Do an element lookup in the 2D image object, returning unnormalized signed integer and unsigned integer values.
int4
read_imagei
(
| read_only image2d_array_t image , |
sampler_t sampler , | |
int4
coord
) |
int4
read_imagei
(
| read_only image2d_array_t image , |
sampler_t sampler , | |
float4
coord
) |
uint4
read_imageui
(
| read_only image2d_array_t image , |
sampler_t sampler , | |
int4
coord
) |
uint4
read_imageui
(
| read_only image2d_array_t image , |
sampler_t sampler , | |
float4
coord
) |
int4
read_imagei
(
| aQual image2d_array_t image , |
int4
coord
) |
uint4
read_imageui
(
| aQual image2d_array_t image , |
int4
coord
) |
cl_khr_mipmap_image
:
int4
read_imagei
(
| image2d_t image , |
sampler_t sampler , | |
float2 coord , | |
float
lod
) |
uint4
read_imageui
(
| image2d_t image , |
sampler_t sampler , | |
float2 coord , | |
float
lod
) |
int4
read_imagei
(
| image2d_t image , |
sampler_t sampler , | |
float2 coord , | |
float2 gradient_x , | |
float2
gradient_y
) |
uint4
read_imageui
(
| image2d_t image , |
sampler_t sampler , | |
float2 coord , | |
float2 gradient_x , | |
float2
gradient_y
) |
int4
read_imagei
(
| image2d_array_t image , |
sampler_t sampler , | |
float4 coord , | |
float
lod
) |
uint4
read_imageui
(
| image2d_array_t image , |
sampler_t sampler , | |
float4 coord , | |
float
lod
) |
int4
read_imagei
(
| image2d_array_t image , |
sampler_t sampler , | |
float4 coord , | |
float2 gradient_x , | |
float2
gradient_y
) |
uint4
read_imageui
(
| image2d_array_t image , |
sampler_t sampler , | |
float4 coord , | |
float2 gradient_x , | |
float2
gradient_y
) |
cl_khr_gl_msaa_sharing
:
int4
read_imagei
(
| image2d_msaa_t image , |
int2 coord , | |
int
sample
) |
uint4
read_imageui
(
| image2d_msaa_t image , |
int2 coord , | |
int
sample
) |
int4
read_imagei
(
| image2d_array_msaa_t image , |
int4 coord , | |
int
sample
) |
uint4
read_imageui
(
| image2d_array_msaa_t image , |
int4 coord , | |
int
sample
) |
aQual
refers to one of the access qualifiers
read_only
, write_only
, or read_write
.
For samplerless read functions this may be read_only
or read_write
.
For the forms that take an image2d_t object, 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 image2d_array_t object, use
the gradients to compute the lod and
coordinate coord.xy to do an element lookup in
the mip-level specified by the computed lod in
the 2D image object specified by image
.
For the forms that take an image2d_t object and gradients, use
coord.xy to do an element lookup in the 2D image identified by
coord.z in the 2D image array specified by image
.
For forms that take image2d_msaa_t,
use the coordinate (coord.x, coord.y
) and sample
to
do an element lookup in the 2D image object
specified by image
.
For forms that take image2d_array_msaa_t,
use coord.xy
and sample
to do an element lookup in
the 2D image identified by coord.z
in the 2D 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.
For the forms that take a sampler, 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, for the forms that take a sampler, the read_imagei
and read_imageui
calls that take integer coordinates must use a sampler with normalized coordinates
set to CLK_NORMALIZED_COORDS_FALSE
and addressing mode set to
CLK_ADDRESS_CLAMP_TO_EDGE
, CLK_ADDRESS_CLAMP
or CLK_ADDRESS_NONE
; otherwise the values returned are undefined.
For the forms that take an image2d_t object,
use the coordinate coord.xy
to
do an element lookup in the mip-level specified by
lod
in the 2D image object specified
by image
.
For the forms that use gradients, use the gradients to compute
the lod and coordinate coord.xy to do an
element lookup in
the mip-level specified by the computed lod in
the 2D image object specified by image
.
For the forms that take an image2d_array_t object,
use the coordinate coord.xy to
do an element lookup in the 2D image identified by
coord.z and mip-level specified by
lod
in the 2D image object specified
by image
.
For the forms that take an image2d_array_t
object and that use gradients,
use the gradients to compute the lod coordinate
and coord.xy to
do an element lookup in the 2D image identified by
coord.z and mip-level specified by
lod
in the 2D image object specified
by image
.
When a multisample image is accessed in a kernel, the access takes one vector of integers describing which pixel to fetch and an integer corresponding to the sample numbers describing which sample within the pixel to fetch. sample identifies the sample position in the multi-sample image.
NOTE: CL_SAMPLER_NORMALIZED_COORDS
must be CL_TRUE
for built-in functions
described in the table above that read from a
mip-mapped image; otherwise the behavior is
undefined. The value specified in the
lod
argument is clamped to the minimum of (actual
number of mip-levels - 1) in the image or value
specified for CL_SAMPLER_LOD_MAX_KHR
.
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.
Note that image writes to sRGB images are only supported if the cl_khr_srgb_image_writes extension is supported; otherwise the behavior of writing to a sRGB image is undefined.
Image memory objects that are being read by a kernel should be declared with the read_only
qualifier. write_image
calls to image memory objects declared with the
read_only
qualifier will generate a compilation error. Image memory objects that
are being written to by a kernel should be declared with the write_only qualifier.
read_image
calls to image memory objects declared with the write_only
qualifier will generate a compilation error. read_image
and
write_image
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
read_write
qualifier.
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 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
.
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
cl_khr_srgb_image_writes
extension will be reported in the
CL_DEVICE_EXTENSIONS
string
if a device supports writing to sRGB images using
write_imagef.
clGetSupportedImageFormats
will return the supported sRGB images if
CL_MEM_READ_WRITE
or
CL_MEM_WRITE_ONLY
is specified in
flags
argument and the
device supports writing to an sRGB image. If
cl_khr_srgb_image_writes
is supported, the
built-in image write functions will perform
the linear to sRGB conversion.
Only the R, G and B components are converted from linear to sRGB and vice-versa. The alpha component is returned as is.
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 ,
CL_sRGB ,
CL_sRGBx
|
(r, g, b, 1.0)
|
CL_RGBA, CL_BGRA, CL_ARGB, CL_ABGR, CL_sRGBA, CL_sBGRA
|
(r, g, b, a)
|
CL_INTENSITY
|
(I, I, I, I)
|
CL_LUMINANCE
|
(L, L, L, 1.0)
|
For CL_DEPTH
images, a scalar value is
returned by read_imagef
or supplied to
write_imagef
.
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.