java - AffineTransform 截断图像，我错了什么？

Question

我这里有一个尺寸为 2156x1728 的黑白 png 文件，我想使用 AffineTransform 将其旋转 90 度。生成的图像比例不正确。这里是一些示例代码(假设我已成功将 png 文件加载到 BufferedImage 中):

public BufferedImage transform(BufferedImage image){

    System.out.println("Input width: "+ image.getWidth());
    System.out.println("Input height: "+ image.getHeight());

    AffineTransform affineTransform = new AffineTransform();
    affineTransform.setToQuadrantRotation(1, image.getWidth() / 2, image.getHeight() / 2);

    AffineTransformOp opRotated = new AffineTransformOp(affineTransform, AffineTransformOp.TYPE_BILINEAR);
    BufferedImage transformedImage = opRotated.createCompatibleDestImage(image, image.getColorModel());
    System.out.println("Resulting width: "+ transformedImage.getWidth());
    System.out.println("Resulting height: "+ transformedImage.getHeight());

    transformedImage = opRotated.filter(image, transformedImage);
    return transformedImage;
}

相应的输出是:

Input width: 2156

Input height: 1728

Resulting width: 1942

Resulting height: 1942

为什么旋转会返回如此完全不相关的维度？

Answer 1

我不是这方面的专家，但为什么不创建一个正确大小的 BufferedImage 呢？另请注意，您的旋转中心不正确。您需要以 [w/2, w/2] 或 [h/2, h/2] 为中心旋转(w 是宽度，h 是高度)，具体取决于您要旋转到的象限，1 或 3 ，以及图像的相对高度和宽度。例如:

import java.awt.geom.AffineTransform;
import java.awt.image.AffineTransformOp;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JOptionPane;

public class RotateImage {
   public static final String IMAGE_PATH = "http://duke.kenai.com/"
         + "models/Duke3DprogressionSmall.jpg";

   public static void main(String[] args) {
      try {
         URL imageUrl = new URL(IMAGE_PATH);
         BufferedImage img0 = ImageIO.read(imageUrl);
         ImageIcon icon0 = new ImageIcon(img0);

         int numquadrants = 1;
         BufferedImage img1 = transform(img0, numquadrants );
         ImageIcon icon1 = new ImageIcon(img1);

         JOptionPane.showMessageDialog(null, new JLabel(icon0));
         JOptionPane.showMessageDialog(null, new JLabel(icon1));

      } catch (MalformedURLException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }

   public static BufferedImage transform(BufferedImage image, int numquadrants) {
      int w0 = image.getWidth();
      int h0 = image.getHeight();
      int w1 = w0;
      int h1 = h0;

      int centerX = w0 / 2;
      int centerY = h0 / 2;

      if (numquadrants % 2 == 1) {
         w1 = h0;
         h1 = w0;
      }

      if (numquadrants % 4 == 1) {
         if (w0 > h0) {
            centerX = h0 / 2;
            centerY = h0 / 2;
         } else if (h0 > w0) {
            centerX = w0 / 2;
            centerY = w0 / 2;
         }
         // if h0 == w0, then use default
      } else if (numquadrants % 4 == 3) {
         if (w0 > h0) {
            centerX = w0 / 2;
            centerY = w0 / 2;
         } else if (h0 > w0) {
            centerX = h0 / 2;
            centerY = h0 / 2;
         }
         // if h0 == w0, then use default
      }

      AffineTransform affineTransform = new AffineTransform();
      affineTransform.setToQuadrantRotation(numquadrants, centerX, centerY);

      AffineTransformOp opRotated = new AffineTransformOp(affineTransform,
            AffineTransformOp.TYPE_BILINEAR);

      BufferedImage transformedImage = new BufferedImage(w1, h1,
            image.getType());

      transformedImage = opRotated.filter(image, transformedImage);
      return transformedImage;
   }
}

编辑 1
您问:

can you explain to me why it must be [w/2, w/2] or [h/2, h/2] ?

为了最好地解释这一点，最好可视化并物理操作一个矩形:

剪出一张矩形纸并将其放在一张纸上，使其左上角位于该纸的左上角上 - 这就是您在屏幕上的图像。现在检查一下需要将矩形旋转 1 或 3 个象限的位置，以便其新的左上角覆盖纸张的左上角，您就会明白为什么需要使用 [w/2, w/2] 或[h/2，h/2]。