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<title>ImageMagick: MagickCore, C API for ImageMagick: Get or Set Image Pixels</title>
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<p class="navigation-index">[ <a href="#AcquireImagePixels">AcquireImagePixels</a> | <a href="#AcquireOnePixel">AcquireOnePixel</a> | <a href="#DestroyCacheInfo">DestroyCacheInfo</a> | <a href="#DestroyImagePixels">DestroyImagePixels</a> | <a href="#GetImagePixels">GetImagePixels</a> | <a href="#GetImageVirtualPixelMethod">GetImageVirtualPixelMethod</a> | <a href="#GetIndexes">GetIndexes</a> | <a href="#GetOnePixel">GetOnePixel</a> | <a href="#GetPixels">GetPixels</a> | <a href="#ModifyCache">ModifyCache</a> | <a href="#ReferenceCache">ReferenceCache</a> | <a href="#RelinquishCacheResources">RelinquishCacheResources</a> | <a href="#SetImagePixels">SetImagePixels</a> | <a href="#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod</a> | <a href="#SyncImagePixels">SyncImagePixels</a> ]</p>
<div style="margin: auto;">
<h2><a name="AcquireImagePixels">AcquireImagePixels</a></h2>
</div>
<p>AcquireImagePixels() obtains a pixel region for read-only access. If the region is successfully accessed, a pointer to it is returned, otherwise NULL is returned. The returned pointer may point to a temporary working copy of the pixels or it may point to the original pixels in memory. Performance is maximized if the selected area is part of one row, or one or more full rows, since then there is opportunity to access the pixels in-place (without a copy) if the image is in RAM, or in a memory-mapped file. The returned pointer should *never* be deallocated by the user.</p>
<p>Pixels accessed via the returned pointer represent a simple array of type PixelPacket. If the image storage class is PsudeoClass, call GetIndexes() after invoking GetImagePixels() to obtain the colormap indexes (of type IndexPacket) corresponding to the region.</p>
<p>If you plan to modify the pixels, use GetImagePixels() instead.</p>
<p>The format of the AcquireImagePixels() method is:</p>
<pre class="code">
const PixelPacket *AcquireImagePixels(const Image *image,const long x,
const long y,const unsigned long columns,const unsigned long rows,
ExceptionInfo *exception)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
<h4>x,y,columns,rows</h4>
<p>These values define the perimeter of a region of pixels.</p>
<h4>exception</h4>
<p>Return any errors or warnings in this structure.</p>
<div style="margin: auto;">
<h2><a name="AcquireOnePixel">AcquireOnePixel</a></h2>
</div>
<p>AcquireOnePixel() returns a single pixel at the specified (x,y) location. The image background color is returned if an error occurs. If you plan to modify the pixel, use GetOnePixel() instead.</p>
<p>The format of the AcquireOnePixel() method is:</p>
<pre class="code">
PixelPacket AcquireOnePixel(const Image image,const long x,
const long y,ExceptionInfo exception)
</pre>
<p>A description of each parameter follows:</p>
<h4>pixels</h4>
<p>AcquireOnePixel() returns a pixel at the specified (x,y) location.</p>
<h4>image</h4>
<p>The image.</p>
<h4>x,y</h4>
<p>These values define the location of the pixel to return.</p>
<h4>exception</h4>
<p>Return any errors or warnings in this structure.</p>
<div style="margin: auto;">
<h2><a name="DestroyCacheInfo">DestroyCacheInfo</a></h2>
</div>
<p>DestroyCacheInfo() deallocates memory associated with the pixel cache.</p>
<p>The format of the DestroyCacheInfo() method is:</p>
<pre class="code">
Cache DestroyCacheInfo(Cache cache)
</pre>
<p>A description of each parameter follows:</p>
<h4>cache</h4>
<p>The pixel cache.</p>
<div style="margin: auto;">
<h2><a name="DestroyImagePixels">DestroyImagePixels</a></h2>
</div>
<p>DestroyImagePixels() deallocates memory associated with the pixel cache.</p>
<p>The format of the DestroyImagePixels() method is:</p>
<pre class="code">
void DestroyImagePixels(Image *image)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
<div style="margin: auto;">
<h2><a name="GetImagePixels">GetImagePixels</a></h2>
</div>
<p>GetImagePixels() obtains a pixel region for read/write access. If the region is successfully accessed, a pointer to a PixelPacket array representing the region is returned, otherwise NULL is returned.</p>
