iOS 图片压缩处理,本地存储

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iOS 图片压缩处理,本地存储

图片压缩处理
图片本地存储
图片上传服务器

1.图片压缩处理

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：

//压缩图片质量  +(UIImage *)reduceImage:(UIImage *)image percent:(float)percent  {      NSData *imageData = UIImageJPEGRepresentation(image, percent);      UIImage *newImage = [UIImage imageWithData:imageData];      return newImage;  }  //压缩图片尺寸  + (UIImage*)imageWithImageSimple:(UIImage*)image scaledToSize:(CGSize)newSize  {      // Create a graphics image context      UIGraphicsBeginImageContext(newSize);      // new size      [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];      // Get the new image from the context      UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();      // End the context      UIGraphicsEndImageContext();      // Return the new image.      return newImage;  }

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：

static size_t getAssetBytesCallback(voidvoid *info, voidvoid *buffer, off_t position, size_t count) {      ALAssetRepresentation *rep = (__bridge id)info;      NSError *error = nil;      size_t countRead = [rep getBytes:(uint8_t *)buffer fromOffset:position length:count error:&error];      if (countRead == 0 && error) {          // We have no way of passing this info back to the caller, so we log it, at least.          NDDebug(@"thumbnailForAsset:maxPixelSize: got an error reading an asset: %@", error);      }      return countRead;  }  static void releaseAssetCallback(voidvoid *info) {      // The info here is an ALAssetRepresentation which we CFRetain in thumbnailForAsset:maxPixelSize:.      // This release balances that retain.      CFRelease(info);  }  // Returns a UIImage for the given asset, with size length at most the passed size.  // The resulting UIImage will be already rotated to UIImageOrientationUp, so its CGImageRef  // can be used directly without additional rotation handling.  // This is done synchronously, so you should call this method on a background queue/thread.  - (UIImage *)thumbnailForAsset:(ALAsset *)asset maxPixelSize:(NSUInteger)size {      NSParameterAssert(asset != nil);      NSParameterAssert(size > 0);      ALAssetRepresentation *rep = [asset defaultRepresentation];      CGDataProviderDirectCallbacks callbacks = {          .version = 0,          .getBytePointer = NULL,          .releaseBytePointer = NULL,          .getBytesAtPosition = getAssetBytesCallback,          .releaseInfo = releaseAssetCallback,      };      CGDataProviderRef provider = CGDataProviderCreateDirect((voidvoid *)CFBridgingRetain(rep), [rep size], &callbacks);      CGImageSourceRef source = CGImageSourceCreateWithDataProvider(provider, NULL);      CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(source, 0, (__bridge CFDictionaryRef) @{                                                                                                        (NSString *)kCGImageSourceCreateThumbnailFromImageAlways : @YES,                                                                                                        (NSString *)kCGImageSourceThumbnailMaxPixelSize : [NSNumber numberWithInt:size],                                                                                                        (NSString *)kCGImageSourceCreateThumbnailWithTransform : @YES,                                                                                                        });      CFRelease(source);      CFRelease(provider);      if (!imageRef) {          return nil;      }      UIImage *toReturn = [UIImage imageWithCGImage:imageRef];      CFRelease(imageRef);      return toReturn;  }

采用上面的方法之后内存占用率很低！

2.图片本地存储

把图片缓存到本地，在很多场景都会用到，如果只是存储文件信息，那建一个plist文件，或者数据库就能很方便的解决问题，但是如果存储图片到沙盒就没那么方便了。这里简单介绍两种保存图片到沙盒的方法。
(1)把图片转为base64的字符串存到数据库中或者plist文件中，然后用到的时候再取出来

