iOS 图片压缩处理,本地存储

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

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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！

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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->preference
NSUserDefaults *users = [NSUserDefaults standardUserDefaults];
            [users setBool:YES forKey:@"login"];
            [users setValue:value forKey:@"userID"];
            NSLog(@"%@",NSHomeDirectory());
            [users synchronize];

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