<p>The returned pointer may point to a temporary working copy of the pixels or it may point to the original pixels in memory. Performance is maximized if the selected area is part of one row, or one or more full rows, since then there is opportunity to access the pixels in-place (without a copy) if the image is in RAM, or in a memory-mapped file. The returned pointer should *never* be deallocated by the user.</p>
<p>Pixels accessed via the returned pointer represent a simple array of type PixelPacket. If the image storage class is PsudeoClass, call GetIndexes() after invoking GetImagePixels() to obtain the colormap indexes (of type IndexPacket) corresponding to the region. Once the PixelPacket (and/or IndexPacket) array has been updated, the changes must be saved back to the underlying image using SyncPixelCache() or they may be lost.</p>
<p>The format of the GetImagePixels() method is:</p>
<pre class="code">
PixelPacket *GetImagePixels(Image *image,const long x,const long y,
const unsigned long columns,const unsigned long rows)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
<h4>x,y,columns,rows</h4>
<p>These values define the perimeter of a region of pixels.</p>
<div style="margin: auto;">
<h2><a name="GetImageVirtualPixelMethod">GetImageVirtualPixelMethod</a></h2>
</div>
<p>GetImageVirtualPixelMethod() gets the "virtual pixels" method for the image. A virtual pixel is any pixel access that is outside the boundaries of the image cache.</p>
<p>The format of the GetImageVirtualPixelMethod() method is:</p>
<pre class="code">
VirtualPixelMethod GetImageVirtualPixelMethod(const Image *image)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
<div style="margin: auto;">
<h2><a name="GetIndexes">GetIndexes</a></h2>
</div>
<p>GetIndexes() returns the colormap indexes associated with the last call to SetImagePixels() or GetImagePixels(). NULL is returned if colormap indexes are not available.</p>
<p>The format of the GetIndexes() method is:</p>
<pre class="code">
IndexPacket *GetIndexes(const Image *image)
</pre>
<p>A description of each parameter follows:</p>
<h4>indexes</h4>
<p>GetIndexes() returns the indexes associated with the last call to SetImagePixels() or GetImagePixels().</p>
<h4>image</h4>
<p>The image.</p>
<div style="margin: auto;">
<h2><a name="GetOnePixel">GetOnePixel</a></h2>
</div>
<p>GetOnePixel() returns a single pixel at the specified (x,y) location. The image background color is returned if an error occurs.</p>
<p>The format of the GetOnePixel() method is:</p>
<pre class="code">
PixelPacket *GetOnePixel(const Image image,const long x,const long y)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
<h4>x,y</h4>
<p>These values define the location of the pixel to return.</p>
<div style="margin: auto;">
<h2><a name="GetPixels">GetPixels</a></h2>
</div>
<p>GetPixels() returns the pixels associated with the last call to SetImagePixels() or GetImagePixels().</p>
<p>The format of the GetPixels() method is:</p>
<pre class="code">
PixelPacket *GetPixels(const Image image)
</pre>
<p>A description of each parameter follows:</p>
<h4>pixels</h4>
<p>GetPixels() returns the pixels associated with the last call to SetImagePixels() or GetImagePixels().</p>
<h4>image</h4>
<p>The image.</p>
<div style="margin: auto;">
<h2><a name="ModifyCache">ModifyCache</a></h2>
</div>
<p>ModifyCache() ensures that there is only a single reference to the pixel cache to be modified, updating the provided cache pointer to point to a clone of the original pixel cache if necessary.</p>
<p>The format of the ModifyCache method is:</p>
<pre class="code">
MagickBooleanType ModifyCache(Image *image,const unsigned long nexus)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
<h4>nexus</h4>
<p>specifies which cache nexus to acquire.</p>
<div style="margin: auto;">
<h2><a name="ReferenceCache">ReferenceCache</a></h2>
</div>
<p>ReferenceCache() increments the reference count associated with the pixel cache returning a pointer to the cache.</p>
<p>The format of the ReferenceCache method is:</p>
<pre class="code">
Cache ReferenceCache(Cache cache_info)
</pre>
