title: OpenCL image2d pixel edit
body: <p>I'm a total newbie in OpenCL but i have a project to do in OpenCL and i'm stuck.
  I need to load image(bmp), throw it into GPU, change some pixels and save it into new bmp file. Everything works fine when i'm just copying an image or reversing Red/Green palette for example. But when i'm trying to change 2,4,6 .... pixel column to black i got error:
  CL_INVALID_KERNEL_NAME.
  As i said i'm a total newbie and i lack of ideas. But i'm sure that whole main code is 100% valid and the problem is with the kernel:</p>
  
  <pre><code>#pragma OPENCL EXTENSION cl_khr_byte_addressable_store : enable
  
  __kernel void image_change(__read_only image2d_t image1, __write_only image2d_t image2)
  {
  const sampler_t sampler=CLK_NORMALIZED_COORDS_FALSE | CLK_ADDRESS_CLAMP | CLK_FILTER_NEAREST;
  
  int x = get_global_id(0);
  int y = get_global_id(1);
  int2 pixelcoord;
  float4 pixel = read_imagef(image1, sampler, pixelcoord(x,y));
  float4 blackpixel = (float4)(0,0,0,0);
  width = get_image_width(image1);
  height = get_image_height(image1);
  for (pixelcoord.x=x-width; pixelcoord.x&lt;width; pixelcoord.y++)
  {
      if(pixelcoord.x % 2 == 0)
      {
      for (pixelcoord.y=y-height; pixelcoord.y&lt;height; pixelcoord.y++) 
          write_imagef(image2, pixelcoord, pixel);
      }
      else
      {
      for (pixelcoord.y=y-height; pixelcoord.y&lt;height; pixelcoord.y++) 
          write_imagef(image2, pixelcoord, blackpixel);
      }
  }
  }
  </code></pre>
  
  <p>I'm sure there is something bad in code from the first "for".</p>
  
  <ol>
  <li>Why i got this error (coz kernel name is 100% ok)?</li>
  <li>How can i change pixels? (I mean i don't get how can i access to certain pixel and it's color)</li>
  </ol>
  
  <p>I would be happy if someone could guide me at this point.</p>