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Java 圖像處理四大核心技巧：裁切、縮放、灰階、色彩反轉完整實作

編輯：Java 程式設計入門

前言

Java AWT/ImageIO 提供靈活的 ImageProducer/ImageConsumer 模型與 BufferedImage 直接像素操作能力。本文彙整四大常見圖像處理需求：區域裁切、任意縮放、灰階轉換、色彩反轉，提供可直接執行的完整代碼與核心 API 解析。

1. 圖像裁切

使用 CropImageFilter + FilteredImageSource 從現有 Image 產生子圖像。


import java.awt.*;
import java.awt.image.*;

public Image cropImage(Image source, int x, int y, int w, int h) {
    ImageFilter filter = new CropImageFilter(x, y, w, h);
    return Toolkit.getDefaultToolkit().createImage(new FilteredImageSource(source.getSource(), filter));
}

// 在 Component 子類中可簡寫為：
// Image cropped = createImage(new FilteredImageSource(source.getSource(), new CropImageFilter(x,y,w,h)));

CropImageFilter(int x, int y, int width, int height)：座標以原圖左上角為原點。
回傳的 Image 為延遲載入，首次繪製時才實際裁切。

2. 圖像縮放

Image.getScaledInstance() 回傳縮放後的 Image，支援多種演算法提示。


// 固定尺寸
Image scaled = source.getScaledInstance(100, 100, Image.SCALE_SMOOTH); // 高品質雙三次

// 按比例放大 2 倍 (在 Component 內)
Image doubled = source.getScaledInstance(
    source.getWidth(this) * 2,
    source.getHeight(this) * 2,
    Image.SCALE_FAST); // 速度優先

// SCALE_* 常數：
// SCALE_FAST / SCALE_SMOOTH / SCALE_DEFAULT / SCALE_REPLICATE / SCALE_AREA_AVERAGING

若需高品質離線處理，建議改用 Graphics2D.drawImage() 配合 RenderingHints.KEY_INTERPOLATION (BILINEAR/BICUBIC) 繪製至 BufferedImage。

3. 灰階轉換 (三種演算法可切換)

核心：實作 RGBImageFilter + 自訂 ColorModel 將 RGB 映射為同值灰階。


import java.awt.image.*;

public class GrayFilter extends RGBImageFilter {
    public static final int MODE_MAX = 0;      // 取 R/G/B 最大值
    public static final int MODE_WEIGHTED = 1; // 加權平均 0.3R+0.59G+0.11B
    public static final int MODE_JAVA = 2;     // JDK 內建 ColorSpace.CS_GRAY

    private final int mode;

    public GrayFilter(int mode) {
        this.mode = mode;
        canFilterIndexColorModel = true; // 支援索引色模型
    }

    @Override
    public void setColorModel(ColorModel model) {
        if (mode == MODE_JAVA) {
            // 使用 JDK 內建灰階 ColorModel
            ColorSpace gray = ColorSpace.getInstance(ColorSpace.CS_GRAY);
            substituteColorModel(model, new ComponentColorModel(gray, false, false,
                Transparency.OPAQUE, DataBuffer.TYPE_BYTE));
        } else {
            substituteColorModel(model, new GrayColorModel(model, mode));
        }
    }

    @Override public int filterRGB(int x, int y, int rgb) { return rgb; } // 實際轉換在 ColorModel

    // --- 內部灰階 ColorModel ---
    static class GrayColorModel extends ColorModel {
        private final ColorModel src;
        private final int mode;

        GrayColorModel(ColorModel src, int mode) {
            super(src.getPixelSize());
            this.src = src; this.mode = mode;
        }

        private int gray(int pixel) {
            int r = src.getRed(pixel), g = src.getGreen(pixel), b = src.getBlue(pixel);
            switch (mode) {
                case MODE_MAX: return Math.max(r, Math.max(g, b));
                case MODE_WEIGHTED: return (int)(r*0.3 + g*0.59 + b*0.11);
                default: return 0;
            }
        }

        @Override public int getRed(int pixel) { return gray(pixel); }
        @Override public int getGreen(int pixel) { return gray(pixel); }
        @Override public int getBlue(int pixel) { return gray(pixel); }
        @Override public int getAlpha(int pixel) { return src.getAlpha(pixel); }
        @Override public int getRGB(int pixel) {
            int gr = gray(pixel), a = src.getAlpha(pixel);
            return (a<<24) | (gr<<16) | (gr<<8) | gr;
        }
    }
}

使用方式：


Image gray1 = createImage(new FilteredImageSource(src.getSource(), new GrayFilter(GrayFilter.MAX)));
Image gray2 = createImage(new FilteredImageSource(src.getSource(), new GrayFilter(GrayFilter.WEIGHTED)));
Image gray3 = createImage(new FilteredImageSource(src.getSource(), new GrayFilter(GrayFilter.JAVA)));

4. 色彩反轉 (負片效果)

