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Use FX to:</p> 89 90<ul> 91 <li>create canvases, gradients, mathematical colormaps</li> 92 <li>move color values between images and channels</li> 93 <li>translate, flip, mirror, rotate, scale, shear and generally distort images</li> 94 <li>merge or composite multiple images together</li> 95 <li>convolve or merge neighboring pixels together</li> 96 <li>generate image metrics or 'fingerprints'</li> 97</ul> 98 99<p>The expression can be simple:</p> 100 101<pre class="highlight"><code>convert -size 64x64 canvas:black -channel blue -fx "1/2" fx_navy.png 102</code></pre> 103 104<p>Here, we convert a black to a navy blue image:</p> 105 106<ul> 107 <a href="../images/black.png"><img src="../images/black.png" width="64" height="64" alt="black" /></a> 108 <img style="margin-top:22px; margin-bottom:22px;" src="../images/right.gif" width="20" height="20" alt="==>" /> 109 <a href="../images/navy.png"><img src="../images/navy.png" width="64" height="64" alt="navy" /></a> 110</ul> 111 112<p>Or the expression can be complex:</p> 113 114<pre class="highlight"><code>convert rose.jpg \ 115 -fx "(1.0/(1.0+exp(10.0*(0.5-u)))-0.006693)*1.0092503" \ 116 rose-sigmoidal.png' 117</code></pre> 118 119<p>This expression results in a high contrast version of the source image:</p> 120 121<ul> 122 <a href="../images/rose.jpg"><img src="../images/rose.jpg" width="70" height="46" alt="rose" /></a> 123 <img style="margin-top:13px; margin-bottom:13px;" src="../images/right.gif" width="20" height="20" alt="==>" /> 124 <a href="../images/rose-sigmoidal.png"><img src="../images/rose-sigmoidal.png" width="70" height="46" alt="rose-sigmoidal" /></a> 125</ul> 126 127<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> 128 129<pre class="highlight"><code>convert -size 70x70 canvas: \ 130 -fx "Xi=i-w/2; Yj=j-h/2; 1.2*(0.5-hypot(Xi,Yj)/70.0)+0.5" 131 radial-gradient.png' 132</code></pre> 133 134<p>The command above returns this image:</p> 135 136<ul> 137 <a href="../images/radial-gradient.png"><img src="../images/radial-gradient.png" width="70" height="70" alt="radial-gradient" /></a> 138</ul> 139 140<p>This FX expression adds random noise to an image:</p> 141 142<pre class="highlight"><code>convert photo.jpg -fx 'iso=32; rone=rand(); rtwo=rand(); \ 143 myn=sqrt(-2*ln(rone))*cos(2*Pi*rtwo); myntwo=sqrt(-2*ln(rtwo))* \ 144 cos(2*Pi*rone); pnoise=sqrt(p)*myn*sqrt(iso)* \ 145 channel(4.28,3.86,6.68,0)/255; max(0,p+pnoise)' noisy.png 146</code></pre> 147 148<p>See <a href="../Usage/transform/index.html#fx">Using FX, The Special Effects Image Operator</a> for more examples.</p> 149 150<p>The next section discusses the FX expression language.</p> 151 152<h2><a class="anchor" id="anatomy"></a>The Anatomy of an FX Expression</h2> 153 154<h3>The FX Expression Language</h3> 155 156<p>The formal FX expression language is defined here:</p> 157 158<dl class="row"> 159 <dt class="col-md-4"> numbers:</dt> 160 <dd class="col-md-8"> integer, floating point, scientific notation (+/- required, e.g. 3.81469e-06), International System number postfixes (.e.g KB, Mib, GB, etc.)</dd> 161 <dt class="col-md-4"> constants: </dt> 162 <dd class="col-md-8"> E (Euler's number), Epsilon, QuantumRange, QuantumScale, Opaque, Phi (golden ratio), Pi, Transparent</dd> 163 <dt class="col-md-4"> FX operators (in order of precedence): </dt> 164 <dd class="col-md-8"> ^ (power), unary -, *, /, % (modulo), +, -, 165 <<, >>, <, <=, >, >=, ==, !=, 166 & (bitwise AND), | (bitwise OR), 167 && (logical AND), || (logical OR), 168 ~ (logical NOT), ?: (ternary conditional)</dd> 169 <dt class="col-md-4"> math functions: </dt> 170 <dd class="col-md-8"> abs(), acos(), acosh(), airy(), alt(), asin(), asinh(), atan(), atanh(), atan2(), ceil(), clamp(), cos(), cosh(), debug(), drc(), erf(), 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> 171 <dt class="col-md-4"> channel functions: </dt> 172 <dd class="col-md-8"> channel(r,g,b,a), channel(c,m,y,k,a)</dd> 173 <dt class="col-md-4"> color names:</dt> 174 <dd class="col-md-8"> red, cyan, black, etc.