- (UIImage*)scaleFromImage:(UIImage*)image scaledToSize:(CGSize)newSize {  CGSize imageSize = image.size;  CGFloat width = imageSize.width;  CGFloat height = imageSize.height;        if (width <= newSize.width && height <= newSize.height){   return image;  }        if (width == 0 || height == 0){   return image;  }        CGFloat widthFactor = newSize.width / width;  CGFloat heightFactor = newSize.height / height;  CGFloat scaleFactor = (widthFactor<heightFactor?widthFactor:heightFactor);        CGFloat scaledWidth = width * scaleFactor;  CGFloat scaledHeight = height * scaleFactor;  CGSize targetSize = CGSizeMake(scaledWidth,scaledHeight);           UIGraphicsBeginImageContext(targetSize);     [image drawInRect:CGRectMake(0,0,scaledWidth,scaledHeight)];     UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();     UIGraphicsEndImageContext();     return newImage; }

#import <Foundation/Foundation.h>  @interface UIImage (UIImageExt)  - (UIImage *)scaleToSize:(UIImage *)img size:(CGSize)size;  - (UIImage *)imageByScalingAndCroppingForSize:(CGSize)targetSize;  @end 

#import "UIImageExt.h"  @implementation UIImage (UIImageExt)  - (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;  }  - (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize  {      UIImage *sourceImage = self;      UIImage *newImage = nil;      CGSize imageSize = sourceImage.size;      CGFloat width = imageSize.width;      CGFloat height = imageSize.height;      CGFloat targetWidth = targetSize.width;      CGFloat targetHeight = targetSize.height;      CGFloat scaleFactor = 0.0;      CGFloat scaledWidth = targetWidth;      CGFloat scaledHeight = targetHeight;      CGPoint thumbnailPoint = CGPointMake(0.0,0.0);      if (CGSizeEqualToSize(imageSize, targetSize) == NO)      {          CGFloat widthFactor = targetWidth / width;          CGFloat heightFactor = targetHeight / height;          if (widthFactor > heightFactor)              scaleFactor = widthFactor; // scale to fit height          else              scaleFactor = heightFactor; // scale to fit width          scaledWidth  = width * scaleFactor;          scaledHeight = height * scaleFactor;          // center the image          if (widthFactor > heightFactor)          {              thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;          }          else              if (widthFactor < heightFactor)              {                  thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;              }      }      UIGraphicsBeginImageContext(targetSize); // this will crop      CGRect thumbnailRect = CGRectZero;      thumbnailRect.origin = thumbnailPoint;      thumbnailRect.size.width  = scaledWidth;      thumbnailRect.size.height = scaledHeight;      [sourceImage drawInRect:thumbnailRect];      newImage = UIGraphicsGetImageFromCurrentImageContext();      if(newImage == nil)          NSLog(@"could not scale image");      //pop the context to get back to the default      UIGraphicsEndImageContext();      return newImage;  }  @end 

-(UIImage *) imageCompressForWidth:(UIImage *)sourceImage targetWidth:(CGFloat)defineWidth {     CGSize imageSize = sourceImage.size;     CGFloat width = imageSize.width;     CGFloat height = imageSize.height;     CGFloat targetWidth = defineWidth;     CGFloat targetHeight = (targetWidth / width) * height;     UIGraphicsBeginImageContext(CGSizeMake(targetWidth, targetHeight));     [sourceImage drawInRect:CGRectMake(0,0,targetWidth,  targetHeight)];     UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();     UIGraphicsEndImageContext();     return newImage; }