图片水印（微博图片上面的个人签名）

- (void)viewDidLoad

{

[super viewDidLoad];

// 1.返回水印图片

UIImage *newImage = [UIImage waterImageWithBg:@"scene" logo:@"logo"];

// 2.显示图片

self.iconView.image = newImage;

}

- (void)testWater

{

UIImage *bgImage = [UIImage imageNamed:@"scene"];

// 上小文 : 基于位图(bitmap) ,  所有的东西需要绘制到一张新的图片上去

// 1.创建一个基于位图的上下文(开启一个基于位图的上下文)

// size : 新图片的尺寸

// opaque : YES : 不透明,  NO : 透明

// 这行代码过后.就相当于常见一张新的bitmap,也就是新的UIImage对象

UIGraphicsBeginImageContextWithOptions(bgImage.size, NO, 0.0);

// 2.画背景

[bgImage drawInRect:CGRectMake(0, 0, bgImage.size.width, bgImage.size.height)];

// 3.画右下角的水印

UIImage *waterImage = [UIImage imageNamed:@"logo"];

CGFloat scale = 0.2;

CGFloat margin = 5;

CGFloat waterW = waterImage.size.width * scale;

CGFloat waterH = waterImage.size.height * scale;

CGFloat waterX = bgImage.size.width - waterW - margin;

CGFloat waterY = bgImage.size.height - waterH - margin;

[waterImage drawInRect:CGRectMake(waterX, waterY, waterW, waterH)];

// 4.从上下文中取得制作完毕的UIImage对象

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

// 5.结束上下文

UIGraphicsEndImageContext();

// 6.显示到UIImageView

self.iconView.image = newImage;

// 7.将image对象压缩为PNG格式的二进制数据

NSData *data = UIImagePNGRepresentation(newImage);

//    UIImageJPEGRepresentation(<#UIImage *image#>, <#CGFloat compressionQuality#>)

// 8.写入文件

NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"new.png"];

[data writeToFile:path atomically:YES];

}

给image添加一类目

/**

*  打水印

*返回带有水印的图片

*  @param bg   背景图片

*  @param logo 右下角的水印图片

*/

+ (instancetype)waterImageWithBg:(NSString *)bg logo:(NSString *)logo

{

UIImage *bgImage = [UIImage imageNamed:bg];

// 1.创建一个基于位图的上下文(开启一个基于位图的上下文)

UIGraphicsBeginImageContextWithOptions(bgImage.size, NO, 0.0);

// 2.画背景

[bgImage drawInRect:CGRectMake(0, 0, bgImage.size.width, bgImage.size.height)];

// 3.画右下角的水印

UIImage *waterImage = [UIImage imageNamed:logo];

CGFloat scale = 0.2;

CGFloat margin = 5;

CGFloat waterW = waterImage.size.width * scale;

CGFloat waterH = waterImage.size.height * scale;

CGFloat waterX = bgImage.size.width - waterW - margin;

CGFloat waterY = bgImage.size.height - waterH - margin;

[waterImage drawInRect:CGRectMake(waterX, waterY, waterW, waterH)];

// 4.从上下文中取得制作完毕的UIImage对象

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

// 5.结束上下文

UIGraphicsEndImageContext();

return newImage;

}