fx.html revision 82a2ff27ee83c3408dce06c0f129386bd13eb17f
1<!DOCTYPE html> 2<html lang="en"> 3<head> 4 <meta charset="utf-8"> 5 <meta http-equiv="X-UA-Compatible" content="IE=edge"> 6 <meta name="viewport" content="width=device-width, initial-scale=1"> 7 <title>ImageMagick: The Fx Special Effects Image Operator</title> 8 <meta http-equiv="content-language" content="en-US"> 9 <meta http-equiv="content-type" content="text/html; charset=utf-8"> 10 <meta http-equiv="reply-to" content="magick-users@imagemagick.org"> 11 <meta name="application-name" content="ImageMagick"> 12 <meta name="description" content="ImageMagick® is a software suite to create, edit, compose, or convert bitmap images. It can read and write images in a variety of formats (over 200) including PNG, JPEG, JPEG-2000, GIF, WebP, Postscript, PDF, and SVG. Use ImageMagick to resize, flip, mirror, rotate, distort, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves."> 13 <meta name="application-url" content="http://www.imagemagick.org"> 14 <meta name="generator" content="PHP"> 15 <meta name="keywords" content="the, fx, special, effects, image, operator, ImageMagick, PerlMagick, image processing, image, photo, software, Magick++, OpenMP, convert"> 16 <meta name="rating" content="GENERAL"> 17 <meta name="robots" content="INDEX, FOLLOW"> 18 <meta name="generator" content="ImageMagick Studio LLC"> 19 <meta name="author" content="ImageMagick Studio LLC"> 20 <meta name="revisit-after" content="2 DAYS"> 21 <meta name="resource-type" content="document"> 22 <meta name="copyright" content="Copyright (c) 1999-2015 ImageMagick Studio LLC"> 23 <meta name="distribution" content="Global"> 24 <meta name="magick-serial" content="P131-S030410-R485315270133-P82224-A6668-G1245-1"> 25 <link rel="icon" href="/images/wand.png"> 26 <link rel="shortcut icon" href="/images/wand.ico" type="images/x-icon"> 27 <link rel="stylesheet" href="css/bootstrap.min.css"> 28 <link rel="stylesheet" href="css/magick.css"> 29</head> 30 31<body> 32<div class="main"> 33<div class="magick-masthead"> 34 <div class="container"> 35 <script type="text/javascript"> 36 <!-- 37 google_ad_client = "pub-3129977114552745"; 38 google_ad_slot = "5439289906"; 39 google_ad_width = 728; 40 google_ad_height = 90; 41 //--> 42 </script> 43 <center><script type="text/javascript" src="http://localhost/pagead/show_ads.js"> 44 </script></center> 45 <nav class="magick-nav"> 46 <a class="magick-nav-item " href="/index.html">Home</a> 47 <a class="magick-nav-item " href="binary-releases.html">Downloads</a> 48 <a class="magick-nav-item " href="command-line-tools.html">Tools</a> 49 <a class="magick-nav-item " href="command-line-options.html">Options</a> 50 <a class="magick-nav-item " href="api.html">Development</a> 51 <a class="magick-nav-item" href="http://www.imagemagick.org/discourse-server/">Community</a> 52 <a class="magick-nav-item pull-right " href="http://www.imagemagick.org/script/search.php">Search</a> 53 </nav> 54 </div> 55</div> 56<div class="container"> 57<div class="magick-header"> 58<p class="text-center"><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> 59 60<a id="fx"></a> 61 62<p class="lead magick-description">Use the Fx special effects image operator to apply a mathematical expression to an image or image channels. Use Fx to:</p> 63 64<ul> 65 <li>create canvases, gradients, mathematical colormaps</li> 66 <li>move color values between images and