</dd> 175 <dt class="col-md-4"> color functions:</dt> 176 <dd class="col-md-8"> srgb(), srgba(), rgb(), rgba(), cmyk(), cmyka(), hsl(), hsla(), etc.</dd> 177 <dt class="col-md-4"> color hex values:</dt> 178 <dd class="col-md-8"> #ccc, #cbfed0, #b9e1cc00, etc.</dd> 179 <dt class="col-md-4"> symbols:</dt><dd class="col-md-8"><dl> 180 <li><code>u</code>=> first image in list</li> 181 <li><code>v</code>=> second image in list</li> 182 <li><code>s</code>=> current image in list (for %[fx:] otherwise = u)</li> 183 <li><code>t</code>=> index of current image (s) in list</li> 184 <li><code>n</code>=> number of images in list</li> 185 186 <li><code>i</code>=> column offset</li> 187 <li><code>j</code>=> row offset</li> 188 <li><code>p</code>=> pixel to use (absolute or relative to current pixel)</li> 189 190 <li><code>w</code>=> width of this image</li> 191 <li><code>h</code>=> height of this image</li> 192 <li><code>z</code>=> channel depth</li> 193 194 <li><code>r</code>=> red value (from RGBA), of a specific or current pixel</li> 195 <li><code>g</code>=> green</li> 196 <li><code>b</code>=> blue</li> 197 <li><code>a</code>=> alpha</li> 198 <li><code>o</code>=> opacity</li> 199 200 <li><code>c</code>=> cyan value of CMYK color of pixel</li> 201 <li><code>y</code>=> yellow</li> 202 <li><code>m</code>=> magenta</li> 203 <li><code>k</code>=> black</li> 204 205 <li><code>intensity</code>=> pixel intensity</li> 206 207 <li><code>hue</code>=> pixel hue</li> 208 <li><code>saturation</code>=> pixel saturation</li> 209 <li><code>lightness</code>=> pixel lightness</li> 210 <li><code>luma</code>=> pixel luma</li> 211 212 <li><code>page.width</code>=> page width</li> 213 <li><code>page.height</code>=> page height</li> 214 <li><code>page.x</code>=> page x offset</li> 215 <li><code>page.y</code>=> page y offset</li> 216 217 <li><code>printsize.x</code>=> x printsize</li> 218 <li><code>printsize.y</code>=> y printsize</li> 219 220 <li><code>resolution.x</code>=> x resolution</li> 221 <li><code>resolution.y</code>=> y resolution</li> 222 223 <li><code>depth</code>=> image depth</li> 224 <li><code>extent</code>=> image extent</li> 225 <li><code>minima</code>=> image minima</li> 226 <li><code>maxima</code>=> image maxima</li> 227 <li><code>mean</code>=> image mean</li> 228 <li><code>standard_deviation</code>=> image standard deviation</li> 229 <li><code>kurtosis</code>=> image kurtosis</li> 230 <li><code>skewness</code>=> image skewness (add a channel specifier to compute a statistic for that channel, e.g. depth.r)</li></dl></dd> 231 <dt class="col-md-4"> iterators:</dt> 232 <dd class="col-md-8"> while()</dd> 233 <dt class="col-md-4"> image attributes:</dt> 234 <dd class="col-md-8"> image.depth, image.kurtosis, image.maxima, image.minima, image.resolution.x, image.resolution.y, image.skewness, image.standard_deviation</dd> 235</dl> 236 237<h3>The FX Expression</h3> 238 239<p>An FX expression may include any combination of the following:</p> 240<dl class="row"> 241<dt class="col-md-4"> <var>x</var> <code>^</code> <var>y</var></dt><dd class="col-md-8"> exponentiation (<var>x<sup>y</sup></var>)</dd> 242<dt class="col-md-4"> <code>(</code> ... <code>)</code></dt><dd class="col-md-8"> grouping</dd> 243<dt class="col-md-4"> <var>x</var> <code>*</code> <var>y</var></dt><dd class="col-md-8"> multiplication (the asterisk <code>*</code> is optional, for example, <code>2u</code> or <code>2(x+y)</code> are acceptable)</dd> 244<dt class="col-md-4"> <var>x</var> <code>/</code> <var>y</var></dt><dd class="col-md-8"> division</dd> 245<dt class="col-md-4"> <var>x</var> <code>%</code> <var>y</var></dt><dd class="col-md-8"> modulo</dd> 246<dt class="col-md-4"> <var>x</var> <code>+</code> <var>y</var></dt><dd class="col-md-8"> addition</dd> 247<dt class="col-md-4"> <var>x</var> <code>-</code> <var>y</var></dt><dd class="col-md-8"> subtraction</dd> 248<dt class="col-md-4"> <var>x</var> <code><<</code> <var>y</var></dt><dd class="col-md-8"> left shift</dd> 249<dt class="col-md-4"> <var>x</var> <code>>></code> <var>y</var></dt><dd class="col-md-8"> right shift</dd> 250<dt class="col-md-4"> <var>x</var> <code><</code> <var>y</var></dt><dd class="col-md-8"> boolean relation, return