如何從iOS中旋轉，縮放和倒置的UIImageView中提取UIImage

Question

我正在從圖庫中拍攝圖像，並使用CGAffineTransform應用縮放，旋轉和反轉轉換。 最后，我將圖像保存到圖庫。 但是，已保存的圖像具有白色矩形邊界！[具有白色背景的旋轉UIImageView] [1]。

- (UIImage *)getTheTransformedOriginalImage:(UIImage *)aTransImage
  {
    CGAffineTransform transform = selImageView.transform;
   CGPathRef rotatedImageRectPath = CGPathCreateWithRect(selImageView.frame, &transform);
    CGRect boundingBox = CGPathGetBoundingBox(rotatedImageRectPath);

   CGSize rotatedSize = boundingBox.size;

   UIGraphicsBeginImageContext(rotatedSize);
   UIGraphicsBeginImageContextWithOptions(rotatedSize, NO, 0.0f);

// Move the origin to the middle of the image so we will rotate and scale around the center.
  CGContextTranslateCTM(UIGraphicsGetCurrentContext(), rotatedSize.width/2,    rotatedSize.height/2);

//Rotate the image context using tranform
   CGContextConcatCTM(UIGraphicsGetCurrentContext(), selImageView.transform);
// Now, draw the rotated/scaled image into the context
   CGContextScaleCTM(UIGraphicsGetCurrentContext(), 1.0, -1.0);
   CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(-aTransImage.size.width / 2, -aTransImage.size.height / 2, aTransImage.size.width, aTransImage.size.height), [aTransImage CGImage]);

  UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return newImage;
}

- (IBAction)saveToGalleryClicked:(id)sender
  {
      UIImage *aTransImage = selImageView.image;
      UIImage *shareImage = [self getTheTransformedOriginalImage:aTransImage]
      UIImageWriteToSavedPhotosAlbum(shareImage, nil, nil, nil);
   }

我在附件中添加了旋轉的UIImage。

Answer 1

為了沒有白色背景（即不透明圖像），您需要使用其他函數來開始圖像上下文：

 UIGraphicsBeginImageContextWithOptions(CGSize size, **BOOL opaque**, CGFloat scale) 

因此，請替換：

 UIGraphicsBeginImageContext(rotatedSize);

帶有：

 UIGraphicsBeginImageContextWithOptions(rotatedSize, NO, [[UIScreen mainScreen]scale])

這樣可以確保上下文透明地繪制。