Swift UIImage.jpegData() 和.pngData() 改變圖像大小

Question

I am using Swift's Vision Framework for Deep Learning and want to upload the input image to backend using REST API - for which I am converting my UIImage to MultipartFormData using jpegData() and pngData() function that swift natively offers.

我使用session.sessionPreset =.vga640x480在我的應用程序中指定要處理的圖像大小。

我在后端看到不同大小的圖像 - 我能夠在應用程序中確認這一點，因為從圖像轉換的UIImage(imageData)大小不同。

這就是我將圖像轉換為multipartData -

let multipartData = MultipartFormData()
if let imageData = self.image?.jpegData(compressionQuality: 1.0) {
    multipartData.append(imageData, withName: "image", fileName: "image.jpeg", mimeType: "image/jpeg")
}

這就是我在 Xcode 調試器中看到的 -

Answer 1

這不起作用，最終以不正確的scale顯示圖像的Data表示：

let ciImage = CIImage(cvImageBuffer: pixelBuffer) // 640×480
let image = UIImage(ciImage: ciImage)             // says it is 640×480 with scale of 1
guard let data = image.pngData() else { ... }     // but if you extract `Data` and then recreate image from that, the size will be off by a multiple of your device’s scale

但是，如果您通過CGImage創建它，您將得到正確的結果：

let ciImage = CIImage(cvImageBuffer: pixelBuffer)
let ciContext = CIContext()
guard let cgImage = ciContext.createCGImage(ciImage, from: ciImage.extent) else { return }
let image = UIImage(cgImage: cgImage)