UIImagePNGRepresentation问题？ /图像旋转90度 [英] UIImagePNGRepresentation issues? / Images rotated by 90 degrees

问题描述

我想从UIImagePickerController加载图片，然后将所选照片保存到我应用的文档目录。

I want to load images from UIImagePickerController, then save the selected photo to my app's document directory.

UIImage *image = [info objectForKey:UIImagePickerControllerOriginalImage];
NSData *data1 = UIImagePNGRepresentation(image);

NSString *fileName = "1.png";
NSString *path = //get Document path, then add fileName
BOOL succ = [data1 writeToFile:path atomically:YES];

但是我将图像保存到我的文档后，我发现图像旋转了90度，然后我将方法UIImagePNGRepresentation改为UIImageJPEGRepresentation，这一次很好，任何人知道是什么问题？

but after I save the image to my document, I found that, the image was rotated 90 degree, then I change the method UIImagePNGRepresentation to UIImageJPEGRepresentation, this time it's fine, anyone know what's the problem?

推荐答案

只是想出了原因：从iOS 4.0开始，当相机拍摄照片，它不保存前旋转它，它只是在JPEG的EXIF数据中设置一个旋转标志。

I had the same problem and just figured out the reason: starting with iOS 4.0 when the camera takes a photo it does not rotate it before saving, it simply sets a rotation flag in the EXIF data of the JPEG.

如果将UIImage保存为JPEG，它将设置旋转标志。

If you save a UIImage as a JPEG, it will set the rotation flag.

PNG不支持旋转标志，因此如果将UIImage保存为一个PNG，它会旋转不正确，没有设置标志来修复它。所以如果你想要PNG，你必须自己旋转它们。

PNGs do not support a rotation flag, so if you save a UIImage as a PNG, it will be rotated incorrectly and not have a flag set to fix it. So if you want PNGs you must rotate them yourself.

我会称之为PNG保存功能的一个bug，但这只是一个意见（他们应该至少警告你这）。

I would call this a bug in the PNG saving function but that's just an opinion (they should at least warn you about this).

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