Java 獲取圖片像素尺寸與像素數據完整指南

核心 API：ImageIO + BufferedImage

public class ImageInfo {
    public static void main(String[] args) throws IOException {
        File file = new File("image.png");
        BufferedImage image = ImageIO.read(file);
        
        if (image == null) {
            System.out.println("不支持的圖片格式或文件損壞");
            return;
        }
        
        // 1. 獲取寬高 (像素)
        int width = image.getWidth();
        int height = image.getHeight();
        System.out.printf("尺寸: %d x %d 像素%n", width, height);
        System.out.printf("總像素: %,d%n", (long) width * height);
        
        // 2. 獲取像素數據 (ARGB)
        int[] pixels = new int[width * height];
        image.getRGB(0, 0, width, height, pixels, 0, width);
        
        // 遍歷像素
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                int argb = pixels[y * width + x];
                int alpha = (argb >> 24) & 0xFF;
                int red   = (argb >> 16) & 0xFF;
                int green = (argb >> 8)  & 0xFF;
                int blue  = argb & 0xFF;
                // 處理像素...
            }
        }
        
        // 3. 獲取圖片類型
        int type = image.getType();
        System.out.println("圖片類型: " + typeName(type));
        
        // 4. 顏色模型
        ColorModel cm = image.getColorModel();
        System.out.println("顏色模型: " + cm);
        System.out.println("是否有 Alpha: " + cm.hasAlpha());
    }
    
    static String typeName(int type) {
        return switch (type) {
            case BufferedImage.TYPE_INT_ARGB -> "TYPE_INT_ARGB";
            case BufferedImage.TYPE_INT_RGB -> "TYPE_INT_RGB";
            case BufferedImage.TYPE_3BYTE_BGR -> "TYPE_3BYTE_BGR";
            case BufferedImage.TYPE_BYTE_GRAY -> "TYPE_BYTE_GRAY";
            case BufferedImage.TYPE_USHORT_565_RGB -> "TYPE_USHORT_565_RGB";
            default -> "UNKNOWN(" + type + ")";
        };
    }
}

高性能像素訪問：DataBuffer 直接訪問

// 避免 getRGB() 數組拷貝開銷，直接操作底層數據
WritableRaster raster = image.getRaster();
DataBuffer buffer = raster.getDataBuffer();

if (buffer instanceof DataBufferInt) {
    // TYPE_INT_ARGB / TYPE_INT_RGB
    int[] data = ((DataBufferInt) buffer).getData();
    // 直接操作 data 數組
} else if (buffer instanceof DataBufferByte) {
    // TYPE_3BYTE_BGR / TYPE_BYTE_GRAY
    byte[] data = ((DataBufferByte) buffer).getData();
    // 注意：BGR 順序，每像素 3 字節
} else if (buffer instanceof DataBufferUShort) {
    // TYPE_USHORT_565_RGB
    short[] data = ((DataBufferUShort) buffer).getData();
}

圖片元信息讀取：ImageReader (不加載像素數據)

public static Dimension getImageSizeFast(File file) throws IOException {
    try (ImageInputStream in = ImageIO.createImageInputStream(file)) {
        Iterator readers = ImageIO.getImageReaders(in);
        if (readers.hasNext()) {
            ImageReader reader = readers.next();
            try {
                reader.setInput(in);
                int width = reader.getWidth(0);
                int height = reader.getHeight(0);
                return new Dimension(width, height);
            } finally {
                reader.dispose();
            }
        }
    }
    return null;
}

• 優勢：只讀取文件頭，不解碼像素數據，極快、內存占用極低
• 適用：批量掃描圖片尺寸、生成縮略圖索引

常見圖片格式支持

TwelveMonkeys ImageIO 擴展支持 (推薦生產使用)

<dependency>
    <groupId>com.twelvemonkeys.imageio</groupId>
    <artifactId>imageio-jpeg</artifactId>
    <version>3.9.4</version>
</dependency>
<dependency>
    <groupId>com.twelvemonkeys.imageio</groupId>
    <artifactId>imageio-tiff</artifactId>
    <version>3.9.4</version>
</dependency>
<dependency>
    <groupId>com.twelvemonkeys.imageio</groupId>
    <artifactId>imageio-webp</artifactId>
    <version>3.9.4</version>
</dependency>
<!-- 統一入口，自動註冊所有格式 -->
<dependency>
    <groupId>com.twelvemonkeys.imageio</groupId>
    <artifactId>imageio-core</artifactId>
    <version>3.9.4</version>
</dependency>

生成縮略圖最佳實踐

public static void createThumbnail(File src, File dest, int maxWidth, int maxHeight) 
        throws IOException {
    try (ImageInputStream in = ImageIO.createImageInputStream(src)) {
        Iterator readers = ImageIO.getImageReaders(in);
        if (!readers.hasNext()) throw new IOException("無讀取器");
        
        ImageReader reader = readers.next();
        try {
            reader.setInput(in);
            
            // 1. 獲取原始尺寸
            int srcWidth = reader.getWidth(0);
            int srcHeight = reader.getHeight(0);
            
            // 2. 計算縮放比例
            double scale = Math.min(
                (double) maxWidth / srcWidth,
                (double) maxHeight / srcHeight
            );
            if (scale >= 1.0) {
                Files.copy(src.toPath(), dest.toPath(), StandardCopyOption.REPLACE_EXISTING);
                return;
            }
            
            // 3. 讀取縮放後圖片 (子采樣)
            ImageReadParam param = reader.getDefaultReadParam();
            int subsample = (int) Math.ceil(1.0 / scale);
            param.setSourceSubsampling(subsample, subsample, 0, 0);
            
            BufferedImage thumb = reader.read(0, param);
            
            // 4. 精細縮放 (如需精確尺寸)
            if (thumb.getWidth() > maxWidth || thumb.getHeight() > maxHeight) {
                thumb = Scalr.resize(thumb, Scalr.Method.QUALITY, Scalr.Mode.FIT_TO_BOUNDS, 
                    maxWidth, maxHeight); // 需 img-scalr-lib 依賴
            }
            
            // 5. 寫入
            String format = getFormatName(dest);
            ImageIO.write(thumb, format, dest);
        } finally {
            reader.dispose();
        }
    }
}

常見問題排查

掌握 ImageIO 核心 API、DataBuffer 零拷貝訪問、ImageReader 輕量級元信息讀取、格式擴展庫與縮略圖生成最佳實踐，構建高性能 Java 圖像處理能力。