <em>y</em>: left shift</li> 389<li> <em>x</em> <code>>></code> <em>y</em>: right shift</li> 390<li> <em>x</em> <code><</code> <em>y</em>: boolean relation, return value 1.0 if <em>x</em> < <em>y</em>, otherwise 0.0</li> 391<li> <em>x</em> <code><=</code> <em>y</em>: boolean relation, return value 1.0 if <em>x</em> <= <em>y</em>, otherwise 0.0</li> 392<li> <em>x</em> <code>></code> <em>y</em>: boolean relation, return value 1.0 if <em>x</em> > <em>y</em>, otherwise 0.0</li> 393<li> <em>x</em> <code>>=</code> <em>y</em>: boolean relation, return value 1.0 if <em>x</em> >= <em>y</em>, otherwise 0.0</li> 394<li> <em>x</em> <code>==</code> <em>y</em>: boolean relation, return value 1.0 if <em>x </em>==<em> y</em>, otherwise 0.0</li> 395<li> <em>x</em> <code>!=</code> <em>y</em>: boolean relation, return value 1.0 if <em>x </em>!=<em> y</em>, otherwise 0.0</li> 396<li> <em>x</em> <code>&</code> <em>y</em>: binary AND</li> 397<li> <em>x</em> <code>|</code> <em>y</em>: binary OR</li> 398<li> <em>x</em> <code>&&</code> <em>y</em>: logical AND connective, return value 1.0 if <em>x</em> > 0 and <em>y</em> > 0, otherwise 0.0</li> 399<li> <em>x</em> <code>||</code> <em>y</em>: logical OR connective (inclusive), return value 1.0 if <em>x</em> > 0 or <em>y</em> > 0 (or both), otherwise 0.0</li> 400<li> <code>~</code><em>x</em>: logical NOT operator, return value 1.0 if <em>not</em> <em>x</em> > 0, otherwise 0.0</li> 401<li> <code>+</code><em>x</em>: unary plus, return 1.0*value</li> 402<li> <code>-</code><em>x</em>: unary minus, return -1.0*value</li> 403<li> <em>x</em> <code>?</code> <em>y</em> : <em>z</em>: ternary conditional expression, return value <em>y</em> if <em>x</em> != 0, otherwise <em>z</em>; only one ternary conditional permitted per statement</li> 404<li> <em>x</em> <code>=</code> <em>y</em>: assignment; assignment variables are restricted to letter combinations only (e.g. Xi not X1)</li> 405<li> <em>x</em> <code>;</code> <em>y</em>: statement separator </li> 406<li> <code>phi</code>: constant (1.618034...)</li> 407<li> <code>pi</code>: constant (3.141659...)</li> 408<li> <code>e</code>: constant (2.71828...)</li> 409<li> <code>QuantumRange</code>: constant maximum pixel value (255 for Q8, 65535 for Q16)</li> 410<li> <code>QuantumScale</code>: constant 1.0/<code>QuantumRange</code></li> 411<li> <code>intensity</code>: pixel intensity; equivalent to 0.299*red+0.587*green+0.114*blue</li> 412<li> <code>hue</code>: pixel hue</li> 413<li> <code>saturation</code>: pixel saturation</li> 414<li> <code>lightness</code>: pixel lightness; equivalent to 0.5*max(red,green,blue) + 0.5*min(red,green,blue)</li> 415<li> <code>luminance</code>: pixel luminance; equivalent to 0.212656*red + 0.715158*green + 0.072186*blue</li> 416<li> <code>red, green, blue</code>, etc.: color names</li> 417<li> <code>#ccc, #cbfed0, #b9e1cc00</code>, etc.: color hex values</li> 418<li> <code>rgb(), rgba(), cmyk(), cmyka(), hsl(), hsla()</code>: color functions</li> 419<li> <code>s, t, u, v, n, i, j, w, h, z, r, g, b, a, o, c, y, m, k</code>: symbols</li> 420<li> <code>abs(</code><em>x</em><code>)</code>: absolute value function</li> 421<li> <code>acos(</code><em>x</em><code>)</code>: arc cosine function</li> 422<li> <code>acosh(</code><em>x</em><code>)</code>: inverse hyperbolic cosine function</li> 423<li> <code>airy(</code><em>x</em><code>)</code>: Airy function (max=1, min=0); airy(<em>x</em>)=[jinc(<em>x</em>)]<sup>2</sup>=[2*j1(<em>pi*x</em>)/(<em>pi*x</em>)]<sup>2</sup></li> 424<li> <code>alt(</code><em>x</em><code>)</code>: sign alternation function (return 1.0 if int(<em>x</em>) is even, -1.0 if int(<em>x</em>) is odd)</li> 425<li> <code>asin(</code><em>x</em><code>)</code>: arc sine function</li> 426<li> <code>asinh(</code><em>x</em><code>)</code>: inverse hyperbolic sine function</li> 427<li> <code>atan(</code><em>x</em><code>)</code>: arc tangent function</li> 428<li> <code>atanh(</code><em>x</em><code>)</code>: inverse hyperbolic tangent function</li> 429<li> <code>atan2(</code><em>y</em>,<em>x</em><code>)</code>: arc tangent function of two variables</li> 430<li> <code>ceil(</code><em>x</em><code>)</code>: smallest integral value not less than argument</li> 431<li> <code>channel(</code><em>r</em>,<em>g</em>,<em>b</em>,<em>a</em><code>)</code>: