PHPhotoKit

加载图片两种方式：

PHAsset *asset = self.phAsset;
    PHImageRequestOptions *option = [[PHImageRequestOptions alloc] init];
    option.synchronous = YES;
    option.resizeMode = PHImageRequestOptionsResizeModeFast;
    option.deliveryMode = PHImageRequestOptionsDeliveryModeFastFormat;

方式1
    [[PHImageManager defaultManager] requestImageDataForAsset:asset options:option resultHandler:^(NSData * _Nullable imageData, NSString * _Nullable dataUTI, UIImageOrientation orientation, NSDictionary * _Nullable info) {
        UIImage *image = [UIImage imageWithData:imageData];
        originImage = image;
        NSLog(@"imageSize: %@", NSStringFromCGSize(image.size));
    }];

方式2
// 从asset中获得图片
    CGSize size = CGSizeMake(asset.pixelWidth, asset.pixelHeight);
    [[PHImageManager defaultManager] requestImageForAsset:asset targetSize:[ImageAssetsModel maxImageSize:size] contentMode:PHImageContentModeAspectFill options:option resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
        //NSLog(@"asset_pixW :%zd, asset_pixH: %zd; imageSize: %@", asset.pixelWidth, asset.pixelHeight, NSStringFromCGSize(result.size));
        BOOL downloadFinined = (![[info objectForKey:PHImageCancelledKey] boolValue] && ![info objectForKey:PHImageErrorKey]);
        if (downloadFinined && result != nil) {
            // info 图片大小不同 里面的键也不同 有些会缺失
            // 调整图片方向
            ImageCropperController *imageCorpper = [[ImageCropperController alloc] init];
            result = [imageCorpper fixOrientation:result];
            originImage = result;
            //下面两个中任一个都可以标示相册中图片的唯一性
            originImage.localIdentifier = asset.localIdentifier;
            originImage.phImageFileURLKey = info[@"PHImageFileURLKey"];
        }
    }];

当同时加载多张原图（大图）的时候，方式2如果target设置成原图大小，那么加载过程会很慢，并且内存瞬间暴涨。但使用方式1则会解决这个问题，速度很快，并且内存不会很大。