imageOrientation返回Up,但照片显示倒置

Question

我正在从iPad照片库中抓取一些照片.我在横向模式下拍了几张测试照片,左边是iPad主页按钮,右边是.

所以在我的应用程序中,由于某种原因,一些照片显示出颠倒.我检查了他们的imageOrientation财产,他们都是0(意思是他们UIImageOrientationUp).这意味着我甚至不知道我需要旋转哪些照片.

发生了什么,我怎么知道哪些照片需要旋转？谢谢

Answer 1

UIImage 有一个属性 imageOrientation，它指示 UIImageView 和其他 UIImage 使用者旋转原始图像数据。该标志很有可能被保存到上传的 jpeg 图像中的 exif 数据中，但您用来查看它的程序不支持该标志。

要旋转 UIImage 以在上传时正确显示，您可以使用如下类别： 在 .h 文件中

UIImagefixOrientation.h

@interface UIImage (fixOrientation)

- (UIImage *)fixOrientation;

@end

UIImagefixOrientation.m

@implementation UIImage (fixOrientation)

- (UIImage *)fixOrientation {

    // No-op if the orientation is already correct
    if (self.imageOrientation == UIImageOrientationUp) return self;

   // We need to calculate the proper transformation to make the image upright.
   // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.
  CGAffineTransform transform = CGAffineTransformIdentity;

  switch (self.imageOrientation) {
      case UIImageOrientationDown:
      case UIImageOrientationDownMirrored:
        transform = CGAffineTransformTranslate(transform, self.size.width, self.size.height);
         transform = CGAffineTransformRotate(transform, M_PI);
          break;

    case UIImageOrientationLeft:
    case UIImageOrientationLeftMirrored:
        transform = CGAffineTransformTranslate(transform, self.size.width, 0);
        transform = CGAffineTransformRotate(transform, M_PI_2);
        break;

    case UIImageOrientationRight:
    case UIImageOrientationRightMirrored:
        transform = CGAffineTransformTranslate(transform, 0, self.size.height);
        transform = CGAffineTransformRotate(transform, -M_PI_2);
        break;
}

switch (self.imageOrientation) {
    case UIImageOrientationUpMirrored:
    case UIImageOrientationDownMirrored:
        transform = CGAffineTransformTranslate(transform, self.size.width, 0);
        transform = CGAffineTransformScale(transform, -1, 1);
        break;

    case UIImageOrientationLeftMirrored:
    case UIImageOrientationRightMirrored:
        transform = CGAffineTransformTranslate(transform, self.size.height, 0);
        transform = CGAffineTransformScale(transform, -1, 1);
        break;
}

// Now we draw the underlying CGImage into a new context, applying the transform
// calculated above.
CGContextRef ctx = CGBitmapContextCreate(NULL, self.size.width, self.size.height,
                                         CGImageGetBitsPerComponent(self.CGImage), 0,
                                         CGImageGetColorSpace(self.CGImage),
                                         CGImageGetBitmapInfo(self.CGImage));
CGContextConcatCTM(ctx, transform);
switch (self.imageOrientation) {
    case UIImageOrientationLeft:
    case UIImageOrientationLeftMirrored:
    case UIImageOrientationRight:
    case UIImageOrientationRightMirrored:
        // Grr...
        CGContextDrawImage(ctx, CGRectMake(0,0,self.size.height,self.size.width), self.CGImage);
        break;

    default:
        CGContextDrawImage(ctx, CGRectMake(0,0,self.size.width,self.size.height), self.CGImage);
        break;
}

// And now we just create a new UIImage from the drawing context
CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
UIImage *img = [UIImage imageWithCGImage:cgimg];
CGContextRelease(ctx);
CGImageRelease(cgimg);
return img;
}

@end

并在捕获图像保存或从图库中选择图像时调用此函数。