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159 google_ad_slot = "0574824969"; 160 google_ad_width = 160; 161 google_ad_height = 600; 162 //--> 163 </script> 164 <script type="text/javascript" 165 src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> 166 </script> 167</div> 168 169<div class="main"> 170 171<p class="navigation-index">[<a href="#fx">The Fx Special Effects Image Operator</a> • <a href="#anatomy">The Anatomy of an Fx Expression</a>]</p> 172 173<h2><a name="fx"></a>The Fx Special Effects Image Operator</h2> 174<div class="doc-section"> 175 176<p>Use the Fx special effects image operator to apply a mathematical expression to an image or image channels. Use Fx to:</p> 177 178<ul> 179 <li>create canvases, gradients, mathematical colormaps</li> 180 <li>move color values between images and channels</li> 181 <li>translate, flip, mirror, rotate, scale, shear and generally distort images</li> 182 <li>merge or composite multiple images together</li> 183 <li>convolve or merge neighboring pixels together</li> 184 <li>generate image metrics or 'fingerprints'</li> 185</ul> 186 187<p>The expression can be simple:</p> 188 189<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert -size 64x64 xc:black -channel blue -fx "1/2" fx_navy.png</span></p> 190<p>Here, we convert a black to a navy blue image:</p> 191 192<p class="image"> 193 <a href="/images/black.png"><img src="/images/black.png" width="64" height="64" alt="black" /></a> 194 <img style="margin-top:22px; margin-bottom:22px;" src="/images/right.gif" width="20" height="20" alt="==>" /> 195 <a href="/images/navy.png"><img src="/images/navy.png" width="64" height="64" alt="navy" /></a> 196</p> 197 198<p>Or the expression can be complex:</p> 199 200<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert rose.jpg \ <br/> 201 -fx "(1.0/(1.0+exp(10.0*(0.5-u)))-0.006693)*1.0092503" \ <br/> 202 rose-sigmoidal.png</span></p> 203<p>This expression results in a high contrast version of the image:</p> 204 205<p class="image"> 206 <a href="/images/rose.jpg"><img src="/images/rose.jpg" width="70" height="46" alt="rose" /></a> 207 <img style="margin-top:13px; margin-bottom:13px;" src="/images/right.gif" width="20" height="20" alt="==>" /> 208 <a href="/images/rose-sigmoidal.png"><img src="/images/rose-sigmoidal.png" width="70" height="46" alt="rose-sigmoidal" /></a> 209</p> 210 211<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> 212 213<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert -size 70x70 xc: \ <br/> 214 -fx "Xi=i-w/2; Yj=j-h/2; 1.2*(0.5-hypot(Xi,Yj)/70.0)+0.5" \ <br/> 215 radial-gradient.png</span></p> 216<p>The command above returns this image:</p> 217 218<p class="image"> 219 <a href="/images/radial-gradient.png"><img src="/images/radial-gradient.png" width="70" height="70" alt="radial-gradient" /></a> 220</p> 221<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> 222 223<p>The next section discusses the Fx expression language.</p> 224 225</div> 226 227<h2><a name="anatomy"></a>The Anatomy of an Fx Expression</h2> 228<div class="doc-section"> 229 230<h3>The Fx Expression Language</h3> 231<div class="doc-section"> 232 233<p>The formal Fx expression language is defined here:</p> 234 235<dl class="doc"> 236 <dt class="doc"> numbers:</dt> 237 <dd> integer, floating point, or scientfic notation (+/- required, e.g. 3.81469e-06)</dd> 238 <dt class="doc"> constants: </dt> 239 <dd> e, Epsilon, QuantumRange, QuantumScale, Opaque, Pi, Transparent</dd> 240 <dt class="doc"> Fx operators (in order of precedence): </dt> 241 <dd> ^ (power), unary -, *, /, % (modulo), +, -, 242 <<, >>, <, <=, >, >=, ==, !