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<title>clEnqueueReadImage</title>
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<div class="refentry">
<a id="id-1"></a>
<div class="titlepage"></div>
<div xmlns="" class="refnamediv">
<a xmlns="http://www.w3.org/1999/xhtml" id="clEnqueueReadImage"></a>
<h1>
clEnqueueReadImage
</h1>
<p>
Enqueue commands to read from an image or image array object to host memory.
</p>
</div>
<div class="refsynopsisdiv">
<h2></h2>
<div class="funcsynopsis">
<table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
<tr valign="bottom">
<td>
<code xmlns="http://www.w3.org/1999/xhtml" class="funcdef">
<a class="link" href="scalarDataTypes.html" target="pagedisplay">cl_int</a>
<strong class="fsfunc">clEnqueueReadImage</strong>
(</code>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_command_queue</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">command_queue</var>
, </td>
</td>
</tr>
<tr valign="top">
<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_mem</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">image</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="enums.html#cl_bool" target="pagedisplay">cl_bool</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">blocking_read</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>const
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*origin</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>const
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*region</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">row_pitch</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">slice_pitch</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">void</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*ptr</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">cl_uint</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">num_events_in_wait_list</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>const
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_event</a>
 <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*event_wait_list</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_event</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*event</var>
<code>)</code></td>
</tr>
</table>
</div>
</div>
<div class="refsect1">
<a id="parameters"></a>
<h2>Parameters</h2>
<div class="variablelist">
<dl class="variablelist">
<dt>
<span class="term"> <code class="varname"> command_queue </code> </span>
</dt>
<dd>
<p>
Refers to the host command-queue in which the read command will be
queued. <code class="varname">command_queue</code> and <code class="varname">image</code>
must be created with the same OpenCL context.
</p>
</dd>
<dt>
<span class="term"> <code class="varname"> image </code> </span>
</dt>
<dd>
<p>
Refers to a valid image or image array object.
</p>
</dd>
<dt>
<span class="term"> <code class="varname"> blocking_read </code> </span>
</dt>
<dd>
<p>
Indicates if the read operations are <code class="varname">blocking</code> or
<code class="varname">non-blocking</code>.
</p>
<p>
If <code class="varname">blocking_read</code> is <code class="constant">CL_TRUE</code>
i.e. the read command is blocking, <code class="function">clEnqueueReadImage</code>
does not return until the buffer data has been read and copied into memory
pointed to by <code class="varname">ptr</code>.
</p>
<p>
If <code class="varname">blocking_read</code> is <code class="constant">CL_FALSE</code>
i.e. map operation is non-blocking, <code class="function">clEnqueueReadImage</code>
queues a non-blocking read command and returns. The contents of the
buffer that <code class="varname">ptr</code> points to cannot be used until the read
command has completed. The <code class="varname">event</code> argument returns an
event object which can be used to query the execution status of the read
command. When the read command has completed, the contents of the buffer
that <code class="varname">ptr</code> points to can be used by the application.
</p>
</dd>
<dt>
<span class="term"> <code class="varname"> origin </code> </span>
</dt>
<dd>
<p>
Defines the (<span class="emphasis"><em>x, y, z</em></span>) offset in pixels in the 1D, 2D, or
3D image, the (<span class="emphasis"><em>x, y</em></span>) offset and the image index in the
image array or the (x) offset and the image index in the 1D image array. If
<code class="varname">image</code> is a 2D image object, <code class="varname">origin</code>[2]
must be 0. If <code class="varname">image</code> is a 1D image or 1D image buffer
object, <code class="varname">origin</code>[1] and <code class="varname">origin</code>[2]
must be 0. If <code class="varname">image</code> is a 1D image array object,
<code class="varname">origin</code>[2] must be 0. If <code class="varname">image</code>
is a 1D image array object, <code class="varname">origin</code>[1] describes the
image index in the 1D image array. If <code class="varname">image</code> is a 2D
image array object, <code class="varname">origin</code>[2] describes the image
index in the 2D image array.
</p>
</dd>
<dt>
<span class="term"> <code class="varname"> region </code> </span>
</dt>
<dd>
<p>
Defines the (<span class="emphasis"><em>width, height, depth</em></span>) in pixels of the
1D, 2D or 3D rectangle, the (<span class="emphasis"><em>width, height</em></span>) in pixels
of the 2D rectangle and the number of images of a 2D image array or the
(<span class="emphasis"><em>width</em></span>) in pixels of the 1D rectangle and the number
of images of a 1D image array. If <code class="varname">image</code> is a 2D image
object, <code class="varname">region</code>[2] must be 1. If <code class="varname">image</code>
is a 1D image or 1D image buffer object, <code class="varname">region</code>[1]
and <code class="varname">region</code>[2] must be 1. If image is a 1D image array
object, <code class="varname">region</code>[2] must be 1. The values in <code class="varname">region</code> cannot be 0.
