使用AffineTransform进行Java图像旋转会输出黑色图像，但在调整大小时效果很好 [英] Java image rotation with AffineTransform outputs black image, but works well when resized

问题描述

我只是想将JPG文件旋转90度。但是我的代码输出完全黑色的图像（ BufferedImage ）。

I am just trying to rotate a JPG file by 90 degrees. However my code outputs image (BufferedImage) that is completely black.

这是重现的方式:(下载3 .jpg 此处 ）

Here's the way to reproduce: (Download 3.jpg here)

private static BufferedImage transform(BufferedImage originalImage) {
    BufferedImage newImage = null;
    AffineTransform tx = new AffineTransform();
    tx.rotate(Math.PI / 2, originalImage.getWidth() / 2, originalImage.getHeight() / 2);

    AffineTransformOp op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BICUBIC);
    newImage = op.filter(originalImage, newImage);

    return newImage;
}

public static void main(String[] args) throws Exception {
    BufferedImage bi = transform(ImageIO.read(new File(
            "3.jpg")));
    ImageIO.write(bi, "jpg", new File("out.jpg"));

}

这里有什么问题？

（如果我将这个黑色输出 BufferedImage 提供给图像缩放器库，它会很好地调整大小，原始图像仍然存在。）

(if I give this black output BufferedImage to a image resizer library, it gets resized well, original image is still there.)

推荐答案

将新的BufferedImage传递给filter（）方法，而不是让它创建自己的作品（不是完全黑色）。

Passing a new BufferedImage into the filter() method rather than letting it create its own works (not completely black).

此外，转换似乎无法正常工作，图像最终在目标中偏移。我能够通过手动应用必要的翻译来修复它，按相反顺序记录这些工作，并在目标图像中宽度=旧高度，高度=旧宽度。

Also the transform did not appear to work correctly, the image ended up being offset in the destination. I was able to fix it by manually applying the necessary translations, note these work in reverse order, and in the destination image the width = the old height, and height = the old width.

AffineTransform tx = new AffineTransform();

// last, width = height and height = width :)
tx.translate(originalImage.getHeight() / 2,originalImage.getWidth() / 2);
tx.rotate(Math.PI / 2);
// first - center image at the origin so rotate works OK
tx.translate(-originalImage.getWidth() / 2,-originalImage.getHeight() / 2);

AffineTransformOp op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BILINEAR);

// new destination image where height = width and width = height.
BufferedImage newImage =new BufferedImage(originalImage.getHeight(), originalImage.getWidth(), originalImage.getType());
op.filter(originalImage, newImage);

filter（）的javadoc声明它会为你创建一个BufferedImage，我仍然不确定为什么这不起作用，这里一定有问题。

The javadoc for filter() states that it will create a BufferedImage for you, I'm still unsure why this does not work, there must be an issue here.

 If the destination image is null, a BufferedImage is created with the source ColorModel.

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