学步园

- (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;  
}


//此算法中先找出image宽和高中缩放程度较小者作为整个图片的缩放比例，
//这样必然有一因素（宽或者高）缩放的程度不够，使其超过期望值，我们再
//将图片放入drawInRect函数的rect的中央，最后将超过的那一因素裁剪得到
//缩放后的图片，在使用此函数时应该检查返回值是否为nil
- (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();
        
    UIGraphicsEndImageContext();
    
    return newImage;  
}

转自：http://blog.csdn.net/zaitianaoxiang/article/details/6752538