channels</li> 67 <li>translate, flip, mirror, rotate, scale, shear and generally distort images</li> 68 <li>merge or composite multiple images together</li> 69 <li>convolve or merge neighboring pixels together</li> 70 <li>generate image metrics or 'fingerprints'</li> 71</ul> 72 73<p>The expression can be simple:</p> 74 75<pre> 76convert -size 64x64 canvas:black -channel blue -fx "1/2" fx_navy.png 77</pre> 78 79<p>Here, we convert a black to a navy blue image:</p> 80 81<ul> 82 <a href="/images/black.png"><img src="/images/black.png" width="64" height="64" alt="black"></a> 83 <img style="margin-top:22px; margin-bottom:22px;" src="/images/right.gif" width="20" height="20" alt="==>"> 84 <a href="/images/navy.png"><img src="/images/navy.png" width="64" height="64" alt="navy"></a> 85</ul> 86 87<p>Or the expression can be complex:</p> 88 89<pre> 90convert rose.jpg \ 91 -fx "(1.0/(1.0+exp(10.0*(0.5-u)))-0.006693)*1.0092503" \ 92 rose-sigmoidal.png' 93</pre> 94 95<p>This expression results in a high contrast version of the image:</p> 96 97<ul> 98 <a href="/images/rose.jpg"><img src="/images/rose.jpg" width="70" height="46" alt="rose"></a> 99 <img style="margin-top:13px; margin-bottom:13px;" src="/images/right.gif" width="20" height="20" alt="==>"> 100 <a href="/images/rose-sigmoidal.png"><img src="/images/rose-sigmoidal.png" width="70" height="46" alt="rose-sigmoidal"></a> 101</ul> 102 103<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> 104 105<pre> 106convert -size 70x70 canvas: \ 107 -fx "Xi=i-w/2; Yj=j-h/2; 1.2*(0.5-hypot(Xi,Yj)/70.0)+0.5" 108 radial-gradient.png' 109</pre> 110 111<p>The command above returns this image:</p> 112 113<ul> 114 <a href="/images/radial-gradient.png"><img src="/images/radial-gradient.png" width="70" height="70" alt="radial-gradient"></a> 115</ul> 116 117<p>This FX expression adds random noise to an image:</p> 118 119<pre> 120convert photo.jpg -fx \'iso=32; rone=rand(); rtwo=rand(); \ 121 myn=sqrt(-2*ln(rone))*cos(2*Pi*rtwo); myntwo=sqrt(-2*ln(rtwo))* \ 122 cos(2*Pi*rone); pnoise=sqrt(p)*myn*sqrt(iso)* \ 123 channel(4.28,3.86,6.68,0)/255; max(0,p+pnoise)\' noisy.png 124</pre> 125 126<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> 127 128<p>The next section discusses the Fx expression language.</p> 129 130<h2 class="magick-header"><a id="anatomy"></a>The Anatomy of an Fx Expression</h2> 131 132<h3>The Fx Expression Language</h3> 133 134<p>The formal Fx expression language is defined here:</p> 135 136<dl class="dl-horizontal"> 137 <dt> numbers:</dt> 138 <dd> integer, floating point, scientfic notation (+/- required, e.g. 3.81469e-06), International System number postfixes (.e.g KB, Mib, GB, etc.)</dd> 139 <dt> constants: </dt> 140 <dd> E (Euler's number), Epsilon, QuantumRange, QuantumScale, Opaque, Phi (golden ratio), Pi, Transparent</dd> 141 <dt> Fx operators (in order of precedence): </dt> 142 <dd> ^ (power), unary -, *, /, % (modulo), +, -, 143 <<, >>, <, <=, >, >=, ==, !=, 144 & (bitwise AND), | (bitwise OR), 145 && (logical AND), || (logical OR), 146 ~ (logical NOT), ?: (ternary conditional)</dd> 147 <dt> math functions: </dt> 148 <dd> abs(), acos(), acosh(), airy(), alt(), asin(), asinh(), atan(), atanh(), atan2(), ceil(), clamp(), 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> 149 <dt> channel functions: </dt> 150 <dd> channel(r,g,b,a), channel(c,m,y,k,a)</dd> 151 <dt> color names:</dt> 152 <dd> red, cyan, black, etc.