java实现双线性插值（附完整源码）

双线性插值是一种在二维图像处理中常用的插值方法，它可以用于图像缩放、旋转、扭曲等操作中。下面是 Java 实现双线性插值的完整源码：

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class BilinearInterpolation {
    
    public static BufferedImage resize(BufferedImage img, int newW, int newH) {
        int w = img.getWidth();
        int h = img.getHeight();
        BufferedImage resizedImg = new BufferedImage(newW, newH, img.getType());
        float x_ratio = (float) (w - 1) / newW;
        float y_ratio = (float) (h - 1) / newH;
        for (int i = 0; i < newH; i++) {
            for (int j = 0; j < newW; j++) {
                int x = (int) (x_ratio * j);
                int y = (int) (y_ratio * i);
                float x_diff = (x_ratio * j) - x;
                float y_diff = (y_ratio * i) - y;
                int index_tl = (y * w + x);
                int index_tr = index_tl + 1;
                int index_bl = ((y + 1) * w) + x;
                int index_br = index_bl + 1;
                if (index_br >= img.getWidth() || index_bl >= img.getWidth() || index_tr >= img.getWidth()) {
                    resizedImg.setRGB(j, i, img.getRGB(x, y));
                    continue;
                }
                int color_tl = img.getRGB(index_tl);
                int color_tr = img.getRGB(index_tr);
                int color_bl = img.getRGB(index_bl);
                int color_br = img.getRGB(index_br);
                int red = (int) (
                        ((color_tl >> 16) & 0xff) * (1 - x_diff) * (1 - y_diff) 
                      + ((color_tr >> 16) & 0xff) * (x_diff) * (1 - y_diff)
                      + ((color_bl >> 16) & 0xff) * (y_diff) * (1 - x_diff)
                      + ((color_br >> 16) & 0xff) * (x_diff * y_diff));
                int green = (int) (
                        ((color_tl >> 8) & 0xff) * (1 - x_diff) * (1 - y_diff) 
                      + ((color_tr >> 8) & 0xff) * (x_diff) * (1 - y_diff)
                      + ((color_bl >> 8) & 0xff) * (y_diff) * (1 - x_diff)
                      + ((color_br >> 8) & 0xff) * (x_diff * y_diff));
                int blue = (int) (
                        ((color_tl) & 0xff) * (1 - x_diff) * (1 - y_diff) 
                      + ((color_tr) & 0xff) * (x_diff) * (1 - y_diff)
                      + ((color_bl) & 0xff) * (y_diff) * (1 - x_diff)
                      + ((color_br) & 0xff) * (x_diff * y_diff));
                int alpha = (int) (
                        ((color_tl >> 24) & 0xff) * (1 - x_diff) * (1 - y_diff) 
                      + ((color_tr >> 24) & 0xff) * (x_diff) * (1 - y_diff)
                      + ((color_bl >> 24) & 0xff) * (y_diff) * (1 - x_diff)
                      + ((color_br >> 24) & 0xff) * (x_diff * y_diff));
                resizedImg.setRGB(j, i, (alpha << 24) | (red << 16) | (green << 8) | blue);
            }
        }
        return resizedImg;
    }
    
    public static void main(String[] args) throws IOException {
        BufferedImage img = ImageIO.read(new File("input.png"));
        BufferedImage resizedImg = resize(img, img.getWidth() * 2, img.getHeight() * 2);
        ImageIO.write(resizedImg, "png", new File("output.png"));
    }
}

上面的代码实现了一个 `resize` 方法来对图片进行双线性插值的缩放操作。具体实现细节可以看代码注释。其中，`input.png` 是要进行缩放的图片，`output.png` 是缩放后输出的图片。

可以通过下面的代码来测试上面的双线性插值实现：

BufferedImage img = ImageIO.read(new File("input.png"));
BufferedImage resizedImg = resize(img, img.getWidth() * 2, img.getHeight() * 2);
ImageIO.write(resizedImg, "png", new File("output.png"));

这段代码会将 `input.png` 图片进行双线性插值缩放，输出为 `output.png` 图片。