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<section id="tiffcolor">
<h1>TIFFcolor<a class="headerlink" href="#tiffcolor" title="Permalink to this heading">¶</a></h1>
<section id="synopsis">
<h2>Synopsis<a class="headerlink" href="#synopsis" title="Permalink to this heading">¶</a></h2>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><tiffio.h></span>
</pre></div>
</div>
<dl class="c function">
<dt class="sig sig-object c" id="c.TIFFYCbCrToRGBInit">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">TIFFYCbCrToRGBInit</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">TIFFYCbCrToRGB</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ycbcr</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">luma</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">refBlackWhite</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.TIFFYCbCrToRGBInit" title="Permalink to this definition">¶</a><br /></dt>
<dd></dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.TIFFYCbCrtoRGB">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">TIFFYCbCrtoRGB</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">TIFFYCbCrToRGB</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ycbcr</span></span>, <span class="n"><span class="pre">uint32_t</span></span><span class="w"> </span><span class="n"><span class="pre">Y</span></span>, <span class="n"><span class="pre">int32_t</span></span><span class="w"> </span><span class="n"><span class="pre">Cb</span></span>, <span class="n"><span class="pre">int32_t</span></span><span class="w"> </span><span class="n"><span class="pre">Cr</span></span>, <span class="n"><span class="pre">uint32_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">R</span></span>, <span class="n"><span class="pre">uint32_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">G</span></span>, <span class="n"><span class="pre">uint32_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">B</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.TIFFYCbCrtoRGB" title="Permalink to this definition">¶</a><br /></dt>
<dd></dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.TIFFCIELabToRGBInit">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">TIFFCIELabToRGBInit</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">TIFFCIELabToRGB</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">cielab</span></span>, <span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="n"><span class="pre">TIFFDisplay</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">displayw</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">refWhite</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.TIFFCIELabToRGBInit" title="Permalink to this definition">¶</a><br /></dt>
<dd></dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.TIFFCIELabToXYZ">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">TIFFCIELabToXYZ</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">TIFFCIELabToRGB</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">cielab</span></span>, <span class="n"><span class="pre">uint32_t</span></span><span class="w"> </span><span class="n"><span class="pre">L</span></span>, <span class="n"><span class="pre">int32_t</span></span><span class="w"> </span><span class="n"><span class="pre">a</span></span>, <span class="n"><span class="pre">int32_t</span></span><span class="w"> </span><span class="n"><span class="pre">b</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">X</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">Y</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">Z</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.TIFFCIELabToXYZ" title="Permalink to this definition">¶</a><br /></dt>
<dd></dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.TIFFXYZToRGB">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">TIFFXYZToRGB</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">TIFFCIELabToRGB</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">cielab</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="n"><span class="pre">X</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="n"><span class="pre">Y</span></span>, <span class="kt"><span class="pre">float</span></span><span class="w"> </span><span class="n"><span class="pre">Z</span></span>, <span class="n"><span class="pre">uint32_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">R</span></span>, <span class="n"><span class="pre">uint32_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">G</span></span>, <span class="n"><span class="pre">uint32_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">B</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.TIFFXYZToRGB" title="Permalink to this definition">¶</a><br /></dt>
<dd></dd></dl>
</section>
<section id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this heading">¶</a></h2>
<p>TIFF supports several color spaces for images stored in that format. There is
usually a problem of application to handle the data properly and convert
between different colorspaces for displaying and printing purposes. To
simplify this task <code class="docutils literal notranslate"><span class="pre">libtiff</span></code> implements several color conversion routines
