保存UIImage的縮略圖可使圖像橫向/上下翻轉

Question

我正在保存UIImage的縮略圖，以提高UICollectionView滾動的性能。 所有圖像都直立保存，直到我嘗試保存從下往上拍攝的全景照片（例如：高度-3000，寬度-1000）。 這樣可以節省下來。 我拍攝人像照片並旋轉90，因為原來圖像是橫向的。 有沒有一種方法可以用一行代碼設置每種類型的圖像，還是我必須捕捉每種類型的照片並相應地進行調整？ 如果是這樣怎么辦？

 - (void) createThumbnail: (UIImage *) image{
     CGSize size = image.size;
     CGFloat imageHeight = size.height;
     CGFloat imageWidth = size.width;

     CGSize croppedSize;
     CGFloat ratio = 200.0;
     CGFloat offsetX = 0.0;
     CGFloat offsetY = 0.0;

     if (imageWidth > imageHeight) {
         offsetX = (imageHeight - imageWidth) / 2;
         croppedSize = CGSizeMake(imageHeight, imageHeight);
     } else {
         offsetY = (imageWidth - imageHeight) / 2;
         croppedSize = CGSizeMake(imageWidth, imageWidth);
     }


     CGRect clippedRect = CGRectMake(offsetX * -1, offsetY * -1, croppedSize.width, croppedSize.height);
     CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], clippedRect);

     CGRect rect = CGRectMake(0.0, 0.0, ratio, ratio);

     UIGraphicsBeginImageContext(rect.size);
     [[UIImage imageWithCGImage:imageRef] drawInRect:rect];
     UIImage *thumbnail;



     if ((imageWidth > imageHeight) || (imageWidth == imageHeight)) {
         thumbnail = [[UIImage alloc]initWithCGImage:UIGraphicsGetImageFromCurrentImageContext().CGImage scale:1.0 orientation:UIImageOrientationUp];
     }else{
         thumbnail = [[UIImage alloc]initWithCGImage:UIGraphicsGetImageFromCurrentImageContext().CGImage scale:1.0 orientation:UIImageOrientationRight];
}

     UIGraphicsEndImageContext();
     return thumbnail;

Answer 1

我必須從didFinishPickingMediaWithInfo選擇的圖像而不是裁剪的縮略圖中獲取圖像方向。

 - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
     choosenImage = info[UIImagePickerControllerOriginalImage];
     long orientation = choosenImage.imageOrientation;

     UIImage *thumbnail = [self createThumbnail:choosenImage withOrientation: orientation];
 }

---

 UIGraphicsBeginImageContext(rect.size);
[[UIImage imageWithCGImage:imageRef] drawInRect:rect];
UIImage *thumbnail;

if (orientation == UIImageOrientationUp) {
    thumbnail = UIGraphicsGetImageFromCurrentImageContext();
}else if (orientation == UIImageOrientationRight){
    thumbnail = [[UIImage alloc]initWithCGImage:UIGraphicsGetImageFromCurrentImageContext().CGImage scale:1.0 orientation:UIImageOrientationRight];
}else if (orientation == UIImageOrientationLeft){
    thumbnail = [[UIImage alloc]initWithCGImage:UIGraphicsGetImageFromCurrentImageContext().CGImage scale:1.0 orientation:UIImageOrientationLeft];
}else if (orientation == UIImageOrientationDown){
    thumbnail = [[UIImage alloc]initWithCGImage:UIGraphicsGetImageFromCurrentImageContext().CGImage scale:1.0 orientation:UIImageOrientationUpMirrored];
}

UIGraphicsEndImageContext();

Answer 2

來自照片應用程序的圖像解決方案 ： https : //developer.apple.com/library/ios/documentation/AssetsLibrary/Reference/ALAssetRepresentation_Class/

ALAssetRepresentation *defaultRepresentation = [asset defaultRepresentation];
UIImage *image = [UIImage imageWithCGImage:
                  [defaultRepresentation fullScreenImage]
                  scale:[defaultRepresentation scale]
                  orientation:0];