value 1.0 if <var>x</var> < <var>y</var>, otherwise 0.0</dd> 251<dt class="col-md-4"> <var>x</var> <code><=</code> <var>y</var></dt><dd class="col-md-8"> boolean relation, return value 1.0 if <var>x</var> <= <var>y</var>, otherwise 0.0</dd> 252<dt class="col-md-4"> <var>x</var> <code>></code> <var>y</var></dt><dd class="col-md-8"> boolean relation, return value 1.0 if <var>x</var> > <var>y</var>, otherwise 0.0</dd> 253<dt class="col-md-4"> <var>x</var> <code>>=</code> <var>y</var></dt><dd class="col-md-8"> boolean relation, return value 1.0 if <var>x</var> >= <var>y</var>, otherwise 0.0</dd> 254<dt class="col-md-4"> <var>x</var> <code>==</code> <var>y</var></dt><dd class="col-md-8"> boolean relation, return value 1.0 if <var>x </var>==<var> y</var>, otherwise 0.0</dd> 255<dt class="col-md-4"> <var>x</var> <code>!=</code> <var>y</var></dt><dd class="col-md-8"> boolean relation, return value 1.0 if <var>x </var>!=<var> y</var>, otherwise 0.0</dd> 256<dt class="col-md-4"> <var>x</var> <code>&</code> <var>y</var></dt><dd class="col-md-8"> binary AND</dd> 257<dt class="col-md-4"> <var>x</var> <code>|</code> <var>y</var></dt><dd class="col-md-8"> binary OR</dd> 258<dt class="col-md-4"> <var>x</var> <code>&&</code> <var>y</var></dt><dd class="col-md-8"> logical AND connective, return value 1.0 if <var>x</var> > 0 and <var>y</var> > 0, otherwise 0.0</dd> 259<dt class="col-md-4"> <var>x</var> <code>||</code> <var>y</var></dt><dd class="col-md-8"> logical OR connective (inclusive), return value 1.0 if <var>x</var> > 0 or <var>y</var> > 0 (or both), otherwise 0.0</dd> 260<dt class="col-md-4"> <code>~</code><var>x</var></dt><dd class="col-md-8"> logical NOT operator, return value 1.0 if <var>not</var> <var>x</var> > 0, otherwise 0.0</dd> 261<dt class="col-md-4"> <code>+</code><var>x</var></dt><dd class="col-md-8"> unary plus, return 1.0*value</dd> 262<dt class="col-md-4"> <code>-</code><var>x</var></dt><dd class="col-md-8"> unary minus, return -1.0*value</dd> 263<dt class="col-md-4"> <var>x</var> <code>?</code> <var>y</var> <code>:</code> <var>z</var> </dt><dd class="col-md-8">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> 264<dt class="col-md-4"> <var>x</var> <code>=</code> <var>y</var></dt><dd class="col-md-8">assignment; single character variables are reserved, instead use 2 or more characters, letter combinations only (e.g. Xi not X1)</dd> 265<dt class="col-md-4"> <var>x</var> <code>;</code> <var>y</var></dt><dd class="col-md-8">statement separator </dd> 266<dt class="col-md-4"> <code>phi</code></dt><dd class="col-md-8"> constant (1.618034...)</dd> 267<dt class="col-md-4"> <code>pi</code></dt><dd class="col-md-8"> constant (3.14159265359...)</dd> 268<dt class="col-md-4"> <code>e</code></dt><dd class="col-md-8"> constant (2.71828...)</dd> 269<dt class="col-md-4"> <code>QuantumRange</code></dt><dd class="col-md-8"> constant maximum pixel value (255 for Q8, 65535 for Q16)</dd> 270<dt class="col-md-4"> <code>QuantumScale</code></dt><dd class="col-md-8"> constant 1.0/<code>QuantumRange</code></dd> 271<dt class="col-md-4"> <code>intensity</code></dt><dd class="col-md-8"> pixel intensity whose value respects the <a href="../www/command-line-options.html#intensity">-intensity</a> option.</dd> 272<dt class="col-md-4"> <code>hue</code></dt><dd class="col-md-8"> pixel hue</dd> 273<dt class="col-md-4"> <code>saturation</code></dt><dd class="col-md-8"> pixel saturation</dd> 274<dt class="col-md-4"> <code>lightness</code></dt><dd class="col-md-8"> pixel lightness; equivalent to 0.5*max(red,green,blue) + 0.5*min(red,green,blue)</dd> 275<dt class="col-md-4"> <code>luminance</code></dt><dd class="col-md-8"> pixel luminance; equivalent to <code>0.212656*red + 0.715158*green + 0.072186*blue</code></dd> 276<dt class="col-md-4"> <code>red, green, blue</code>, etc.</dt><dd class="col-md-8"> color names</dd> 277<dt class="col-md-4"> <code>#ccc, #cbfed0, #b9e1cc00</code>, etc.