java - How do I find the extents of an object within a BufferedImage

So I am trying to find the upper, lower, left and right extents of an object in a png image. The image has a transparent background and a black circle in the middle. How do I find the upper, lower, left and right extents of the circle (which is completely black) thus isolating the circle from the transparent background?

What I tried so far:

    public static BufferedImage trimImage(BufferedImage image) {
int left = 0, right = 0, up = 0, down = 0;
for(int i = 0; i<image.getHeight(); i++) {
for(int j = 0; j<image.getWidth(); j++) {
if(image.getRGB(j, i)==0) {
up = i;
break;
}
}
}
for(int i = 0; i<image.getWidth(); i++) {
for(int j = 0; j<image.getHeight(); j++) {
if(image.getRGB(i, j)==0) {
left = i;
break;
}
}
}
for(int i = 0; i<image.getHeight(); i++) {
for(int j = 0; j<image.getWidth(); j++) {
if(image.getRGB(j, i)==0&&i>down) {
down = i;
}
}
}
for(int i = 0; i<image.getWidth(); i++) {
for(int j = 0; j<image.getHeight(); j++) {
if(image.getRGB(i, j)==0&&i>down) {
right = i;
}
}
}
System.out.println(up+","+down+","+left+","+right);
BufferedImage temp = image.getSubimage(left, up, right-left, down-up);
return temp;
}

Do you know a simpler method? This gives me the following error:

Exception in thread "main" java.awt.image.RasterFormatException: (x + width) is outside raster

Any help is appreciated. Thanks!

edit: Here's the complete stackTrace():

Exception in thread "main" java.awt.image.RasterFormatException: (x + width) is outside raster
at sun.awt.image.IntegerInterleavedRaster.createWritableChild(Unknown Source)
at java.awt.image.BufferedImage.getSubimage(Unknown Source)
at main.ImageHandler.trimLetter(ImageHandler.java:114)
at main.HandwritingReader.<init>(HandwritingReader.java:48)
at main.HandwritingReader.main(HandwritingReader.java:55)

Consider that the left is the lowest x coordinate, top is the lowest y coordinate, right is the highest x coordinate and bottom is the highest y coordinate.

int left = Integer.MAX_VALUE;
int right = 0;
int top = Integer.MAX_VALUE;
int bottom = 0;
for(int i = 0; i<image.getWidth(); i++) {
for(int j = 0; j<image.getHeight(); j++) {
if(image.getRGB(i, j)==0) {
left = Math.min(left, i);
right = Math.max(right, i);
top = Math.min(top, j);
bottom = Math.max(bottom, j);
}
}
}

That should give you the bounds when the loop completes.

I made an example image and tried it out.

		BufferedImage image = new BufferedImage(256, 256, BufferedImage.TYPE_INT_ARGB);
Graphics g = image.getGraphics();
g.setColor(Color.BLACK);
g.fillOval(25, 25, 32, 32);
g.dispose();

In this case, I had to check if image.getRGB() != 0 because the transparent pixels are 0, but the black pixels have 255 alpha value.