[转] iPhone：UIImage 图像截取，等比例缩放

@interface UIImage(UIImageScale)
-(UIImage*)getSubImage:(CGRect)rect;
-(UIImage*)scaleToSize:(CGSize)size;
@end
 
@implementation UIImage(UIImageScale)
 
//截取部分图像
-(UIImage*)getSubImage:(CGRect)rect
{
    CGImageRef subImageRef = CGImageCreateWithImageInRect(self.CGImage, rect);
	CGRect smallBounds = CGRectMake(0, 0, CGImageGetWidth(subImageRef), CGImageGetHeight(subImageRef));
	
    UIGraphicsBeginImageContext(smallBounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, smallBounds, subImageRef);
    UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];
    UIGraphicsEndImageContext();
	
    return smallImage;
}
 
//等比例缩放
-(UIImage*)scaleToSize:(CGSize)size 
{
	CGFloat width = CGImageGetWidth(self.CGImage);
    CGFloat height = CGImageGetHeight(self.CGImage);
	
	float verticalRadio = size.height*1.0/height; 
	float horizontalRadio = size.width*1.0/width;
	
	float radio = 1;
	if(verticalRadio>1 && horizontalRadio>1)
	{
		radio = verticalRadio > horizontalRadio ? horizontalRadio : verticalRadio;	
	}
	else
	{
		radio = verticalRadio < horizontalRadio ? verticalRadio : horizontalRadio;	
	}
	
	width = width*radio;
	height = height*radio;
	
	int xPos = (size.width - width)/2;
	int yPos = (size.height-height)/2;
	
	// 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  
    [self drawInRect:CGRectMake(xPos, yPos, width, 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;
}
@end