Depth map normalization - ios

Question

I am applying CIDepthBlurEffect filter to a PHAsset as follows:
PHImageManager.default().requestImageDataAndOrientation(for: self.asset!, options: imageOptions) { (data, responseString, imageOrientation, info) in
if data != nil {
DispatchQueue.main.async {
if let depthImage = CIImage(data: data!, options: [CIImageOption.auxiliaryDisparity : true])?.oriented(imageOrientation) {
if let newMainImage = CIImage(data: data!)?.oriented(imageOrientation) {
let filter = CIFilter(name : "CIDepthBlurEffect",
parameters: [kCIInputImageKey : newMainImage,
kCIInputDisparityImageKey: depthImage,
"inputAperture" : withRadius])
self.imageView.image = UIImage(ciImage: filter!.outputImage!)
}
}
}
}
This works great most of the time. However, sometimes, the filter blur planes seem to be off. Almost as the Z plane is wrong or shifted.
Does this method require the depth data to be normalized?
Previously, when CVPixelBuffer was used, I was using this extension:
final func normalize() -> CVPixelBuffer {
let width = CVPixelBufferGetWidth(self)
let height = CVPixelBufferGetHeight(self)
CVPixelBufferLockBaseAddress(self, CVPixelBufferLockFlags(rawValue: 0))
let floatBuffer = unsafeBitCast(CVPixelBufferGetBaseAddress(self), to: UnsafeMutablePointer<Float>.self)
var minPixel: Float = 1.0
var maxPixel: Float = 0.0
for y in 0 ..< height {
for x in 0 ..< width {
let pixel = floatBuffer[y * width + x]
minPixel = min(pixel, minPixel)
maxPixel = max(pixel, maxPixel)
}
}
let range = maxPixel - minPixel
for y in 0 ..< height {
for x in 0 ..< width {
let pixel = floatBuffer[y * width + x]
floatBuffer[y * width + x] = (pixel - minPixel) / range
}
}
CVPixelBufferUnlockBaseAddress(self, CVPixelBufferLockFlags(rawValue: 0))
return self
}
Is there such a way to do this to a CIImage?