select numeric argument based on current channel</li> 432<li> <code>channel(</code><em>c</em>,<em>m</em>,<em>y</em>,<em>k</em>,<em>a</em><code>)</code>: select numeric argument based on current channel</li> 433<li> <code>cos(</code><em>x</em><code>)</code>: cosine function</li> 434<li> <code>cosh(</code><em>x</em><code>)</code>: hyperbolic cosine function</li> 435<li> <code>debug(</code><em>x</em><code>)</code>: print <em>x</em> (useful for debugging your expression)</li> 436<li> <code>drc(</code><em>x</em>,<em>y</em><code>)</code>: dynamic range compression (knee curve); drc(<em>x</em>,<em>y</em>)=(<em>x</em>)/(<em>y</em>*(<em>x</em>-1)+1); -1<<em>y</em><1 </li> 437<li> <code>exp(</code><em>x</em><code>)</code>: natural exponential function (<em>e<sup>x</sup></em>)</li> 438<li> <code>floor(</code><em>x</em><code>)</code>: largest integral value not greater than argument</li> 439<li> <code>gauss(</code><em>x</em><code>)</code>: gaussian function; gauss(<em>x</em>)=exp(<em>-x*x/2</em>)/sqrt(2*pi)</li> 440<li> <code>gcd(</code><em>x</em>,<em>y</em><code>)</code>: greatest common denominator</li> 441<li> <code>hypot(</code><em>x</em>,<em>y</em><code>)</code>: the square root of x<sup>2</sup>+y<sup>2</sup></li> 442<li> <code>int(</code><em>x</em><code>)</code>: greatest integer function (return greatest integer less than or equal to <em>x</em>)</li> 443<li> <code>isnan(</code><em>x</em><code>)</code>: return 1.0 if <em>x</em> is NAN, 0.0 otherwise</li> 444<li> <code>j0(</code><em>x</em><code>)</code>: Bessel functions of <em>x</em> of the first kind of order 0</li> 445<li> <code>j1(</code><em>x</em><code>)</code>: Bessel functions of <em>x</em> of the first kind of order 1</li> 446<li> <code>jinc(</code><em>x</em><code>)</code>: jinc function (max=1, min=-0.1323); jinc(<em>x</em>)=2*j1(pi*<em>x</em>)/(pi*<em>*x</em>)</li> 447<li> <code>ln(</code><em>x</em><code>)</code>: natural logarithm function</li> 448<li> <code>log(</code><em>x</em><code>)</code>: logarithm base 10</li> 449<li> <code>logtwo(</code><em>x</em><code>)</code>: logarithm base 2</li> 450<li> <code>ln(</code><em>x</em><code>)</code>: natural logarithm</li> 451<li> <code>max(</code><em>x</em>, <em>y</em><code>)</code>: maximum of <em>x</em> and <em>y</em></li> 452<li> <code>min(</code><em>x</em>, <em>y</em><code>)</code>: minimum of <em>x</em> and <em>y</em></li> 453<li> <code>mod(</code><em>x</em>, <em>y</em><code>)</code>: floating-point remainder function</li> 454<li> <code>not(</code><em>x</em><code>)</code>: return 1.0 if <em>x</em> is zero, 0.0 otherwise</li> 455<li> <code>pow(</code><em>x</em>,<em>y</em><code>)</code>: power function (<em>x<sup>y</sup></em>)</li> 456<li> <code>rand()</code>: value uniformly distributed over the interval [0.0, 1.0) with a 2 to the 128th-1 period</li> 457<li> <code>round()</code>: round to integral value, regardless of rounding direction</li> 458<li> <code>sign(</code><em>x</em><code>)</code>: return -1.0 if <em>x</em> is less than 0.0 otherwise 1.0</li> 459<li> <code>sin(</code><em>x</em><code>)</code>: sine function</li> 460<li> <code>sinc(</code><em>x</em><code>)</code>: sinc function (max=1, min=-0.21); sinc(<em>x</em>)=sin(<em>pi*x</em>)/(<em>pi*x</em>)</li> 461<li> <code>squish(</code><em>x</em><code>)</code>: squish function; squish(<em>x</em>)=1.0/(1.0+exp(<em>-x</em>))</li> 462<li> <code>sinh(</code><em>x</em><code>)</code>: hyperbolic sine function</li> 463<li> <code>sqrt(</code><em>x</em><code>)</code>: square root function</li> 464<li> <code>tan(</code><em>x</em><code>)</code>: tangent function</li> 465<li> <code>tanh(</code><em>x</em><code>)</code>: hyperbolic tangent function</li> 466<li> <code>trunc(</code><em>x</em><code>)</code>: round to integer, towards zero</li> 467<li> <code>while(</code><em>condition</em>,<em>expression</em><code>)</code>: interate while the condition is not equal to 0</li> 468</ul> 469 470<p>The expression semantics include these rules:</p> 471 472<ul> 473<li>symbols are case insensitive</li> 474<li>only one ternary conditional (e.g. x ? y : z) per statement</li> 475<li>statements are assignments or the final expression to return</li> 476<li>an assignment starts a statement, it is not an operator</li> 477<li>assignments to built-ins do not throw an exception and have no effect; e.g. <code>r=3.0; r</code> returns the pixel red color value, not 3.0</li> 478<li>Unary operators have a lower priority than binary operators, that is, the unary minus (negation) has lower precedence than exponentiation, so -3^2 is interpreted as -(3^2) = -9. Use parentheses to clarify your intent (e.g. (-3)^2 = 9).