比较BufferedImages有什么问题？

Question

public static void main(final String[] args) throws Exception {
    final BufferedImage data = new BufferedImage(500, 500, BufferedImage.TYPE_INT_ARGB_PRE);
    {//all images include alpha
        final Graphics2D g2d = data.createGraphics();
        final BufferedImage img1 = ImageIO.read(new File("z:\\img1.png"));
        g2d.drawImage(img1, 0, 0, null);
        final BufferedImage img2 = ImageIO.read(new File("z:\\img2.png"));
        g2d.drawImage(img2, 100, 100, null);
        g2d.dispose();
    }

    final File fa = new File("z:\\a\\test.png");
    ImageIO.write(data, "png", fa);
    final BufferedImage newData = ImageIO.read(fa);

    final File fb = new File("z:\\b\\test.png");
    ImageIO.write(newData, "png", fb);
    final BufferedImage newData2 = ImageIO.read(fb);

    System.out.println(equal(data, data));          // true
    System.out.println(equal(data, newData));       // false
    System.out.println(equal(newData, newData2));   // true
}

public static boolean equal(final BufferedImage img1, final BufferedImage img2) {
    final int width = img1.getWidth();
    final int height = img1.getHeight();
    if (width == img2.getWidth() && height == img2.getHeight()) {
        for (int x = 0; x < width; x++) {
            for (int y = 0; y < height; y++) {
                final int argb1 = img1.getRGB(x, y);
                final int argb2 = img2.getRGB(x, y);
                if (argb1 != argb2){
                    return false;
                }
            }
        }
        return true;
    } else {
        return false;
    }
}

我尝试验证图像的一致性，但是结果是，为什么相等的data和newData之间返回false？我应该如何纠正代码？

顺便说一句，ImageIO.write似乎有一个可疑的问题。 我已经通过ImageIO.write，PngEncoderB（http://catcode.com/pngencoder/），PngEncoder（http://objectplanet.com/pngencoder/）和image4j（https://github.com/imcdonagh/image4j）编写了一些图像。 PngEncoderB，PngEncoder和image4j是相同的图像像素，只是ImageIO.write不同。其实我不知道哪一个是正确的。如果您有兴趣，请使用比对/ DiffImg等图像比较软件来检查Alpha。