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<title>read_imagei (2D)</title>
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<h1>read_image{i|ui} (2D)</h1>
<p>
Do an element lookup in the 2D image object, returning unnormalized signed integer and unsigned integer values.
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<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="sampler_t.html" target="pagedisplay">sampler_t</a>
<var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">sampler</var>
, </td>
</tr>
<tr valign="top">
<td> </td>
<td>
<a xmlns="http://www.w3.org/1999/xhtml" class="link" href="vectorDataTypes.html" target="pagedisplay">float4</a>
<var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">coord</var>
<code>)</code></td>
</tr>
</table>
</div>
</div>
<div class="refsect1">
<a id="description"></a>
<h2>Description</h2>
<p>
For the forms that take an <span class="type">image2d_t</span> object, use the coordinate
<span class="emphasis"><em>(coord.x, coord.y)</em></span> to do an element lookup in the 2D image object
specified by <code class="varname">image</code>.
</p>
<p>
For the forms that take an <span class="type">image2d_array_t</span> object, use
<span class="emphasis"><em>coord.xy</em></span> to do an element lookup in the 2D image identified by
<span class="emphasis"><em>coord.z</em></span> in the 2D image array specified by <code class="varname">image</code>.
</p>
<p>
The samplerless read image functions behave exactly as the corresponding read
image functions that take integer coordinates and a sampler with filter mode
set to <code class="constant">CLK_FILTER_NEAREST</code>, normalized coordinates set
to <code class="constant">CLK_NORMALIZED_COORDS_FALSE</code> and addressing mode to
<code class="constant">CLK_ADDRESS_NONE</code>.
</p>
<p>
<code class="function">read_imagei</code> and <code class="function">read_imageui</code> return
unnormalized signed integer and unsigned integer values respectively. Each channel
will be stored in a 32-bit integer.
</p>
<p>
<code class="function">read_imagei</code> can only be used with image objects created with
<code class="varname">image_channel_data_type</code> set to one of the following values:
<code class="constant">CL_SIGNED_INT8</code>, <code class="constant">CL_SIGNED_INT16</code>, or
<code class="constant">CL_SIGNED_INT32</code>. If the <code class="varname">image_channel_data_type</code>
is not one of the above values, the values returned by <code class="function">read_imagei</code>
are undefined.
</p>
<p>
<code class="function">read_imageui</code> can only be used with image objects created with
<code class="varname">image_channel_data_type</code> set to one of the following values:
<code class="constant">CL_UNSIGNED_INT8</code>, <code class="constant">CL_UNSIGNED_INT16</code>, and
<code class="constant">CL_UNSIGNED_INT32</code>. If the <code class="varname">image_channel_data_type</code>
is not one of the above values, the values returned by <code class="function">read_imageui</code>
are undefined.
</p>
<p>
The <code class="function">read_imagei</code> and <code class="function">read_imageui</code> calls
support a nearest filter only. The <code class="varname">filter_mode</code> specified in
<code class="varname">sampler</code> must be set to <code class="constant">CLK_FILTER_NEAREST</code>;
otherwise the values returned are undefined.
</p>
<p>
Furthermore, the <code class="function">read_imagei</code> and <code class="function">read_imageui</code>
calls that take integer coordinates must use a sampler with normalized coordinates
set to <code class="constant">CLK_NORMALIZED_COORDS_FALSE</code> and addressing mode set to
<code class="constant">CLK_ADDRESS_CLAMP_TO_EDGE</code>, <code class="constant">CLK_ADDRESS_CLAMP</code>
or <code class="constant">CLK_ADDRESS_NONE</code>; otherwise the values returned are undefined.
</p>
</div>
<div class="refsect1">
<a id="notes"></a>
<h2>Notes</h2>
<p>
The built-in functions defined in this section
can only be used with image memory objects. An image memory object can be accessed by
specific function calls that read from and/or write to specific locations in the image.
</p>
<p>
Image memory objects that are being read by a kernel should be declared with the <a class="citerefentry" href="accessQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__read_only</span></span></a>
qualifier. <code class="function">write_image</code> calls to image memory objects declared with the
<a class="citerefentry" href="accessQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__read_only</span></span></a>
qualifier will generate a compilation error. Image memory objects that
are being written to by a kernel should be declared with the <a class="citerefentry" href="accessQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__write_only</span></span></a> qualifier.
