用ALAssetsLibrary将过滤后图片写入照片库

CIImage *saveToSave = [filter outputImage];

CGImageRef cgImg = [context createCGImage:saveToSave fromRect:[saveToSave extent]];

ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];

[library writeImageToSavedPhotosAlbum:cgImg 
                             metadata:[saveToSave properties] 
                      completionBlock:^(NSURL *assetURL, NSError *error) {
                                       CGImageRelease(cgImg);
                              }];