=, 243 & (bitwise AND), | (bitwise OR), 244 && (logical AND), || (logical OR), 245 ~ (logical NOT), ?: (ternary conditional)</dd> 246 <dt class="doc"> math functions: </dt> 247 <dd> abs(), acos(), airy(), alt(), asin(), atan(), atan2(), ceil(), cos(), cosh(), debug(), exp(), floor(), 248 hypot(), int(), j0(), j1(), jinc(), ln(), log(), logtwo(), max(), min(), mod(), pow(), rand(), round(), 249 sign(), sin(), sinc(), sinh(), sqrt(), tan(), tanh(), trunc()</dd> 250 <dt class="doc"> channel functions: </dt> 251 <dd> channel(r,g,b,a), channel(c,m,y,k,a)</dd> 252 <dt class="doc"> color names:</dt> 253 <dd> red, cyan, black, etc.</dd> 254 <dt class="doc"> color functions:</dt> 255 <dd> rgb(), rgba(), cmyk(), cmyka(), hsl(), hsla()</dd> 256 <dt class="doc"> color hex values:</dt> 257 <dd> #ccc, #cbfed0, #b9e1cc00</dd> 258 <dt class="doc"> symbols:</dt> 259 <dd style="white-space:pre"> 260 s = current image in sequence 261 t = scene number of current image in sequence 262 u = first image in sequence 263 v = second image in sequence 264 n = number of images in sequence 265 266 i = column offset 267 j = row offset 268 p = pixel to use (absolute or relative to current pixel) 269 270 w = width of this image 271 h = height of this image 272 z = channel depth 273 274 r = red value (from RGBA), of a specific or current pixel 275 g = green '' 276 b = blue '' 277 a = alpha '' 278 o = opacity '' 279 280 c = cyan value of CMYK color of pixel 281 y = yellow '' 282 m = magenta '' 283 k = black '' 284 285 intensity = pixel intensity 286 287 hue = pixel hue 288 saturation = pixel saturation 289 lightness = pixel lightness 290 luminance = pixel luminance 291 292 page.width = page width 293 page.height = page height 294 page.x = page x offset 295 page.y = page y offset 296 297 resolution.x = x resolution 298 resolution.y = y resolution 299 300 depth = image depth 301 minima = image minima 302 maxima = image maxima 303 mean = image mean 304 standard_deviation = image standard deviation 305 kurtosis = image kurtosis 306 skewness = image skewness 307 (add a channel specifier to compute a statistic for that channel, e.g. depth.r) 308 </dd> 309</dl> 310 311</div> 312 313<h3>The Fx Expression</h3> 314<div class="doc-section"> 315 316<p>An Fx expression may include any combination of the following:</p> 317<ul> 318<li> <em>x</em> <kbd>^</kbd> <em>y</em>: exponentiation (<em>x<sup>y</sup></em>)</li> 319<li> <kbd>(</kbd> ... <kbd>)</kbd>: grouping</li> 320<li> <em>x</em> <kbd>*</kbd> <em>y</em>: multiplication (the asterisk <kbd>*</kbd> is optional, for example, <kbd>2u</kbd> or <kbd>2(x+y)</kbd> are acceptable)</li> 321<li> <em>x</em> <kbd>/</kbd> <em>y</em>: division</li> 322<li> <em>x</em> <kbd>%</kbd> <em>y</em>: modulo</li> 323<li> <em>x</em> <kbd>+</kbd> <em>y</em>: addition</li> 324<li> <em>x</em> <kbd>-</kbd> <em>y</em>: subtraction</li> 325<li> <em>x</em> <kbd><<</kbd> <em>y</em>: left shift</li> 326<li> <em>x</em> <kbd>>></kbd> <em>y</em>: right shift</li> 327<li> <em>x</em> <kbd><</kbd> <em>y</em>: boolean relation, return value 1.0 if <em>x</em> < <em>y</em>, otherwise 0.0</li> 328<li> <em>x</em> <kbd><=</kbd> <em>y</em>: boolean relation, return value 1.0 if <em>x</em> <= <em>y</em>, otherwise 0.0</li> 329<li> <em>x</em> <kbd>></kbd> <em>y</em>: boolean relation, return value 1.0 if <em>x</em> > <em>y</em>, otherwise 0.0</li> 330<li> <em>x</em> <kbd>>=</kbd> <em>y</em>: boolean relation, return value 1.0 if <em>x</em> >= <em>y</em>, otherwise 0.0</li> 331<li> <em>x</em> <kbd>==</kbd> <em>y</em>: boolean relation, return value 1.0 if <em>x </em>==<em> y</em>, otherwise 0.0</li> 332<li> <em>x</em> <kbd>!