Pycuda, Issues Sending Multiple Single Variable Arguments

I have a pycuda program here that reads in an image from the command line and saves a version back with the colors inverted: import pycuda.autoinit import pycuda.driver as device f

Solution 1:

The device.In and relatives are designed for use with objects which support the Python buffer protocols (like numpy arrays). The source of your problem is using them to transfer non-buffer objects.

Just pass your scalars with the correct numpy dtype directly to your kernel call. Don't use device.In. The fact this worked in the original case was a complete accident

Solution 2:

Okay, so by changing the variable arguments to pointers in the kernel it fixed the code, i'm not sure how or why. Here is the modified version of the kernel;

__global__ void modify_image(int* pixelcount, int* width, unsignedchar* inputimage, unsignedchar* outputimage)
{
  intid = threadIdx.x + blockIdx.x * blockDim.x;
  if (id >= *pixelcount)
    return;

  outputimage[id] = 255 - inputimage[id];
}

The remainder of the code is unchanged. If anybody wants to explain why this is a successful fix, I would greatly appreciate it.