</li> 479<li>Similarly, care must be exercised when using the slash ('/') symbol. The string of characters <em>1/2x</em> is interpreted as (1/2)x. The contrary interpretation should be written explicitly as 1/(2x). Again, the use of parentheses helps clarify the meaning and should be used whenever there is any chance of misinterpretation.</li> 480</ul> 481 482 483</div> 484 485<h3>Source Images</h3> 486<div class="doc-section"> 487 488<p>The symbols <code>u</code> and <code>v</code> refer to the first and second images, respectively, in the current image sequence. Refer to a particular image in a sequence by appending its index to any image reference (usually <code>u</code>), with a zero index for the beginning of the sequence. A negative index counts from the end. For example, <code>u[0]</code> is the first image in the sequence, <code>u[2]</code> is the third, <code>u[-1]</code> is the last image, and <code>u[t]</code> is the current image. The current image can also be referenced by <code>s</code>. If the sequence number exceeds the length of the sequence, the count is wrapped. Thus in a 3-image sequence, <code>u[-1]</code>, <code>u[2]</code>, and <code>u[5]</code> all refer to the same (third) image.</p> 489 490<p>As an example, we form an image by averaging the first image and third images (the second (index 1) image is ignored and just junked):</p> 491 492<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert image1.jpg image2.jpg image3.jpg -fx "(u+u[2])/2.0" image.jpg</span></p> 493<p>By default, the image to which <code>p</code>, <code>r</code>, <code>g</code>, <code>b</code>, <code>a</code>, etc., are applied is the current image <code>s</code> in the image list. This is equivelent to <code>u</code> except when used in an escape sequence <code>%[fx:...]</code>. </p> 494 495<p>It is important to note the special role played by the first image. This is the only image in the image sequence that is modified, other images are used only for their data. As an illustrative example, consider the following, and note that the setting <a href="command-line-options.html#channel">-channel red</a> instructs <a href="command-line-options.html#fx">-fx</a> to modify only the red channel; nothing in the green or blue channels will change. It is instructive to ponder why the result is not symmetric.</p> 496 497<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert -channel red logo: -flop logo: -resize "20%" -fx "(u+v)/2" image.jpg</span></p> 498<div class="image"> 499 <a href="/images/logo-sm-flop.png"><img src="/images/logo-sm-flop.png" width="128" height="96" alt="logo-sm-flop.png" /></a> 500 <a href="/images/logo-sm.png"><img src="/images/logo-sm.png" width="128" height="96" alt="logo-sm.png" /></a> 501<img style="margin-top:38px; margin-bottom:38px;" src="/images/right.gif" width="20" height="20" alt="==>" /> 502 <a href="/images/logo-sm-fx.png"><img src="/images/logo-sm-fx.png" width="128" height="96" alt="logo-sm-fx.png" /></a> 503</div> 504 505 506</div> 507 508<h3>Accessing Pixels</h3> 509<div class="doc-section"> 510 511<p>All color values are normalized to the range of 0.0 to 1.0. The alpha channel ranges from 0.0 (fully transparent) to 1.0 (fully opaque).</p> 512 513<p>The pixels are processed one at a time, but a different pixel of an image can be specified using a pixel index represented by <code>p</code>. For example,</p> 514 515<pre class="text"> 516 p[-1].g green value of pixel to the immediate left of the current pixel 517 p[-1,-1].r red value of the pixel diagonally left and up from current pixel 518</pre> 519 520<p>To specify an absolute position, use braces, rather than brackets.</p> 521 522<pre class="text"> 523 p{0,0}.r red value of the pixel in the upper left corner of the image 524 p{12,34}.b blue pixel value at column number 12, row 34 of the image 525</pre> 526 527<p>Integer values of the position retrieve the color of the pixel referenced, while non-integer position values return a blended color according to the current <a href="command-line-options.html#interpolate">-interpolate</a> setting.