=</kbd> <em>y</em>: boolean relation, return value 1.0 if <em>x </em>!=<em> y</em>, otherwise 0.0</li> 333<li> <em>x</em> <kbd>&</kbd> <em>y</em>: binary AND</li> 334<li> <em>x</em> <kbd>|</kbd> <em>y</em>: binary OR</li> 335<li> <em>x</em> <kbd>&&</kbd> <em>y</em>: logical AND connective, return value 1.0 if <em>x</em> > 0 and <em>y</em> > 0, otherwise 0.0</li> 336<li> <em>x</em> <kbd>||</kbd> <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> 337<li> <kbd>~</kbd><em>x</em>: logical NOT operator, return value 1.0 if <em>not</em> <em>x</em> > 0, otherwise 0.0</li> 338<li> <kbd>+</kbd><em>x</em>: unary plus, return 1.0*value</li> 339<li> <kbd>-</kbd><em>x</em>: unary minus, return -1.0*value</li> 340<li> <em>x</em> <kbd>?</kbd> <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> 341<li> <em>x</em> <kbd>=</kbd> <em>y</em>: assignment; assignment variables are restricted to letter combinations only (e.g. Xi not X1)</li> 342<li> <em>x</em> <kbd>;</kbd> <em>y</em>: statement separator </li> 343<li> <kbd>pi</kbd>: constant (3.141659...)</li> 344<li> <kbd>e</kbd>: constant (2.71828...)</li> 345<li> <kbd>QuantumRange</kbd>: constant maximum pixel value (255 for Q8, 65535 for Q16)</li> 346<li> <kbd>QuantumScale</kbd>: constant 1.0/<kbd>QuantumRange</kbd></li> 347<li> <kbd>intensity</kbd>: pixel intensity; equivalent to 0.299*red+0.587*green+0.114*blue</li> 348<li> <kbd>hue</kbd>: pixel hue</li> 349<li> <kbd>saturation</kbd>: pixel saturation</li> 350<li> <kbd>lightness</kbd>: pixel lightness; equivalent to 0.5*max(red,green,blue) + 0.5*min(red,green,blue)</li> 351<li> <kbd>luminance</kbd>: pixel luminance; equivalent to 0.2126*red + 0.7152*green + 0.0722*blue</li> 352<li> <kbd>red, green, blue</kbd>, etc.: color names</li> 353<li> <kbd>#ccc, #cbfed0, #b9e1cc00</kbd>, etc.: color hex values</li> 354<li> <kbd>rgb(), rgba(), cmyk(), cmyka(), hsl(), hsla()</kbd>: color functions</li> 355<li> <kbd>s, t, u, v, n, i, j, w, h, z, r, g, b, a, o, c, y, m, k</kbd>: symbols</li> 356<li> <kbd>abs(</kbd><em>x</em><kbd>)</kbd>: absolute value function</li> 357<li> <kbd>acos(</kbd><em>x</em><kbd>)</kbd>: arc cosine function</li> 358<li> <kbd>airy(</kbd><em>x</em><kbd>)</kbd>: Airy function (max=1, min=0); <kbd>airy(</kbd><em>x</em><kbd>)</kbd>=<kbd>[jinc(</kbd><em>x</em><kbd>)]<sup>2</sup></kbd>=<kbd>[2*j1(</kbd><em>pi*x</em><kbd>)/(</kbd><em>pi*x</em><kbd>)]<sup>2</sup></kbd></li> 359<li> <kbd>alt(</kbd><em>x</em><kbd>)</kbd>: sign alternation function (return 1.0 if <kbd>int(</kbd><em>x</em><kbd>)</kbd> is even, -1.0 if <kbd>int(</kbd><em>x</em><kbd>)</kbd> is odd)</li> 360<li> <kbd>asin(</kbd><em>x</em><kbd>)</kbd>: arc sine function</li> 361<li> <kbd>atan(</kbd><em>x</em><kbd>)</kbd>: arc tangent function</li> 362<li> <kbd>atan2(</kbd><em>y</em>,<em>x</em><kbd>)</kbd>: arc tangent function of two variables</li> 363<li> <kbd>ceil(</kbd><em>x</em><kbd>)</kbd>: smallest integral value not less than