UIImage添加水印（Logo+文字）

写在前面

添加水印是经常遇到的需求了，也算是图像数字处理比较容易的一个环节，网上能搜出好几种解决方案，但作为新手的我还是折腾了好长时间。

简单介绍

没有什么逻辑，就是把你所需要用到的素材全都渲染到contex中，最后再作为一个整体取出来。

// 创建一个bitmap的contextUIGraphicsBeginImageContext();// 渲染背景图// 渲染素材logo+文字// 用的是同一个方法drawInRect：. . .// 取出UIImageUIImage *imageNew = UIGraphicsGetImageFromCurrentImageContext();//一些释放操作UIGraphicsEndImageContext();

应用

由于是UIImage的一些处理，这种需求最合适写进category里面

- (UIImage *)imageWater1:(UIImage *)imageLogo waterString:(NSString *)waterString{    NSUInteger inputWidth = self.size.width;    // 创建一个bitmap的context    UIGraphicsBeginImageContext(self.size);//    开始图片渲染    [self drawInRect:CGRectMake(0, 0, self.size.width, self.size.height)];//    logo渲染    CGFloat ghostImageAspectRatio = imageLogo.size.width / imageLogo.size.height;    NSInteger targetGhostWidth = inputWidth * 0.3;    [imageLogo drawInRect:CGRectMake(0, 0, targetGhostWidth, targetGhostWidth/ghostImageAspectRatio)];//    渲染文字    NSUInteger wordHigh = 120;    NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle defaultParagraphStyle] mutableCopy];    paragraphStyle.lineBreakMode = NSLineBreakByCharWrapping;    NSDictionary *dic = @{NSFontAttributeName:[UIFont systemFontOfSize:100], NSForegroundColorAttributeName:[UIColor whiteColor], NSParagraphStyleAttributeName:paragraphStyle};    [waterString drawInRect:CGRectMake(targetGhostWidth, 0, self.size.width*0.6, wordHigh) withAttributes:dic];    [@"RNO:0000023034001230" drawInRect:CGRectMake(targetGhostWidth, wordHigh*1, self.size.width*0.6, wordHigh) withAttributes:dic];    [@"GPS:27.34223132,4533.2313324" drawInRect:CGRectMake(targetGhostWidth, wordHigh*2, self.size.width*0.6, wordHigh) withAttributes:dic];    [@"地址:需要您的同意,才能访问相册" drawInRect:CGRectMake(targetGhostWidth, wordHigh*3, self.size.width*0.6, wordHigh) withAttributes:dic];//    UIImage    UIImage *imageNew = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();    return imageNew;}

这样写是OK的，刚开始在渲染logo是这样写的
[imageLogo drawInRect:CGRectMake(0, 0, imageLogo.size.width, imageLogo.size.height)];
渲染出来的 图片特小，因为是位图（bitmap）的关系吧，
要想用logo实际大小可以这样

CGImageRef logoCGImg = [imageLogo CGImage];CGFloat w = CGImageGetWidth(logoCGImg);CGFloat h = CGImageGetHeight(logoCGImg);[imageLogo drawInRect:CGRectMake(0, 0, w, h)];