// 1.创建一个滤镜

CIFilter *filter = [CIFilter filterWithName:@"CIQRCodeGenerator"];

// 2.设置默认的属性

[filter setDefaults];

// 3.给滤镜设置数据

NSString *string = @"http://www.baidu.com";

NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];

[filter setValue:data forKeyPath:@"inputMessage"];

// 4.获取出输出的数据

CIImage *outputImage = [filter outputImage];

// 5.设置到imageView上面

// self.imageView.image = [UIImage imageWithCIImage:outputImage];

   self.imageView.image = [self createNonInterpolatedUIImageFormCIImage:outputImage withSize:];

第5步骤中有一方法是为了得到高清的二维码图片。所用的方法

/**

 *  根据CIImage生成指定大小的UIImage

 *

 *  @param image CIImage

 *  @param size  图片宽度

 */

- (UIImage *)createNonInterpolatedUIImageFormCIImage:(CIImage *)image withSize:(CGFloat) size

{

    CGRect extent = CGRectIntegral(image.extent);

    CGFloat scale = MIN(size/CGRectGetWidth(extent), size/CGRectGetHeight(extent));

    // 1.创建bitmap;

    size_t width = CGRectGetWidth(extent) * scale;

    size_t height = CGRectGetHeight(extent) * scale;

    CGColorSpaceRef cs = CGColorSpaceCreateDeviceGray();

    CGContextRef bitmapRef = CGBitmapContextCreate(nil, width, height, , , cs, (CGBitmapInfo)kCGImageAlphaNone);

    CIContext *context = [CIContext contextWithOptions:nil];

    CGImageRef bitmapImage = [context createCGImage:image fromRect:extent];

    CGContextSetInterpolationQuality(bitmapRef, kCGInterpolationNone);

    CGContextScaleCTM(bitmapRef, scale, scale);

    CGContextDrawImage(bitmapRef, extent, bitmapImage);

    // 2.保存bitmap到图片

    CGImageRef scaledImage = CGBitmapContextCreateImage(bitmapRef);

    CGContextRelease(bitmapRef);

    CGImageRelease(bitmapImage);

    return [UIImage imageWithCGImage:scaledImage];

}