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Problems rotating BufferedImage

I have some problems with rotating images in Java using the AffineTransform class.

I have the following method for creating a rotated (90 degrees) copy of an image:

private BufferedImage createRotatedCopy(BufferedImage img, Rotation rotation) {
    int w = img.getWidth();
    int h = img.getHeight();

    BufferedImage rot = new BufferedImage(h, w, BufferedImage.TYPE_INT_RGB);

    double theta;
    switch (rotation) {
        case CLOCKWISE:
            theta = Math.PI / 2;
            break;
        case COUNTERCLOCKWISE:
            theta = -Math.PI / 2;
            break;
        default:
            throw new AssertionError();
    }

    AffineTransform xform = AffineTransform.getRotateInstance(theta, w / 2, h / 2);
    Graphics2D g = (Graphics2D) rot.createGraphics();
    g.drawImage(img, xform, null);
    g.dispose();

    return rot;
}

Rotation is a simple enum with the values NONE, CLOCKWISE and COUNTERCLOCKWISE.

The symptoms of my problems are displayed here:

http://perp.se/so/rotate_problems.html

So, the rotation works OK, but the resulting images aren't anchored to the correct coordinates (or how one should put it). And since I don't really know what the heck I'm doing in the first place (my linear algebra is weak), I don't know how to solve this on my own.

I've tried with some random fiddling with the AffineTransform instance, but it hasn't helped me (of course). I've tried googling (and searching SO), but all examples I've seen basically use the same approach as I do... which doesn't work for me.

Thankful for advice.

like image 604
perp Avatar asked Feb 13 '10 10:02

perp


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What is the difference between BufferedImage and image?

A BufferedImage is essentially an Image with an accessible data buffer. It is therefore more efficient to work directly with BufferedImage. A BufferedImage has a ColorModel and a Raster of image data. The ColorModel provides a color interpretation of the image's pixel data.

What is rotation in image processing?

Image rotation is a common image processing routine with applications in matching, alignment, and other image-based algorithms. The input to an image rotation routine is an image, the rotation angle θ, and a point about which rotation is done. The aim is to achieve the result shown in Figure 4.3.


2 Answers

If you must express the transform as a single rotation, the anchor point depends on the direction of rotation: Either (w/2, w/2) or (h/2, h/2).

But it's probably simpler to express as translate; rotate; translate, e.g.

AffineTransform xform = new AffineTransform();
xform.translate(0.5*h, 0.5*w);
xform.rotate(theta);
xform.translate(-0.5*w, -0.5*h);

Also consider using getQuadrantRotateInstance instead of getRotateInstance.

like image 111
finnw Avatar answered Oct 16 '22 13:10

finnw


Since you only need 90 degree rotation you can avoid using the AffineTransform stuff:

public BufferedImage rotate90DX(BufferedImage bi) {
    int width = bi.getWidth();
    int height = bi.getHeight();
    BufferedImage biFlip = new BufferedImage(height, width, bi.getType());
    for(int i=0; i<width; i++)
        for(int j=0; j<height; j++)
            biFlip.setRGB(height-1-j, width-1-i, bi.getRGB(i, j));
    return biFlip;
}

This also avoids cutting off edges of rectangular images.

From: http://snippets.dzone.com/posts/show/2936

like image 28
David Tinker Avatar answered Oct 16 '22 13:10

David Tinker