write_image

Write color value to location in a 2D image object.

void write_imagef ( image2d_t image,
  int2 coord,
  float4 color)
void write_imagei ( image2d_t image,
  int2 coord,
  int4 color)
void write_imageui ( image2d_t image,
  int2 coord,
  uint4 color)

Description

Write color value to location specified by coordinate (x, y) in the 2D image object specified by image. Appropriate data format conversion to the specified image format is done before writing the color value. x and y are considered to be unnormalized coordinates and must be in the range 0... image width - 1, and 0... image height - 1.

write_imagef can only be used with image objects created with image_channel_data_type set to one of the pre-defined packed formats or set to CL_SNORM_INT8, CL_UNORM_INT8, CL_SNORM_INT16, CL_UNORM_INT16, CL_HALF_FLOAT, or CL_FLOAT. Appropriate data format conversion will be done to convert channel data from a floating-point value to actual data format in which the channels are stored.

write_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.

write_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, or CL_UNSIGNED_INT32.

The behavior of write_imagef, write_imagei and write_imageui for image objects created with image_channel_data_type values not specified in the description above or with (x, y) coordinate values that are not in the range (0... image width - 1, 0... image height - 1), respectively, is undefined.

Notes

The built-in functions defined in this section can only be used with image memory objects created with clCreateImage2D, or clCreateImage3D. 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 __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.

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 image read functions take a sampler argument. The sampler can be passed as an argument to the kernel using clSetKernelArg, or it can be a constant variable of type sampler_t declared in the program source.

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 unsigned int4 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

Also see

Image Functions

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