UIImage的扩展方法——裁剪图片和等比列缩放图片

来源：互联网发布：巴黎高等师范学院知乎编辑：程序博客网时间：2024/05/21 11:02

[原文转自：http://xbiii3s.iteye.com/blog/1188008]

首先创建一个UIImage类别，如下：

@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