iOS：等比压缩截图代码

将一幅图片按着需要的尺寸进行等比的压缩和放大，最后再截取需要尺寸部分，不知道说清楚没，反正就那意思吧！

+(UIImage *)compressImageWith:(UIImage *)image (float)width height:(float)height
{
    float imageWidth = image.size.width;
    float imageHeight = image.size.height;
    
    float widthScale = imageWidth /width;
    float heightScale = imageHeight /height;
    
    // 创建一个bitmap的context
    // 并把它设置成为当前正在使用的context
    UIGraphicsBeginImageContext(CGSizeMake(width, height));
    
    if (widthScale > heightScale) {
        [image drawInRect:CGRectMake(0, 0, imageWidth /heightScale , height)];    
    }
    else {
        [image drawInRect:CGRectMake(0, 0, width , imageHeight /widthScale)];
    }
    
    // 从当前context中创建一个改变大小后的图片
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    [newImage retain];
    // 使当前的context出堆栈
    UIGraphicsEndImageContext();
    
    return newImage;
    
}