iOS 图片压缩

    //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：[objc] view plaincopy    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;      }