Provided by: opencl-1.2-man-doc_1.0~svn33624-1_all 
NAME
read_image{i|ui}_(1D) - Do an element lookup in the 1D image object, returning
unnormalized signed integer and unsigned integer values.
int4 read_imagei(image1d_t image, sampler_t sampler, int coord);
int4 read_imagei(image1d_t image, sampler_t sampler, float coord);
uint4 read_imageui(image1d_t image, sampler_t sampler, int coord);
uint4 read_imageui(image1d_t image, sampler_t sampler, float coord);
int4 read_imagei(image1d_t image, int coord);
uint4 read_imageui(image1d_t image, int coord);
int4 read_imagei(image1d_buffer_t image, int coord);
uint4 read_imageui(image1d_buffer_t image, int coord);
int4 read_imagei(image1d_array_t image, int2 coord);
uint4 read_imageui(image1d_array_t image, int2 coord);
int4 read_imagei(image1d_array_t image, sampler_t sampler, int2 coord);
int4 read_imagei(image1d_array_t image, sampler_t sampler, float2 coord);
uint4 read_imageui(image1d_array_t image, sampler_t sampler, int2 coord);
uint4 read_imageui(image1d_array_t image, sampler_t sampler, float2 coord);
DESCRIPTION
For the forms that take an image1d_t, use the coordinate (coord.x, coord.y) to do an
element lookup in the 2D image object specified by image.
For the forms that take an image1d_array_t, use coord.x to do an element lookup in the 1D
image identified by coord.y in the 1D image array specified by image.
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
CLK_FILTER_NEAREST, normalized coordinates set to CLK_NORMALIZED_COORDS_FALSE and
addressing mode to CLK_ADDRESS_NONE.
read_imagei and read_imageui return unnormalized signed integer and unsigned integer
values respectively. Each channel will be stored in a 32-bit integer.
read_imagei can only be used with image objects created with image_channel_data_type set
to one of the following values: CL_SIGNED_INT8, CL_SIGNED_INT16, or CL_SIGNED_INT32. If
the image_channel_data_type is not one of the above values, the values returned by
read_imagei are undefined.
read_imageui can only be used with image objects created with image_channel_data_type set
to one of the following values: CL_UNSIGNED_INT8, CL_UNSIGNED_INT16, and
CL_UNSIGNED_INT32. If the image_channel_data_type is not one of the above values, the
values returned by read_imageui are undefined.
The read_imagei and read_imageui calls support a nearest filter only. The filter_mode
specified in sampler must be set to CLK_FILTER_NEAREST; otherwise the values returned are
undefined.
Furthermore, the read_imagei returned are undefined. and read_imageui calls that take
integer coordinates must use a returned are undefined. sampler with normalized coordinates
set to CLK_NORMALIZED_COORDS_FALSE and addressing returned are undefined. mode set to
CLK_ADDRESS_CLAMP_TO_EDGE, CLK_ADDRESS_CLAMP or CLK_ADDRESS_NONE; otherwise returned are
undefined. the values returned are undefined. returned are undefined.
NOTES
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.
Image memory objects that are being read by a kernel should be declared with the
accessQualifiers(3clc) qualifier. write_image calls to image memory objects declared with
the accessQualifiers(3clc) qualifier will generate a compilation error. Image memory
objects that are being written to by a kernel should be declared with the
accessQualifiers(3clc) qualifier. read_image calls to image memory objects declared with
the accessQualifiers(3clc) qualifier will generate a compilation error. read_image and
write_image calls to the same image memory object in a kernel are not supported.
The read_image calls returns a four component floating-point, integer or unsigned integer
color value. The color values returned by read_image are identified as x, y, z, w where x
refers to the red component, y refers to the green component, z refers to the blue
component and w refers to the alpha component.
The following table describes the mapping of the number of channels of an image element to
the appropriate components in the float4, int4 or uint4 vector data type for the color
values returned by read_image{f|i|ui} or supplied to write_image{f|i|ui}. The unmapped
components will be set to 0.0 for red, green and blue channels and will be set to 1.0 for
the alpha channel.
┌──────────────────────────┬──────────────────────────────────┐
│ Channel Order │ float4, int4 or uint4 components │
│ │ of channel data │
├──────────────────────────┼──────────────────────────────────┤
│ CL_R, CL_Rx │ (r, 0.0, 0.0, 1.0) │
├──────────────────────────┼──────────────────────────────────┤
│ CL_A │ (0.0, 0.0, 0.0, a) │
├──────────────────────────┼──────────────────────────────────┤
│ CL_RG, CL_RGx │ (r, g, 0.0, 1.0) │
├──────────────────────────┼──────────────────────────────────┤
│ CL_RA │ (r, 0.0, 0.0, a) │
├──────────────────────────┼──────────────────────────────────┤
│ CL_RGB, CL_RGBx │ (r, g, b, 1.0) │
├──────────────────────────┼──────────────────────────────────┤
│CL_RGBA, CL_BGRA, CL_ARGB │ (r, g, b, a) │
├──────────────────────────┼──────────────────────────────────┤
│ CL_INTENSITY │ (I, I, I, I) │
├──────────────────────────┼──────────────────────────────────┤
│ CL_LUMINANCE │ (L, L, L, 1.0) │
└──────────────────────────┴──────────────────────────────────┘
A kernel that uses a sampler with the CL_ADDRESS_CLAMP 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 read_image{f|i|ui}, 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 CL_DEVICE_MAX_SAMPLERS. Enqueuing a kernel
that requires more samplers than the implementation can support will result in a
CL_OUT_OF_RESOURCES error being returned.
SPECIFICATION
OpenCL Specification[1]
SEE ALSO
imageFunctions(3clc)
AUTHORS
The Khronos Group
COPYRIGHT
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.
NOTES
1. OpenCL Specification
page 292, section 6.12.14 - Image Read and Write Functions