</p>
</dd>
<dt>
<span class="term"> <code class="varname"> row_pitch </code> </span>
</dt>
<dd>
<p>
The length of each row in bytes. This value must be greater than or
equal to the element size in bytes * <code class="varname">width</code>. If
<code class="varname">row_pitch</code> is set to 0, the appropriate row pitch
is calculated based on the size of each element in bytes multiplied by
<code class="varname">width</code>.
</p>
</dd>
<dt>
<span class="term"> <code class="varname"> slice_pitch </code> </span>
</dt>
<dd>
<p>
Size in bytes of the 2D slice of the 3D region of a 3D image or
each image of a 1D or 2D image array being read. This must be 0 if
<code class="varname">image</code> is a 1D or 2D image. Otherwise this value must be greater
than or equal to <code class="varname">row_pitch</code> * <code class="varname">height</code>.
If <code class="varname">slice_pitch</code> is set to 0, the appropriate slice
pitch is calculated based on the <code class="varname">row_pitch</code> *
<code class="varname">height</code>.
</p>
</dd>
<dt>
<span class="term"> <code class="varname"> ptr </code> </span>
</dt>
<dd>
<p>
The pointer to a buffer in host memory where image data is to be written to.
</p>
</dd>
<dt>
<span class="term"> <code class="varname">
event_wait_list
,</code>
<code class="varname">
num_events_in_wait_list
</code>
</span>
</dt>
<dd>
<p>
Specify events that need to complete before this particular
command can be executed. If <code class="varname">event_wait_list</code>
is NULL, then this particular command does not wait on any
event to complete. If <code class="varname">event_wait_list</code> is
NULL, <code class="varname">num_events_in_wait_list</code> must be 0. If
<code class="varname">event_wait_list</code> is not NULL, the list of events
pointed to by <code class="varname">event_wait_list</code> must be valid
and <code class="varname">num_events_in_wait_list</code> must be greater
than 0. The events specified in <code class="varname">event_wait_list</code>
act as synchronization points. The context associated with events in
<code class="varname">event_wait_list</code> and <code class="varname">command_queue</code> must
be the same. The memory associated with <code class="varname">event_wait_list</code>
can be reused or freed after the function returns.
</p>
</dd>
<dt>
<span class="term">
<code class="varname">
event
</code>
</span>
</dt>
<dd>
<p>
Returns an event object that identifies this particular read command
and can be used to query or queue a wait for this particular command
to complete. <code class="varname">event</code> can be NULL in which case
it will not be possible for the application to query the status of
this command or queue a wait for this command to complete. If the
<code class="varname">event_wait_list</code> and the <code class="varname">event</code>
arguments are not NULL, the <code class="varname">event</code> argument should not
refer to an element of the <code class="varname">event_wait_list</code> array.
</p>
</dd>
</dl>
</div>
</div>
<div class="refsect1">
<a id="notes"></a>
<h2>Notes</h2>
<p>
Calling <code class="function">clEnqueueReadImage</code> to read a region of the
<code class="varname">image</code> with the <code class="varname">ptr</code> argument value set to
<code class="varname">host_ptr</code> + (<code class="varname">origin</code>[2] * <code class="varname">image
slice pitch</code> + <code class="varname">origin</code>[1] * <code class="varname">image
row pitch</code> + <code class="varname">origin</code>[0] * <code class="varname">bytes per
pixel</code>), where <code class="varname">host_ptr</code> is a pointer to the memory
region specified when the <code class="varname">image</code> being read is created with
<code class="constant">CL_MEM_USE_HOST_PTR</code>, must meet the following requirements in
order to avoid undefined behavior:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem" style="list-style-type: disc">
All commands that use this image object have finished execution before the read
command begins execution.
</li>
<li class="listitem" style="list-style-type: disc">
The <code class="varname">row_pitch</code> and <code class="varname">slice_pitch</code> argument
values in <code class="function">clEnqueueReadImage</code> must be set to the image row
pitch and slice pitch.
</li>
<li class="listitem" style="list-style-type: disc">
The image object is not mapped.
</li>
<li class="listitem" style="list-style-type: disc">
The image object is not used by any command-queue until the read command has
finished execution.
</li>
</ul>
</div>
<p>
If the mipmap extensions are enabled with <a class="citerefentry" href="cl_khr_mipmap_image.html"><span class="citerefentry"><span class="refentrytitle">cl_khr_mipmap_image</span></span></a>,
calls to <code class="function">clEnqueueReadImage</code>,
<a class="citerefentry" href="clEnqueueWriteImage.html"><span class="citerefentry"><span class="refentrytitle">clEnqueueWriteImage</span></span></a> and
<a class="citerefentry" href="clEnqueueMapImage.html"><span class="citerefentry"><span class="refentrytitle">clEnqueueMapImage</span></span></a> can be used to read
from or write to a specific mip-level of a mip-mapped image.
