UIImageWriteToSavedPhotosAlbum（）不保存裁剪的图像 [英] UIImageWriteToSavedPhotosAlbum() doesn't save cropped image

问题描述

我正在尝试将裁剪的图像保存到相机胶卷。

（我需要以编程方式进行，我无法让用户编辑它）

I'm trying to save a cropped image to the camera roll.
(I need to do it programmatically, I can't have the user edit it)

这是我的（仍然非常基本的）剪切和保存代码：

This is my (still quite basic) cut and save code:

- (void)cutAndSaveImage:(UIImage*)rawImage
{
    CIImage *workingImage = [[CIImage alloc] initWithImage:rawImage];

    CGRect croppingRect = CGRectMake(0.0f, 0.0f, 3264.0f, 1224.0f);
    CIImage *croppedImage = [workingImage imageByCroppingToRect:croppingRect];

    UIImage *endImage = [UIImage imageWithCIImage:croppedImage scale: 1.0f orientation:UIImageOrientationRight];

    self.testImage.image = endImage;

    UIImageWriteToSavedPhotosAlbum(rawImage, self, @selector(image:didFinishSavingWithError:contextInfo:) , nil);
    UIImageWriteToSavedPhotosAlbum(endImage, self, @selector(image:didFinishSavingWithError:contextInfo:) , nil);
}

该方法在以下范围内调用：

- （void）imagePickerController：（UIImagePickerController *）picker didFinishPickingMediaWithInfo：（NSDictionary *）info

The method is called within:
- (void)imagePickerController:(UIImagePickerController*)picker didFinishPickingMediaWithInfo:(NSDictionary*)info

• 我首先使用原始 UIImage 创建 CIImage 。


• 然后我使用第一个实例方法获得裁剪 CIImage 。


• 之后我使用裁剪的CIImage创建一个新的 UIImage 。

• I first create a CIImage using the raw UIImage.
• Then I get a cropped CIImage using an instance method of the first one.
• After that I create a new UIImage using the cropped CIImage.

此时，为了获得一些反馈，我设置了新裁剪的 UIImage 作为 UIImageView 的支持图像。这是有效的，我可以清楚地看到图像完全按照我想要的方式裁剪。

At this point, to have some feedback, I set the new cropped UIImage as the backing image of a UIImageView. This works, and I can clearly see the image cropped exactly how I desired.

然而，当我尝试将其保存到相机胶卷时，事情就会停止工作。

我无法保存新创建的 endImage 。

如你所见，我添加了一行来保存原来的 UIImage ，仅供参考比较。原始版本正常保存。

When I try to save it to the camera roll, however, things stop working.
I can't save the newly created endImage.
As you can see, I added a line to save the original UIImage too, just for comparison. The original one saves normally.

另一个令人困惑的事情是 NSError 对象传递给 image：didFinishSavingWithError：contextInfo：回调为零。 （通常会对两次保存尝试执行回调）

Another confusing thing is that the NSError object passed to the image:didFinishSavingWithError:contextInfo: callback is nil. (the callback is normally executed for both saving attempts)

编辑：
刚做了一个实验：

Just made an experiment:

NSLog(@"rawImage: %@    -   rawImage.CGImage: %@", rawImage, rawImage.CGImage);
NSLog(@"endImage: %@    -   endImage.CGImage: %@", endImage, endImage.CGImage);

看起来只有 rawImage （即将推出）来自 UIImagePickerController ）拥有支持 CGImageRef 。另一个是从 CIImage 创建的，但却没有。

It looks like only the rawImage (coming from the UIImagePickerController) possesses a backing CGImageRef. The other one, created from a CIImage, doesn't.

是否可以 UIImageWriteToSavedPhotosAlbum 使用支持 CGImageRef ？

推荐答案

UIImageWriteToSavedPhotosAlbum可以使用支持CGImageRef工作吗？

Can it be that UIImageWriteToSavedPhotosAlbum works using the backing CGImageRef?

正确。 CIImage不是图像，只有CIImage支持的UIImage也不是图像;它只是一种包装。你为什么一直在使用CIImage？您没有使用CIFilter，所以这没有任何意义。或者，如果 使用CIFilter，则必须通过CIContext渲染才能将输出作为位图。

Correct. A CIImage is not an image, and a UIImage backed only by a CIImage is not an image either; it is just a kind of wrapper. Why are you using CIImage at all here? You aren't using CIFilter so this makes no sense. Or if you are using CIFilter, you must render through a CIContext to get the output as a bitmap.

您可以通过绘图轻松裁剪较小的图形上下文。

You can crop easily by drawing into a smaller graphics context.

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