</dt><dd class="col-md-8"> color hex values</dd> 278<dt class="col-md-4"> <code>rgb(), rgba(), cmyk(), cmyka(), hsl(), hsla()</code></dt><dd class="col-md-8"> color functions</dd> 279<dt class="col-md-4"> <code>s, t, u, v, n, i, j, w, h, z, r, g, b, a, o, c, y, m, k</code></dt><dd class="col-md-8"> symbols</dd> 280<dt class="col-md-4"> <code>abs(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> absolute value function</dd> 281<dt class="col-md-4"> <code>acos(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> arc cosine function</dd> 282<dt class="col-md-4"> <code>acosh(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> inverse hyperbolic cosine function</dd> 283<dt class="col-md-4"> <code>airy(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> 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> 284<dt class="col-md-4"> <code>alt(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> sign alternation function (return 1.0 if int(<var>x</var>) is even, -1.0 if int(<var>x</var>) is odd)</dd> 285<dt class="col-md-4"> <code>asin(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> arc sine function</dd> 286<dt class="col-md-4"> <code>asinh(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> inverse hyperbolic sine function</dd> 287<dt class="col-md-4"> <code>atan(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> arc tangent function</dd> 288<dt class="col-md-4"> <code>atanh(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> inverse hyperbolic tangent function</dd> 289<dt class="col-md-4"> <code>atan2(</code><var>x</var>,<var>y</var><code>)</code></dt><dd class="col-md-8"> arc tangent function of two variables</dd> 290<dt class="col-md-4"> <code>ceil(</code><var>x</var><code>)</code></dt><dd class="col-md-8">smallest integral value not less than argument</dd> 291<dt class="col-md-4"> <code>channel(</code><var>r</var>,<var>g</var>,<var>b</var>,<var>a</var><code>)</code></dt><dd class="col-md-8">select numeric argument based on current channel</dd> 292<dt class="col-md-4"> <code>channel(</code><var>c</var>,<var>m</var>,<var>y</var>,<var>k</var>,<var>a</var><code>)</code></dt><dd class="col-md-8">select numeric argument based on current channel</dd> 293<dt class="col-md-4"> <code>clamp(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> clamp value</dd> 294<dt class="col-md-4"> <code>cos(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> cosine function</dd> 295<dt class="col-md-4"> <code>cosh(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> hyperbolic cosine function</dd> 296<dt class="col-md-4"> <code>debug(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> print <var>x</var> (useful for debugging your expression)</dd> 297<dt class="col-md-4"> <code>drc(</code><var>x</var>,<var>y</var><code>)</code></dt><dd class="col-md-8"> 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> 298<dt class="col-md-4"> <code>erf(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> error function</dd> 299<dt class="col-md-4"> <code>exp(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> natural exponential function (<var>e<sup>x</sup></var>)</dd> 300<dt class="col-md-4"> <code>floor(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> largest integral value not greater than argument</dd> 301<dt class="col-md-4"> <code>gauss(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> gaussian function; gauss(<var>x</var>)=exp(<var>-x*x/2</var>)/sqrt(2*pi)</dd> 302<dt class="col-md-4"> <code>gcd(</code><var>x</var>,<var>y</var><code>)</code></dt><dd class="col-md-8"> greatest common denominator</dd> 303<dt class="col-md-4"> <code>hypot(</code><var>x</var>,<var>y</var><code>)</code></dt><dd class="col-md-8"> the square root of x<sup>2</sup>+y<sup>2</sup></dd> 304<dt class="col-md-4"> <code>int(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> greatest integer function (return greatest integer less than or equal to <var>x</var>)</dd> 305<dt class="col-md-4"> <code>isnan(</code><var>x</var><code>)</code></dt><dd class="col-md-8">return 1.0 if <var>x</var> is NAN, 0.0 otherwise</dd> 306<dt class="col-md-4"> <code>j0(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> Bessel functions of <var>x</var> of the first kind of order 0</dd> 307<dt class="col-md-4"> <code>j1(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> Bessel functions of <var>x</var> of the