Zoom in and out on mouse position. You need to put a image file in the data folder.

zoomImage.pde

PImage img;
float scaleValue;
float diff;
float SCALE_VALUE_MIN = 1.0;
float SCALE_VALUE_MAX = 3.0;
float EASE_VALUE = 0.2;

void setup() {
    img = loadImage("image.jpg");
    size(img.width, img.height);
    scaleValue = SCALE_VALUE_MIN;
}

void draw() {
    background(255);
    if(mousePressed) {
        diff = SCALE_VALUE_MAX - scaleValue;
        scaleValue += diff * EASE_VALUE;
    } else {
        diff = scaleValue - SCALE_VALUE_MIN;
        scaleValue -= diff * EASE_VALUE;
    }
    if(scaleValue <= SCALE_VALUE_MIN) {
        scaleValue = SCALE_VALUE_MIN;
    } else if(scaleValue >= SCALE_VALUE_MAX) {
        scaleValue = SCALE_VALUE_MAX;
    }

    pushMatrix();
    translate(mouseX, mouseY);
    scale(scaleValue);
    translate(-mouseX, -mouseY);
    image(img, 0, 0);
    popMatrix();
}