argument</li> 364<li> <kbd>channel(</kbd><em>r</em>,<em>g</em>,<em>b</em>,<em>a</em><kbd>)</kbd>: select numeric argument based on current channel</li> 365<li> <kbd>channel(</kbd><em>c</em>,<em>m</em>,<em>y</em>,<em>k</em>,<em>a</em><kbd>)</kbd>: select numeric argument based on current channel</li> 366<li> <kbd>cos(</kbd><em>x</em><kbd>)</kbd>: cosine function</li> 367<li> <kbd>cosh(</kbd><em>x</em><kbd>)</kbd>: hyperbolic cosine function</li> 368<li> <kbd>debug(</kbd><em>x</em><kbd>)</kbd>: print <em>x</em> (useful for debugging your expression)</li> 369<li> <kbd>exp(</kbd><em>x</em><kbd>)</kbd>: natural exponential function (<em>e<sup>x</sup></em>)</li> 370<li> <kbd>floor(</kbd><em>x</em><kbd>)</kbd>: largest integral value not greater than argument</li> 371<li> <kbd>hypot(</kbd><em>x</em>,<em>y</em><kbd>)</kbd>: the square root of x<sup>2</sup>+y<sup>2</sup></li> 372<li> <kbd>int(</kbd><em>x</em><kbd>)</kbd>: greatest integer function (return greatest integer less than or equal to <em>x</em>)</li> 373<li> <kbd>j0(</kbd><em>x</em><kbd>)</kbd>: Bessel functions of <em>x</em> of the first kind of order 0</li> 374<li> <kbd>j1(</kbd><em>x</em><kbd>)</kbd>: Bessel functions of <em>x</em> of the first kind of order 1</li> 375<li> <kbd>jinc(</kbd><em>x</em><kbd>)</kbd>: jinc function (max=1, min=-0.1323); <kbd>jinc(</kbd><em>x</em><kbd>)</kbd>=<kbd>2*j1(</kbd><em>pi*x</em><kbd>)/(</kbd><em>pi*x</em><kbd>)</kbd></li> 376<li> <kbd>ln(</kbd><em>x</em><kbd>)</kbd>: natural logarithm function</li> 377<li> <kbd>log(</kbd><em>x</em><kbd>)</kbd>: logarithm base 10</li> 378<li> <kbd>logtwo(</kbd><em>x</em><kbd>)</kbd>: logarithm base 2</li> 379<li> <kbd>ln(</kbd><em>x</em><kbd>)</kbd>: natural logarithm</li> 380<li> <kbd>max(</kbd><em>x</em>, <em>y</em><kbd>)</kbd>: maximum of <em>x</em> and <em>y</em></li> 381<li> <kbd>min(</kbd><em>x</em>, <em>y</em><kbd>)</kbd>: minimum of <em>x</em> and <em>y</em></li> 382<li> <kbd>mod(</kbd><em>x</em>, <em>y</em><kbd>)</kbd>: floating-point remainder function</li> 383<li> <kbd>pow(</kbd><em>x</em>,<em>y</em><kbd>)</kbd>: power function (<em>x<sup>y</sup></em>)</li> 384<li> <kbd>rand()</kbd>: value uniformly distributed over the interval [0.0, 1.0) with a 2 to the 128th-1 period</li> 385<li> <kbd>round()</kbd>: round to integral value, regardless of rounding direction</li> 386<li> <kbd>sign(</kbd><em>x</em><kbd>)</kbd>: return -1.0 if <em>x</em> is less than 0.0 otherwise 1.0</li> 387<li> <kbd>sin(</kbd><em>x</em><kbd>)</kbd>: sine function</li> 388<li> <kbd>sinc(</kbd><em>x</em><kbd>)</kbd>: sinc function (max=1, min=-0.21); <kbd>sinc(</kbd><em>x</em><kbd>)</kbd>=<kbd>sin(</kbd><em>pi*x</em><kbd>)/(</kbd><em>pi*x</em><kbd>)</kbd></li> 389<li> <kbd>sinh(</kbd><em>x</em><kbd>)</kbd>: hyperbolic sine function</li> 390<li> <kbd>sqrt(</kbd><em>x</em><kbd>)</kbd>: square root function</li> 391<li> <kbd>tan(</kbd><em>x</em><kbd>)</kbd>: tangent function</li> 392<li> <kbd>tanh(</kbd><em>x</em><kbd>)</kbd>: hyperbolic tangent function</li> 393<li> <kbd>trunc(</kbd><em>x</em><kbd>)</kbd>: round to integer, towards zero</li> 394</ul> 395 396<p>The expression semantics include these rules:</p> 397 398<ul> 399<li>symbols are case insensitive</li> 400<li>only one ternary conditional (e.g. x ? y : z) per statement</li> 401<li>statements are assignments or the final expression to return</li> 402<li>an assignment starts a statement, it is not