旋转CGImage [英] Rotating a CGImage

问题描述

我有一个UIImage，我是从UIImagePickerController获取的。当我从 - （void）imagePickerController接收图像时：（UIImagePickerController *）选择器didFinishPickingMediaWithInfo：（NSDictionary *）info 方法我把它直接放到UIImageView中进行预览并给出用户可选择保存或放弃图像。

I have a UIImage that I'm getting from a UIImagePickerController. When I receive the image from the - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info method I put it straight into a UIImageView for preview and give the user the option to either save or discard the image.

当用户选择保存选项时，应用程序将获取图像的png数据并将其保存到文档目录中。但是在2种可能的设备方向之一（仅景观）下发生的事情是图像被颠倒保存（更具体地说，从它应该的位置旋转180度）。因此，当我在图库中加载图片时，它会显示为颠倒。

When the user selects the save option the application get the png data for the image and saves it to it's documents directory. But what happens under one of the 2 possible device orientations (landscape only) is that the image is saved upside down (more specifically, rotated 180 degrees from what it should be). So when I load the image in the gallery it appears upside down.

（请参阅图库中的左下角图片）

(See the bottom left image in the gallery)

我已经解决了UIImage来自UIImage的UIImage中的原始图像数据没有旋转，而是将方向存储为对象的属性，仅在显示时应用。所以我试图使用我在网上找到的一些代码来旋转与UIImage相关联的CGImage。但它似乎对图像完全没有影响。我正在使用的代码如下：

I have worked this out to be that the raw image data in the UIImage from the UIImagePickerController is not rotated, rather, the orientation is stored as a property on the object and only applied when displaying. So I'm trying to rotate the CGImage associated with the UIImage using some code I found online. But it appears to have absolutely no affect on the image. The code I'm using follows:

- (void)rotateImage:(UIImage*)image byRadians:(CGFloat)rads
{   
    // calculate the size of the rotated view's containing box for our drawing space 
    UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,image.size.width, image.size.height)];
    CGAffineTransform t = CGAffineTransformMakeRotation(rads);
    rotatedViewBox.transform = t;
    CGSize rotatedSize = rotatedViewBox.frame.size;

    // Create the bitmap context
    UIGraphicsBeginImageContext(rotatedSize);
    CGContextRef bitmap = UIGraphicsGetCurrentContext();

    // Move the origin to the middle of the image you want to rotate and scale around the center. 
    CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2); 

    // Rotate the image context
    CGContextRotateCTM(bitmap, rads);

    // Now, draw the rotated/scaled image into the context
    CGContextScaleCTM(bitmap, 1.0, -1.0);
    CGContextDrawImage(bitmap, CGRectMake(image.size.width / 2, image.size.height / 2, image.size.width, image.size.height), [image CGImage]);

    image = UIGraphicsGetImageFromCurrentImageContext();
    image = [UIImage imageWithCGImage:image.CGImage scale:1.0 orientation:UIImageOrientationDown];
    UIGraphicsEndImageContext();
}

我想知道为什么这段代码无效，因为每件我在网上找到这个图像旋转的代码看起来不起作用。

I would like to know why this code isn't working, since every piece of code I find online to do this image rotation appears to not work.

推荐答案

-(UIImage*) rotate:(UIImage*) src andOrientation:(UIImageOrientation)orientation
{
    UIGraphicsBeginImageContext(src.size);

    CGContextRef context=(UIGraphicsGetCurrentContext());

    if (orientation == UIImageOrientationRight) {
        CGContextRotateCTM (context, 90/180*M_PI) ;
    } else if (orientation == UIImageOrientationLeft) {
        CGContextRotateCTM (context, -90/180*M_PI);
    } else if (orientation == UIImageOrientationDown) {
        // NOTHING
    } else if (orientation == UIImageOrientationUp) {
        CGContextRotateCTM (context, 90/180*M_PI);
    }

    [src drawAtPoint:CGPointMake(0, 0)];
    UIImage *img=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;

}

使用这个..它完美无缺！从UIImagePicker中选择图像时，请确保使用此功能：

use this one .. it works perfect ! Just make sure you use this function when you are picking images from UIImagePicker:

示例：

UIImage *image;
image = [self rotate:image andOrientation:image.imageOrientation];

确保在从文档目录中选择照片的位置使用此功能。

Make sure to use this function in place where you pick photos from documents directory.

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