</dd> 153 <dt> color functions:</dt> 154 <dd> srgb(), srgba(), rgb(), rgba(), cmyk(), cmyka(), hsl(), hsla(), etc.</dd> 155 <dt> color hex values:</dt> 156 <dd> #ccc, #cbfed0, #b9e1cc00, etc.</dd> 157 <dt> symbols:</dt><dd><dl> 158 </dl><li><code>u</code>=> first image in list</li> 159 <li><code>v</code>=> second image in list</li> 160 <li><code>s</code>=> current image in list (for %[fx:] otherwise = u)</li> 161 <li><code>t</code>=> index of current image (s) in list</li> 162 <li><code>n</code>=> number of images in list</li> 163 164 <li><code>i</code>=> column offset</li> 165 <li><code>j</code>=> row offset</li> 166 <li><code>p</code>=> pixel to use (absolute or relative to current pixel)</li> 167 168 <li><code>w</code>=> width of this image</li> 169 <li><code>h</code>=> height of this image</li> 170 <li><code>z</code>=> channel depth</li> 171 172 <li><code>r</code>=> red value (from RGBA), of a specific or current pixel</li> 173 <li><code>g</code>=> green ''</li> 174 <li><code>b</code>=> blue ''</li> 175 <li><code>a</code>=> alpha ''</li> 176 <li><code>o</code>=> opacity ''</li> 177 178 <li><code>c</code>=> cyan value of CMYK color of pixel</li> 179 <li><code>y</code>=> yellow ''</li> 180 <li><code>m</code>=> magenta ''</li> 181 <li><code>k</code>=> black ''</li> 182 183 <li><code>intensity</code>=> pixel intensity</li> 184 185 <li><code>hue</code>=> pixel hue</li> 186 <li><code>saturation</code>=> pixel saturation</li> 187 <li><code>lightness</code>=> pixel lightness</li> 188 <li><code>luma</code>=> pixel luma</li> 189 190 <li><code>page.width</code>=> page width</li> 191 <li><code>page.height</code>=> page height</li> 192 <li><code>page.x</code>=> page x offset</li> 193 <li><code>page.y</code>=> page y offset</li> 194 195 <li><code>resolution.x</code>=> x resolution</li> 196 <li><code>resolution.y</code>=> y resolution</li> 197 198 <li><code>depth</code>=> image depth</li> 199 <li><code>minima</code>=> image minima</li> 200 <li><code>maxima</code>=> image maxima</li> 201 <li><code>mean</code>=> image mean</li> 202 <li><code>standard_deviation</code>=> image standard deviation</li> 203 <li><code>kurtosis</code>=> image kurtosis</li> 204 <li><code>skewness</code>=> image skewness (add a channel specifier to compute a statistic for that channel, e.g. depth.r)</li></dd></dl> 205 <dt> iterators:</dt> 206 <dd> while()</dd> 207 208 209 210<h3>The Fx Expression</h3> 211 212<p>An Fx expression may include any combination of the following:</p> 213<dl class="dl-horizontal"> 214<dt> <var>x</var> <code>^</code> <var>y</var></dt><dd> exponentiation (<var>x<sup>y</sup></var>)</dd> 215<dt> <code>(</code> ... <code>)</code></dt><dd> grouping</dd> 216<dt> <var>x</var> <code>*</code> <var>y</var></dt><dd> multiplication (the asterisk <code>*</code> is optional, for example, <code>2u</code> or <code>2(x+y)</code> are acceptable)</dd> 217<dt> <var>x</var> <code>/</code> <var>y</var></dt><dd> division</dd> 218<dt> <var>x</var> <code>%</code> <var>y</var></dt><dd> modulo</dd> 219<dt> <var>x</var> <code>+</code> <var>y</var></dt><dd> addition</dd> 220<dt> <var>x</var> <code>-</code> <var>y</var></dt><dd> subtraction</dd> 221<dt> <var>x</var> <code><<</code> <var>y</var></dt><dd> left shift</dd> 222<dt> <var>x</var> <code>>></code> <var>y</var></dt><dd> right shift</dd> 223<dt> <var>x</var> <code><</code> <var>y</var></dt><dd> boolean relation, return value 1.0 if <var>x</var> < <var>y</var>, otherwise 0.0</dd> 224<dt> <var>x</var> <code><=</code> <var>y</var></dt><dd> boolean relation, return value 1.0 if <var>x</var> <= <var>y</var>, otherwise 0.0</dd> 225<dt> <var>x</var> <code>></code> <var>y</var></dt><dd> boolean relation, return value 1.0 if <var>x</var> > <var>y</var>, otherwise 0.0</dd> 226<dt> <var>x</var> <code>>=</code> <var>y</var></dt><dd> boolean relation, return value 1.0 if <var>x</var> >= <var>y</var>, otherwise 0.0</dd> 227<dt> <var>x</var> <code>==</code> <var>y</var></dt><dd> boolean relation, return value 1.0 if <var>x </var>==<var> y</var>, otherwise 0.0</dd> 228<dt> <var>x</var> <code>!=</code> <var>y</var></dt><dd> boolean relation, return value 1.0 if <var>x </var>!=<var> y</var>, otherwise 0.0</dd> 229<dt> <var>x</var> <code>&</code> <var>y</var></dt><dd> binary AND</dd> 230<dt> <var>x</var> <code>|</code> <var>y</var></dt><dd> binary OR</dd> 231<dt> <var>x</var> <code>&&</code> <var>y</var></dt><dd> logical AND connective, return value 1.0 if <var>x</var> > 0 and <var>y</var> > 0, otherwise 0.0</dd> 232<dt> <var>x</var> <code>||</code> <var>y</var></dt><dd> logical OR connective (inclusive), return value 1.0 if <var>x</var> > 0 or <var>y</var> > 0 (or both), otherwise 0.0</dd> 233<dt> <code>~</code><var>x</var></dt><dd> logical NOT operator, return value 1.0 if <var>not</var> <var>x</var> > 0, otherwise 0.0</dd> 234<dt> <code>+</code><var>x</var></dt><dd> unary plus, return 1.0*value</dd> 235<dt> <code>-</code><var>x</var></dt><dd> unary minus, return -1.0*value</dd> 236<dt> <var>x</var> <code>?</code> <var>y</var> </dt><dd><var>z</var>: ternary conditional expression, return value <var>y</var> if <var>x</var> != 0, otherwise <var>z</var>; only one ternary conditional permitted per statement</dd> 237<dt> <var>x</var> <code>=</code> <var>y</var></dt><dd>assignment; assignment variables are restricted to letter combinations only (e.g. Xi not X1)</dd> 238<dt> <var>x</var> <code>;</code> <var>y</var></dt><dd>statement separator </dd> 239<dt> <code>phi</code></dt><dd> constant (1.618034...)</dd> 240<dt> <code>pi</code></dt><dd> constant (3.141659...)</dd> 241<dt> <code>e</code></dt><dd> constant (2.71828...)</dd> 242<dt> <code>QuantumRange</code></dt><dd> constant maximum pixel value (255 for Q8, 65535 for Q16)</dd> 243<dt> <code>QuantumScale</code></dt><dd> constant 1.0/<code>QuantumRange</code></dd> 244<dt> <code>intensity</code></dt><dd> pixel intensity; equivalent to 0.299*red+0.587*green+0.114*blue</dd> 245<dt> <code>hue</code></dt><dd> pixel hue</dd> 246<dt> <code>saturation</code></dt><dd> pixel saturation</dd> 247<dt> <code>lightness</code></dt><dd> pixel lightness; equivalent to 0.5*max(red,green,blue) + 0.5*min(red,green,blue)</dd> 248<dt> <code>luminance</code></dt><dd> pixel luminance; equivalent to 0.212656*red + 0.715158*green + 0.072186*blue</dd> 249<dt> <code>red, green, blue</code>, etc.</dt><dd> color names</dd> 250<dt> <code>#ccc, #cbfed0, #b9e1cc00</code>, etc.