Changing size of image obtained from camera explanation - ios

Question

I am new to iOS and have experience with image processing coding in other languages, which I was hoping to translate into an app, however I am getting some unusual behavior which I don't understand. When I convert an image to a Data array and look at the number of elements in the array, with every new image this number changes. When I look at the specific data in the array, the values are 0-255 which matches what I would expect for a grayscale image, but I am confused why the size (or number of elements) in the data array changes. I would expect it to be held constant since I set the captureSession to 640x480. Why is this not the case? Even if it wasn't a grayscale image, I would expect the size to remain the same and not change picture to picture.
UPDATE:
I am getting the uiimage from AV, and the code is shown below. The other rest of the code not shown is just beginning the session. I basically want to turn the image into raw pixel data, which I have seen a lot of different ways to do this, but this seems like a good method.
Relevant Code:
#objc func timerHandle() {
imageView.image = uiimages
}
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
uiimages = sampleBuffer.image(orientation: .down, scale: 1.0)!
print(uiimages) //output1
let data = sampleBuffer.data()
let newData = Array(data!)
print(data!.count) //output2
}
extension CMSampleBuffer {
func image(orientation: UIImageOrientation = .left, scale: CGFloat = 1.0) -> UIImage? {
if let buffer = CMSampleBufferGetImageBuffer(self) {
let ciImage = CIImage(cvPixelBuffer: buffer).applyingFilter("CIColorControls", parameters: [kCIInputSaturationKey:0.0])
return UIImage(ciImage: ciImage, scale: scale, orientation: orientation)
}
return nil
}
func data(orientation: UIImageOrientation = .left, scale: CGFloat = 1.0) -> Data? {
if let buffer = CMSampleBufferGetImageBuffer(self) {
let size = self.image()?.size
let scale = self.image()?.scale
let ciImage = CIImage(cvPixelBuffer: buffer).applyingFilter("CIColorControls", parameters: [kCIInputSaturationKey:0.0])
UIGraphicsBeginImageContextWithOptions(size!, false, scale!)
defer { UIGraphicsEndImageContext() }
UIImage(ciImage: ciImage).draw(in: CGRect(origin: .zero, size: size!))
guard let redraw = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
return UIImagePNGRepresentation(redraw)
}
return nil
}
}
At output1, when I straight print the uiimage variable I get:
<UIImage: 0x1c40b0ec0>, {640, 480}
which shows correct dimensions
at output2, when I print the count, every time captureOutput is called I get a different value:
225726
224474
225961
640x480 should give me 307,200, so why am I not getting constant numbers at least, even if the value isn't correct.