How to read QR code from static image

Question

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?

Answer 1

Swift 4 version of @Neimsz's answer

func detectQRCode(_ image: UIImage?) -> [CIFeature]? {     if let image = image, let ciImage = CIImage.init(image: image){         var options: [String: Any]         let context = CIContext()         options = [CIDetectorAccuracy: CIDetectorAccuracyHigh]         let qrDetector = CIDetector(ofType: CIDetectorTypeQRCode, context: context, options: options)         if ciImage.properties.keys.contains((kCGImagePropertyOrientation as String)){             options = [CIDetectorImageOrientation: ciImage.properties[(kCGImagePropertyOrientation as String)] ?? 1]         } else {             options = [CIDetectorImageOrientation: 1]         }         let features = qrDetector?.features(in: ciImage, options: options)         return features      }     return nil } 

How to use

if let features = detectQRCode(#imageLiteral(resourceName: "qrcode")), !features.isEmpty{     for case let row as CIQRCodeFeature in features{         print(row.messageString ?? "nope")     } } 

And during the execution this doesn't produce the Finalizing CVPixelBuffer 0x170133e20 while lock count is 1

I used the following QRCode Image (QRCode = https://jingged.com)

(Tested on iPhone 6 simulator with iOS version 11.2)

Output:

2018-03-14 15:31:13.159400+0530 TestProject[25889:233062] [MC] Lazy loading NSBundle MobileCoreServices.framework 2018-03-14 15:31:13.160302+0530 TestProject[25889:233062] [MC] Loaded MobileCoreServices.framework https://jingged.com 

Answer 2

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.

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 = image.CIImage; // assuming underlying data is a CIImage         //CIImage* ciImage = [[CIImage alloc] initWithCGImage: image.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;      } } 

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.

To obtain the encoded string :

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

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.

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):

Finalizing CVPixelBuffer 0x170133e20 while lock count is 1.

Source :

Apple Dev API Reference - CIDetector

Apple Dev API Programming guide - Face detection