itself. In particular, these routines used in the <a class="reference internal" href="TIFFRGBAImage.html"><span class="doc">TIFFRGBAImage</span></a>
interface.</p>
<p><a class="reference internal" href="#c.TIFFYCbCrToRGBInit" title="TIFFYCbCrToRGBInit"><code class="xref c c-func docutils literal notranslate"><span class="pre">TIFFYCbCrToRGBInit()</span></code></a> used to initialize <em>YCbCr</em> to <em>RGB</em>
conversion state. Allocating and freeing of the <em>ycbcr</em> structure
belongs to programmer. <code class="xref c c-struct docutils literal notranslate"><span class="pre">TIFFYCbCrToRGB</span></code> is defined in
<code class="file docutils literal notranslate"><span class="pre">tiffio.h</span></code> as:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="cm">/* YCbCr->RGB support */</span>
<span class="w"> </span><span class="n">TIFFRGBValue</span><span class="o">*</span><span class="w"> </span><span class="n">clamptab</span><span class="p">;</span><span class="w"> </span><span class="cm">/* range clamping table */</span>
<span class="w"> </span><span class="kt">int</span><span class="o">*</span><span class="w"> </span><span class="n">Cr_r_tab</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="o">*</span><span class="w"> </span><span class="n">Cb_b_tab</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int32_t</span><span class="o">*</span><span class="w"> </span><span class="n">Cr_g_tab</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int32_t</span><span class="o">*</span><span class="w"> </span><span class="n">Cb_g_tab</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int32_t</span><span class="o">*</span><span class="w"> </span><span class="n">Y_tab</span><span class="p">;</span>
<span class="p">}</span><span class="w"> </span><span class="n">TIFFYCbCrToRGB</span><span class="p">;</span>
</pre></div>
</div>
<p><em>luma</em> is a float array of three values representing proportions of the
red, green and blue in luminance, Y (see section 21 of the TIFF 6.0
specification, where YCbCr images are discussed).
<code class="xref c c-macro docutils literal notranslate"><span class="pre">TIFFTAG_YCBCRCOEFFICIENTS</span></code> hold these values in TIFF file.
<em>refBlackWhite</em> is a float array of 6 values which specifies a pair of
headroom and footroom image data values (codes) for each image component
(see section 20 of the TIFF 6.0 specification where the colorimetry
fields are discussed).
<code class="xref c c-macro docutils literal notranslate"><span class="pre">TIFFTAG_REFERENCEBLACKWHITE</span></code> is responsible for storing these
values in TIFF file. The following code snippet should help to
understand the the technique:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">float</span><span class="w"> </span><span class="o">*</span><span class="n">luma</span><span class="p">,</span><span class="w"> </span><span class="o">*</span><span class="n">refBlackWhite</span><span class="p">;</span>
<span class="kt">uint16_t</span><span class="w"> </span><span class="n">hs</span><span class="p">,</span><span class="w"> </span><span class="n">vs</span><span class="p">;</span>
<span class="cm">/* Initialize structures */</span>
<span class="n">ycbcr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="n">TIFFYCbCrToRGB</span><span class="o">*</span><span class="p">)</span>
<span class="w"> </span><span class="n">_TIFFmalloc</span><span class="p">(</span><span class="n">TIFFroundup</span><span class="p">(</span><span class="k">sizeof</span><span class="p">(</span><span class="n">TIFFYCbCrToRGB</span><span class="p">),</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">long</span><span class="p">))</span>
<span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="mi">256</span><span class="o">*</span><span class="k">sizeof</span><span class="p">(</span><span class="n">TIFFRGBValue</span><span class="p">)</span>
<span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="mi">256</span><span class="o">*</span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span>
<span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="o">*</span><span class="mi">256</span><span class="o">*</span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int32_t</span><span class="p">));</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">ycbcr</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nb">NULL</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">TIFFError</span><span class="p">(</span><span class="s">"YCbCr->RGB"</span><span class="p">,</span>
<span class="w"> </span><span class="s">"No space for YCbCr->RGB conversion state"</span><span class="p">);</span>
<span class="w"> </span><span class="n">exit</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">TIFFGetFieldDefaulted</span><span class="p">(</span><span class="n">tif</span><span class="p">,</span><span class="w"> </span><span class="n">TIFFTAG_YCBCRCOEFFICIENTS</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">luma</span><span class="p">);</span>
