- (UIImage *)scaleToSize:(UIImage *)img size:(CGSize)size{          // 创建一个bitmap的context          // 并把它设置成为当前正在使用的context        UIGraphicsBeginImageContext(size);          // 绘制改变大小的图片          [img drawInRect:CGRectMake(0,0, size.width, size.height)];          // 从当前context中创建一个改变大小后的图片          UIImage* scaledImage =UIGraphicsGetImageFromCurrentImageContext();          // 使当前的context出堆栈        UIGraphicsEndImageContext();          //返回新的改变大小后的图片          return scaledImage;      }

等比例压缩  -(UIImage *) imageCompressForSize:(UIImage *)sourceImage targetSize:(CGSize)size{      UIImage *newImage = nil;      CGSize imageSize = sourceImage.size;      CGFloat width = imageSize.width;      CGFloat height = imageSize.height;      CGFloat targetWidth = size.width;      CGFloat targetHeight = size.height;      CGFloat scaleFactor = 0.0;      CGFloat scaledWidth = targetWidth;      CGFloat scaledHeight = targetHeight;      CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);          if(CGSizeEqualToSize(imageSize, size) == NO){          CGFloat widthFactor = targetWidth / width;          CGFloat heightFactor = targetHeight / height;                  if(widthFactor > heightFactor){              scaleFactor = widthFactor;          }        else{              scaleFactor = heightFactor;          }          scaledWidth = width * scaleFactor;          scaledHeight = height * scaleFactor;                  if(widthFactor > heightFactor){              thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;          }else if(widthFactor < heightFactor){              thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;          }      }         UIGraphicsBeginImageContext(size);         CGRect thumbnailRect = CGRectZero;      thumbnailRect.origin = thumbnailPoint;      thumbnailRect.size.width = scaledWidth;      thumbnailRect.size.height = scaledHeight;      [sourceImage drawInRect:thumbnailRect];      newImage = UIGraphicsGetImageFromCurrentImageContext();          if(newImage == nil){          NSLog(@"scale image fail");      }         UIGraphicsEndImageContext();          return newImage;         }  -(UIImage *) imageCompressForWidth:(UIImage *)sourceImage targetWidth:(CGFloat)defineWidth{      UIImage *newImage = nil;      CGSize imageSize = sourceImage.size;      CGFloat width = imageSize.width;      CGFloat height = imageSize.height;      CGFloat targetWidth = defineWidth;      CGFloat targetHeight = height / (width / targetWidth);      CGSize size = CGSizeMake(targetWidth, targetHeight);      CGFloat scaleFactor = 0.0;      CGFloat scaledWidth = targetWidth;      CGFloat scaledHeight = targetHeight;      CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);          if(CGSizeEqualToSize(imageSize, size) == NO){          CGFloat widthFactor = targetWidth / width;          CGFloat heightFactor = targetHeight / height;                  if(widthFactor > heightFactor){              scaleFactor = widthFactor;          }        else{              scaleFactor = heightFactor;          }          scaledWidth = width * scaleFactor;          scaledHeight = height * scaleFactor;                  if(widthFactor > heightFactor){              thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;          }else if(widthFactor < heightFactor){              thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;          }      }      UIGraphicsBeginImageContext(size);      CGRect thumbnailRect = CGRectZero;      thumbnailRect.origin = thumbnailPoint;      thumbnailRect.size.width = scaledWidth;      thumbnailRect.size.height = scaledHeight;         [sourceImage drawInRect:thumbnailRect];         newImage = UIGraphicsGetImageFromCurrentImageContext();          if(newImage == nil){          NSLog(@"scale image fail");      }         UIGraphicsEndImageContext();          return newImage;  }

 //指定缩放比例压缩    NSData *thumbImageData = UIImageJPEGRepresentation([UIImage imageWithData:logoData], 0.5);