在不重新压缩的情况下保存到用户库中/从中获取JPEG [英] Saving to/getting JPEG from user gallery without recompression

问题描述

我试图找到一种方法来读取和写入JPEG图像到用户图库（相机胶卷），而无需重新压缩iOS。
UIImage似乎是这里的瓶颈。我发现保存到用户库的唯一方法是UIImageWriteToSavedPhotosAlbum（）。有没有办法解决这个问题？

I am trying to find a way to read and write JPEG images to user gallery (camera roll) without iOS re-compressing them. UIImage seems to be the bottleneck here. The only method for saving to user gallery I've found is UIImageWriteToSavedPhotosAlbum(). Is there a way around this?

现在我的例程看起来像这样

For now my routine looks like this

-Ask UIImagePickerController的照片。当它确实完成了PickinPickingMediaWithInfo时，执行：

–Ask UIImagePickerController for a photo. And when it didFinishPickingMediaWithInfo, do:

NSData *imgdata = [NSData dataWithData:UIImageJPEGRepresentation([info objectForKey:@"UIImagePickerControllerOriginalImage"], 1)];
[imgdata writeToFile:filePath atomically:NO];

- 在磁盘上无损处理JPEG格式。

–Process JPEG losslessly on disk.

- 然后保存回来：

–Then save it back:

UIImageWriteToSavedPhotosAlbum([UIImage imageWithContentsOfFile:[self getImagePath]], self, @selector(image:didFinishSavingWithError:contextInfo:), nil);

以下是3次传球后质量下降情况的微小动画：

Here is a tiny animation of what quality degradation looks like after 3 passes:

每次我这样做都会变得更糟，但我无法自动化图像拾取部分，以便在50/100/1000周期内对其进行全面测试。

It obviously gets worse each time I do this, but I couldn't automate the image picking part in order to fully test it for 50/100/1000 cycles.

推荐答案

UIImage 解码图像数据，以便对其进行编辑和显示，所以

UIImage decodes the image data so it can be edited and displayed, so

UIImageWriteToSavedPhotosAlbum([UIImage imageWithContentsOfFile:[NSData dataWithContentsOfFile:[self getImagePath]]], self, @selector(image:didFinishSavingWithError:contextInfo:), nil);

首先解码图像，然后通过 UIImageWriteToSavedPhotosAlbum 方法。

would first decode the image, and than encode it back by the UIImageWriteToSavedPhotosAlbum method.

相反，你应该使用 ALAssetsLibrary / writeImageDataToSavedPhotosAlbum：metadata：completionBlock：，类似这样：

Instead, you should use ALAssetsLibrary/writeImageDataToSavedPhotosAlbum:metadata:completionBlock:, something like this:

ALAssetsLibrary *assetLib = [[[ALAssetsLibrary alloc] init] autorelease];
[assetLib writeImageDataToSavedPhotosAlbum:[self getImagePath] metadata:nil completionBlock:nil];

您还可以将元数据和完成块传递给通话。

You may also pass metadata and the completion block to the call.

编辑：

获取图片：

[info objectForKey：@UIImagePickerControllerOriginalImage] 包含从 UIImagePickerController中选择的已解码 UIImage / code>。你应该使用

[info objectForKey:@"UIImagePickerControllerOriginalImage"] contains the decoded UIImage selected from UIImagePickerController. You should instead use

NSURL *assetURL = [info objectForKey:UIImagePickerControllerReferenceURL];

使用 assetURL 您现在可以获得使用 ALAsset ＃// apple_ref / occ / instm / ALAssetsLibrary / assetForURL％3aresultBlock％3afailureBlock％3a> ALAssetsLibrary / assetForURL：resultBlock：failureBlock：方法：

Using the assetURL you can now get the ALAsset for it using the ALAssetsLibrary/assetForURL:resultBlock:failureBlock: method:

ALAssetsLibrary *assetLib = [[[ALAssetsLibrary alloc] init] autorelease];
[assetLib assetForURL:assetURL resultBlock:resultBlock failureBlock:failureBlock];

您现在可以获得该图像的未更改的NSData：

You can now get the unaltered NSData of that image:

ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *asset){
  ALAssetRepresentation *assetRep = [asset defaultRepresentation];
  long long imageDataSize = [assetRepresentation size];
  uint8_t* imageDataBytes = malloc(imageDataSize);
  [assetRepresentation getBytes:imageDataBytes fromOffset:0 length:imageDataSize error:nil];
  NSData *imageData = [NSData dataWithBytesNoCopy:imageDataBytes length:imageDataSize freeWhenDone:YES]; // you could for instance read data in smaller buffers and append them to your file instead of reading it all at once
  // save it
  [imgdata writeToFile:filePath atomically:NO];
};
ALAssetsLibraryAccessFailureBlock failureblock  = ^(NSError *myerror){
  NSLog(@"Cannot get image - %@",[myerror localizedDescription]);
  //
};

我可能在代码中犯了一些错误，但步骤如上所列。如果某些东西不能正常工作，或者你想让它更有效率，那么有很多例子可以从<$ c $中读取 NSData 。 c> stackoverflow或其他网站上的ALAsset 。

I may have made some mistakes in the code, but the steps are as listed above. In case of something not working right, or if you want to make this a little more efficient, there are plenty of examples of doing stuff like reading NSData from an ALAsset on stackoverflow or other sites.

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