Java ARGB到JPG

Question

如何使用BufferedImage将TYPE_INT_ARGB保存到jpg？

程序为我生成了这个图像：

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没关系，但当我用这种方式保存它时：

    ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
    BufferedOutputStream bos = new BufferedOutputStream(byteStream);
    try {
        ImageIO.write(buffImg, "jpg", bos);
        // argb
        byteStream.flush();
        byte[] newImage = byteStream.toByteArray();

        OutputStream out = new BufferedOutputStream(new FileOutputStream("D:\\test.jpg"));
        out.write(newImage);
        out.close();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

结果是：

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理解这是由于alpha层，但不知道如何修复它。Png格式不适合我，需要jpg。

Answer 1

好的!我已经解决了。一切都很简单。不知道这是一个好的决定，它有多快。我还没找到其他的。所以..。我们需要的是定义新的BufferedImage。

BufferedImage buffImg = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
Graphics2D g2 = buffImg.createGraphics();

// ... other code we need

BufferedImage img= new BufferedImage(buffImg.getWidth(), buffImg.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = img.createGraphics();
g2d.drawImage(buffImg, 0, 0, null);
g2d.dispose();

如果有任何改进这一方法的想法，请见谅。

Answer 2

具有4个彩色通道的图像不应该写入jpeg文件。我们可以在ARGB和RGB图像之间进行转换，而无需重复像素值。这对于大图像来说是有用的。举个例子：

int a = 10_000;

BufferedImage im = new BufferedImage(a, a, BufferedImage.TYPE_INT_ARGB);
Graphics2D g = im.createGraphics();
g.setColor(Color.RED);
g.fillRect(a/10, a/10, a/5, a*8/10);
g.setColor(Color.GREEN);
g.fillRect(a*4/10, a/10, a/5, a*8/10);
g.setColor(Color.BLUE);
g.fillRect(a*7/10, a/10, a/5, a*8/10);

//preserve transparency in a png file
ImageIO.write(im, "png", new File("d:/rgba.png"));

//pitfall: in a jpeg file 4 channels will be interpreted as CMYK... this is no good
ImageIO.write(im, "jpg", new File("d:/nonsense.jpg"));

//we need a 3-channel BufferedImage to write an RGB-colored jpeg file
//we can make up a new image referencing part of the existing raster
WritableRaster ras = im.getRaster().createWritableChild(0, 0, a, a, 0, 0, new int[] {0, 1, 2}); //0=r, 1=g, 2=b, 3=alpha
ColorModel cm = new BufferedImage(1, 1, BufferedImage.TYPE_INT_RGB).getColorModel(); //we need a proper ColorModel
BufferedImage imRGB = new BufferedImage(cm, ras, cm.isAlphaPremultiplied(), null);

//this image we can encode to jpeg format
ImageIO.write(imRGB, "jpg", new File("d:/rgb1.jpg"));