Java 圖片縮放高保真：getScaledInstance 慢且模糊，改用 Graphics2D 雙線性/雙三次插值 + RenderingHints

`Image.getScaledInstance()` 預設最近鄰插值，質量差且同步阻塞。高保真方案：

Graphics2D 高質量縮放

public static BufferedImage scaleHighQuality(BufferedImage src, int w, int h) {
    BufferedImage dst = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
    Graphics2D g2 = dst.createGraphics();
    
    // 關鍵渲染提示
    g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC); // 雙三次
    g2.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    
    g2.drawImage(src, 0, 0, w, h, null);
    g2.dispose();
    return dst;
}

多級縮放（縮小超過 2 倍時）

while (src.getWidth() > w * 2 || src.getHeight() > h * 2) {
    src = scaleHighQuality(src, src.getWidth()/2, src.getHeight()/2);
}
return scaleHighQuality(src, w, h);

從數據庫 Blob 讀取並縮放

Blob blob = rs.getBlob("img_col");
try (InputStream is = blob.getBinaryStream()) {
    BufferedImage src = ImageIO.read(is);
    BufferedImage thumb = scaleHighQuality(src, 200, 200);
    // 輸出/存儲 thumb
}

**注意**：縮放本質是信息丟失，無法「無損放大」。原圖分辨率決定上限。