Some of latest iPhone models with multiple built-in cameras have increased "minimum focus distance" (usually 200mm) on their default camera. That means if you are using the default camera and holding the device too close to the object the image will be blurry and scanning is likely to fail.
The solution is to let the system use multiple cameras and select the appropriate one on the fly. This way the system will switch to ultra wide camera if it detects that the object is too close for the default camera. The ultra wide camera has smaller "minimum focus distance" and will produce sharper images. In your code instead of retrieving the default camera you should retrieve a virtual camera consisting of multiple cameras.
// let device = AVCaptureDevice.default(for: .video)
let discoverySession = AVCaptureDeviceDiscoverySession(deviceTypes: [.builtInTripleCamera],
mediaType: .video,
position: .back)
let device = discoverySession.devices.first
Unfortunately the story doesn't end here. Two problems remained:
builtInTripleCamera virtual camera is available only for devices with 3 cameras built-in. For complete compatibility you have to use some logic to retrieve the appropriate AVCaptureDevice. For this you might use this code snippet:
// sortedDeviceTypes parameter should be sorted by priority (1st is the most desired device type)
- (AVCaptureDevice *) selectAvailableDeviceFromSortedTypes:(NSArray<AVCaptureDeviceType> *)sortedDeviceTypes forPosition:(AVCaptureDevicePosition)position {
if (@available(iOS 10.0, *)) {
AVCaptureDeviceDiscoverySession *discoverySession = [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:sortedDeviceTypes
mediaType:AVMediaTypeVideo
position:position];
NSArray<AVCaptureDevice *> *sortedDiscoveredDevices = [discoverySession.devices sortedArrayUsingComparator:^NSComparisonResult(AVCaptureDevice *device1, AVCaptureDevice *device2) {
NSUInteger index1 = [sortedDeviceTypes indexOfObject:device1.deviceType];
NSUInteger index2 = [sortedDeviceTypes indexOfObject:device2.deviceType];
if (index1 < index2)
return NSOrderedAscending;
if (index1 > index2)
return NSOrderedDescending;
return NSOrderedSame;
}];
return sortedDiscoveredDevices.firstObject;
}
// under iOS 10.0
else {
NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
for (AVCaptureDevice *device in devices)
if (device.position == position)
return device;
return nil;
}
}
// sorted by priority (1st is the most desired device type)
- (NSArray<AVCaptureDeviceType> *)sortedDeviceTypes API_AVAILABLE(ios(10.0));
{
if (@available(iOS 13.0, *)) {
return @[AVCaptureDeviceTypeBuiltInTripleCamera,
AVCaptureDeviceTypeBuiltInDualWideCamera,
AVCaptureDeviceTypeBuiltInDualCamera,
AVCaptureDeviceTypeBuiltInWideAngleCamera,
AVCaptureDeviceTypeBuiltInUltraWideCamera,
AVCaptureDeviceTypeBuiltInTelephotoCamera];
}
if (@available(iOS 10.2, *)) {
return @[AVCaptureDeviceTypeBuiltInDualCamera,
AVCaptureDeviceTypeBuiltInWideAngleCamera,
AVCaptureDeviceTypeBuiltInTelephotoCamera];
}
// iOS 10.0
else {
return @[AVCaptureDeviceTypeBuiltInWideAngleCamera,
AVCaptureDeviceTypeBuiltInTelephotoCamera];
}
}
- Using virtual camera like
builtInTripleCamera means that the system will start using ultra wide camera and you might not want to initially show ultra wide preview for the user. To fix this you have to raise the zoom factor. A raised zoom factor will make the system change to the standard/default camera. You might ask how the system will change back to ultra wide camera if we bring the phone too close to the object (under the minimum focus distance value). The phone has a proximity sensor that will make the system change to ultra wide camera despite of having raised zoom factor. To apply appropriate zoom factor the following code is recommended:
- (float) zoomFactorScale {
if (@available(iOS 13.0, *)) {
if (self.device &&
(self.device.deviceType == AVCaptureDeviceTypeBuiltInTripleCamera ||
self.device.deviceType == AVCaptureDeviceTypeBuiltInDualWideCamera))
{
NSArray<NSNumber*> *zoomFactors = [self.device virtualDeviceSwitchOverVideoZoomFactors];
if (zoomFactors.count > 0)
return zoomFactors.firstObject.floatValue;
else
return 1;
}
else
return 1;
}
}
