How Do I Process an Image File to fit buffer dimensions for Vision Framework on MacOS? - swift

Question

I'm trying to make something simple to test Vision Framework on MacOS.
I tried to modify code from this tutorial to use a single image from screenshot instead of camera feed.
https://www.appcoda.com/vision-framework-introduction/
However, I get this error:
Error Domain=com.apple.vis Code=3 "Failed to create image for processing due to invalid requested buffer dimensions"
Is it because screenshot image doesn't fit certain specification? Do I need to preprocess the file?
If so, how can I process it in order to fit the dimensions?
My testing code is below.
Thanks!
import Cocoa
import Vision
class ViewController: NSViewController {
var requests = [VNRequest]()
func start() {
let textRequest = VNDetectTextRectanglesRequest(completionHandler: self.detectTextHandler)
textRequest.reportCharacterBoxes = true
self.requests = [textRequest]
let url = URL(fileURLWithPath:NSString(string:"~/Screenshot.png").expandingTildeInPath)
let imageRequestHandler = VNImageRequestHandler(url:url)
do {
try imageRequestHandler.perform(self.requests)
} catch {
print(error)
}
}
func detectTextHandler(request: VNRequest, error: Error?) {
guard let observations = request.results else {
print("no result")
return
}
let result = observations.map({$0 as? VNTextObservation})
DispatchQueue.main.async() {
for region in result {
guard let rg = region else {
continue
}
self.highlightWord(box: rg)
if let boxes = region?.characterBoxes {
for characterBox in boxes {
self.highlightLetters(box: characterBox)
}
}
}
}
}
func highlightWord(box: VNTextObservation) {
guard let boxes = box.characterBoxes else {
return
}
var maxX: CGFloat = 9999.0
var minX: CGFloat = 0.0
var maxY: CGFloat = 9999.0
var minY: CGFloat = 0.0
for char in boxes {
if char.bottomLeft.x < maxX {
maxX = char.bottomLeft.x
}
if char.bottomRight.x > minX {
minX = char.bottomRight.x
}
if char.bottomRight.y < maxY {
maxY = char.bottomRight.y
}
if char.topRight.y > minY {
minY = char.topRight.y
}
}
let xCord = maxX
let yCord = (1 - minY)
let width = (minX - maxX)
let height = (minY - maxY)
let frame = CGRect(x: xCord, y: yCord, width: width, height: height)
print("Word: \(frame)")
}
func highlightLetters(box: VNRectangleObservation) {
let xCord = box.topLeft.x
let yCord = (1 - box.topLeft.y)
let width = (box.topRight.x - box.bottomLeft.x)
let height = (box.topLeft.y - box.bottomLeft.y)
let frame = CGRect(x: xCord, y: yCord, width: width, height: height)
print("Letter: \(frame)")
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
start()
}
override var representedObject: Any? {
didSet {
// Update the view, if already loaded.
}
}
}