java对图片进行等比例缩放

 

public  class ImageUtils {
		private Image	srcImage	= null;
		private File	srcFile  = null;
		private File	destFile	= null;
		private String	fileSuffix	= null;
        
		private int imageWidth = 0;
		private int imageHeight = 0;

		public ImageUtils(String fileName) throws IOException {
			this(new File(fileName));
		}

		public ImageUtils(File fileName) throws IOException {
			File _file = fileName;
			_file.setReadOnly();
			this.srcFile = _file;
			this.fileSuffix = _file.getName().substring(
					(_file.getName().indexOf(".") + 1),
					(_file.getName().length()));
			this.destFile = new File(this.srcFile.getPath().substring(0,
					(this.srcFile.getPath().lastIndexOf(".")))
					+ PIC_TEMPORARY + "." + this.fileSuffix);
			srcImage = javax.imageio.ImageIO.read(_file);
			//得到图片的原始大小， 以便按比例压缩。
			imageWidth = srcImage.getWidth(null);
			imageHeight = srcImage.getHeight(null);
			System.out.println("width: " + imageWidth);
			System.out.println("height: " + imageHeight);		
		}

		/**
		 * 强制压缩/放大图片到固定的大小
		 * @param w int 新宽度
		 * @param h int 新高度
		 * @throws IOException
		 */
		public void resize(int w, int h) throws IOException {
			//得到合适的压缩大小，按比例。
			if ( imageWidth >= imageHeight)
			{
				w = w;
				h = (int)Math.round((imageHeight * w * 1.0 / imageWidth));
			}
			else 
			{
				h = h;
				w = (int)Math.round((imageWidth * h * 1.0 / imageHeight));
			}

			//构建图片对象
			BufferedImage _image = new BufferedImage(w, h,
					BufferedImage.TYPE_INT_RGB);
			//绘制缩小后的图
			_image.getGraphics().drawImage(srcImage, 0, 0, w, h, null);
			//输出到文件流
			FileOutputStream out = new FileOutputStream(destFile);
			JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
			encoder.encode(_image);
			out.flush();
			out.close();
			
		}
	}

下边是另外一种模式，不过原理都是一样的，就是等比例压缩，比较原图的宽高来确定压缩的比例。

Java中图片的缩放（按比例）

现在的一些应用中，我们常常需要把原始图片存到数据库中去，而显示的时候可能是各种缩小后的图片（长宽比例不变，不然图片会变形）。比如图片管理的时候先显示一系列小图片，点击后显示放大的图片。但是现在的图片有的height>width,而有的height<width,长宽比例个不相同，当显示一系列小图片的时候可能不整齐，一般网页上的方法是用固定的正方形做底色，然后在上面显示缩小后的图片。下面的resizeImage方法正是此问题的solution,输入参数maxDim就是固定的正方形的长度：

    此外，此方法的类需要：
    import com.sun.jimi.core.raster.JimiRasterImage;
    import com.sun.jimi.core.Jimi;  
            

    /** resize the image in byte stream(format: [in]GIF, JPG; [out]JPG)
     *  @param in - the binary stream of the original picture in GIF or JPG
     *  @param maxDim - the bigger one between height and width after the picture is resized
     *  @return the binary stream of the resized picture in JPG
     */
    public static byte[] resizeImage(byte[] in,int maxDim)
    {
        try
        {
            Image inImage=Toolkit.getDefaultToolkit().createImage(in);
            ImageIcon inImageIcon = new ImageIcon(in); 

            int imh = inImageIcon.getIconHeight();
            int imw = inImageIcon.getIconWidth();
            double scale;
            if( imh <= maxDim && imw <= maxDim )
                scale = 1;
            else if( imh > imw )
               scale = (double) maxDim / (double) imh;
            else
               scale = (double) maxDim / (double) imw; 

            int scaledW = (int) (scale * imw);
            int scaledH = (int) (scale * imh); 

            Image img = inImage.getScaledInstance(scaledW, scaledH, Image.SCALE_FAST);
            ByteArrayOutputStream outStream = new ByteArrayOutputStream();
            JimiRasterImage raster = Jimi.createRasterImage(img.getSource());
            // --java.io.ByteArrayOutputStream
            Jimi.putImage("image/jpeg", raster, outStream);
            outStream.flush();
            outStream.close();
            return outStream.toByteArray(); 

        }
        catch(Exception ex)
        {
            ex.printStackTrace();
            return null;
        }
    }