How can I change UIimage to binary data in Swift

Question

I want to send Image data(capture a snapshot) to Python server by decoding information to byte(UInt8) array but did't well :(

My code is here

typealias Byte = UInt8

let captureImage:UIImage = self.sceneView.snapshot()

//change UIImage to binary data

let imageData: NSData = UIImageJPEGRepresentation(captureImage, 0)! as NSData

let AR_IMG_WIDTH = Int(captureImage.size.width) //750
let AR_IMG_HEIGHT = Int(captureImage.size.height) //1334
let AR_BUFFER_SIZE = AR_IMG_WIDTH * AR_IMG_HEIGHT * 3 + 6 //3001506 , 3(R,G,B),6 (MMS+MME)

print("size of imageData 750 * 1334 * 3 : \(imageData.length)")

//NSData to [Byte]
var mms: [Byte] = [Byte]("MMS".utf8) // 3Byte
let mme: [Byte] = [Byte]("MME".utf8) // 3Byte
var copyArray = [Byte](repeating: 0, count: imageData.length)
imageData.getBytes(&copyArray, length: imageData.length)
mms.append(contentsOf: copyArray)
mms.append(contentsOf: mme)

My question is this

1) Why imageData.length(size of byte) value is mutable? I tought this value must be ImageWidth * ImageHeight * 3(R,G,B data) + 6 (MMS, MME) byte

2) If i want to transfer the image information, use another function or class?

Answer 1

Let me answer your question 1)

JPEG, like many other image formats, compresses the RGB image data. This means that the number of bytes is not a bit more than width X height X 3, but much less.