</dt><dd> color hex values</dd> 251<dt> <code>rgb(), rgba(), cmyk(), cmyka(), hsl(), hsla()</code></dt><dd> color functions</dd> 252<dt> <code>s, t, u, v, n, i, j, w, h, z, r, g, b, a, o, c, y, m, k</code></dt><dd> symbols</dd> 253<dt> <code>abs(</code><var>x</var><code>)</code></dt><dd> absolute value function</dd> 254<dt> <code>acos(</code><var>x</var><code>)</code></dt><dd> arc cosine function</dd> 255<dt> <code>acosh(</code><var>x</var><code>)</code></dt><dd> inverse hyperbolic cosine function</dd> 256<dt> <code>airy(</code><var>x</var><code>)</code></dt><dd> Airy function (max=1, min=0); airy(<var>x</var>)=[jinc(<var>x</var>)]<sup>2</sup>=[2*j1(<var>pi*x</var>)/(<var>pi*x</var>)]<sup>2</sup></dd> 257<dt> <code>alt(</code><var>x</var><code>)</code></dt><dd> sign alternation function (return 1.0 if int(<var>x</var>) is even, -1.0 if int(<var>x</var>) is odd)</dd> 258<dt> <code>asin(</code><var>x</var><code>)</code></dt><dd> arc sine function</dd> 259<dt> <code>asinh(</code><var>x</var><code>)</code></dt><dd> inverse hyperbolic sine function</dd> 260<dt> <code>atan(</code><var>x</var><code>)</code></dt><dd> arc tangent function</dd> 261<dt> <code>atanh(</code><var>x</var><code>)</code></dt><dd> inverse hyperbolic tangent function</dd> 262<dt> <code>atan2(</code><var>y</var>,<var>x</var><code>)</code></dt><dd> arc tangent function of two variables</dd> 263<dt> <code>ceil(</code><var>x</var><code>)</code></dt><dd>smallest integral value not less than argument</dd> 264<dt> <code>channel(</code><var>r</var>,<var>g</var>,<var>b</var>,<var>a</var><code>)</code></dt><dd>select numeric argument based on current channel</dd> 265<dt> <code>channel(</code><var>c</var>,<var>m</var>,<var>y</var>,<var>k</var>,<var>a</var><code>)</code></dt><dd>select numeric argument based on current channel</dd> 266<dt> <code>clamp(</code><var>x</var><code>)</code></dt><dd> clamp value</dd> 267<dt> <code>cos(</code><var>x</var><code>)</code></dt><dd> cosine function</dd> 268<dt> <code>cosh(</code><var>x</var><code>)</code></dt><dd> hyperbolic cosine function</dd> 269<dt> <code>debug(</code><var>x</var><code>)</code></dt><dd> print <var>x</var> (useful for debugging your expression)</dd> 270<dt> <code>drc(</code><var>x</var>,<var>y</var><code>)</code></dt><dd> dynamic range compression (knee curve); drc(<var>x</var>,<var>y</var>)=(<var>x</var>)/(<var>y</var>*(<var>x</var>-1)+1); -1<<var>y</var><1 </dd> 271<dt> <code>exp(</code><var>x</var><code>)</code></dt><dd> natural exponential function (<var>e<sup>x</sup></var>)</dd> 272<dt> <code>floor(</code><var>x</var><code>)</code></dt><dd> largest integral value not greater than argument</dd> 273<dt> <code>gauss(</code><var>x</var><code>)</code></dt><dd> gaussian function; gauss(<var>x</var>)=exp(<var>-x*x/2</var>)/sqrt(2*pi)</dd> 274<dt> <code>gcd(</code><var>x</var>,<var>y</var><code>)</code></dt><dd> greatest common denominator</dd> 275<dt> <code>hypot(</code><var>x</var>,<var>y</var><code>)</code></dt><dd> the square root of x<sup>2</sup>+y<sup>2</sup></dd> 276<dt> <code>int(</code><var>x</var><code>)</code></dt><dd> greatest integer function (return greatest integer less than or equal to <var>x</var>)</dd> 277<dt> <code>isnan(</code><var>x</var><code>)</code></dt><dd>return 1.0 if <var>x</var> is NAN, 0.0 otherwise</dd> 278<dt> <code>j0(</code><var>x</var><code>)</code></dt><dd> Bessel functions of <var>x</var> of the first kind of order 0</dd> 279<dt> <code>j1(</code><var>x</var><code>)</code></dt><dd> Bessel functions of <var>x</var> of the first kind of order 1</dd> 280<dt> <code>jinc(</code><var>x</var><code>)</code></dt><dd> jinc function (max=1, min=-0.1323); jinc(<var>x</var>)=2*j1(pi*<var>x</var>)/(pi*<var>*x</var>)</dd> 281<dt> <code>ln(</code><var>x</var><code>)</code></dt><dd> natural logarithm function</dd> 282<dt> <code>log(</code><var>x</var><code>)</code></dt><dd> logarithm