Fix image processing. (#6153)

Summary:
Pull Request resolved: #6153
overriding_review_checks_triggers_an_audit_and_retroactive_review
Oncall Short Name: executorch

Differential Revision: D64218669

fbshipit-source-id: 63e5aea82d65515977fa3c411e0190683e2cb061
(cherry picked from commit 4204e50)

Author: shoumikhin

examples/demo-apps/apple_ios/LLaMA/LLaMA/Application/ContentView.swift

@@ -19,66 +19,39 @@ class RunnerHolder: ObservableObject {
 extension UIImage {
   func resized(to newSize: CGSize) -> UIImage {
     let format = UIGraphicsImageRendererFormat.default()
-    let renderer = UIGraphicsImageRenderer(size: newSize, format: format)
-    let image = renderer.image { _ in
-      draw(in: CGRect(origin: .zero, size: newSize))
+    format.scale = 1
+    return UIGraphicsImageRenderer(size: newSize, format: format).image {
+      _ in draw(in: CGRect(origin: .zero, size: newSize))
     }
     return image
   }
 
   func toRGBArray() -> [UInt8]? {
-    guard let cgImage = self.cgImage else {
-      NSLog("Failed to get CGImage from UIImage")
-      return nil
-    }
+    guard let cgImage = self.cgImage else { return nil }
 
-    let width = cgImage.width
-    let height = cgImage.height
-    let colorSpace = CGColorSpaceCreateDeviceRGB()
-    let bytesPerPixel = 4
-    let bytesPerRow = bytesPerPixel * width
-    let bitsPerComponent = 8
-    let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue
+    let width = Int(cgImage.width), height = Int(cgImage.height)
+    let totalPixels = width * height, bytesPerPixel = 4, bytesPerRow = bytesPerPixel * width
+    var rgbValues = [UInt8](repeating: 0, count: totalPixels * 3)
+    var pixelData = [UInt8](repeating: 0, count: width * height * bytesPerPixel)
 
     guard let context = CGContext(
-      data: nil,
-      width: width,
-      height: height,
-      bitsPerComponent: bitsPerComponent,
-      bytesPerRow: bytesPerRow,
-      space: colorSpace,
-      bitmapInfo: bitmapInfo
-    ) else {
-      NSLog("Failed to create CGContext")
-      return nil
-    }
+      data: &pixelData, width: width, height: height, bitsPerComponent: 8,
+      bytesPerRow: bytesPerRow, space: CGColorSpaceCreateDeviceRGB(),
+      bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Big.rawValue
+    ) else { return nil }
 
     context.draw(cgImage, in: CGRect(x: 0, y: 0, width: width, height: height))
 
-    guard let pixelBuffer = context.data else {
-      NSLog("Failed to get pixel data from CGContext")
-      return nil
-    }
-
-    let pixelData = pixelBuffer.bindMemory(to: UInt8.self, capacity: width * height * bytesPerPixel)
-
-    var rgbArray = [UInt8](repeating: 0, count: width * height * 3)
-
     for y in 0..<height {
       for x in 0..<width {
         let pixelIndex = (y * width + x) * bytesPerPixel
-        let r = UInt8(pixelData[pixelIndex])
-        let g = UInt8(pixelData[pixelIndex + 1])
-        let b = UInt8(pixelData[pixelIndex + 2])
-
-        let rgbIndex = (y * width + x)
-        rgbArray[rgbIndex] = r
-        rgbArray[rgbIndex + height * width] = g
-        rgbArray[rgbIndex + 2 * height * width] = b
+        let rgbIndex = y * width + x
+        rgbValues[rgbIndex] = pixelData[pixelIndex]
+        rgbValues[rgbIndex + totalPixels] = pixelData[pixelIndex + 1]
+        rgbValues[rgbIndex + totalPixels * 2] = pixelData[pixelIndex + 2]
       }
     }
-
-    return rgbArray
+    return rgbValues
   }
 }