如何从静态图像中读取QR码 [英] How to read QR code from static image

问题描述

我知道您可以使用 AVFoundation 使用设备的相机扫描QR码。现在问题是，如何从静态 UIImage 对象中执行此操作？

I know that you can use AVFoundation to scan a QR code using the device's camera. Now here comes the problem, how can I do this from an static UIImage object?

推荐答案

iOS API提供CoreImage框架中的CIDetector类。
CIDetector让你在图像中找到特定的模式，比如面部，微笑，眼睛，或者在我们的例子中：QRCodes。

The iOS API provides the CIDetector class from CoreImage framework. CIDetector let you find specific patterns in images, like faces, smiles, eyes, or in our case : QRCodes.

这是检测QRCode的代码来自Objective-C中的UIImage：

Here is the code to detect a QRCode from an UIImage in Objective-C:

-(NSArray *)detectQRCode:(UIImage *) image
{
    @autoreleasepool {
        NSLog(@"%@ :: %@", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
        NSCAssert(image != nil, @"**Assertion Error** detectQRCode : image is nil");

        CIImage* ciImage = UIImage.CIImage; // assuming underlying data is a CIImage
        //CIImage* ciImage = [CIImage initWithCGImage: UIImage.CGImage]; // to use if the underlying data is a CGImage

        NSDictionary* options;
        CIContext* context = [CIContext context];
        options = @{ CIDetectorAccuracy : CIDetectorAccuracyHigh }; // Slow but thorough
        //options = @{ CIDetectorAccuracy : CIDetectorAccuracyLow}; // Fast but superficial

        CIDetector* qrDetector = [CIDetector detectorOfType:CIDetectorTypeQRCode
                                                    context:context
                                                    options:options];
        if ([[ciImage properties] valueForKey:(NSString*) kCGImagePropertyOrientation] == nil) {
            options = @{ CIDetectorImageOrientation : @1};
        } else {
            options = @{ CIDetectorImageOrientation : [[ciImage properties] valueForKey:(NSString*) kCGImagePropertyOrientation]};
        }

        NSArray * features = [qrDetector featuresInImage:ciImage
                                                 options:options];

        return features;

    }
}

返回的如果存在并检测到QRCode，NSArray * 将包含 CIFeature * 。如果没有QRCode， NSArray * 将是 nil 。如果QRCode解码失败， NSArray * 将没有元素。

The returned NSArray* will contain CIFeature* if a QRCode is present and detected. If there was no QRCode, the NSArray* will be nil. If the QRCode decoding fails, the NSArray* will have no element.

获取编码的字符串：

if (features != nil && features.count > 0) {
    for (CIQRCodeFeature* qrFeature in features) {
        NSLog(@"QRFeature.messageString : %@ ", qrFeature.messageString);
    }
}

在@ Duncan-C的回答中，你然后可以提取QRCode角并在图像上绘制QRCode的封闭边界框。

As in the answer of @Duncan-C, you can then extract QRCode corners and draw an enclosing bounding box of the QRCode on the image.

注意：
在iOS10.0下测试版6，调用 [qrDetector featuresInImage：ciImage选项：选项] 当使用来自cameraSampleBuffer的图像时，会记录此内部警告（它运行顺利，但会通过此消息向控制台发送垃圾邮件，我现在找不到摆脱它的方法）：

Note : Under iOS10.0 beta 6, the call to [qrDetector featuresInImage:ciImage options:options] when using images coming from the cameraSampleBuffer logs this internal warning (it runs smoothly but spam the console with this message, and I could not find a way to get rid of it for now):

锁定计数为1时，最终确定CVPixelBuffer 0x170133e20。

Finalizing CVPixelBuffer 0x170133e20 while lock count is 1.

资料来源：

Apple Dev API参考 - CIDetector

Apple Dev API编程指南 - 人脸检测

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