I want to write a CUDA program to make a negative image using cuda and c. I have a partial code but need help feeling in the rest

#include <stdio.h>
#include "image.h"

__global__ void negative_kernal (unsigned char *pixel, unsigned char max_value, int n)
{
    /******************/
    /* your code here */
    /******************/

    /* calculate thread ID */
    /* calculate number of threads from grid dimension */
    /* use a while loop to process data, jumping appropriate index */
}

void process_data (image *photo)
{
    /******************/
    /* your code here */
    /******************/

    /* Note that all information can be retrieved from photo */

    /* step 1: allocate device memory */
    /* step 2: copy pixel data to device memory */
    /* step 3: invoke kernel function */
    /* step 4: copy result from device memory to host */
    /* step 5: clear device memory */
}

image *setup (int argc, char **argv)
{
    image *photo;

    if (argc < 3)
    {
        fprintf (stderr, "Usage: %s <infile> <outfile>\n\n", argv [0]);
        return NULL;
    }

    photo = read_image (argv [1]);
    if (photo == NULL)
    {
        fprintf (stderr, "Unable to read input file %s\n\n", argv [1]);
        return NULL;
    }

    return photo;
}

void cleanup (image *photo, char **argv)
{
    int rc = write_image (argv [2], photo);
    if (!rc)
    {
        fprintf (stderr, "Unable to write output file %s\n\n", argv [2]);
    }

    clear_image (photo);
}

int main (int argc, char **argv)
{
    image *photo = setup (argc, argv);
    process_data (photo);
    cleanup (photo, argv);
    return 0;
}

What I have tried:

I have tried YouTube and Chegg. Both were unsuccessful and I am still very confused.