an operator</li> 403<li>assignments to built-ins do not throw an exception and have no effect; e.g. <kbd>r=3.0; r</kbd> returns the pixel red color value, not 3.0</li> 404<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> 405<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> 406</ul> 407 408 409</div> 410 411<h3>Source Images</h3> 412<div class="doc-section"> 413 414<p>The symbols <kbd>u</kbd> and <kbd>v</kbd> 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 <kbd>u</kbd>), with a zero index for the beginning of the sequence. A negative index counts from the end. For example, <kbd>u[0]</kbd> is the first image in the sequence, <kbd>u[2]</kbd> is the third, <kbd>u[-1]</kbd> is the last image, and <kbd>u[t]</kbd> is the current image. The current image can also be referenced by <kbd>s</kbd>. If the sequence number exceeds the length of the sequence, the count is wrapped. Thus in a 3-image sequence, <kbd>u[-1]</kbd>, <kbd>u[2]</kbd>, and <kbd>u[5]</kbd> all refer to the same (third) image.</p> 415 416<p>As an example, we form an image by averaging the first image and third images:</p> 417 418<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert image1.jpg image2.jpg image3.jpg -fx "(u+u[2])/2.0" image.jpg</span></p> 419<p>By default, the image to which <kbd>p</kbd>, <kbd>r</kbd>, <kbd>g</kbd>, <kbd>b</kbd>, <kbd>a</kbd>, etc., are applied is the first image <kbd>u</kbd> in the image list, which may also be referenced using <kbd>s</kbd>. </p> 420 421<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="/www/command-line-options.html#channel">-channel red</a> instructs <a href="/www/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> 422 423<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert -channel red logo: -flop logo: -resize "20%" -fx "(u+v)/2" image.jpg</span></p> 424<div class="image"> 425<p> 426 <a href="/images/logo-sm-flop.png"><img src="/images/logo-sm-flop.png" width="128" height="96" alt="logo-sm-flop.png" /></a> 427 <a href="/images/logo-sm.png"><img src="/images/logo-sm.png" width="128" height="96" alt="logo-sm.png" /></a> 428<img style="margin-top:38px; margin-bottom:38px;" src="/images/right.gif" width="20" height="20" alt="==>" /> 429 <a href="/images/logo-sm-fx.png"><img src="/images/logo-sm-fx.png" width="128" height="96" alt="logo-sm-fx.png" /></a> 430</p> 431</div> 432 433 434</div> 435 436<h3>Accessing Pixels</h3> 437<div class="doc-section"> 438 439<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> 440 441<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 <kbd>p</kbd>. For example,</p> 442 443<pre class="text"> 444 p[-1].g green value of pixel to the immediate left of the current pixel 445 p[-1,-1].r red value of the pixel diagonally left and up from current pixel 446</pre> 447 448<p>To specify an absolute position, use braces, rather than brackets.</p> 449 450<pre class="text"> 451 p{0,0}.r red value of the pixel in the upper left corner of the image 452 p{12,34}.b blue pixel value at column number 12, row 34 of the image 453</pre> 454 455<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="/www/command-line-options.html#interpolate">-interpolate</a> setting.</p> 456 457<p>A position outside the boundary of the image retrieves a value dictated by the <a href="/www/command-line-options.html#virtual-pixel">-virtual-pixel</a> option setting.