如何从ALAssetRepresentation获得正确旋转的UIImage？ [英] How to get a correctly rotated UIImage from an ALAssetRepresentation?

问题描述

我正在尝试使用从 ALAssetRepresentation 获得正确旋转的 UIImage fullScreenImage 方法。我有几张以不同设备方向拍摄的测试照片;照片在照片应用中正确显示。 fullScreenImage 的文档说：

I’m trying to get a correctly rotated UIImage from an ALAssetRepresentation using the fullScreenImage method. I have several testing photos shot in various device orientations; the photos show up correctly in the Photos app. The documentation for fullScreenImage says:

在iOS 5及更高版本中，此方法返回完全裁剪，旋转和
调整后的图像 - 完全按照用户在照片或图片中看到的
选择器。

In iOS 5 and later, this method returns a fully cropped, rotated, and adjusted image—exactly as a user would see in Photos or in the image picker.

创建一个正确旋转 UIImage 来自 CGImage 的对象，你使用
imageWithCGImage：scale ：orientation：或
initWithCGImage：scale：orientation：，传递 orientation的值
和 scale 。

To create a correctly-rotated UIImage object from the CGImage, you use imageWithCGImage:scale:orientation: or initWithCGImage:scale:orientation:, passing the values of orientation and scale.

鉴于文档，我的代码如下所示：

Given the docs, my code looks like this:

ALAssetRepresentation *rep = [asset defaultRepresentation];
UIImage *img = [UIImage
    imageWithCGImage:[rep fullScreenImage]
    scale:[rep scale]
    orientation:[rep orientation]];

但结果 UIImage 的轮换是错误。当我用 UIImageOrientationUp 替换 [rep orientation] 时，图像适用于所有测试照片。显然我对于坚持这个解决方案犹豫不决，因为它感觉像是一个黑客。我做错了什么？

But the resulting UIImage’s rotation is wrong. When I replace [rep orientation] with UIImageOrientationUp, the image is fine for all testing photos. Obviously I’m hesitating to stick with this "solution", as it feels like a hack. What am I doing wrong?

推荐答案

ALAssetRepresentation *rep = [asset defaultRepresentation];
UIImage *img = [UIImage
    imageWithCGImage:[rep fullScreenImage]
    scale:[rep scale]
    orientation:UIImageOrientationUp];

在iOS 5下是正确的，全屏图像已经旋转（所以它总是向上）。在iOS 4下，行为是不同的。请参阅使用Photo中的方向行为不正确ALAsset 有更深入的解释。

Is correct as under iOS 5 the fullscreenimages is already rotated (so it’s always "up"). Under iOS 4 the behaviour is different. Please see Orientation does not behave correctly with Photo in ALAsset for a more in depth explanation.

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