first kind of order 1</dd> 308<dt class="col-md-4"> <code>jinc(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> jinc function (max=1, min=-0.1323); jinc(<var>x</var>)=2*j1(pi*<var>x</var>)/(pi*<var>*x</var>)</dd> 309<dt class="col-md-4"> <code>ln(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> natural logarithm function</dd> 310<dt class="col-md-4"> <code>log(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> logarithm base 10</dd> 311<dt class="col-md-4"> <code>logtwo(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> logarithm base 2</dd> 312<dt class="col-md-4"> <code>ln(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> natural logarithm</dd> 313<dt class="col-md-4"> <code>max(</code><var>x</var>, <var>y</var><code>)</code></dt><dd class="col-md-8"> maximum of <var>x</var> and <var>y</var></dd> 314<dt class="col-md-4"> <code>min(</code><var>x</var>, <var>y</var><code>)</code></dt><dd class="col-md-8"> minimum of <var>x</var> and <var>y</var></dd> 315<dt class="col-md-4"> <code>mod(</code><var>x</var>, <var>y</var><code>)</code></dt><dd class="col-md-8"> floating-point remainder function</dd> 316<dt class="col-md-4"> <code>not(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> return 1.0 if <var>x</var> is zero, 0.0 otherwise</dd> 317<dt class="col-md-4"> <code>pow(</code><var>x</var>,<var>y</var><code>)</code></dt><dd class="col-md-8"> power function (<var>x<sup>y</sup></var>)</dd> 318<dt class="col-md-4"> <code>rand()</code></dt><dd class="col-md-8"> value uniformly distributed over the interval [0.0, 1.0) with a 2 to the 128th-1 period</dd> 319<dt class="col-md-4"> <code>round()</code></dt><dd class="col-md-8"> round to integral value, regardless of rounding direction</dd> 320<dt class="col-md-4"> <code>sign(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> return -1.0 if <var>x</var> is less than 0.0 otherwise 1.0</dd> 321<dt class="col-md-4"> <code>sin(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> sine function</dd> 322<dt class="col-md-4"> <code>sinc(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> sinc function (max=1, min=-0.21); sinc(<var>x</var>)=sin(<var>pi*x</var>)/(<var>pi*x</var>)</dd> 323<dt class="col-md-4"> <code>squish(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> squish function; squish(<var>x</var>)=1.0/(1.0+exp(<var>-x</var>))</dd> 324<dt class="col-md-4"> <code>sinh(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> hyperbolic sine function</dd> 325<dt class="col-md-4"> <code>sqrt(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> square root function</dd> 326<dt class="col-md-4"> <code>tan(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> tangent function</dd> 327<dt class="col-md-4"> <code>tanh(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> hyperbolic tangent function</dd> 328<dt class="col-md-4"> <code>trunc(</code><var>x</var><code>)</code></dt><dd class="col-md-8"> round to integer, towards zero</dd> 329<dt class="col-md-4"> <code>while(</code><var>condition</var>,<var>expression</var><code>)</code></dt><dd class="col-md-8"> iterate while the condition is not equal to 0</dd> 330<dt class="col-md-4"> <code>image.depth, image.kurtosis, image.maxima, image.minima, image.resolution.x, image.resolution.y, image.skewness, image.standard_deviation</code></dt><dd class="col-md-8"> image attributes</dd> 331</dl> 332<p>The expression semantics include these rules:</p> 333 334<ul> 335<li>symbols are case insensitive</li> 336<li>only one ternary conditional (e.g. x ? y : z) per statement</li> 337<li>statements are assignments or the final expression to return</li> 338<li>an assignment starts a statement, it is not an operator</li> 339<li>single character variables are reserved. Assignments to reserved 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> 340<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> 341<li>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> 342</ul> 343<br/> 344 345 346<h3>Source Images</h3> 347 348<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> 349 350<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> 351 352<pre class="highlight"><code>convert image1.jpg image2.jpg image3.jpg -fx "(u+u[2])/2.0" image.jpg 353</code></pre> 354 355<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 equivalent to <code>u</code> except when used in an escape sequence <code>%[fx:...]