压缩成指定大小代码##

- (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;
}