<span class="n">TIFFGetFieldDefaulted</span><span class="p">(</span><span class="n">tif</span><span class="p">,</span><span class="w"> </span><span class="n">TIFFTAG_REFERENCEBLACKWHITE</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">refBlackWhite</span><span class="p">);</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">TIFFYCbCrToRGBInit</span><span class="p">(</span><span class="n">ycbcr</span><span class="p">,</span><span class="w"> </span><span class="n">luma</span><span class="p">,</span><span class="w"> </span><span class="n">refBlackWhite</span><span class="p">)</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">exit</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span>
<span class="p">}</span>
<span class="cm">/* Start conversion */</span>
<span class="kt">uint32_t</span><span class="w"> </span><span class="n">r</span><span class="p">,</span><span class="w"> </span><span class="n">g</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">;</span>
<span class="kt">uint32_t</span><span class="w"> </span><span class="n">Y</span><span class="p">;</span>
<span class="kt">int32_t</span><span class="w"> </span><span class="n">Cb</span><span class="p">,</span><span class="w"> </span><span class="n">Cr</span><span class="p">;</span>
<span class="k">for</span><span class="w"> </span><span class="n">each</span><span class="w"> </span><span class="n">pixel</span><span class="w"> </span><span class="n">in</span><span class="w"> </span><span class="n">image</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">TIFFYCbCrtoRGB</span><span class="p">(</span><span class="n">img</span><span class="o">-></span><span class="n">ycbcr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Cb</span><span class="p">,</span><span class="w"> </span><span class="n">Cr</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">r</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">g</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">b</span><span class="p">);</span>
<span class="p">}</span>
<span class="cm">/* Free state structure */</span>
<span class="n">_TIFFfree</span><span class="p">(</span><span class="n">ycbcr</span><span class="p">);</span>
</pre></div>
</div>
<p><a class="reference internal" href="#c.TIFFCIELabToRGBInit" title="TIFFCIELabToRGBInit"><code class="xref c c-func docutils literal notranslate"><span class="pre">TIFFCIELabToRGBInit()</span></code></a> initializes the <em>CIE L*a*b* 1976</em> to
<em>RGB</em> conversion state. <code class="xref c c-struct docutils literal notranslate"><span class="pre">TIFFCIELabToRGB</span></code> is defined as:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#define CIELABTORGB_TABLE_RANGE 1500</span>
<span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="cm">/* CIE Lab 1976->RGB support */</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">range</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Size of conversion table */</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">rstep</span><span class="p">,</span><span class="w"> </span><span class="n">gstep</span><span class="p">,</span><span class="w"> </span><span class="n">bstep</span><span class="p">;</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">X0</span><span class="p">,</span><span class="w"> </span><span class="n">Y0</span><span class="p">,</span><span class="w"> </span><span class="n">Z0</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Reference white point */</span>
<span class="w"> </span><span class="n">TIFFDisplay</span><span class="w"> </span><span class="n">display</span><span class="p">;</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">Yr2r</span><span class="p">[</span><span class="n">CIELABTORGB_TABLE_RANGE</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">];</span><span class="w"> </span><span class="cm">/* Conversion of Yr to r */</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">Yg2g</span><span class="p">[</span><span class="n">CIELABTORGB_TABLE_RANGE</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">];</span><span class="w"> </span><span class="cm">/* Conversion of Yg to g */</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">Yb2b</span><span class="p">[</span><span class="n">CIELABTORGB_TABLE_RANGE</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">];</span><span class="w"> </span><span class="cm">/* Conversion of Yb to b */</span>
<span class="p">}</span><span class="w"> </span><span class="n">TIFFCIELabToRGB</span><span class="p">;</span>
</pre></div>
</div>
<p><em>display</em> is a display device description, declared as:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_mat</span><span class="p">[</span><span class="mi">3</span><span class="p">][</span><span class="mi">3</span><span class="p">];</span><span class="w"> </span><span class="cm">/* XYZ -> luminance matrix */</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_YCR</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Light o/p for reference white */</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_YCG</span><span class="p">;</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_YCB</span><span class="p">;</span>
