Image resize - maintain aspect ratio

Question

How could I resize an image and still keep it's aspect ratio?

This is the method that I use :

private static BufferedImage resizeImage(BufferedImage originalImage,
            int type) {
        BufferedImage resizedImage = new BufferedImage(IMG_WIDTH, IMG_HEIGHT,
                type);
        Graphics2D g = resizedImage.createGraphics();
        g.drawImage(originalImage, 0, 0, IMG_WIDTH, IMG_HEIGHT, null);
        g.dispose();

        return resizedImage;
    }

The type variable :

BufferedImage original = ImageIO.read(new File(imagePath));
int type = original.getType() == 0 ? BufferedImage.TYPE_INT_ARGB
                    : original.getType();

The problem is that some images are correctly resized but others lose their aspect ratio because of the IMG_WIDTH and IMG_HEIGHT.

Is there a way to get the original image dimensions and then apply some kind of proportion resize to maintain the aspect ratio of the resized image?

Answer 1

Why don't you use originalImage.getWidth() and originalImage.getHeight() ? Then you can easily calculate aspect ratio. Don't forget that int/int = int, so you need to do

double ratio = 1.0 * originalImage.getWidth() / originalImage.getHeight();

or 

double ratio = (double) originalImage.getWidth() / originalImage.getHeight();

Regarding the additional math, you can calculate

int height = (int) IMG_WIDTH/ratio;

int width = (int) IMG_HEIGHT*ratio;

Then see which one fits your needs better and resize to (IMG_WIDTH, height) or (width, IMG_HEIGHT)

Answer 2

To get the image size, see getWidth() / getHeight() . The rest is just some relatively simple math.

Presuming the IMG_WIDTH & IMG_HEIGHT represent the largest size desired:

• Find which is going to hit the limit first.
• Calculate the ratio between the natural size and that maximum size.
• Multiply the other image dimension by the same ratio.