Hello so I was hoping someone knew how to move or change color and position actual image pixels and could explain and show the code to do so.

I know how to write pixels on a surface or screen-surface

usigned int *ptr = static_cast <unsigned int *> (screen-pixels);

int offset = y * (screen->pitch / sizeof(unsigned int));

ptr[offset + x] = color;

But I don't know how to alter or manipulate a image pixel of a png image my thoughts on this was

How do I get the values and locations of pixels and what do I have to write to make it happen?

Then how do I actually change the values or locations of those gotten pixels and how do I make that happen?

any ideas tip suggestions are also welcome!

  int main(int argc , char *argv[])
    {

        SDL_Surface *Screen = SDL_SetVideoMode(640,480,32,SDL_SWSURFACE);

        SDL_Surface *Image;

        Image = IMG_Load("image.png");

        bool done = false;

        SDL_Event event;

        while(!done)
        {

            SDL_FillRect(Screen,NULL,(0,0,0));

            SDL_BlitSurface(Image,NULL,Screen,NULL);

                while(SDL_PollEvent(&event))
                {

                    switch(event.type)
                    {

                            case SDL_QUIT:
                            return 0;
                            break;

                    }

                }

                SDL_Flip(Screen);

        }

    return 0;

}