iphone 压缩图片到指定的大小

1.本文摘自：http://www.cocoachina.com/bbs/read.php?tid-20940.html

 

1. #import <Foundation/Foundation.h>
4. @interface UIImage (UIImageExt)
6. - (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize;
8. @end

复制代码

2. #import "UIImageExt.h"
5. @implementation UIImage (UIImageExt)
7. - (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize
8. {
9.     UIImage *sourceImage = self;
10.     UIImage *newImage = nil;      
11.     CGSize imageSize = sourceImage.size;
12.     CGFloat width = imageSize.width;
13.     CGFloat height = imageSize.height;
14.     CGFloat targetWidth = targetSize.width;
15.     CGFloat targetHeight = targetSize.height;
16.     CGFloat scaleFactor = 0.0;
17.     CGFloat scaledWidth = targetWidth;
18.     CGFloat scaledHeight = targetHeight;
19.     CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
20.     
21.     if (CGSizeEqualToSize(imageSize, targetSize) == NO)
22.     {
23.         CGFloat widthFactor = targetWidth / width;
24.         CGFloat heightFactor = targetHeight / height;
25.         
26.         if (widthFactor > heightFactor)
27.             scaleFactor = widthFactor; // scale to fit height
28.         else
29.             scaleFactor = heightFactor; // scale to fit width
30.         scaledWidth  = width * scaleFactor;
31.         scaledHeight = height * scaleFactor;
32.         
33.         // center the image
34.         if (widthFactor > heightFactor)
35.         {
36.             thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
37.         }
38.         else
39.             if (widthFactor < heightFactor)
40.             {
41.                 thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
42.             }
43.     }      
44.     
45.     UIGraphicsBeginImageContext(targetSize); // this will crop
46.     
47.     CGRect thumbnailRect = CGRectZero;
48.     thumbnailRect.origin = thumbnailPoint;
49.     thumbnailRect.size.width  = scaledWidth;
50.     thumbnailRect.size.height = scaledHeight;
51.     
52.     [sourceImage drawInRect:thumbnailRect];
53.     
54.     newImage = UIGraphicsGetImageFromCurrentImageContext();
55.     if(newImage == nil)
56.         NSLog(@"could not scale image");
57.     
58.     //pop the context to get back to the default
59.     UIGraphicsEndImageContext();
60.     return newImage;
61. }
63. @end