IOS 图片压缩

淩亂°似流年 2022-08-07 16:38 233阅读 0赞

原文：[http://blog.csdn.net/apple\_app/article/details/38847357][http_blog.csdn.net_apple_app_article_details_38847357]

最近做论坛功能，发帖的时候需要用到从相册中选取图片然后上传，由于每次上传图片的最大数量为9张，所以需要对图片进行压缩。开始时用了以前经常用的压缩的方法：

**\[objc\]** [view plain][] [copy][view plain]

1.  //压缩图片质量
2.  \+(**UIImage** \*)reduceImage:(**UIImage** \*)image percent:(**float**)percent 
3.  \{ 
4.  **NSData** \*imageData = UIImageJPEGRepresentation(image, percent); 
5.  **UIImage** \*newImage = \[UIImage imageWithData:imageData\]; 
6.  **return** newImage; 
7.  \} 
8.  //压缩图片尺寸
9.  \+ (UIImage\*)imageWithImageSimple:(UIImage\*)image scaledToSize:(CGSize)newSize 
10. \{ 
11. // Create a graphics image context
12.  UIGraphicsBeginImageContext(newSize); 
13. // new size
14.  \[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)\]; 
15. // Get the new image from the context
16.  UIImage\* newImage = UIGraphicsGetImageFromCurrentImageContext(); 
17. 
18. // End the context
19.  UIGraphicsEndImageContext(); 
20. // Return the new image.
21. **return** newImage; 
22. \}

上面的方法比较常见，可是需要加载到内存中来处理图片，当图片数量多了的时候就会收到内存警告，程序崩溃。研究半天终于在一篇博客中找到了解决方法：

**\[objc\]** [view plain][] [copy][view plain]

1.  **static****size\_t** getAssetBytesCallback(**void****void** \*info, **void****void** \*buffer, off\_t position, **size\_t** count) \{ 
2.  **ALAssetRepresentation** \*rep = (\_\_bridge **id**)info; 
3.  
4.  **NSError** \*error = **nil**; 
5.  **size\_t** countRead = \[rep getBytes:(**uint8\_t** \*)buffer fromOffset:position length:count error:&error\]; 
6.  
7.  **if** (countRead == 0 && error) \{ 
8.  // We have no way of passing this info back to the caller, so we log it, at least.
9.   NDDebug(@"thumbnailForAsset:maxPixelSize: got an error reading an asset: %@", error); 
10.  \} 
11. 
12. **return** countRead; 
13. \} 
14. 
15. **static****void** releaseAssetCallback(**void****void** \*info) \{ 
16. // The info here is an ALAssetRepresentation which we CFRetain in thumbnailForAsset:maxPixelSize:.
17. // This release balances that retain.
18.  CFRelease(info); 
19. \} 
20. 
21. // Returns a UIImage for the given asset, with size length at most the passed size.
22. // The resulting UIImage will be already rotated to UIImageOrientationUp, so its CGImageRef
23. // can be used directly without additional rotation handling.
24. // This is done synchronously, so you should call this method on a background queue/thread.
25. \- (**UIImage** \*)thumbnailForAsset:(**ALAsset** \*)asset maxPixelSize:(NSUInteger)size \{ 
26.  NSParameterAssert(asset != **nil**); 
27.  NSParameterAssert(size > 0); 
28. 
29. **ALAssetRepresentation** \*rep = \[asset defaultRepresentation\]; 
30. 
31.  CGDataProviderDirectCallbacks callbacks = \{ 
32. .version = 0, 
33. .getBytePointer = **NULL**, 
34. .releaseBytePointer = **NULL**, 
35. .getBytesAtPosition = getAssetBytesCallback, 
36. .releaseInfo = releaseAssetCallback, 
37.  \}; 
38. 
39.  CGDataProviderRef provider = CGDataProviderCreateDirect((**void****void** \*)CFBridgingRetain(rep), \[rep size\], &callbacks); 
40.  CGImageSourceRef source = CGImageSourceCreateWithDataProvider(provider, **NULL**); 
41. 
42.  CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(source, 0, (\_\_bridge CFDictionaryRef) @\{ 
43.  (**NSString** \*)kCGImageSourceCreateThumbnailFromImageAlways : **@YES**, 
44.  (**NSString** \*)kCGImageSourceThumbnailMaxPixelSize : \[NSNumber numberWithInt:size\], 
45.  (**NSString** \*)kCGImageSourceCreateThumbnailWithTransform : **@YES**, 
46.  \}); 
47.  CFRelease(source); 
48.  CFRelease(provider); 
49. 
50. **if** (!imageRef) \{ 
51. **return** **nil**; 
52.  \} 
53. 
54. **UIImage** \*toReturn = \[UIImage imageWithCGImage:imageRef\]; 
55. 
56.  CFRelease(imageRef); 
57. 
58. **return** toReturn; 
59. \}

采用上面的方法之后内存占用率很低！

原文地址：[http://www.mindsea.com/2012/12/downscaling-huge-alassets-without-fear-of-sigkill/][http_www.mindsea.com_2012_12_downscaling-huge-alassets-without-fear-of-sigkill]

[http_blog.csdn.net_apple_app_article_details_38847357]: http://blog.csdn.net/apple_app/article/details/38847357
[view plain]: http://blog.csdn.net/apple_app/article/details/38847357#
[http_www.mindsea.com_2012_12_downscaling-huge-alassets-without-fear-of-sigkill]: http://www.mindsea.com/2012/12/downscaling-huge-alassets-without-fear-of-sigkill/