~ubuntu-branches/ubuntu/natty/libraw/natty

files in the usual way (by calling <a href="API-CXX-eng.html#open_file">open_file()</a> (or other input methods), then <a href="API-CXX-eng.html#unpack">unpack()</a>,

etc.).

</dd>

</dl>

<li>The macro LIBRAW_FATAL_ERROR(error code) checks if an error is fatal or not.</li>

<li>The error codes are <a href="API-datastruct-eng.html#errors">listed and deciphered here</a>.</li>

</ol>

<h2>Nonstandard Situations That Are Not Errors</h2>

<p>If the program has encountered a nonstandard situation that does not prevent retrieval of some data

from a file, it sends a signal by setting the corresponding bit in <a href="API-datastruct-eng.html#libraw_data_t">imgdata.process_warnings</a>.

The possible types of warnings are <a href="API-datastruct-eng.html#warnings">listed and deciphered here</a>.

</p>

<h2>Input Layer Abstraction</h2>

<p>

LibRaw uses objects derived from

<a href="API-CXX-eng.html#datastream">LibRaw_abstract_datastream</a> for data input.

Semantics of these objects is similar to 'file with arbitrary seek' object: both read and seek

operations are used.

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</p>

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<p>

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Some RAW formats requires temporary switch to another data stream created on top on memory buffer for metadata

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read. Methods for doing so are implemented in base class

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<a href="API-CXX-eng.html#datastream">LibRaw_abstract_datastream</a> by internal data field <b>substream</b>.

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Look into source code of <a href="API-CXX-eng.html#file_datastream">LibRaw_file_datastream</a> class

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in <b>libraw/libraw_datastream.h</b> file for more details.

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<br/>

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When implementing own datastream classes, you need to take <b>substream</b> into account and pass control to

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methods of this field if it is active (not NULL).

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</p>

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<p>

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If datastream implementaton knows name of input file, it should provide fname() call. This name will be used

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in <a href="API-CXX-eng.html#callbacks">error callbacks</a> and in guessing name of JPEG file with metadata

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(for RAW files with external metadata).

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</p>

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<p>

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For external metadata support input class should implement

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<b>subfile_open()/subfile_close()</b> methods.

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�� .

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<br/>

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Sample of these methods implementation may be found in

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<a href="API-CXX-eng.html#file_datastream">LibRaw_file_datastream</a> class (look into

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<b>libraw/libraw_datastream.h</b> file for details).

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</p>

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<h2>Thread safety</h2>

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<p>

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Thread safety is ensured if a LibRaw object is created and used within one thread. At the same time, the number

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of threads (each with its own LibRaw object) is not limited in any way (except by memory requirements).

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</p>

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<p>

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If a LibRaw object is created in one execution thread and used in another, external synchronization is

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necessary.

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</p>

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<p>

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There is two libraries under Unix enviroment (Linux/FreeBSD/MacOS): libraw_r.a (thread-safe) and libraw.a

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(single-threaded, slightly faster).

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</p>

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<p>

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Thread-safe library version stores intermediate unpacker data into LibRaw class data. So, several copies of

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LibRaw, working in parallel, is possible.

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</p>

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<p>

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Not thread-safe library uses global variable for intermediate data store which is faster but not reenterant.

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This library may be used in multi-threaded apps, but only if exactly one LibRaw class copy exists in program.

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</p>

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<p>

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Windows version is similar to multi-threaded Unix one.

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</p>

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<p>

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Exception situations within LibRaw are handled using the C++ exception mechanism. All exceptions are caught inside

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the library functions and should not penetrate outside.

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</p>

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<p>

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Memory is allocated/freed using functions malloc(calloc)/free rather than new/delete.

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</p>

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<p>

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No specific libraries (STL, Boost, smart pointers) are used. </p>

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<p>

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If C API is used, references to C++ calls new/delete still remain, and so linking with libstdc++(Unix)/....(Windows) is necessary.

