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<td>build the shared libraries and support for loading coder and process modules. Shared libraries are preferred because they allow programs to share common code, making the individual programs much smaller. In addition shared libraries are required in order for PerlMagick to be dynamically loaded by an installed PERL (otherwise an additional PERL (PerlMagick) must be installed.
<p>Access to the virtual pixels are controlled by the SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <ahref="/command-line-options/#virtual-pixel">-virtual-pixel</a> option from the command line. The methods include:</p>
<td>the area surrounding the image is the background color</td>
@@ -236,7 +236,7 @@ <h2>Cache Storage and Resource Requirements</h2>
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<p>Recall that this simple and elegant design of the ImageMagick pixel cache comes at a cost in terms of storage and processing speed. The pixel cache storage requirements scales with the area of the image and the bit depth of the pixel components. For example, if we have a 640 by 480 image and we are using the non-HDRI Q16 version of ImageMagick, the pixel cache consumes image <var>width * height * bit-depth / 8 * channels</var> bytes or approximately 2.3 mebibytes (i.e. 640 * 480 * 2 * 4). Not too bad, but what if your image is 25000 by 25000 pixels? The pixel cache requires approximately 4.7 gibibytes of storage. Ouch. ImageMagick accounts for possible huge storage requirements by caching large images to disk rather than memory. Typically the pixel cache is stored in memory using heap memory. If heap memory is exhausted, we create the pixel cache on disk and attempt to memory-map it. If memory-map memory is exhausted, we simply use standard disk I/O. Disk storage is plentiful and cheap, but it is also very slow-- upwards of 1000 times slower than accessing pixels in memory. We can get some speed improvements, up to 5 times, if we memory-map the disk-based cache. These decisions about storage are made <var>automagically</var> by the pixel cache manager negotiating with the operating system. However, you can influence how the pixel cache manager allocates the pixel cache with <var>cache resource limits</var>. The limits include:</p>
<p>For a more accurate color conversion to or from the linear RGB, CMYK, or grayscale colorspaces, use the <ahref="#profile">-profile</a> option. Note, ImageMagick assumes the sRGB colorspace if the image format does not indicate otherwise. For colorspace conversion, the gamma function is first removed to produce linear RGB.</p>
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