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iOS 图片压缩

iOS 图片压缩

作者: LiwaySun | 来源:发表于2017-09-06 22:49 被阅读26次

    //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;
      }

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