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</p>

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<h2>Parameters of the LibRaw::imgdata.params Structure Affecting the Behavior of open_file/unpack/unpack_thumb</h2>

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<p>

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Most data fields of structure LibRaw::imgdata.params affect only <a href="API-CXX-eng.html#dcrawemu">data

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postprocessing</a>, but there are some exceptions, which have been inherited by the current version of LibRaw

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from/ dcraw source texts (these dependences will be gradually removed).

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<dl>

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<dt><b>imgdata.params.use_camera_matrix and imgdata.params.use_camera_wb</b></dt>

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<dd>

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These fields affect loading of RAW data for cameras with a color matrix.<br/>

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<b>Attention!</b> If parameter <b>imgdata.params.use_camera_matrix</b> is not set by the user, it is copied from

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<b>imgdata.params.use_camera_wb</b> at the stage of file opening.

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</dd>

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<dt><b>imgdata.params.user_flip</b></dt>

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<dd>

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If this parameter is greater than or equal to zero, assignment <code>imgdata.sizes.flip = imgdata.params.user_flip</code> is

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performed at the <a href="API-CXX-eng.html#open_file">open_file()</a> stage.

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</dd>

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<dt><b>imgdata.params.shot_select</b></dt>

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<dd>

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This parameter makes it possible to select the number of the extracted image for data formats in which storage

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of several RAW images in one data file is possible.

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</dd>

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<dt><b>imgdata.params.half_size</b></dt>

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<dd>

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Affects RAW data loading for Phase One and Sinar backs. Also, it this parameter is set then image bitmap

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will be reduced by half in each dimension. In later case, all 4 components of bitmap will be filled during

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data extraction phase.

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</dd>

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<dt><b>imgdata.params.threshold, imgdata.params.aber</b></dt>

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<dd>

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If these parameters used, then half-sized bitmap will be used for data unpacking. See above for details.

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</dd>

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<dt><b>imgdata.params.filtering_mode</b></dt>

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<dd>

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Affects RAW data loading for cameras with black level subtraction/de-banding during RAW read phase:

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Canon A600, A5, CRW/CR2; cameras with LJPEG-compression (some Nikon, Kodak and Hasselblad cameras).

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</dd>

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<dt><b>imgdata.params.use_camera_wb</b></dt>

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<dd>

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Affects loading of white balance matrix for Leaf backs.

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</dd>

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<dt><b>imgdata.params.document_mode</b></dt>

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<dd>

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<b>Does not affect data reading in the current version of LibRaw</b>. In dcraw, this parameter affects the thumbnail data for certain Kodak cameras.

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</dd>

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</dl>

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<h2>RAW-data filtration</h2>

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<p>

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During RAW unpacking and post-process stages LibRaw can filter RAW data:

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</p>

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<ul>

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<li>Black level subtraction (required if not already done by camera firmware).</li>

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<li>Zero pixels removal (averaging with nearest pixel values).</li>

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<li>Tone curve operations on RAW-data.</li>

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</ul>

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<p>

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Current LibRaw version allows tuning of filtration process by setting <b>imgdata.params.filtering_mode</b>

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option to one of <a href="API-datastruct-eng.html#LibRaw_filtering">enum LibRaw_filtering</a> vales:

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</p>

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<ul>

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<li>Dcraw-compatible filtration. This mode is default for old LibRaw versions compatibility. This mode

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is not recommended for new applications.</li>

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<li>One or several (or all) filtering stages can be turned off. This mode recommended for

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RAW analysers and advanced data filtration made by calling program (this programs may

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calculate black level by analyzing <a href=#masked-border>masked frame data</a>.</li>

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<li>Automatic selection of best filtration avaliable in LibRaw (e.g. camera/model specific

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routines). This mode is recommended for most applications.

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</li>

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</ul>

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<h2>Masked pixels storage</h2>

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<p>

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Some of RAW images contains data for not-active ("black","masked") pixels. For some of these formats

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LibRaw can extract these pixels values and store it in

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<a href="API-datastruct-eng.html#libraw_masked_t">imgdata.masked_pixels</a> data structure.

