Image Read and Write Functions

Built-in functions to read, write, and query image memory objects. Click an item in the table below for details about that function.

read_imagef for 1D Do an element lookup in the 1D image object with or without a sampler, returning floating-point values (including optional mipmap support).
read_image{i|ui} for 1D Do an element lookup in the 1D image object with or without a sampler, returning unnormalized signed integer and unsigned integer values (including optional mipmap support).
read_imageh for 1D OPTIONAL function to do an element lookup in the 1D image object with or without a sampler, returning floating-point values. Enabled with cl_khr_fp16.
write_image {f|i|ui|h} for 1D Write color value to location in the 2D image object (including optional mipmap support). The half type is enabled with cl_khr_fp16.
read_imagef for 2D Do an element lookup in the 2D image object with or without a sampler, returning floating-point values (including optional mipmap support).
read_image{i|ui} for 2D Do an element lookup in the 2D image object with or without a sampler, returning unnormalized signed integer and unsigned integer values (including optional mipmap support).
read_imageh for 2D OPTIONAL function to do an element lookup in the 2D image object with or without a sampler, returning floating-point values. Enabled with cl_khr_fp16.
write_image {f|i|ui|h} for 2D Write color value to location in the 2D image object (including optional mipmap support). The half type is enabled with cl_khr_fp16.
read_imagef for 3D Do an element lookup in the 3D image object with or without a sampler, returning floating-point values (including optional mipmap support).
read_image{i|ui} for 3D Do an element lookup in the 3D image object with or without a sampler, returning unnormalized signed integer and unsigned integer values (including optional mipmap support).
read_imageh for 3D OPTIONAL function to do an element lookup in the 3D image object with or without a sampler, returning floating-point values. Enabled with cl_khr_fp16.
write_image {f|i|ui|h} for 3D Write color value to location in the 2D image object (including optional mipmap support). The half type is enabled with cl_khr_fp16.
get_image_width Return the image width in pixels
get_image_height Return the image height in pixels.
get_image_depth Return the 3D image depth in pixels
get_image_channel_data_type Return the image channel data type
get_image_channel_order Return the image channel order
get_image_dim Return the image dimensions
get_image_array_size Return the number of images in an image array
get_image_num_mip_levels Return the number of mip-levels. Enabled with extension cl_khr_mipmap_image
get_image_num_samples Return the number of samples in the 2D MSAA image. Enabled with extension cl_khr_gl_msaa_sharing

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.

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.

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 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.

Specification

OpenCL Specification

Also see

sampler_t, cl_khr_srgb_image_writes, cl_khr_mipmap_image

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