Episode #303
Capturing High Resolution Photos
Series: Camera Capture and Detection
Episode #303
First, we'll add a property to store our photo output instance:
var photoOutput: AVCapturePhotoOutput?
Then, when we are setting up our capture session, we'll also add this output to it:
let photoOutput = AVCapturePhotoOutput()
self.photoOutput = photoOutput
captureSession.addOutput(photoOutput)
Later on, when we want to take a photo, we no longer need the wantsPhoto flag. Instead, we can just tell the output to capture a photo. This requires us to tell the AVCapturePhotoOutput what pixel format we want to use (among other things).
If we don't do this we'll get a processed JPEG image, and this would need to get converted back to an uncompressed type for us to use Core Image on.
func takePhoto() {
guard let formats = photoOutput?.supportedPhotoPixelFormatTypes(for: .tif) else { return }
print("available pixel formats: \(formats)")
guard let uncompressedPixelType = formats.first else {
print("No pixel format types available")
return
}
let settings = AVCapturePhotoSettings(format: [
kCVPixelBufferPixelFormatTypeKey as String : uncompressedPixelType
])
settings.flashMode = .auto
photoOutput?.capturePhoto(with: settings, delegate: self)
}
The formats returned by the method above are of type OSType. these are special integers that have a nifty attribute: they can be printed as text!
If you want to print out the actual 4-letter code for a given OSType, you can use this function:
func str4 (_ n: Int) -> String {
var s: String = String (describing: UnicodeScalar((n >> 24) & 255)!)
s.append(String(describing: UnicodeScalar((n >> 16) & 255)!))
s.append(String(describing: UnicodeScalar((n >> 8) & 255)!))
s.append(String(describing: UnicodeScalar(n & 255)!))
return s
}
This delegate method will be called once the photo has been taken and pixel data is available. We want to hand this data off to core image.
extension CaptureViewController : AVCapturePhotoCaptureDelegate {
func photoOutput(_ output: AVCapturePhotoOutput,
didFinishProcessingPhoto photo: AVCapturePhoto,
error: Error?) {
guard let rect = lastDetectedRectangle else { return }
imageProcessingQueue.async {
guard let pixelBuffer = photo.pixelBuffer else {
print("No pixel buffer provided. Settings may missing pixel format")
return
}
let ciimage = CIImage(cvPixelBuffer: pixelBuffer)
if let correctedImage = self.perspectiveCorrect(ciimage, rectFeature: rect) {
DispatchQueue.main.async {
self.displayImage(ciImage: correctedImage)
}
}
}
}
}
Since we're using the built-in camera features, we can delete the code that flashes the screen and plays the camera shutter sound. It's not needed anymore!
This episode uses Xcode 9.0-beta6, Swift 4.