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These values can be explored for:

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</p>

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<ul>

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<li>Black level calculation (with banding suppression on some cameras).</li>

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<li>Noise level calculation, e.g. per-channel noise. This is useful for cameras with per-channel

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amplification.</li>

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</ul>

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<p>Masked pixel data avaliable only for bayer-pattern data (one component per pixel) and only for cameras

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with masked frame. Masked pixels extraction for other color models (Canon sRAW, Kodak YRGB, Sinar 4-shot

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files) will possibly be added in future LibRaw versions.</p>

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<p>

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LibRaw provides interface for merging active pixel data and masked pixels into one bitmap:

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<a href="API-CXX-eng.html#add_masked_borders_to_bitmap">add_masked_borders_to_bitmap()</a>.

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This call is useful for RAW analyzers.

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</p>

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<h2>Memory Usage</h2>

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<h3>Stack Usage</h3>

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<p>

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An instance of the LibRaw class has its own size about <b>100 Kb</b>; if constructions like <code>LibRaw

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imageProcessor;</code> are used, this memory is stack-allocated.

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</p>

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<p>

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Methods of class LibRaw (and C API calls) may allocate up to 130-140 Kb of data on the stack (to place auto

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variables) during their work.

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</p>

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<p>Thus, the work of one LibRaw instance may require about 250 Kb of stack memory. This is not a problem for most

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contemporary architectures. However, when working in a multithreaded environment, one should not forget to

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allocate a sufficient amount of memory for the thread stack.

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</p>

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<p>In the case of dynamic allocation (<code>LibRaw *iProcessor = new LibRaw;</code>), the requirements to stack

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memory will decrease by 100 Kb, which is the size of a class instance). If <a href="API-C-eng.html">C API</a> is

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used, the LibRaw instance is allocated dynamically.

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</p>

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<h3>Dynamic Memory Management</h3>

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<p>LibRaw keeps record of all allocated dynamic memory blocks; in the case of an exceptional situation (fatal

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error), they are all freed. The code for keeping this record is fairly primitive and not designed to consider

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allocation of many blocks (in the normal situation, allocation takes place from 2 to 6 times during file

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processing); this fact should be taken into account by developers trying to add new methods to LibRaw.

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</p>

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<h3>Dynamic Memory Usage</h3>

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<p>LibRaw uses dynamic memory</p>

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<ul>

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<li>for the decoded image;</li>

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<li>for the decoded thumbnail;</li>

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<li>for the ICC profile retrieved from the RAW file (if available);</li>

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<li>for temporary data at the stage of RAW file unpacking;</li>

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<li>for temporary data at the stage of postprocessing and result output;</li>

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<li>for reading of the RAW source file (only under Win32).</li>

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</ul>

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<h4>Memory for the Decoded Image</h4>

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<p>

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To simplify further processing, memory for the extracted RAW data is allocated with a fourfold (for Bayer sensor

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cameras) excess: <b>for each pixel, four 16-bit components are available</b> (three of them will be zero after

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RAW unpacking). Thus, one can perform debayer and other postprocessing actions directly in the same buffer as

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the one used for data extraction, but the required amount of memory becomes four times higher. <br/>

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<b>Hence, the size of memory for the image buffer is 6-10 times greater than the size of the source RAW

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file.</b><br/> <i>It is quite likely that allocation of this buffer in next versions of LibRaw will be more

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economical, under the condition that postprocessing calls inherited from dcraw will not be used.</i>.

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</p>

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<p>The buffer for the decoded image is allocated upon calling <a href="API-CXX-eng.html#unpack">unpack()</a> and

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freed upon calling <a href="API-CXX-eng.html#recycle">recycle()</a>.

