per-pixel collision using getRGB of a BufferedImage (Java2D Api)

Question

Hello I'm currently working on a 2D platformer game. I would like to have per-pixel collisions between my player (a Rectangle) and a freeform terrain (uses slopes, a BufferedImage).

I am a bit confused on the concept to check if any part of my rectangle collides with the terrain.

Currently I'm trying to see if a part of my terrain contains a non-transparent pixel. I compare this to each coordinate in my rectangle and see if they meet, however I am not having luck.

Here is my code:

    public boolean rgbCollide () {
    int a = terrain.getRGB(x, y);
    System.out.println(a);
    // Per-pixel Bitwise collision check
    for (int i =0; i < width; i++) {
        for (int j =0; j < height; j++) {
           //Hmm what to do here...? 
        }
    }
    return false;
}

where: terrain is my bufferedImage x,y,width, and height are my player's Rectangle coordinates