</p> 528 529<p>A position outside the boundary of the image retrieves a value dictated by the <a href="command-line-options.html#virtual-pixel">-virtual-pixel</a> option setting.</p> 530 531</div> 532 533<h3>Apply an Expression to Select Image Channels</h3> 534<div class="doc-section"> 535 536<p>Use the <a href="command-line-options.html#channel">-channel</a> setting to specify the output channel of the result. If no output channel is given, the result is set over all channels except the opacity channel. For example, to replace the red channel of <code>alpha.png</code> with the average of the green channels from the images <code>alpha.png</code> and <code>beta.png</code>, use:</p> 537 538<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert alpha.png beta.png -channel red -fx "(u.g+v.g)/2" gamma.png</span></p> 539</div> 540 541<h3>Results</h3> 542<div class="doc-section"> 543 544<p>The <a href="command-line-options.html#fx">-fx</a> operator evaluates the given expression for each channel (set by <a href="command-line-options.html#channel">-channel</a>) of each pixel in the first image (<code>u</code>) in the sequence. The computed values are temporarily stored in a copy (clone) of that first image until all the pixels have been processed, after which this single new image replaces the list of images in the current image sequence. As such, in the previous example the updated version of <code>alpha.png</code> replaces both of the original images, <code>alpha.png</code> and <code>beta.png</code>, before being saved as <code>gamma.png</code>.</p> 545 546<p>The current image <code>s</code> is set to the first image in the sequence (<code>u</code>), and <code>t</code> to its index, 0. The symbols <code>i</code> and <code>j</code> reference the current pixel being processed.</p> 547 548 549<p>For use with <a href="command-line-options.html#format_identify_">-format</a>, the value-escape <code>%[fx: ]</code> is evaluated just once for each image in the current image sequence. As each image in the sequence is being evaluated, <code>s</code> and <code>t</code> successively refer to the current image and its index, while <code>i</code> and <code>j</code> are set to zero, and the current channel set to red (<a href="command-line-options.html#channel">-channel</a> is ignored). An example:</p> 550 551<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert canvas:'rgb(25%,50%,75%)' rose: -colorspace rgb \ <br/> 552 -format 'Red channel of NW corner of image #%[fx:t] is %[fx: s]' info:</span><span class='crtout'>Red channel of NW corner of image #0 is 0.453758 <br/> 553 Red channel of NW corner of image #1 is 0.184588</span></p> 554<p>Here we use the image indexes to <em>rotate</em> each image differently, and use <code>-set</code> with the image index to set a different <em>pause delay</em> on the first image in the animation:</p> 555 556<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert rose: -duplicate 29 -virtual-pixel Gray -distort SRT '%[fx:360.0*t/n]' \ <br /> 557 -set delay '%[fx:t == 0 ? 240 : 10]' -loop 0 rose.gif</span></p><p>The color-escape <code>%[pixel: ]</code> is evaluated once per image and per color channel in that image (<a href="command-line-options.html#channel">-channel</a> is ignored), The values generated are then converted into a color string (a named color or hex color value). The symbols <code>i</code> and <code>j</code> are set to zero, and <code>s</code> and <code>t</code> refer to each successively current image and index.</p> 558 559</div> 560</div> 561 562</div> 563 564<div id="linkbar"> 565 <span id="linkbar-west"> </span> 566 567 <span id="linkbar-center"> 568 <a href="http://www.imagemagick.org/discourse-server/">Discourse Server</a> • 569 <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">Studio</a> • 570 <a href="http://jqmagick.imagemagick.org/">JqMagick</a> 571 </span> 572 <span id="linkbar-east"> </span> 573 </div> 574 <div class="footer"> 575 <span id="footer-west">© 1999-2013 ImageMagick Studio LLC</span> 576 <span id="footer-east"> <a href="contact.html">Contact the Wizards</a></span> 577 </div> 578 <div style="clear: both; margin: 0; width: 100%; "></div> 579</body> 580</html> 581