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</p>

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<h4>Memory for the Decoded Thumbnail</h4>

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<p>

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Memory for the thumbmail is allocated upon calling <a href="API-CXX-eng.html#unpack_thumb">unpack_thumb()</a> and freed upon

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calling <a href="API-CXX-eng.html#recycle">recycle()</a>. The size of the allocated buffer is precisely adjusted to the thumbnail size,

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i.e., up to several Mb.

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</p>

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<h4>Memory for the Decoded ICC Profile</h4>

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<p>

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Memory for the ICC profile is allocated upon calling <a href="API-CXX-eng.html#unpack_profile">unpack_profile()</a> and freed upon

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calling <a href="API-CXX-eng.html#recycle">recycle()</a>. The size of the allocated buffer is precisely adjusted to the ICC profile size,

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i.e., up to several hundred Kb.

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</p>

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<h4>Memory for RAW Unpacking</h4>

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<p>

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Memory for temporary buffer needed during RAW data unpacking may be allocated during the work of <a

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href="API-CXX-eng.html#unpack">unpack()</a> and freed before completion of this function. The sizes of the allocated

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buffers are small, up to tens of Kb.

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</p>

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<h4>Memory for Postprocessing</h4>

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<p>During image postprocessing (inherited from dcraw), memory for the histogram (128 Kb) is allocated.

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This memory is allocated upon calling <a

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href="API-CXX-eng.html#dcraw_document_mode_processing">dcraw_document_mode_processing()</a> and

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<a href="API-CXX-eng.html#dcraw_process">dcraw_process()</a> and freed upon calling

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<a href="API-CXX-eng.html#recycle">recycle()</a>.

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</p>

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<p>

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In addition, during the work of <a href="API-CXX-eng.html#dcraw_process">dcraw_process()</a> and during the

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usage of some available possibilities, like

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</p>

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<ul>

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<li>rotation of images from FUJI cameras;</li>

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<li>correction of chromatic aberrations;</li>

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<li>image size changes (including correction of non-square pixels);</li>

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<li>highlight recovery;</li>

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</ul>

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<p>

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a temporary buffer with the size equal to the size of the resultant image (6-8 bytes per pixel for various processing stages)

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will be allocated. As soon as the intermediate substage of processing is completed, the buffer with the previous copy

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of the image will be freed.<br/>

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If postprocessing is not used, then temporary buffers are not allocated.

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</p>

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<h4>Memory for File Writing</h4>

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<p>

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Upon calling <a href="API-CXX-eng.html#dcraw_ppm_tiff_writer">dcraw_ppm_tiff_writer()</a>, memory for a single row of the

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output image is allocated. The allocated memory is freed before the end of this call.

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</p>

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<h4>Unpacking into memory buffer</h4>

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<p>

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Functons <a href="API-CXX-eng.html#dcraw_make_mem_image">dcraw_make_mem_image()</a> �

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<a href="API-CXX-eng.html#dcraw_make_mem_thumb">dcraw_make_mem_thumb()</a> (and complementary calls in C-API)

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allocates memory for entire output datasets (full RGB bitmap and thumbnail, respectively).

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<b>Calling function should free() this memory themself.</b>

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</p>

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<h2>Incompatibilities with dcraw</h2>

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<h3>Processing of Thumbnails from Kodak cameras</h3>

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<p>In some Kodak cameras, the preview (thumbnail) is stored in the form of uncorrected image. During its extraction using

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<b>dcraw -e</b>, the white balance, color conversion, and other settings are the same as those used for extraction of the main RAW data

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(including defect removal and dark frame subtraction, which is erroneous, since the image size is different).

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<br/>

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In LibRaw::unpack_thumb() calls, the white balance taken from the camera ("as shot") is used and no settings from

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imgdata.params are considered.

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</p>

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<p>

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For all other cameras, thumbnails are extracted "as is," without any color conversions, both in dcraw and in LibRaw.

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</p>

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<a href=index-eng.html>[back to Index]</a>

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<hr>

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<address><a href="mailto:info@libraw.org">LibRaw Team</a></address>

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Last modified: Sun Mar 28 22:08:30 MSD 2010

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