Get UIImage from PKDrawing and convert to Float array of pixels

Using Swift
1

I am trying to take a user input drawing and convert it into a float array of pixel values. The background of the drawing is white. I am retrieving the UIImage from the PKDrawing by calling the drawing.image function. Afterwards, I use the following code to convert to float array

 func normalized() -> [Float32]? {
        guard let cgImage = self.cgImage else {
            return nil
        }
        let w = cgImage.width
        let h = cgImage.height
        let bytesPerPixel = 4
        let bytesPerRow = bytesPerPixel * w
        let bitsPerComponent = 8
        var rawBytes: [UInt8] = [UInt8](repeating:0, count: w * h * 4)
        rawBytes.withUnsafeMutableBytes { ptr in
            if let cgImage = self.cgImage,
               let context = CGContext(data: ptr.baseAddress,
                                       width: w,
                                       height: h,
                                       bitsPerComponent: bitsPerComponent,
                                       bytesPerRow : bytesPerRow,
                                       space: CGColorSpaceCreateDeviceRGB(),
                                       bitmapInfo:  CGImageAlphaInfo.premultipliedLast.rawValue) {
                let rect = CGRect(x: 0, y: 0, width: w, height: h)
                context.draw(cgImage, in: rect)
            }
        }
        var normalizedBuffer: [Float32] = [Float32](repeating: 0, count: w * h * 3)
        for i in 0 ..< w * h {
            normalizedBuffer[i] = Float32(rawBytes[i * 4 + 0]) / 255.0
            normalizedBuffer[w * h + i] = Float32(rawBytes[i * 4 + 1]) / 255.0
            normalizedBuffer[w * h * 2 + i] = Float32(rawBytes[i * 4 + 2]) / 255.0
        }
        return normalizedBuffer
    }

However, running the code on the UIImage however, is giving me an array of all zero floats. However, when I load the image from imageAsset using UIImage(named:) function and run the code, I am able to get the normalised intensity values. How should I modify the code to get the correct normalised intensity values?