sdk/2.0/docs/man/imageFunctionsInc.xml

  <para>
    <!-- section 6.13.14 --> 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.
  </para>

  <para>
    Note that image writes to sRGB images are only supported if the 
    <citerefentry><refentrytitle>cl_khr_srgb_image_writes</refentrytitle></citerefentry> 
    extension is supported; 
    otherwise the behavior of writing to a sRGB image is undefined.
  </para>


<!-- Note: use <function> instead of <citerefentry> for the read and write functions in the text below. -->

  <para>
    Image memory objects that are being read by a kernel should be declared with the <citerefentry
    href="accessQualifiers"><refentrytitle>read_only</refentrytitle></citerefentry>
    qualifier. <function>write_image</function> calls to image memory objects declared with the
    <citerefentry href="accessQualifiers"><refentrytitle>read_only</refentrytitle></citerefentry>
    qualifier will generate a compilation error. Image memory objects that
    are being written to by a kernel should be declared with the <citerefentry
    href="accessQualifiers"><refentrytitle>write_only</refentrytitle></citerefentry> qualifier.
    <function>read_image</function> calls to image memory objects declared with the <citerefentry
    href="accessQualifiers"><refentrytitle>write_only</refentrytitle></citerefentry>
    qualifier will generate a compilation error. <function>read_image</function> and
    <function>write_image</function> calls to the same image memory object in a kernel are
    not supported.
    Image memory objects that are being read and written by a kernel should be declared with the 
    <citerefentry
    href="accessQualifiers"><refentrytitle>read_write</refentrytitle></citerefentry> 
    qualifier.
  </para>

  <para>
    The <function>read_image</function> calls returns a four component floating-point, integer or
    unsigned integer color value. The color values returned by <function>read_image</function>
    are identified as <code>x, y, z, w</code> where <code>x</code> refers to the red component,
    <code>y</code> refers to the green component, <code>z</code> refers to the blue component
    and <code>w</code> refers to the alpha component.
  </para>

  <bridgehead>sRGB Images</bridgehead>

  <para>
    <!-- 6.13.14.1.2 sRGB Images -->
    The built-in image read functions will perform
     sRGB to linear RGB conversions if the image is 
    an sRGB image. Writing to sRGB images from a 
    kernel is an optional extension. The 
    <citerefentry><refentrytitle>cl_khr_srgb_image_writes</refentrytitle></citerefentry> 
    extension will be reported in the 
    <constant>CL_DEVICE_EXTENSIONS</constant> string 
    if a device supports writing to sRGB images using 
    <citerefentry href="imageFunctions"><refentrytitle>write_imagef</refentrytitle></citerefentry>. 
    <citerefentry><refentrytitle>clGetSupportedImageFormats</refentrytitle></citerefentry> 
    will return the supported sRGB images if 
    <constant>CL_MEM_READ_WRITE</constant> or 
    <constant>CL_MEM_WRITE_ONLY</constant> is specified in 
    <varname>flags</varname> argument and the 
    device supports writing to an sRGB image. If 
    <citerefentry><refentrytitle>cl_khr_srgb_image_writes</refentrytitle></citerefentry> 
    is supported, the 
    built-in image write functions will perform 
    the linear to sRGB conversion. 
  </para>

  <para>
    Only the R, G and B components are converted from 
    linear to sRGB and vice-versa. The alpha 
    component is returned as is.
  </para>

    <para>
      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 <constant>CLK_FILTER_NEAREST</constant>, normalized coordinates set
      to <constant>CLK_NORMALIZED_COORDS_FALSE</constant> and addressing mode to
      <constant>CLK_ADDRESS_NONE</constant>.
    </para>

<!-- 17-Dec-2013, rev. 19 -->