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