1 2 3 4 5<!doctype html> 6<html lang="en"> 7<head> 8 <meta charset="utf-8" /> 9 <meta name="viewport" content="width=device-width, initial-scale=1" /> 10 <title>ImageMagick - Color Thresholding</title> 11 <meta name="application-name" content="ImageMagick" /> 12 <meta name="description" content="Use ImageMagick® to create, edit, compose, and convert digital images. 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All colors between the start and stop colors (inclusively) become white and the rest of the image pixels become black. The two colors are separated with a hyphen between them. Thresholding, by default, take place in the sRGB colorspace. Use the <code>-colorspace</code> to perform the thresholding in an alternative colorspaces (currently limited to sRGB, Gray, HSV, HSL, HCL, HSB, and HSW). Start and stop colors can be specified in any colorspace (recognized by ImageMagick), but in general, we advise you specify them in the colorspace corresponding to the <code>-colorspace</code> option. For colorspace Gray, be sure to use a start value lower than the stop value. Note that Hue is cyclical -- 0 and 360 are the same. However, a range of colors that spans hue = 0 may still be useful, if the start hue value is higher than the stop hue value.</p> 96 97<p>Caution is advised when mixing the colorspace of the start and stop colors and that of the image. A large range in one colorspace may map to only a narrow range in another colorspace. For example, one might naively think that <code>sRGB(0,0,0)</code> to <code>sRGB(255,255,255)</code> would produce a white image, catching all colors, even when using -colorspace HSV. But these two colors are black and white and so map only to a range of grayscale as <code>hsv(0,0%,0%)</code> and <code>hsv(0,0%,100%)</code>. For a color image, you would likely not find too many gray pixels.</p> 98 99<p>To illustrate how color thresholding performs, use this image:</p> 100 101<ul><pre class="code">convert <var>input-image</var> -colorspace <var>XXX</var> -color-threshold <var>"start - stop"</var> <var>output-image</var></pre></ul> 102 103<p>The following are some typical examples of use:</p> 104 105<ul><img class="img-fluid d-block" src="../images/color-thresholding.jpg" alt="[Color Thresholding]" width="265" height="333" name="color-thresholding" /></ul> 106 107<p>Start by choosing one sRGB color (somewhere on the image -- in this case the yellow of the flowers) and offset it low and high to form two sRGB colors. The lower values form the start color and the higher values form the stop color. Begin with <code>sRGB(183,132,20)</code>. Offset its values by +-20 to identify the start color (-) and the stop color (+); namely, R=183+-20, G=132+-20, and B=40+-20:</p> 108 109<ul><pre class="code">magick monet.jpg -color-threshold 'sRGB(163,112,0)-sRGB(203,152,40)' monet.gif</pre></ul> 110 111<p>this returns the outline of the yellow flower petals:</p> 112 113<ul><img class="img-fluid d-block" src="../images/color-thresholding-hsv.gif" alt="[Color Thresholding]" width="265" height="333" name="color-thresholding" /></ul> 114 115<p>Now, pick two RGB colors: <code>sRGB(159,150,0)</code> and <code>sRGB(205,100,45):</code></p> 116 117<ul><pre class="code">magick monet.jpg -color-threshold 'sRGB(159,150,0)-sRGB(205,100,45)' monet.gif</code></ul> 118 119<ul><img class="img-fluid d-block" src="../images/color-thresholding-rgb.gif" alt="[Color Thresholding]" width="265" height="333" name="color-thresholding" /></ul> 120 121<p>Next, select one sRGB color and convert it to HSV and offset its values low and high to generate the start and stop HSV colors. Use -colorspace HSV to convert the image to HSV. For our HSV example, we pick <code>sRGB(183,132,20)</code> and convert to HSV:</p> 122 123<ul><pre class="code"> 124magick xc:"srgb(183,132,20)" -colorspace HSV txt: 125# ImageMagick pixel enumeration: 1,1,65535,hsv 1260,0: (41.227,89.071%,71.7647%) #1D51E405B7B7 hsv(41.227,89.071%,71.7647%) 127</pre></ul> 128 129<p>Now, offset its HSV values as H=41+-20, S=89+-10, and V=72+-10, to create the start color (-) and stop color (+):</p> 130 131<ul><pre class="code">magick monet.jpg -colorspace HSV -color-threshold 'hsv(21,79%,62%)-hsv(61,99%,85%)' monet.gif</pre></ul> 132 133<ul><img class="img-fluid d-block" src="../images/color-thresholding-rgb.gif" alt="[Color Thresholding]" width="265" height="333" name="color-thresholding" /></ul> 