base 10</dd> 283<dt> <code>logtwo(</code><var>x</var><code>)</code></dt><dd> logarithm base 2</dd> 284<dt> <code>ln(</code><var>x</var><code>)</code></dt><dd> natural logarithm</dd> 285<dt> <code>max(</code><var>x</var>, <var>y</var><code>)</code></dt><dd> maximum of <var>x</var> and <var>y</var></dd> 286<dt> <code>min(</code><var>x</var>, <var>y</var><code>)</code></dt><dd> minimum of <var>x</var> and <var>y</var></dd> 287<dt> <code>mod(</code><var>x</var>, <var>y</var><code>)</code></dt><dd> floating-point remainder function</dd> 288<dt> <code>not(</code><var>x</var><code>)</code></dt><dd> return 1.0 if <var>x</var> is zero, 0.0 otherwise</dd> 289<dt> <code>pow(</code><var>x</var>,<var>y</var><code>)</code></dt><dd> power function (<var>x<sup>y</sup></var>)</dd> 290<dt> <code>rand()</code></dt><dd> value uniformly distributed over the interval [0.0, 1.0) with a 2 to the 128th-1 period</dd> 291<dt> <code>round()</code></dt><dd> round to integral value, regardless of rounding direction</dd> 292<dt> <code>sign(</code><var>x</var><code>)</code></dt><dd> return -1.0 if <var>x</var> is less than 0.0 otherwise 1.0</dd> 293<dt> <code>sin(</code><var>x</var><code>)</code></dt><dd> sine function</dd> 294<dt> <code>sinc(</code><var>x</var><code>)</code></dt><dd> sinc function (max=1, min=-0.21); sinc(<var>x</var>)=sin(<var>pi*x</var>)/(<var>pi*x</var>)</dd> 295<dt> <code>squish(</code><var>x</var><code>)</code></dt><dd> squish function; squish(<var>x</var>)=1.0/(1.0+exp(<var>-x</var>))</dd> 296<dt> <code>sinh(</code><var>x</var><code>)</code></dt><dd> hyperbolic sine function</dd> 297<dt> <code>sqrt(</code><var>x</var><code>)</code></dt><dd> square root function</dd> 298<dt> <code>tan(</code><var>x</var><code>)</code></dt><dd> tangent function</dd> 299<dt> <code>tanh(</code><var>x</var><code>)</code></dt><dd> hyperbolic tangent function</dd> 300<dt> <code>trunc(</code><var>x</var><code>)</code></dt><dd> round to integer, towards zero</dd> 301<dt> <code>while(</code><var>condition</var>,<var>expression</var><code>)</code></dt><dd> interate while the condition is not equal to 0</dd> 302</dl> 303<br> 304<p>The expression semantics include these rules:</p> 305 306<ul> 307<li>symbols are case insensitive</li> 308<li>only one ternary conditional (e.g. x ? y : z) per statement</li> 309<li>statements are assignments or the final expression to return</li> 310<li>an assignment starts a statement, it is not an operator</li> 311<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> 312<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> 313<li>Similarly, care must be exercised when using the slash ('/') symbol. The string of characters <var>1/2x</var> 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> 314</ul> 315<br> 316 317 318<h3>Source Images</h3> 319 320<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> 321 322<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> 323 324<pre> 325convert image1.jpg image2.jpg image3.jpg -fx "(u+u[2])/2.0" image.jpg 326</pre> 327 328<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> 329 330<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> 331 332<pre> 333convert -channel red logo: -flop logo: -resize "20%" -fx "(u+v)/2" image.jpg 334</pre> 335 336<ul> 337 <a href="/images/logo-sm-flop.png"><img src="/images/logo-sm-flop.png" width="128" height="96" alt="logo-sm-flop.png"></a> 338 <a