If image argument is a 1D image, <code class="varname">origin</code>[1] specifies the mip-level to use.
If image argument is a 1D image array, <code class="varname">origin</code>[2] specifies the mip-level to use.
If image argument is a 2D image, <code class="varname">origin</code>[3] specifies the mip-level to use.
If image argument is a 2D image array or a 3D image, <code class="varname">origin</code>[3] specifies the mip-level to use.
</p>
</div>
<div class="refsect1">
<a id="errors"></a>
<h2>Errors</h2>
<p>
<code class="function">clEnqueueReadImage</code> returns <span class="errorname">CL_SUCCESS</span> if
the function is executed successfully. Otherwise, it returns one of the following errors.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_COMMAND_QUEUE</span> if <code class="varname">command_queue</code>
is not a valid host command-queue.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_CONTEXT</span> if the context associated with
<code class="varname">command_queue</code> and <code class="varname">image</code> are not the same
or if the context associated with <code class="varname">command_queue</code> and events in
<code class="varname">event_wait_list</code> are not the same.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_MEM_OBJECT</span> if <code class="varname">image</code> is not
a valid image object.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_VALUE</span> if the region being read specified by
<code class="varname">origin</code> and <code class="varname">region</code> is out of bounds or if
<code class="varname">ptr</code> is a NULL value.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_VALUE</span> if values in <code class="varname">origin</code>
and <code class="varname">region</code> do not follow rules described in the argument
description for <code class="varname">origin</code> and <code class="varname">region</code>.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_EVENT_WAIT_LIST</span>
if <code class="varname">event_wait_list</code> is NULL and
<code class="varname">num_events_in_wait_list</code> &gt; 0,
or <code class="varname">event_wait_list</code> is not NULL and
<code class="varname">num_events_in_wait_list</code> is 0, or if event objects in
<code class="varname">event_wait_list</code> are not valid events.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_IMAGE_SIZE</span> if image dimensions (image width,
height, specified or compute row and/or slice pitch) for <code class="varname">image</code>
are not supported by device associated with <code class="varname">queue</code>.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_IMAGE_FORMAT_NOT_SUPPORTED</span> if image format (image channel
order and data type) for <code class="varname">image</code> are not supported by device
associated with <code class="varname">queue</code>.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_MEM_OBJECT_ALLOCATION_FAILURE</span> if there is a failure to
allocate memory for data store associated with <code class="varname">image</code>.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_OPERATION</span> if the device associated
with <code class="varname">command_queue</code> does not support images
(i.e. <code class="constant">CL_DEVICE_IMAGE_SUPPORT</code> specified in
the table of allowed values for <code class="varname">param_name</code> for
<a class="citerefentry" href="clGetDeviceInfo.html"><span class="citerefentry"><span class="refentrytitle">clGetDeviceInfo</span></span></a>
is <code class="constant">CL_FALSE</code>).
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_OPERATION</span> if
<code class="function">clEnqueueReadImage</code> is called on <code class="varname">image</code>
which has been created with <code class="constant">CL_MEM_HOST_WRITE_ONLY</code> or
<code class="constant">CL_MEM_HOST_NO_ACCESS</code></li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST</span> if the read
and write operations are blocking and the execution status of any of the events
in <code class="varname">event_wait_list</code> is a negative integer value.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_OUT_OF_RESOURCES</span> if there is a failure to allocate
resources required by the OpenCL implementation on the device.
</li>
<li class="listitem" style="list-style-type: disc"><span class="errorname">CL_OUT_OF_HOST_MEMORY</span> if there is a failure to allocate
resources required by the OpenCL implementation on the host.
</li>
</ul>
</div>
</div>
<div class="refsect1">
<a id="specification"></a>
<h2>Specification</h2>
<p>
<img src="pdficon_small1.gif" />
<a href="https://www.khronos.org/registry/cl/specs/opencl-2.1.pdf#namedest=clEnqueueReadImage" target="OpenCL Spec">OpenCL Specification</a>
</p>
</div>
<div class="refsect1">
<a id="seealso"></a>
<h2>Also see</h2>
<p>
<a class="citerefentry" href="clEnqueueWriteImage.html"><span class="citerefentry"><span class="refentrytitle">clEnqueueWriteImage</span></span></a>,
<a class="citerefentry" href="clEnqueueCopyImage.html"><span class="citerefentry"><span class="refentrytitle">clEnqueueCopyImage</span></span></a>,
<a class="citerefentry" href="cl_khr_mipmap_image.html"><span class="citerefentry"><span class="refentrytitle">cl_khr_mipmap_image</span></span></a>
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<div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2015 The Khronos Group Inc.
Permission is hereby granted, free of charge, to any person obtaining a
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without limitation the rights to use, copy, modify, merge, publish,
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permit persons to whom the Materials are furnished to do so, subject to
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