<span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">d_Vrwr</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Pixel values for ref. white */</span>
<span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">d_Vrwg</span><span class="p">;</span>
<span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">d_Vrwb</span><span class="p">;</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_Y0R</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Residual light for black pixel */</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_Y0G</span><span class="p">;</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_Y0B</span><span class="p">;</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_gammaR</span><span class="p">;</span><span class="w"> </span><span class="cm">/* Gamma values for the three guns */</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_gammaG</span><span class="p">;</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">d_gammaB</span><span class="p">;</span>
<span class="p">}</span><span class="w"> </span><span class="n">TIFFDisplay</span><span class="p">;</span>
</pre></div>
</div>
<p>For example, one can use sRGB device, which has the following parameters:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">TIFFDisplay</span><span class="w"> </span><span class="n">display_sRGB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="cm">/* XYZ -> luminance matrix */</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="mf">3.2410F</span><span class="p">,</span><span class="w"> </span><span class="mf">-1.5374F</span><span class="p">,</span><span class="w"> </span><span class="mf">-0.4986F</span><span class="w"> </span><span class="p">},</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="mf">-0.9692F</span><span class="p">,</span><span class="w"> </span><span class="mf">1.8760F</span><span class="p">,</span><span class="w"> </span><span class="mf">0.0416F</span><span class="w"> </span><span class="p">},</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="mf">0.0556F</span><span class="p">,</span><span class="w"> </span><span class="mf">-0.2040F</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0570F</span><span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">},</span>
<span class="w"> </span><span class="mf">100.0F</span><span class="p">,</span><span class="w"> </span><span class="mf">100.0F</span><span class="p">,</span><span class="w"> </span><span class="mf">100.0F</span><span class="p">,</span><span class="w"> </span><span class="cm">/* Light o/p for reference white */</span>
<span class="w"> </span><span class="mi">255</span><span class="p">,</span><span class="w"> </span><span class="mi">255</span><span class="p">,</span><span class="w"> </span><span class="mi">255</span><span class="p">,</span><span class="w"> </span><span class="cm">/* Pixel values for ref. white */</span>
<span class="w"> </span><span class="mf">1.0F</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0F</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0F</span><span class="p">,</span><span class="w"> </span><span class="cm">/* Residual light o/p for black pixel */</span>
<span class="w"> </span><span class="mf">2.4F</span><span class="p">,</span><span class="w"> </span><span class="mf">2.4F</span><span class="p">,</span><span class="w"> </span><span class="mf">2.4F</span><span class="p">,</span><span class="w"> </span><span class="cm">/* Gamma values for the three guns */</span>
<span class="p">};</span>
</pre></div>
</div>
<p><em>refWhite</em> is a color temperature of the reference white. The
<code class="xref c c-macro docutils literal notranslate"><span class="pre">TIFFTAG_WHITEPOINT</span></code> contains the chromaticity of the white
point of the image from where the reference white can be calculated
using following formulae:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">refWhite_Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">100.0</span>
<span class="n">refWhite_X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">whitePoint_x</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">whitePoint_y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">refWhite_Y</span>
<span class="n">refWhite_Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">whitePoint_x</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">whitePoint_y</span><span class="p">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">whitePoint_y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">refWhite_X</span>
</pre></div>
</div>
<p>The conversion itself performed in two steps: at the first one we will convert
<em>CIE L*a*b* 1976</em> to <em>CIE XYZ</em> using the <a class="reference internal" href="#c.TIFFCIELabToXYZ" title="TIFFCIELabToXYZ"><code class="xref c c-func docutils literal notranslate"><span class="pre">TIFFCIELabToXYZ()</span></code></a> routine,
and at the second step we will convert <em>CIE XYZ</em> to <em>RGB</em> using
<a class="reference internal" href="#c.TIFFXYZToRGB" title="TIFFXYZToRGB"><code class="xref c c-func docutils literal notranslate"><span class="pre">TIFFXYZToRGB()</span></code></a>. Look at the code sample below:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">float</span><span class="w"> </span><span class="o">*</span><span class="n">whitePoint</span><span class="p">;</span>
