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<h1>csgfx/inv_cmap.h File Reference</h1>Compute an inverse colormap. <a href="#_details">More...</a>
<p>
<code>#include "csextern.h"</code><br>
<code>#include "<a class="el" href="rgbpixel_8h-source.html">rgbpixel.h</a>"</code><br>
<p>
<a href="inv__cmap_8h-source.html">Go to the source code of this file.</a><table border="0" cellpadding="0" cellspacing="0">
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<tr><td colspan="2"><br><h2>Functions</h2></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="inv__cmap_8h.html#99836a24c4badc2aab116648dc3ffd58">csInverseColormap</a> (int colors, <a class="el" href="structcsRGBpixel.html">csRGBpixel</a> *colormap, int rbits, int gbits, int bbits, <a class="el" href="group__util.html#gdde6aaee8457bee49c2a92621fe22b79">uint8</a> *&rgbmap, <a class="el" href="group__util.html#g1134b580f8da4de94ca6b1de4d37975e">uint32</a> *dist_buf=0)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Compute an inverse colormap efficiently. <a href="#99836a24c4badc2aab116648dc3ffd58"></a><br></td></tr>
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<hr><a name="_details"></a><h2>Detailed Description</h2>
Compute an inverse colormap.
<p>
<p>Definition in file <a class="el" href="inv__cmap_8h-source.html">inv_cmap.h</a>.</p>
<hr><h2>Function Documentation</h2>
<a class="anchor" name="99836a24c4badc2aab116648dc3ffd58"></a><!-- doxytag: member="inv_cmap.h::csInverseColormap" ref="99836a24c4badc2aab116648dc3ffd58" args="(int colors, csRGBpixel *colormap, int rbits, int gbits, int bbits, uint8 *&rgbmap, uint32 *dist_buf=0)" -->
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<td class="memname">void csInverseColormap </td>
<td>(</td>
<td class="paramtype">int </td>
<td class="paramname"> <em>colors</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype"><a class="el" href="structcsRGBpixel.html">csRGBpixel</a> * </td>
<td class="paramname"> <em>colormap</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">int </td>
<td class="paramname"> <em>rbits</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">int </td>
<td class="paramname"> <em>gbits</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">int </td>
<td class="paramname"> <em>bbits</em>, </td>
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<td class="paramkey"></td>
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<td class="paramtype"><a class="el" href="group__util.html#gdde6aaee8457bee49c2a92621fe22b79">uint8</a> *& </td>
<td class="paramname"> <em>rgbmap</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype"><a class="el" href="group__util.html#g1134b580f8da4de94ca6b1de4d37975e">uint32</a> * </td>
<td class="paramname"> <em>dist_buf</em> = <code>0</code></td><td> </td>
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<td>)</td>
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<p>
Compute an inverse colormap efficiently.
<p>
<pre>Inputs:
colors: Number of colors in the forward colormap.
colormap: The forward colormap.
rbits, gbits, bbits:
Number of quantization bits. The inverse
colormap will have N=(2^rbits)*(2^gbits)*(2^bbits)
entries.
dist_buf: An array of N long integers to be used as scratch
space. If 0, the dist_buff will be allocated
and freed before exiting the routine.
Outputs:
rgbmap: The output inverse colormap. The entry
rgbmap[(r<<(gbits+bbits)) + (g<<bbits) + b]
is the colormap entry that is closest to the
(quantized) color (r,g,b). If 0, it will be
allocated with "new uint8* []"
Assumptions:
Quantization is performed by right shift (low order bits are
truncated). Thus, the distance to a quantized color is
actually measured to the color at the center of the cell
(i.e., to r+.5, g+.5, b+.5, if (r,g,b) is a quantized color).
Algorithm:
Uses a "distance buffer" algorithm:
The distance from each representative in the forward color map
to each point in the rgb space is computed. If it is less
than the distance currently stored in dist_buf, then the
corresponding entry in rgbmap is replaced with the current
representative (and the dist_buf entry is replaced with the
new distance).</pre><p>
<pre> The distance computation uses an efficient incremental formulation.</pre><p>
<pre> Distances are computed "outward" from each color. If the
colors are evenly distributed in color space, the expected
number of cells visited for color I is N^3/I.
Thus, the complexity of the algorithm is O(log(K) N^3),
where K = colors, and N = 2^bits.
</pre> BUGBUG: For some unknown reason the routine generates colormaps shifted towards red if green is bigger than red (and vice versa, shifted to green if red is bigger). Thus it is adviced to use same resolution for R and G. If someone can find out why it happens, he is free to do it -- A.Z.
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