C Specification

The cl_image_desc image descriptor structure describes the image type and dimensions of an image or image array when creating an image using clCreateImage or clCreateImageWithProperties, and is defined as:

typedef struct cl_image_desc {
    cl_mem_object_type    image_type;
    size_t                image_width;
    size_t                image_height;
    size_t                image_depth;
    size_t                image_array_size;
    size_t                image_row_pitch;
    size_t                image_slice_pitch;
    cl_uint               num_mip_levels;
    cl_uint               num_samples;
    union {
        cl_mem buffer;
        cl_mem mem_object;
    };
} cl_image_desc;

Members

  • image_type describes the image type and must be either CL_MEM_OBJECT_IMAGE1D, CL_MEM_OBJECT_IMAGE1D_BUFFER, CL_MEM_OBJECT_IMAGE1D_ARRAY, CL_MEM_OBJECT_IMAGE2D, CL_MEM_OBJECT_IMAGE2D_ARRAY, or CL_MEM_OBJECT_IMAGE3D.

  • image_width is the width of the image in pixels. For a 2D image and image array, the image width must be a value ≥ 1 and ≤ CL_DEVICE_IMAGE2D_MAX_WIDTH. For a 3D image, the image width must be a value ≥ 1 and ≤ CL_DEVICE_IMAGE3D_MAX_WIDTH. For a 1D image buffer, the image width must be a value ≥ 1 and ≤ CL_DEVICE_IMAGE_MAX_BUFFER_SIZE. For a 1D image and 1D image array, the image width must be a value ≥ 1 and ≤ CL_DEVICE_IMAGE2D_MAX_WIDTH.

  • image_height is the height of the image in pixels. This is only used if the image is a 2D or 3D image, or a 2D image array. For a 2D image or image array, the image height must be a value ≥ 1 and ≤ CL_DEVICE_IMAGE2D_MAX_HEIGHT. For a 3D image, the image height must be a value ≥ 1 and ≤ CL_DEVICE_IMAGE3D_MAX_HEIGHT.

  • image_depth is the depth of the image in pixels. This is only used if the image is a 3D image and must be a value ≥ 1 and ≤ CL_DEVICE_IMAGE3D_MAX_DEPTH.

  • image_array_size [1] is the number of images in the image array. This is only used if the image is a 1D or 2D image array. The values for image_array_size, if specified, must be a value ≥ 1 and ≤ CL_DEVICE_IMAGE_MAX_ARRAY_SIZE.

  • image_row_pitch is the scan-line pitch in bytes. This must be 0 if host_ptr is NULL and can be either 0 or ≥ image_width × size of element in bytes if host_ptr is not NULL. If host_ptr is not NULL and image_row_pitch = 0, image_row_pitch is calculated as image_width × size of element in bytes. If image_row_pitch is not 0, it must be a multiple of the image element size in bytes. For a 2D image created from a buffer, the pitch specified (or computed if pitch specified is 0) must be a multiple of the maximum of the CL_DEVICE_IMAGE_PITCH_ALIGNMENT value for all devices in the context associated with the buffer specified by mem_object that support images.

  • image_slice_pitch is the size in bytes of each 2D slice in the 3D image or the size in bytes of each image in a 1D or 2D image array. This must be 0 if host_ptr is NULL. If host_ptr is not NULL, image_slice_pitch can be either 0 or ≥ image_row_pitch × image_height for a 2D image array or 3D image and can be either 0 or ≥ image_row_pitch for a 1D image array. If host_ptr is not NULL and image_slice_pitch = 0, image_slice_pitch is calculated as image_row_pitch × image_height for a 2D image array or 3D image and image_row_pitch for a 1D image array. If image_slice_pitch is not 0, it must be a multiple of the image_row_pitch.

  • num_mip_levels and num_samples must be 0.

  • mem_object may refer to a valid buffer or image memory object. mem_object can be a buffer memory object if image_type is CL_MEM_OBJECT_IMAGE1D_BUFFER or CL_MEM_OBJECT_IMAGE2D [2]. mem_object can be an image object if image_type is CL_MEM_OBJECT_IMAGE2D [3]. Otherwise it must be NULL. The image pixels are taken from the memory objects data store. When the contents of the specified memory objects data store are modified, those changes are reflected in the contents of the image object and vice-versa at corresponding synchronization points.

Description

For a 1D image buffer created from a buffer object, the image_width × size of element in bytes must be ≤ size of the buffer object. The image data in the buffer object is stored as a single scanline which is a linear sequence of adjacent elements.

For a 2D image created from a buffer object, the image_row_pitch × image_height must be ≤ size of the buffer object specified by mem_object. The image data in the buffer object is stored as a linear sequence of adjacent scanlines. Each scanline is a linear sequence of image elements padded to image_row_pitch bytes.

For an image object created from another image object, the values specified in the image descriptor except for mem_object must match the image descriptor information associated with mem_object.

Image elements are stored according to their image format as described in Image Format Descriptor.

If the buffer object specified by mem_object was created with CL_MEM_USE_HOST_PTR, the host_ptr specified to clCreateBuffer or clCreateBufferWithProperties must be aligned to the maximum of the CL_DEVICE_IMAGE_BASE_ADDRESS_ALIGNMENT value for all devices in the context associated with the buffer specified by mem_object that support images.

Creating a 2D image object from another 2D image object creates a new 2D image object that shares the image data store with mem_object but views the pixels in the image with a different image channel order. Restrictions are:

  • All of the values specified in image_desc must match the image descriptor information associated with mem_object, except for mem_object.

  • The image channel data type specified in image_format must match the image channel data type associated with mem_object.

  • The image channel order specified in image_format must be compatible with the image channel order associated with mem_object. Compatible image channel orders [4] are:

See Also

Document Notes

For more information, see the OpenCL Specification

This page is extracted from the OpenCL Specification. Fixes and changes should be made to the Specification, not directly.

Copyright 2014-2023 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0


1. Note that reading and writing 2D image arrays from a kernel with image_array_size equal to one may perform worse than 2D images.
2. To create a 2D image from a buffer object that share the data store between the image and buffer object.
3. To create an image object from another image object that share the data store between these image objects.
4. This allows creation of a sRGB view of the image from a linear RGB view or vice-versa, i.e. the pixels stored in the image can be accessed as linear RGB or sRGB values.