Wrong result on Barcode scanning using AVFoundation framework - ios

Question

I am using iOS 7 AVFoundation framework for Barcode scanning. It works fine for me but on some Barcodes it gives me wrong result.
I am adding code file and Barcode also to generate the issue. Please take a look and help me to find out the problem.
Code Sample:
ViewController.h Class-
#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>
#interface ViewController : UIViewController <AVCaptureMetadataOutputObjectsDelegate>
{
AVCaptureSession *_session;
AVCaptureDevice *_device;
AVCaptureDeviceInput *_input;
AVCaptureMetadataOutput *_output;
AVCaptureVideoPreviewLayer *_prevLayer;
UIView *_highlightView;
IBOutlet UIView *_viewBg;
IBOutlet UIButton *_btnScanning;
}
#end
ViewController.m Class Methods -
- (void)setScanningVideoOrientation
{
if ([UIDevice currentDevice].orientation == UIInterfaceOrientationPortrait)
{
_prevLayer.connection.videoOrientation = AVCaptureVideoOrientationPortrait;
}
else if ([UIDevice currentDevice].orientation == UIInterfaceOrientationPortraitUpsideDown)
{
_prevLayer.connection.videoOrientation = AVCaptureVideoOrientationPortraitUpsideDown;
}
else if ([UIDevice currentDevice].orientation == UIInterfaceOrientationLandscapeLeft)
{
_prevLayer.connection.videoOrientation = AVCaptureVideoOrientationLandscapeLeft;
}
else if ([UIDevice currentDevice].orientation == UIInterfaceOrientationLandscapeRight)
{
_prevLayer.connection.videoOrientation = AVCaptureVideoOrientationLandscapeRight;
}
}
- (void)startScanning
{
// Create Session.------------------------------------------------------
_session = nil;
_session = [[AVCaptureSession alloc] init];
_device = nil;
_device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error = nil;
_input = nil;
_input = [AVCaptureDeviceInput deviceInputWithDevice:_device error:&error];
if (_input)
{
[_session addInput:_input];
_output = nil;
_output = [[AVCaptureMetadataOutput alloc] init];
[_output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
[_session addOutput:_output];
_output.metadataObjectTypes = [_output availableMetadataObjectTypes];
_prevLayer = nil;
_prevLayer = [AVCaptureVideoPreviewLayer layerWithSession:_session];
_prevLayer.frame = _viewBg.frame;
_prevLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[self setScanningVideoOrientation];
[self.view.layer addSublayer:_prevLayer];
[_session startRunning];
} else
{
NSLog(#"Error: %#", error);
}
//----------------------------------------------------------------------
}
In this delegate method. I am getting wrong barcode string. Please take a look on 'detectionString'.
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection
{
CGRect highlightViewRect = CGRectZero;
AVMetadataMachineReadableCodeObject *barCodeObject;
NSString *detectionString = nil;
NSArray *barCodeTypes = #[AVMetadataObjectTypeUPCECode, AVMetadataObjectTypeCode39Code, AVMetadataObjectTypeCode39Mod43Code,
AVMetadataObjectTypeEAN13Code, AVMetadataObjectTypeEAN8Code, AVMetadataObjectTypeCode93Code, AVMetadataObjectTypeCode128Code,
AVMetadataObjectTypePDF417Code, AVMetadataObjectTypeQRCode, AVMetadataObjectTypeAztecCode];
for (AVMetadataObject *metadata in metadataObjects) {
for (NSString *type in barCodeTypes) {
if ([metadata.type isEqualToString:type])
{
barCodeObject = (AVMetadataMachineReadableCodeObject *)[_prevLayer transformedMetadataObjectForMetadataObject:(AVMetadataMachineReadableCodeObject *)metadata];
highlightViewRect = barCodeObject.bounds;
detectionString = [(AVMetadataMachineReadableCodeObject *)metadata stringValue];
break;
}
}
if (detectionString != nil)
{
NSLog(#"ViewController-->captureOutput-->detectionString = %#",detectionString);
[self stopScanning];
break;
}
}
barCodeObject = nil;
detectionString = nil;
barCodeTypes = nil;
}
Barcode Image -
I am getting result - 0649954006029
But it should be - 649954006029.
As for some other barcodes, i am seeing 'l' before actual barcode scanning string.
Hope it will help you to identify the problem.
Thanks.

Answer 1

The reason you're getting a 13 digit code is because you're trying to scan a UPC-A code (649954..) and iOS doesn't have a separate category for UPC-A codes.
UPC-A codes come scanned in as EAN13 codes, and those are 13 digits long, so they get a prefix of 0.
From AVFoundation/AVMetadata.h
/*! #constant AVMetadataObjectTypeEAN13Code
#abstract An identifier for an instance of
AVMetadataMachineReadableCodeObject having a type
AVMetadataObjectTypeEAN13Code.
#discussion
AVMetadataMachineReadableCodeObject objects generated from EAN-13 (including UPC-A) codes return this constant as their type. */
AVF_EXPORT NSString *const AVMetadataObjectTypeEAN13Code NS_AVAILABLE(NA, 7_0);