Why does AWTRobot getPixelColor() give varying result?

Question

I am trying to create an application similar to DigitalColor Meter in Mac OS X. (Note: DigitalColor Meter is a small application for Mas OS to pick pixel colour below the mouse cursor).

To implement it in Java, I have tried using AWTRobot getPixelColor() but getPixelColor() seems to be not efficient. Below is my code:

public class AWT_Robot {

public static void main(String[] args) {
    int mouseX = 0;
    int mouseY = 0;
    try {
        Robot robot = new Robot();          
        while(true){
            robot.delay(1000);
            mouseX = MouseInfo.getPointerInfo().getLocation().x;
            mouseY = MouseInfo.getPointerInfo().getLocation().x;
            Color color = robot.getPixelColor(mouseX, mouseY);
            System.out.println("x: "+mouseX+" y: "+mouseY+"   RGB: ("+color.getRed()+", "+color.getGreen()+", "+color.getBlue()+")");
        }           
    } catch (AWTException e) {
        e.printStackTrace();
    }       
}
}

When I hovered the mouse over a red image (RGB: 243,0,0), it prints with varying RGB as below:

x: 313 y: 313   RGB: (239, 0, 0)
x: 313 y: 313   RGB: (239, 0, 0)
x: 294 y: 294   RGB: (239, 0, 0)
x: 186 y: 186   RGB: (79, 116, 163)
x: 104 y: 104   RGB: (67, 104, 154)
x: 116 y: 116   RGB: (79, 117, 164)
x: 159 y: 159   RGB: (68, 105, 155)

1) What could be the reason behind this issue?

2) Also is there any other way to implement the application (DigitalColor Meter) in Java?

I found similar questions in the below links but none of them seem to have the answer that I am expecting.

java robot.getPixelColor(x,y) question

awtrobot reads incorrect colors

How does Robot's getPixelColor(int x, int y) method work?

Answer 1

Your mouseX and mouseY are both gotten using getLocation().x. This is likely the cause of your problem.