</p> 458 459</div> 460 461<h3>Apply an Expression to Select Image Channels</h3> 462<div class="doc-section"> 463 464<p>Use the <a href="/www/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 <kbd>alpha.png</kbd> with the average of the green channels from the images <kbd>alpha.png</kbd> and <kbd>beta.png</kbd>, use:</p> 465 466<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert alpha.png beta.png -channel red -fx "(u.g+v.g)/2" gamma.png</span></p> 467</div> 468 469<h3>Results</h3> 470<div class="doc-section"> 471 472<p>The <a href="/www/command-line-options.html#fx">-fx</a> operator evaluates the given expression for each channel (set by <a href="/www/command-line-options.html#channel">-channel</a>) of each pixel in the first image (<kbd>u</kbd>) 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 <kbd>alpha.png</kbd> replaces both of the original images, <kbd>alpha.png</kbd> and <kbd>beta.png</kbd>, before being saved as <kbd>gamma.png</kbd>.</p> 473 474<p>The current image <kbd>s</kbd> is set to the first image in the sequence (<kbd>u</kbd>), and <kbd>t</kbd> to its index, 0. The symbols <kbd>i</kbd> and <kbd>j</kbd> reference the current pixel being processed.</p> 475 476 477<p>For use with <a href="/www/command-line-options.html#format_identify_">-format</a>, the value-escape <kbd>%[fx: ]</kbd> is evaluated just once for each image in the current image sequence. As each image in the sequence is being evaluated, <kbd>s</kbd> and <kbd>t</kbd> successively refer to the current image and its index, while <kbd>i</kbd> and <kbd>j</kbd> are set to zero, and the current channel set to red (<a href="/www/command-line-options.html#channel">-channel</a> is ignored). An example:</p> 478 479<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert xc:'rgb(25%,50%,75%)' rose: -colorspace rgb \ <br/> 480 -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 0.250004 <br/> 481 Red channel of NW corner of image # 1 is 0.188235</span></p> 482<p>Use <kbd>%[fxc: ]</kbd> if your expression is a constant (e.g. <kbd>%[fxc:page.x/2]</kbd>. The result is cached and the cached result returned rather than evaluating the expression each time.</p> 483 484<p>The color-escape <kbd>%[pixel: ]</kbd> is evaluated once per image and per color channel in that image (<a href="/www/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 <kbd>i</kbd> and <kbd>j</kbd> are set to zero, and <kbd>s</kbd> and <kbd>t</kbd> refer to each successively current image and index.</p> 485 486</div> 487</div> 488 489</div> 490 491<div id="linkbar"> 492 <span id="linkbar-west"> </span> 493 <span id="linkbar-center"> 494 <a href="http://www.imagemagick.org/discourse-server/">Discourse Server</a> • 495 <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">Studio</a> 496 </span> 497 <span id="linkbar-east"> </span> 498 </div> 499 <div class="footer"> 500 <span id="footer-west">© 1999-2011 ImageMagick Studio LLC</span> 501 <span id="footer-east"> <a href="http://www.imagemagick.org/script/contact.php">Contact the Wizards</a></span> 502 </div> 503 <div style="clear: both; margin: 0; width: 100%; "></div> 504 <script type="text/javascript"> 505 var _gaq = _gaq || []; 506 _gaq.push(['_setAccount', 'UA-17690367-1']); 507 _gaq.push(['_trackPageview']); 508 509 (function() { 510 var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; 511 ga.src = ('https:' == document.location.protocol ? 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