I am trying to figure out how to access images that are of format CL_R and channel_type cl_uint8. As far as I can tell, the smallest read is read_imageh, does the read value get put in the low order bits of X?
section 126.96.36.199 of the opencl (1.1) specification (page 245) states that cl_uint8 must be read with read_imageui(). It reads a full zero-extended 32-bit integer value.
If it's real image data you're using, you probably want unorm_int8 and read/write_imagef as working with floats is a lot faster/simpler.