<span class="kt">float</span><span class="w"> </span><span class="n">refWhite</span><span class="p">[</span><span class="mi">3</span><span class="p">];</span>
<span class="cm">/* Initialize structures */</span>
<span class="n">img</span><span class="o">-></span><span class="n">cielab</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="n">TIFFCIELabToRGB</span><span class="w"> </span><span class="o">*</span><span class="p">)</span>
<span class="w"> </span><span class="n">_TIFFmalloc</span><span class="p">(</span><span class="k">sizeof</span><span class="p">(</span><span class="n">TIFFCIELabToRGB</span><span class="p">));</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">cielab</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">TIFFError</span><span class="p">(</span><span class="s">"CIE L*a*b*->RGB"</span><span class="p">,</span>
<span class="w"> </span><span class="s">"No space for CIE L*a*b*->RGB conversion state."</span><span class="p">);</span>
<span class="w"> </span><span class="n">exit</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">TIFFGetFieldDefaulted</span><span class="p">(</span><span class="n">tif</span><span class="p">,</span><span class="w"> </span><span class="n">TIFFTAG_WHITEPOINT</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">whitePoint</span><span class="p">);</span>
<span class="n">refWhite</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">100.0F</span><span class="p">;</span>
<span class="n">refWhite</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">whitePoint</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">whitePoint</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">refWhite</span><span class="p">[</span><span class="mi">1</span><span class="p">];</span>
<span class="n">refWhite</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="mf">1.0F</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">whitePoint</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">whitePoint</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span>
<span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">whitePoint</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">refWhite</span><span class="p">[</span><span class="mi">1</span><span class="p">];</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">TIFFCIELabToRGBInit</span><span class="p">(</span><span class="n">cielab</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">display_sRGB</span><span class="p">,</span><span class="w"> </span><span class="n">refWhite</span><span class="p">)</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">TIFFError</span><span class="p">(</span><span class="s">"CIE L*a*b*->RGB"</span><span class="p">,</span>
<span class="w"> </span><span class="s">"Failed to initialize CIE L*a*b*->RGB conversion state."</span><span class="p">);</span>
<span class="w"> </span><span class="n">_TIFFfree</span><span class="p">(</span><span class="n">cielab</span><span class="p">);</span>
<span class="w"> </span><span class="n">exit</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span>
<span class="p">}</span>
<span class="cm">/* Now we can start to convert */</span>
<span class="kt">uint32_t</span><span class="w"> </span><span class="n">r</span><span class="p">,</span><span class="w"> </span><span class="n">g</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">;</span>
<span class="kt">uint32_t</span><span class="w"> </span><span class="n">L</span><span class="p">;</span>
<span class="kt">int32_t</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">;</span>
<span class="kt">float</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">;</span>
<span class="k">for</span><span class="w"> </span><span class="n">each</span><span class="w"> </span><span class="n">pixel</span><span class="w"> </span><span class="n">in</span><span class="w"> </span><span class="n">image</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">TIFFCIELabToXYZ</span><span class="p">(</span><span class="n">cielab</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">Z</span><span class="p">);</span>
<span class="w"> </span><span class="n">TIFFXYZToRGB</span><span class="p">(</span><span class="n">cielab</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">r</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">g</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">b</span><span class="p">);</span>
<span class="p">}</span>
<span class="cm">/* Don't forget to free the state structure */</span>
<span class="n">_TIFFfree</span><span class="p">(</span><span class="n">cielab</span><span class="p">);</span>
</pre></div>
</div>
</section>
<section id="see-also">
<h2>See also<a class="headerlink" href="#see-also" title="Permalink to this heading">¶</a></h2>
<p><a class="reference internal" href="TIFFRGBAImage.html"><span class="doc">TIFFRGBAImage</span></a> (3tiff),
<a class="reference internal" href="libtiff.html"><span class="doc">libtiff</span></a> (3tiff)</p>
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