 //获取沙盒路径，   NSString *path_sandox = NSHomeDirectory();   //创建一个存储plist文件的路径   NSString *newPath = [path_sandox stringByAppendingPathComponent:@/Documents/pic.plist];   NSMutableArray *arr = [[NSMutableArray alloc] init];   UIImage *image = [UIImage imageNamed:@"1.png"];   /*   把图片转换为Base64的字符串     在iphone上有两种读取图片数据的简单方法: UIImageJPEGRepresentation和UIImagePNGRepresentation.    UIImageJPEGRepresentation函数需要两个参数:图片的引用和压缩系数.而UIImagePNGRepresentation只需要图片引用作为参数.通过在实际使用过程中,   比较发现: UIImagePNGRepresentation(UIImage* image) 要比UIImageJPEGRepresentation(UIImage* image, 1.0) 返回的图片数据量大很多.   譬如,同样是读取摄像头拍摄的同样景色的照片, UIImagePNGRepresentation()返回的数据量大小为199K ,   而 UIImageJPEGRepresentation(UIImage* image, 1.0)返回的数据量大小只为140KB,比前者少了50多KB.   如果对图片的清晰度要求不高,还可以通过设置 UIImageJPEGRepresentation函数的第二个参数,大幅度降低图片数据量.譬如,刚才拍摄的图片,    通过调用UIImageJPEGRepresentation(UIImage* image, 1.0)读取数据时,返回的数据大小为140KB,但更改压缩系数后,   通过调用UIImageJPEGRepresentation(UIImage* image, 0.5)读取数据时,返回的数据大小只有11KB多,大大压缩了图片的数据量 ,   而且从视角角度看,图片的质量并没有明显的降低.因此,在读取图片数据内容时,建议优先使用UIImageJPEGRepresentation,   并可根据自己的实际使用场景,设置压缩系数,进一步降低图片数据量大小.   */   NSData *_data = UIImageJPEGRepresentation(image, 1.0f);   //将图片的data转化为字符串   NSString *strimage64 = [_data base64EncodedString];   [arr addObject:image64];        //写入plist文件       if ([arr writeToFile:newPath atomically:YES]) {          NSLog(@"写入成功");      };   //可以到沙河路径下查看plist文件中的图片数据    //这样就存起来的，然后用到的时候再利用存储的字符串转化为图片   //NSData *_decodedImageData = [[NSData alloc] initWithBase64Encoding:image64];  这是iOS7之前的一个方法    NSData *_decodedImageData = [[NSData alloc]initWithBase64EncodedString:strimage64 options:NSDataBase64DecodingIgnoreUnknownCharacters];   UIImage *_decodedImage = [UIImage imageWithData:_decodedImageData];   //可以打印下图片是否存在   NSLog(@"===Decoded image size: %@", NSStringFromCGSize(_decodedImage.size));  // 查看沙盒路径 NSLog(@"imgPath = %@", NSHomeDirectory());

(2)把图片直接保存到沙盒中，然后再把路径存储起来，等到用图片的时候先获取图片的路径，再通过路径拿到图片

//拿到图片  UIImage *image2 = [UIImage imageNamed:@"1.png"];   NSString *path_document = NSHomeDirectory();  //设置一个图片的存储路径  NSString *imagePath = [path_document stringByAppendingString:@"/Documents/pic.png"];  //把图片直接保存到指定的路径（同时应该把图片的路径imagePath存起来，下次就可以直接用来取）  [UIImagePNGRepresentation(image2) writeToFile:imagePath atomically:YES]; // 下次利用图片的地址直接来拿图片。UIImage *getimage2 = [UIImage imageWithContentsOfFile:imagePath];  NSLog(@"image2 is size %@",NSStringFromCGSize(getimage2.size));

常用沙盒路径

//Home目录NSString *homeDirectory = NSHomeDirectory();  //Document目录NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);    NSString *path = [paths objectAtIndex:0];  //Cache目录NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);    NSString *path = [paths objectAtIndex:0];  //Libaray目录NSArray *paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES);   NSString *path = [paths objectAtIndex:0];  // NSUserDefaults 路径在 Library->preferenceNSUserDefaults *users = [NSUserDefaults standardUserDefaults];            [users setBool:YES forKey:@"login"];            [users setValue:value forKey:@"userID"];            NSLog(@"%@",NSHomeDirectory());            [users synchronize];

参考博客:
1.http://blog.csdn.net/u012716788/article/details/49564027
2.http://blog.csdn.net/apple_app/article/details/38847357

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