href="/images/logo-sm.png"><img src="/images/logo-sm.png" width="128" height="96" alt="logo-sm.png"></a> 339<img style="margin-top:38px; margin-bottom:38px;" src="/images/right.gif" width="20" height="20" alt="==>"> 340 <a href="/images/logo-sm-fx.png"><img src="/images/logo-sm-fx.png" width="128" height="96" alt="logo-sm-fx.png"></a> 341</ul> 342 343<br> 344<h3>Accessing Pixels</h3> 345 346<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> 347 348<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> 349 350<pre> 351 p[-1].g green value of pixel to the immediate left of the current pixel 352 p[-1,-1].r red value of the pixel diagonally left and up from current pixel 353</pre> 354 355<p>To specify an absolute position, use braces, rather than brackets.</p> 356 357<pre> 358 p{0,0}.r red value of the pixel in the upper left corner of the image 359 p{12,34}.b blue pixel value at column number 12, row 34 of the image 360</pre> 361 362<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> 363 364<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> 365 366<h3>Apply an Expression to Select Image Channels</h3> 367 368<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> 369 370<pre> 371convert alpha.png beta.png -channel red -fx "(u.g+v.g)/2" gamma.png 372</pre> 373 374 375<h3>Results</h3> 376 377<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> 378 379<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> 380 381 382<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> 383 384<pre> 385convert canvas:'rgb(25%,50%,75%)' rose: -colorspace rgb \ 386 -format 'Red channel of NW corner of image #%[fx:t] is %[fx:s]' info: 387Red channel of NW corner of image #0 is 0.453758 388Red channel of NW corner of image #1 is 0.184588 389</pre> 390 391<p>Here we use the image indexes to <var>rotate</var> each image differently, and use <code>-set</code> with the image index to set a different <var>pause delay</var> on the first image in the animation:</p> 392 393<pre> 394convert rose: -duplicate 29 -virtual-pixel Gray -distort SRT '%[fx:360.0*t/n]' \ 395 -set delay '%[fx:t == 0 ? 240 : 10]' -loop 0 rose.gif" 396</pre> 397 398<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> 399 400</div> 401 <footer class="magick-footer"> 402 <div class="magick-nav-item pull-left"> 403 <a href="support.html">Donate</a> 404 </div> 405 <p><a href="sitemap.html">Sitemap</a> • 406 <a href="links.html">Related</a> • 407 <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">Image Studio</a> • 408 <a href="http://jqmagick.imagemagick.org/">JqMagick</a> • 409 <a href="http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> 410</p> 411 <p><a href="fx.html#">Back to top</a> • 412 <a href="http://www.imagemagick.org/script/contact.php">Contact Us</a></p> 413 <p class="small">© 1999-2015 ImageMagick Studio LLC</p> 414 </footer> 415</div><!-- /.container --> 416 417 <script src="https://localhost/ajax/libs/jquery/1.11.2/jquery.min.js"></script> 418 <script src="/js/bootstrap.min.js"></script> 419 <script type="text/javascript"> 420 /* <![CDATA[ */ 421 (function() { 422 var s = document.createElement('offline-script'), t = document.getElementsByTagName('offline-script')[0]; 423 s.type = 'text/javascript'; 424 s.async = true; 425 s.src = 'http://api.flattr.com/js/0.6/load.js?mode=auto'; 426 t.parentNode.insertBefore(s, t); 427 })(); 428 /* ]]> */ 429 </script> 430</div> 431</body> 432</html> 433