<code class="function">read_image</code> calls to image memory objects declared with the <a class="citerefentry" href="accessQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__write_only</span></span></a>
qualifier will generate a compilation error. <code class="function">read_image</code> and
<code class="function">write_image</code> calls to the same image memory object in a kernel are
not supported.
</p>
<p>
The <code class="function">read_image</code> calls returns a four component floating-point, integer or
unsigned integer color value. The color values returned by <code class="function">read_image</code>
are identified as <code class="code">x, y, z, w</code> where <code class="code">x</code> refers to the red component,
<code class="code">y</code> refers to the green component, <code class="code">z</code> refers to the blue component
and <code class="code">w</code> refers to the alpha component.
</p>
<p>
The following table describes the mapping
of the number of channels of an image element to the appropriate components in the
<span class="type">float4</span>, <span class="type">int4</span> or <span class="type">uint4</span> vector data type for
the color values returned by <code class="function">read_image{f|i|ui}</code> or supplied
to <code class="function">write_image{f|i|ui}</code>. The unmapped components will be set
to <code class="constant">0.0</code> for red, green and blue channels and will be set to
<code class="constant">1.0</code> for the alpha channel.
</p>
<p>
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col align="center" class="col1" />
<col align="center" class="col2" />
</colgroup>
<thead>
<tr>
<th align="center">Channel Order</th>
<th align="center"><span class="type">float4</span>, <span class="type">int4</span> or <span class="type">uint4</span> components of channel data</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center"><code class="constant">CL_R</code>, <code class="constant">CL_Rx</code></td>
<td align="center">
<code class="constant">(r, 0.0, 0.0, 1.0)</code>
</td>
</tr>
<tr>
<td align="center">
<code class="constant">CL_A</code>
</td>
<td align="center">
<code class="constant">(0.0, 0.0, 0.0, a)</code>
</td>
</tr>
<tr>
<td align="center"><code class="constant">CL_RG</code>, <code class="constant">CL_RGx</code></td>
<td align="center">
<code class="constant">(r, g, 0.0, 1.0)</code>
</td>
</tr>
<tr>
<td align="center">
<code class="constant">CL_RA</code>
</td>
<td align="center">
<code class="constant">(r, 0.0, 0.0, a)</code>
</td>
</tr>
<tr>
<td align="center"><code class="constant">CL_RGB</code>, <code class="constant">CL_RGBx</code></td>
<td align="center">
<code class="constant">(r, g, b, 1.0)</code>
</td>
</tr>
<tr>
<td align="center">
<code class="constant">CL_RGBA, CL_BGRA, CL_ARGB</code>
</td>
<td align="center">
<code class="constant">(r, g, b, a)</code>
</td>
</tr>
<tr>
<td align="center">
<code class="constant">CL_INTENSITY</code>
</td>
<td align="center">
<code class="constant">(I, I, I, I)</code>
</td>
</tr>
<tr>
<td align="center">
<code class="constant">CL_LUMINANCE</code>
</td>
<td align="center">
<code class="constant">(L, L, L, 1.0)</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
A kernel that uses a sampler with the <code class="constant">CL_ADDRESS_CLAMP</code> addressing
mode with multiple images may result in additional samplers being used internally
by an implementation. If the same sampler is used with multiple images called via
<code class="function">read_image{f|i|ui}</code>, then it is possible that an implementation may
need to allocate an additional sampler to handle the different border color values that
may be needed depending on the image formats being used. These implementation allocated
samplers will count against the maximum sampler values supported by the device and given by
<code class="constant">CL_DEVICE_MAX_SAMPLERS</code>. Enqueuing a kernel that requires more samplers
than the implementation can support will result in a <code class="constant">CL_OUT_OF_RESOURCES</code>
error being returned.
</p>
</div>
<div class="refsect1">
<a id="specification"></a>
<h2>Specification</h2>
<p>
<img src="pdficon_small1.gif" />
<a href="http://www.khronos.org/registry/cl/specs/opencl-1.2.pdf#page=292" target="OpenCL Spec">OpenCL Specification</a>
</p>
</div>
<div class="refsect1">
<a id="seealso"></a>
<h2>Also see</h2>
<p>
<a class="citerefentry" href="imageFunctions.html"><span class="citerefentry"><span class="refentrytitle">Image Functions</span></span></a>
</p>
</div>
<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 © 2007-2011 The Khronos Group Inc.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials.
</div>
</div>
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