"Fossies" - the Fresh Open Source Software Archive  

Source code changes of the file "doc/How-it-opens-files.xml" between
vips-8.10.6.tar.gz and vips-8.11.0.tar.gz

About: VIPS is a free image processing system (see also the GUI nip2).

How-it-opens-files.xml  (vips-8.10.6):How-it-opens-files.xml  (vips-8.11.0)
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</para> </para>
<refsect3 xml:id="direct-access"> <refsect3 xml:id="direct-access">
<title>Direct access</title> <title>Direct access</title>
<para> <para>
This is the fastest and simplest one. The file is mapped directly into the p rocess’s address space and can be read with ordinary pointer access. Small files are completely mapped; large files are mapped in a series of small windows that are shared and which scroll about as pixels are read. Files which are accessed like this can be read by many threads at once, making them especially quick. The y also interact well with the computer’s operating system: your OS will use spar e memory to cache recently used chunks of the file. This is the fastest and simplest one. The file is mapped directly into the p rocess’s address space and can be read with ordinary pointer access. Small files are completely mapped; large files are mapped in a series of small windows that are shared and which scroll about as pixels are read. Files which are accessed like this can be read by many threads at once, making them especially quick. The y also interact well with the computer’s operating system: your OS will use spar e memory to cache recently used chunks of the file.
</para> </para>
<para> <para>
For this to be possible, the file format needs to be a simple dump of a memo ry array. libvips supports direct access for vips, 8-bit binary ppm/pbm/pnm, ana lyse and raw. For this to be possible, the file format needs to be a simple dump of a memo ry array. libvips supports direct access for vips, 8-bit binary ppm/pbm/pnm, ana lyse and raw.
</para> </para>
<para> <para>
libvips has a special direct write mode where pixels can be written directly to the file image. This is used for the <link xlink:href="libvips-draw.html">dr aw operators</link>. libvips has a special direct write mode where pixels can be written directly to the file image. This is used for the <ulink url="libvips-draw.html">draw ope rators</ulink>.
</para> </para>
</refsect3> </refsect3>
<refsect3 xml:id="random-access-via-load-library"> <refsect3 xml:id="random-access-via-load-library">
<title>Random access via load library</title> <title>Random access via load library</title>
<para> <para>
Some image file formats have libraries which allow true random access to ima ge pixels. For example, libtiff lets you read any tile out of a tiled tiff image very quickly. Because the libraries allow true random access, libvips can simpl y hook the image load library up to the input of the operation pipeline. Some image file formats have libraries which allow true random access to ima ge pixels. For example, libtiff lets you read any tile out of a tiled tiff image very quickly. Because the libraries allow true random access, libvips can simpl y hook the image load library up to the input of the operation pipeline.
</para> </para>
<para> <para>
These libraries are generally single-threaded, so only one thread may read a t once, making them slower than simple direct access. Additionally, tiles are of ten compressed, meaning that each time a tile is fetched it must be decompressed . libvips keeps a cache of recently-decompressed tiles to try to avoid repeatedl y decompressing the same tile. These libraries are generally single-threaded, so only one thread may read a t once, making them slower than simple direct access. Additionally, tiles are of ten compressed, meaning that each time a tile is fetched it must be decompressed . libvips keeps a cache of recently-decompressed tiles to try to avoid repeatedl y decompressing the same tile.
</para> </para>
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