將每個色彩通道取補數 (255 - value)。


public class InvertFilter extends RGBImageFilter {
    public InvertFilter() { canFilterIndexColorModel = true; }

    @Override
    public void setColorModel(ColorModel model) {
        substituteColorModel(model, new InvertColorModel(model));
    }

    @Override public int filterRGB(int x, int y, int rgb) { return rgb; }

    static class InvertColorModel extends ColorModel {
        private final ColorModel src;
        InvertColorModel(ColorModel src) { super(src.getPixelSize()); this.src = src; }

        @Override public int getRed(int p)   { return 255 - src.getRed(p); }
        @Override public int getGreen(int p) { return 255 - src.getGreen(p); }
        @Override public int getBlue(int p)  { return 255 - src.getBlue(p); }
        @Override public int getAlpha(int p) { return src.getAlpha(p); }
        @Override public int getRGB(int p) {
            return (src.getAlpha(p)<<24) | ((255-src.getRed(p))<<16) | ((255-src.getGreen(p))<<8) | (255-src.getBlue(p));
        }
    }
}

擴充：修改 getRed/Green/Blue 即可實現任意通道映射 (如紅綠交換、色相旋轉、閾值二值化)。

整合展示程式


import javax.swing.*;
import java.awt.*;
import java.awt.image.*;

public class ImageFilterDemo extends JFrame {
    private Image src, crop, scale, grayMax, grayWeight, grayJava, invert;

    public ImageFilterDemo() {
        src = new ImageIcon("test.jpg").getImage(); // 請自備圖片
        MediaTracker mt = new MediaTracker(this);
        mt.addImage(src, 0);
        try { mt.waitForAll(); } catch (InterruptedException ignored) {}

        int w = src.getWidth(this), h = src.getHeight(this);

        crop   = cropImage(src, 10, 10, w-20, h-20);
        scale  = src.getScaledInstance(w*2, h*2, Image.SCALE_SMOOTH);
        grayMax    = createImage(new FilteredImageSource(src.getSource(), new GrayFilter(GrayFilter.MAX)));
        grayWeight = createImage(new FilteredImageSource(src.getSource(), new GrayFilter(GrayFilter.WEIGHTED)));
        grayJava   = createImage(new FilteredImageSource(src.getSource(), new GrayFilter(GrayFilter.JAVA)));
        invert     = createImage(new FilteredImageSource(src.getSource(), new InvertFilter()));

        mt.addImage(grayMax, 1); mt.addImage(grayWeight, 2); mt.addImage(grayJava, 3); mt.addImage(invert, 4);
        try { mt.waitForAll(); } catch (InterruptedException ignored) {}

        setTitle("Java 圖像處理技巧展示");
        setSize(900, 500);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);
    }

    @Override public void paint(Graphics g) {
        super.paint(g);
        Graphics2D g2 = (Graphics2D) g;
        int x = 20, y = 40, gap = 10;
        g2.drawString("原圖", x, y-5); g2.drawImage(src, x, y, this);
        x += src.getWidth(this) + gap;
        g2.drawString("裁切", x, y-5); g2.drawImage(crop, x, y, this);
        x += crop.getWidth(this) + gap;
        g2.drawString("放大2倍", x, y-5); g2.drawImage(scale, x, y, this);
        x = 20; y += src.getHeight(this) + 30;
        g2.drawString("灰階-MAX", x, y-5); g2.drawImage(grayMax, x, y, this);
        x += grayMax.getWidth(this) + gap;
        g2.drawString("灰階-加權", x, y-5); g2.drawImage(grayWeight, x, y, this);
        x += grayWeight.getWidth(this) + gap;
        g2.drawString("灰階-JDK內建", x, y-5); g2.drawImage(grayJava, x, y, this);
        x += grayJava.getWidth(this) + gap;
        g2.drawString("色彩反轉", x, y-5); g2.drawImage(invert, x, y, this);
    }

    public static void main(String[] args) { SwingUtilities.invokeLater(ImageFilterDemo::new); }

    // 裁切輔助方法 (見上文)
    private Image cropImage(Image src, int x, int y, int w, int h) { ... }
}

進階建議：棄用舊 API 改用 BufferedImage 直接操作

ImageProducer/Consumer 模型屬於 JDK 1.0 時代設計，現代代碼建議：

將來源轉為 BufferedImage：BufferedImage buf = toBufferedImage(src);
直接操作像素陣列或使用 Graphics2D + ColorConvertOp / LookupOp / RescaleOp / AffineTransformOp。
灰階範例：ColorConvertOp op = new ColorConvertOp(ColorSpace.getInstance(ColorSpace.CS_GRAY), null); op.filter(buf, dest);
縮放範例：AffineTransformOp op = new AffineTransformOp(AffineTransform.getScaleInstance(2,2), AffineTransformOp.TYPE_BICUBIC); op.filter(buf, dest);