134 135<p>Next, pick two RGB colors. Use <code>-colorspace HSV</code> to convert the image to HSV, and apply the RGB start and stop colors. Choose <code>sRGB(158,77,33)</code> and <code>sRGB(213,217,2)</code>:</p> 136 137<ul><pre class="code">magick monet.jpg -colorspace HSV -color-threshold "sRGB(158,77,33)-sRGB(213,217,2)" monet.gif</pre></ul> 138 139<p>Here is the expected results:</p> 140 141<ul><img class="img-fluid d-block" src="../images/color-thresholding-hsv-rgb.gif" alt="[Color Thresholding]" width="265" height="333" name="color-thresholding" /></ul> 142 143<p>Next, choose two sRGB colors and convert them to gray. Now convert the image to gray and use the gray thresholding colors.</p> 144 145<ul><pre class="code"> 146magick xc:"sRGB(159,150,0)" -colorspace gray txt: 147# ImageMagick pixel enumeration: 1,1,65535,gray 1480,0: (36259.1) #8DA38DA38DA3 gray(55.3278%) 149 150magick xc:"sRGB(205,100,45)" -colorspace gray txt: 151# ImageMagick pixel enumeration: 1,1,65535,gray 1520,0: (30418.2) #76D276D276D2 gray(46.4152%) 153</pre></ul> 154 155<p>Notice that the start intensity must be smaller than stop intensity:</p> 156 157<ul><pre class="code">magick monet.jpg -colorspace gray -color-threshold 'gray(46.4152%)-gray(55.3278%)' monet.gif</pre></ul> 158 159<p>Here is the results of the color thresholding operation:</p> 160 161<ul><img class="img-fluid d-block" src="../images/color-thresholding-gray.gif" alt="[Color Thresholding]" width="265" height="333" name="Color Thresholding" /></ul> 162</div> 163 </div> 164 </main><!-- /.container --> 165 <footer class="magick-footer"> 166 <div class="container-fluid"> 167 <a href="../www/security-policy.html">Security</a> • 168 <a href="../www/news.html">News</a> 169 170 <a href="color-thresholding.html#"><img class="d-inline" id="wand" alt="And Now a Touch of Magick" width="16" height="16" src="../images/wand.ico"/></a> 171 172 <a href="../www/links.html">Related</a> • 173 <a href="../www/sitemap.html">Sitemap</a> 174 <br/> 175 <a href="../www/support.html">Sponsor</a> • 176 <a href="../www/cite.html">Cite</a> • 177 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> • 178 <a href="../www/https://imagemagick.org/script/contact.php">Contact Us</a> 179 <br/> 180 <a href="https://github.com/imagemagick/imagemagick" target="_blank" rel="noopener" aria-label="GitHub"><svg xmlns="http://www.w3.org/2000/svg" class="navbar-nav-svg" viewBox="0 0 512 499.36" width="2%" height="2%" role="img" focusable="false"><title>GitHub</title><path fill="currentColor" fill-rule="evenodd" d="M256 0C114.64 0 0 114.61 0 256c0 113.09 73.34 209 175.08 242.9 12.8 2.35 17.47-5.56 17.47-12.34 0-6.08-.22-22.18-.35-43.54-71.2 15.49-86.2-34.34-86.2-34.34-11.64-29.57-28.42-37.45-28.42-37.45-23.27-15.84 1.73-15.55 1.73-15.55 25.69 1.81 39.21 26.38 39.21 26.38 22.84 39.12 59.92 27.82 74.5 21.27 2.33-16.54 8.94-27.82 16.25-34.22-56.84-6.43-116.6-28.43-116.6-126.49 0-27.95 10-50.8 26.35-68.69-2.63-6.48-11.42-32.5 2.51-67.75 0 0 21.49-6.88 70.4 26.24a242.65 242.65 0 0 1 128.18 0c48.87-33.13 70.33-26.24 70.33-26.24 14 35.25 5.18 61.27 2.55 67.75 16.41 17.9 26.31 40.75 26.31 68.69 0 98.35-59.85 120-116.88 126.32 9.19 7.9 17.38 23.53 17.38 47.41 0 34.22-.31 61.83-.31 70.23 0 6.85 4.61 14.81 17.6 12.31C438.72 464.97 512 369.08 512 256.02 512 114.62 397.37 0 256 0z"/></svg></a> • 181 <a href="https://twitter.com/imagemagick" target="_blank" rel="noopener" aria-label="Twitter"><svg xmlns="http://www.w3.org/2000/svg" class="navbar-nav-svg" viewBox="0 0 512 416.32" width="2%" height="2%" role="img" focusable="false"><title>Twitter</title><path fill="currentColor" d="M160.83 416.32c193.2 0 298.92-160.22 298.92-298.92 0-4.51 0-9-.2-13.52A214 214 0 0 0 512 49.38a212.93 212.93 0 0 1-60.44 16.6 105.7 105.7 0 0 0 46.3-58.19 209 209 0 0 1-66.79 25.37 105.09 105.09 0 0 0-181.73 71.91 116.12 116.12 0 0 0 2.66 24c-87.28-4.3-164.73-46.3-216.56-109.82A105.48 105.48 0 0 0 68 159.6a106.27 106.27 0 0 1-47.53-13.11v1.43a105.28 105.28 0 0 0 84.21 103.06 105.67 105.67 0 0 1-47.33 1.84 105.06 105.06 0 0 0 98.14 72.94A210.72 210.72 0 0 1 25 370.84a202.17 202.17 0 0 1-25-1.43 298.85 298.85 0 0 0 160.83 46.92"/></svg></a> 182 <br/> 183 <small>© 1999-2021 ImageMagick Studio LLC</small> 184 </div> 185 </footer> 186 187 <!-- Javascript assets --> 188 <script src="assets/magick.js" ></script> 189 </body> 190</html> 191<!-- Magick Cache 13th February 2021 13:05 -->
