Java文档图像缩放和旋转

Question

我有不同维度的文档图像，我希望能够有效地缩放和旋转他们在以下方式（标准的“旋转”和“缩放”逻辑）。我怎么做？

一幅图像是H像素高，W像素宽。最初，它应该缩放到600像素宽。在每次旋转时，面板的宽度和高度应该互换，缩放图像应该旋转90度。在每次缩放时，图像应按因子“比例”缩放。

以下是我到目前为止在BufferedImage...得到的BufferedImage会缩放和旋转，但不会平移（旋转90度后位于面板顶部的中心）：

double scale = zoom * 600.0 / img.getWidth();
rotation = (rotation + degrees) % 360;
int scaledWidth = (int)(scale * img.getWidth());
int scaledHeight = (int)(scale * img.getHeight());
BufferedImage bufferedImage = new BufferedImage(scaledWidth, scaledHeight, img.getType());
if (rotation % 180 == 0)
    bufferedImage = new BufferedImage(scaledWidth, scaledHeight, img.getType());
else
    bufferedImage = new BufferedImage(scaledHeight, scaledWidth, img.getType());

AffineTransform transform = AffineTransform.getRotateInstance(Math.toRadians(rotation), scaledWidth/2, scaledHeight/2);
transform.scale(scale, scale);
AffineTransformOp operation = new AffineTransformOp(transform, AffineTransformOp.TYPE_BILINEAR);
scaledImage = operation.filter(img, bufferedImage);
imagePanel.setPreferredSize(new Dimension(bufferedImage.getWidth(), bufferedImage.getHeight()));

Answer 1

啊哈！关键（JavaDoc很混乱）在于意识到在AffineTransform、Rotate()和其他方法上转换的是矩阵，而不是图像！下面的代码是自动工作的！

/**
 * Transforms the image efficiently without losing image quality.
 * Scales the image to a width of (600 * scale) pixels, rotates the image,
 * and translates (moves) the image to recenter it if rotated 90 or 270 degrees.
 */
protected BufferedImage transformImage(BufferedImage image)
{
    int scaledWidth = (int)(scale * image.getWidth());
    int scaledHeight = (int)(scale * image.getHeight());

    // Methods AffineTransform.rotate(), AffineTransform.scale() and AffineTransform.translate()
    // transform AffineTransform's transformation matrix to multiply with the buffered image.
    // Therefore those methods are called in a counterintuitive sequence.
    AffineTransform transform;
    if (rotation % 180 == 0)
    {
        // First scale and second rotate image
        transform = AffineTransform.getRotateInstance(Math.toRadians(rotation), scaledWidth/2, scaledHeight/2);
        transform.scale(scale, scale);
    }
    else
    {
        // First scale, second rotate, and third translate image
        transform = AffineTransform.getTranslateInstance((scaledHeight-scaledWidth)/2, (scaledWidth-scaledHeight)/2);
        transform.rotate(Math.toRadians(rotation), scaledWidth/2, scaledHeight/2);
        transform.scale(scale, scale);
    }
    AffineTransformOp operation = new AffineTransformOp(transform, AffineTransformOp.TYPE_BICUBIC);
    BufferedImage transformedImage = operation.createCompatibleDestImage(image, image.getColorModel());
    return operation.filter(image, transformedImage);
}