</code>. </p> 356 357<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> 358 359<pre class="highlight"><code>convert -channel red logo: -flop logo: -resize "20%" -fx "(u+v)/2" image.jpg 360</code></pre> 361 362<ul> 363 <a href="../images/logo-sm-flop.png"><img src="../images/logo-sm-flop.png" width="128" height="96" alt="logo-sm-flop.png" /></a> 364 <a href="../images/logo-sm.png"><img src="../images/logo-sm.png" width="128" height="96" alt="logo-sm.png" /></a> 365<img style="margin-top:38px; margin-bottom:38px;" src="../images/right.gif" width="20" height="20" alt="==>" /> 366 <a href="../images/logo-sm-fx.png"><img src="../images/logo-sm-fx.png" width="128" height="96" alt="logo-sm-fx.png" /></a> 367</ul> 368 369<br/> 370<h3>Accessing Pixels</h3> 371 372<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> 373 374<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> 375 376<pre class="highlight"><code>p[-1].g green value of pixel to the immediate left of the current pixel 377p[-1,-1].r red value of the pixel diagonally left and up from current pixel 378</code></pre> 379 380<p>To specify an absolute position, use braces, rather than brackets.</p> 381 382<pre class="highlight"><code>p{0,0}.r red value of the pixel in the upper left corner of the image 383p{12,34}.b blue pixel value at column number 12, row 34 of the image 384</code></pre> 385 386<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> 387 388<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> 389 390<h3>Apply an Expression to Select Image Channels</h3> 391 392<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 <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> 393 394<pre class="highlight"><code>convert alpha.png beta.png -channel red -fx "(u.g+v.g)/2" gamma.png 395</code></pre> 396 397 398<h3>Results</h3> 399 400<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 (<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> 401 402<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> 403 404 405<p>For use with <a href="../www/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="../www/command-line-options.html#channel">-channel</a> is ignored). An example:</p> 406 407<pre class="highlight"><code>$ convert canvas:'rgb(25%,50%,75%)' rose: -colorspace rgb \ 408 -format 'Red channel of NW corner of image #%[fx:t] is %[fx:s]' info: 409Red channel of NW corner of image #0 is 0.453758 410Red channel of NW corner of image #1 is 0.184588 411</code></pre> 412 413<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> 414 415<pre class="highlight"><code>convert rose: -duplicate 29 -virtual-pixel Gray -distort SRT '%[fx:360.0*t/n]' \ 416 -set delay '%[fx:t == 0 ? 240 : 10]' -loop 0 rose.gif" 417</code></pre> 418 419<p>The color-escape <code>%[pixel:]</code> or <code>%[hex:]</code> 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 <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> 420 421</div> 422 </div> 423 </main><!-- /.container --> 424 <footer class="magick-footer"> 425 <p><a href="../www/security-policy.html">Security</a> • 426 <a href="../www/architecture.html">Architecture</a> • 427 <a href="../www/links.html">Related</a> • 428 <a href="../www/sitemap.html">Sitemap</a> 429 430 <a href="fx.html#"><img class="d-inline" id="wand" alt="And Now a Touch of Magick" width="16" height="16" src="../images/wand.ico"/></a> 431 432 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> • 433 <a href="../www/support.html">Donate</a> • 434 <a href="../www/https://imagemagick.org/script/contact.php">Contact Us</a> 435 <br/> 436 <small>© 1999-2019 ImageMagick Studio LLC</small></p> 437 </footer> 438 439 <!-- Javascript assets --> 440 <script src="assets/magick.js" crossorigin="anonymous"></script> 441 <script>window.jQuery || document.write('<script src="https://localhost/ajax/libs/jquery/3.3.1/jquery.min.js"><\/script>')</script> 442</body> 443</html> 444