<p>A description of each parameter follows:</p>
<h4>cache_info</h4>
<p>The pixel cache.</p>
<div style="margin: auto;">
<h2><a name="RelinquishCacheResources">RelinquishCacheResources</a></h2>
</div>
<p>RelinquishCacheResources() relinquishes cache resources.</p>
<p>The format of the RelinquishCacheResources() method is:</p>
<pre class="code">
void RelinquishCacheResources(const Image *image)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
<div style="margin: auto;">
<h2><a name="SetImagePixels">SetImagePixels</a></h2>
</div>
<p>SetImagePixels() initializes a pixel region for write-only access. If the region is successfully intialized a pointer to a PixelPacket array representing the region is returned, otherwise NULL is returned. The returned pointer may point to a temporary working buffer for the pixels or it may point to the final location of the pixels in memory.</p>
<p>Write-only access means that any existing pixel values corresponding to the region are ignored. This is useful while the initial image is being created from scratch, or if the existing pixel values are to be completely replaced without need to refer to their pre-existing values. The application is free to read and write the pixel buffer returned by SetImagePixels() any way it pleases. SetImagePixels() does not initialize the pixel array values. Initializing pixel array values is the application's responsibility.</p>
<p>Performance is maximized if the selected area is part of one row, or one or more full rows, since then there is opportunity to access the pixels in-place (without a copy) if the image is in RAM, or in a memory-mapped file. The returned pointer should *never* be deallocated by the user.</p>
<p>Pixels accessed via the returned pointer represent a simple array of type PixelPacket. If the image storage class is PsudeoClass, call GetIndexes() after invoking GetImagePixels() to obtain the colormap indexes (of type IndexPacket) corresponding to the region. Once the PixelPacket (and/or IndexPacket) array has been updated, the changes must be saved back to the underlying image using SyncPixelCache() or they may be lost.</p>
<p>The format of the SetImagePixels() method is:</p>
<pre class="code">
PixelPacket *SetImagePixels(Image *image,const long x,const long y,
const unsigned long columns,const unsigned long rows)
</pre>
<p>A description of each parameter follows:</p>
<h4>pixels</h4>
<p>SetImagePixels returns a pointer to the pixels if they are transferred, otherwise a NULL is returned.</p>
<h4>image</h4>
<p>The image.</p>
<h4>x,y,columns,rows</h4>
<p>These values define the perimeter of a region of pixels.</p>
<div style="margin: auto;">
<h2><a name="SetImageVirtualPixelMethod">SetImageVirtualPixelMethod</a></h2>
</div>
<p>SetImageVirtualPixelMethod() sets the "virtual pixels" method for the image. A virtual pixel is any pixel access that is outside the boundaries of the image cache.</p>
<p>The format of the SetImageVirtualPixelMethod() method is:</p>
<pre class="code">
MagickBooleanType SetImageVirtualPixelMethod(const Image *image,
const VirtualPixelMethod method)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
<h4>method</h4>
<p>choose from these access types:</p>
<p>EdgeVirtualPixelMethod: the edge pixels of the image extend infinitely. Any pixel outside the image is assigned the same value as the pixel at the edge closest to it.</p>
<p>TileVirtualPixelMethod: the image extends periodically or tiled. The pixels wrap around the edges of the image.</p>
<p>MirrorVirtualPixelMethod: mirror the image at the boundaries.</p>
<p>ConstantVirtualPixelMethod: every value outside the image is a constant as defines by the pixel parameter.</p>
<div style="margin: auto;">
<h2><a name="SyncImagePixels">SyncImagePixels</a></h2>
</div>
<p>SyncImagePixels() saves the image pixels to the in-memory or disk cache. The method returns MagickTrue if the pixel region is synced, otherwise MagickFalse.</p>
<p>The format of the SyncImagePixels() method is:</p>
<pre class="code">
MagickBooleanType SyncImagePixels(Image *image)
</pre>
<p>A description of each parameter follows:</p>
<h4>image</h4>
<p>The image.</p>
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