OpenCL images and samplers are the counterparts to CUDA Arrays and textures.
Images are memory objects (like buffers), and are allocated with the following syntax (in OpenCL 1.1):
cl_mem clCreateImage2D(cl_context ctx, cl_mem_flags flags,
cl_image_format *fmt, size_t width, size_t height,
size_t row_pitch, void *host_ptr, cl_int *error);where the row pitch is the pitch in bytes of a single line in the
host data (if host_ptr is not NULL).
The image format specifies the format of the data:
typedef struct _cl_image_format {
cl_channel_order image_channel_order;
cl_channel_type image_channel_data_type;
} cl_image_format;with the channel order specifying which channels are present in the
data, and in which order they are returned (e.g. CL_R, CL_RG,
CL_RGB, CL_RGBA or CL_ARGB), whereas the channel data type
specifies the format (signed or unsigned integer, short, or float,
normalized or unnormalized).
(For a full list of channel orders and data types, see the OpenCL reference)
Images are read using a sampler, which is just a set of flat that
determine whether to normalize coordinates, how addressing beyond the
image is handled (NONE, MIRROR, REPEAT) and whether texture
filtering should be enabled (CLK_FILTER_LINEAR) or not
(CLK_FILTER_NEAREST).
In contrast to CUDA, images can be read from and written to by kernels, but in a given kernel an image can only be read from, or written to (it is not possible to read and write the same image in a single kernel).
Reading and writing is always done with 4-components vector
(uint4, int4 or float4), where only the channels defined by the
image channel order are used.
Read functions (read_imagef, read_imagei, read_imageui) take as
parameters an image, a sampler and the coordinates. The coordinates are
either an int2 (unnormalized) or a float2 (normalized).
Write functions (write_imagef, write_imagei, write_imageui) take
as parameters an image, the coordinates and the value to be written.
Example OpenCL program and kernel using OpenCL images for transposition can be found here and here.